Introduction to C Generation of ‘C’ Language

Introduction to C Generation of ‘C’ Language
In 1967, Martin Richards developed a language called BCPL (Basic Combined Programming Language) In 1970, Ken Thompson created a language using many features of BCPL and called it simply B. In 1972, ‘C’ is Introduced by Dennis Ritchie at Bell laboratories and in the UNIX operating system.

History of ‘C’ 1960 ALGOL International Group 1967 BCPL
Martin Richards 1970 B Ken Thompson 1972 Traditional C Dennits Ritchie 1978 K & R C Kernighan and Ritchie 1989 ANSI C ANSI Committee 1990 ANSI / ISO C ISO Committee

Why are using ‘C’ TYPES OF ‘C’ COMPILER 2. Turbo ‘C’ Compiler
It is a Structured Programming Language High – Level Language Machine Independent Language It allows software developers to develop programs without worrying about the hardware platforms where they will be implemented TYPES OF ‘C’ COMPILER 1. Borland ‘C’ Compiler 2. Turbo ‘C’ Compiler 3. Microsoft ‘C’ Compiler 4. ANCI ‘C’ Compiler

Characteristics of C We briefly list some of C's characteristics that define the language Small size Extensive use of function calls Loose typing -- unlike PASCAL Structured language Low level (Bitwise) programming readily available Pointer implementation - extensive use of pointers for memory, array, structures and functions. C has now become a widely used professional language for various reasons. It has high-level constructs. It can handle low-level activities. It produces efficient programs. It can be compiled on a variety of computers.

Steps in Learning C Character set Files Data Structures Structures and
Unions Algorithms Constants, variable And Data types Control statements Pointers Programs Functions Arrays

Documentation section
C’S Program Structure Documentation section Preprocessor section Definition section Global declaration section main() { Declaration part; Executable part; } Sub program section { Body of the subprogram }

C’s Character set

C TOKENS C TOKENS Constants Strings Identifiers Operators + - * /
-15.5 100 “ABC” “YEAR” Identifiers Operators main amount + - * / Keywords Special Symbols float while [ ] { }

C’s Identifiers Program elements where Identifiers are used
Variables Functions Arrays Function parameters Macros and macro parameters Type definitions Rules for Using Identifiers Only Letter, Digits and Underscore(_) 1st character should be letter or _ Both Upper/lower case can be used It can be of any length No space and Special symbol is used It cant be a keyword

C’s keyword Basic Building Block of the Program
This are the Reserved words This word’s cant be changed C keywords auto break case char const continue default do double else enum extern float for goto if int long register return short signed sizeof static struct switch typedef union unsigned void volatile while

Data Types C’s Data Type
This are the type of the data that are going to access within the program. C’s Data Type Primary User defined Derived Empty Char Int Float Double typedef Arrays Pointers Structures Union Void

C’s Data types cont. The primary data types are further classified as below. Integers are the whole numbers, both positive and negative.

C’s Data types cont. Float are the numbers which contain fractional parts, both Positive and Negative.

C’s Data types cont. Char are the characters which contain alpha-numeric character. Characters are usually stored in 8 bits (one byte) of internal storage The void is the Null Data type.

Rules for Naming the Variables
C’s Variables A variable is a data name as well as identifier that may be used to store a data value. Rules for Naming the Variables A variable can be of any combination of alphabets, digits and underscore. The first character of the variable can’t be digits. The length of the variable can’t be exceeded by 8.(ANSI C – 32 Character) No commas, blanks or special symbol are allowed within a variable name. Uppercase and lowercase are significant. That is, the variable Total is not the same as total or TOTAL. It should not be a keyword. White space is not allowed.

C’s Variables cont. Variable Declaration Syntax Description Example
It tells the computer what the variable name and type of the data Syntax data_type a1,a2,a3……..an; Description data_type is the type of the data. a1,a2,a3……an are the list of variables Example int number; char alpha; float price;

C’s Variables cont. Initializing Variables Syntax Description Example
Initialization of variables can be done using assignment operator(=) Syntax a1 = c1 ;(or) data_type a1 = c1; Description a is the variable c is the constant data_type is the type of the data Example int a1 = 29; float f1 = 34.45; char c1 = ‘d’

C’s constant The item whose values can’t be changed during execution of program are called constants

C’s constant Conti… Integer constant eg: roll_number = 12345;
Real Constant eg: pi = 3.14; Decimal Constant Eg. 35 Octal constant Eg. 043 Hexadecimal constant Eg. 0x23 Single Precision Constant Double Precision Constant

Rules for constructing Integer constants
1. An integer constant may be positive or negative (Default sign is positive). 2. An integer constant should not have a decimal point. 3. No commas and blank spaces are allowed in an integer constant. 4. An integer constant, should not use exponent e. The suffix u or U is used for denoting unsigned int constants, I or L is used for denoting long int constants, and s is used for denoting short int constants. Positive integer Constants 123 4000 +7257 Negative integer Constants -78 -9876 -23 Unsigned integer Constants 1234u 5678u 21057u Short integer Constants -5008s -23s 1234s Long integer Constant L 0x52123L Unsigned short integer Constants 1234us 5008us 8476us Unsigned long integer Constants ul ul

Real Constants are often called as Floating – point constants. Real
constants is classified as two types. 1. Fractional form. 2. Exponential form. Rules for constructing real constants (fractional form) 1. A real constant may be positive or negative (Default sign in positive 2. A real constant must have a decimal point. 3. No commas and blank spaces are allowed in a real constant. Example:

Rules for constructing Real Constants (Exponential Form)
1. The mantissa part and the exponential part should be separated by a letter e. 2. The mantissa part and the exponential part may be positive or negative (Default sign is positive) 3. The mantissa and the exponent part must have at least one digit. 4. No commas and blank spaces are allowed in a real constant. Example: +3.2e+5 3.4e e-5 -10.9e5 9.7e e8

Rules for constructing String Constants
1. A string constant may be a single alphabet or a digit, or a special character or sequence of alphabets or digits enclosed in double quotes. 2. Every string constant ends up with a NULL character, which is automatically assigned. Example: “w” “100” “Madhu” “ABC 123” “Good_Morning” “s1000” “219.71” “ ”

C’ Delimiters Delimiters are the symbols, which has some syntactic meaning and has got significance. Symbol Name Meaning # Hash Pre-processor directive , comma Variable delimiters (to separate list of variables) : colon Label delimiters ; Semi colon Statement delimiters () parenthesis Used in expressions or in functions {} Curly braces Used in blocking ‘C’ structure [] Square braces Used along with arrays

C’ Statements Statement can be defined as set of declarations (or) sequence of action All statements in ‘C’ ends with semicolon(;) except condition and control statement

C’ Statements

Equivalent C Expression
Expression Statement 1. An Expression is a combination of constant, variables, operators, and function calls written in any form as per the syntax of the C language. 2. The values evaluated in these expressions can be stored in variables and used as a part for evaluating larger expressions. 3. They are evaluated using an assignment statement of the form. variable = expression; 4. For Example, age = 21; result = pow(2,2); simple_interest = (p * n * r) / 100; Algebraic Expression Equivalent C Expression (mnp + qr – at) (m*n* p+q*r-s*t) (a+b+c) (x+y+z) (a+b+c)*(x+y+z) abc / x+y (a*b*c) / (x+y) 8a3 + 3a2 + 2a 8*a*a*a+3*a*a+2*a (a-b)+(x-y) / mn ((a-b)+(x-y)) / (m*n) 8.8(a+b-c) + c / pq 8.8 * (a+b-c) + (c / (p*q)) Lecture Notes 1

Compound Statements 1. A group of valid C expression statements placed within an opening flower brace ‘{‘ and closing flower brace ‘}’ is referred as a Compound Statements. 2. For Example, { X = (A + (B * 3) – C); Y = A + B * 3; Z = A * (B * 3 – C); } Control Statements 1. This statement normally executed sequentially as they appear in the program. 2. In some situations where we may have to change the order of execution of statements until some specified conditions are met. 3. The control statement alter the execution of statements depending upon the conditions specified inside the parenthesis. 4. For Example, if (a == b) if ((x < y) && (y > z)) { { } } Lecture Notes 1

ESCAPE SEQUENTIAL CHARACTER OR BACKSLASH CHARACTER CONSTANTS
Meaning ‘\a’ Audible alert (bell) ‘\b’ Back space ‘\f’ Form feed ‘\n’ New line ‘\r’ Carriage return ‘\t’ Horizontal tab ‘\v’ Vertical tab ‘\’’ Single quote ‘\”’ Double quote ‘\?’ Question mark ‘\\’ Backslash ‘\0’ Null

Operators An operator is a symbol that specifies an operation to be performed on the operands Some operator needs two operands (binary) Eg: a+b; ‘+’ is an operator and ‘a’ and ‘b’ are the operands Some operator needs one operand (unary) Eg: ++a; ‘++’ is an operator and a is the operand

Types of Operators

Arithmetic Operators This operators help us to carryout basic arithmetic operations such addition, subtraction, multiplication, division Operator Meaning Examples + Addition 1+2 = 3 - Subtraction 3 -2 = 1 * Multiplication 2*2 = 4 / Division 2/2 = 1 % Modulo division 10/3= 1 Operation Result Examples Int/int int 2/2 = 1 Real/int real 7.0/2 = 3.5 Int/real 7/2.0 = 3.5 Real/real 7.0/2.0 = 3.5

Relational Operator This are used to compare two or more operands.
Operands can be variables, constants or expression. eg: comparison of two marks or two values. Operator Meaning Example Return value < is less than 5<6 1 <= is less than or equal to 4<=4 > is greater than 5>7 >= is greater than or equal to 7>=5 == equal to 6==6 != not equal to 5!=5

Logical Operator This operators are used to combine the results of two or more conditions. Operator Meaning Example Return value && Logical And (9>2) && (6>4) 1 || Logical OR (9>2) || (3.4) ! Logical Not 4 ! 4 AND truth table True False OR truth table True False

Assignment Operator This are used to assign a value or an expression or a variable to another variable eg: a = 10; n1 = 20; Syntax: identifier = expression; Compound Assignment This operator are used to assign a value to a variable in order to assign a new value to a variable after performing a specified operation. eg: a+=10,n1-=20; Nested Assignment (Multiple) This operator are used to assign a single value to multiple variables eg: a=b=c=d=e=10;

List of Shorthand or Compound Assignment Operator
Meaning += Assign Sum -= Assign Difference *= Assign Product /= Assign Quotient %= Assign Remainder ~= Assign One’s Complement <<= Assign Left Shift >>= Assign Right Shift &= Assign Bitwise AND != Assign Bitwise OR ^= Assign Bitwise X - OR

Increment and Decrement operator
C provide two operator for incrementing a value or decrementing a value a) Increment operator (adds one to the variable) b) Decrement operator (Minus one to the variable) eg: a++ (if a= 10 then the output would be 11) Operator Meaning ++X Pre increment X++ Post increment --X Pre decrement X-- Post decrement

Increment and Decrement operator Conti…
If the value of the operand x is 3 then the various expressions and their results are Expression Result + + X 4 X + + 3 - - X 2 X - - The pre – increment operation (++X) increments x by 1 and then assign the value to x. The post – increment operation (X++) assigns the value to x and then increments 1. The pre-decrement operation ( --X) decrements 1 and then assigns to x. The post – decrement operation (x--) assigns the value to x and then decrements 1. These operators are usually very efficient, but causes confusion if your try to use too many evaluations in a single statement.

Conditional Operator It is used check the condition and execute the statement depending upon the condition Syntax Condition?exp1:exp2 Description The ‘?’ operator act as ternary operator, it first evaluate the condition, if it is true then exp1 is evaluated if the condition is false then exp2 is evaluated Example a= 2; b=3 ans = a>b?a:b; printf (ans);

Bitwise Operator This are used to manipulate the data at bit level
It operates only on integers Operator Meaning & Bitwise AND | Bitwise OR ^ Bitwise XOR << Shift left >> Shift right ~ One’s complement

Bitwise Operator cont. The truth table for Bitwise AND,OR and XOR Bitwise AND (both the operand should be high for 1) 1 Eg: x = 3 = y = 4 = x&y = Bitwise OR (either of the operand should be high for 1) 1 Eg: x = 3 = y = 4 = x|y = Bitwise XOR (the two operands should be different for 1) 1 Eg: x = 3 = y = 4 = x ^ y =

Bitwise Operator cont. Bitwise One’s Complement
The one’s complement operator (~) is a unary operator, which causes the bits of the operand to be inverted (i.e., one’s becomes zero’s and zero’s become one’s) For Example, if x = 7 i.e 8 – bit binary digit is The One’s Complement is Bitwise Left Shift Operator The Left shift operator (<<) shifts each bit of the operand to its Left. The general form or the syntax of Left shift operator is variable << no. of bits positions if x = 7 (i.e., ) the value of y in the expression y = x <<1 is 14 = 14 since it shifts the bit position to its left by one bit. The value stored in x is multiplied by 2N (where n is the no of bit positions) to get the required value. For example, if x = 7 the result of the expression y = x << 2 is y = x * 22 (i.e. 28)

Bitwise Operator cont. Bitwise Left Shift Operator
The Right shift operator (>>) shifts each bit of the operand to its Right. The general form or the syntax of Right shift operator is variable >> no. of bits positions if x = 7 (i.e., ) the value of y in the expression y = x >> 1 is 3 = 3 since it shifts the bit position to its right by one bit. The value stored in x is divided by 2N (where n is the no of bit positions) to get the required value. For example, if x = 7 the result of the expression y = x << 2 is y = x / 22 (i.e. 1). If you use the left shift operator i.e. x = x << 1 the value of x will be equal to 2 (i.e., ) since the lost bit cannot be taken back.

Special Operator Some of the special operators used in C language. These operators are referred as separators or punctuators. 1. Ampersand (&) 2. Comma (,) 3. Asterisk ( * ) 4. Ellipsis (…) 5. Braces ({}) 6. Hash (#) 7. Brackets ([]) 8. Parenthesis (()) 9. Colon (:) 10. Semicolon(;)

Special Operator Operator Meaning Ampersand (&)
Ampersand (&) also referred as address operator usually precedes the identifier name, which indicates the memory location (Address) of the identifier. Asterisk ( * ) Asterisk ( * ) also referred as an indirection operator, is an unary operator usally precedes the identifier name, which indicates the creation of a pointer operator. Braces ( {} ) The opening ( { ) and closing ( } ) braces indicate the start and end of compound statement or a function. A semicolon is not necessary after the closing brace of the statement, except in case of structure declaration. Brackets ( [ ] ) Brackets [ ] also referred as array subscript operator is used to indicate single and multi dimensional array subscripts.

Special Operator Operator Meaning Colon ( : )
Colon ( : ) is used in labels. Comma ( , ) Comma ( , ) operator is used to link the related expressions together. Comma used expressions are linked from left to right and the value of the right most expression is the value of the combined expression. The comma operator has the lowest precedence of all operators. For Example: sum = (x = 5, y = 3, x + y); The result will be sum = 8 Ellipsis (. . .) Ellipsis (…) are three successive periods with no white space in between them. It is used in function prototypes to indicate that this function can have any number of arguments with varying types. For Example: void fun(char cName, int iAge, float fSalary, . . .); The above declaration indicates that fun () is a function that takes at least three arguments, a char, an int and a float in the order specified but can have any number of additional arguments of any type. Hash ( # ) Hash ( # ) also referred as pound sign is used to indicate preprocessor directives.

Special Operator Operator Meaning Parenthesis ( () )
Parenthesis ( ) also referred as function call operator is used to indicate the opening and closing of function prototypes, function calls, function parameters, etc., Parenthesis are also used to group expressions, and there by changing the order of evaluation of expressions. Semicolon ( ; ) Semicolon ( ; ) is a statement terminator. It is used to end a C statement. All valid C statements must end with a semicolon. Which the C compiler interprets as the end of the statement. Sizeof ( ) The sizeof operator is not a library function but a keyword, which returns the size of the operand in bytes. The sizeof operator always, precedes its operand. This operator can be used for dynamic memory allocation. Example: sizeof(char) = 1 2. sizeof(int) = 2 3. sizeof(float) = 4 4. sizeof(doubles) = 8

Operator Precedence and Associativity of Operator

What is Precedence Rule and Associative Rule
Each operator in C has a precedence associated with it. This precedence is used to determine how an expression involving more than one operator is evaluated. These are distinct levels of precedence and an operator may belong to one of these levels. The operators at the higher level of precedence are evaluated first. The operators of the same precedence are evaluated either from ‘left to right’ or from ‘right to left’, depending on the level. That is known as the associativity property of an operator.

Arithmetic operators precedence
The precedence of an operator gives the order in which operators are applied in expressions: the highest precedence operator is applied first, followed by the next highest, and so on. eg: Arithmetic operator precedence Precedence operator High *,/,% Low +,- The arithmetic expression evaluation is carried out using two phases from left to right through the expressions

Relational operators precedence
Example: if (x == && y <10) The precedence rules say that the addition operator has a higher priority than the logical operator (&&) and the relational operators (== and <). Therefore, the addition of 10 and 15 is executed first. This is equivalent to: if (x == 25 && y < 10) The next step is to determine whether x is equal to 25 and y is less than 10, if we assume a value of 20 for x and 5 for y, then x == 25 is FALSE (0) y <10 is TRUE (1) Note that since the operator < enjoys a higher priority compared to ==, y < 10 is tested first and then x ==25 is tested. Finally we get, if (FALSE && TRUE) Because one of the conditions is FALSE, the complex condition is FALSE. In the case of &&, it is guaranteed that the second operand will not be evaluated if the first is zero and in the case of || , the second operand will not be evaluated if the first is non – zero.

Precedence and Associativity Table
The following table lists all the operators, in order of precedence, with their associativity Operators Operations Associativity priority () Function call Left to Right 1 [] Square brackets -> Structure operator . Dot operator + Unary plus Right to Left 2 - Unary minus ++ Increment -- Decrement ! Not

Precedence and Associativity Table cont.
Operators Operations Associativity priority ~ Complement Right to Left 2 * Pointer operation & Address operator Sizeof Size of operator type Type cast Multiplication Left to Right 3 / Division % Modulo + Addition 4 - Subtraction

Operators Operations Associativity priority << Left shift Left to Right 5 6 >> Right shift < is less than <= is less than or equal to > is greater than >= is greater than or equal to == equal to != not equal to & Bitwise AND 7 | Bitwise OR ^ Bitwise XOR

Operators Operations Associativity priority && Logical And Left to Right 8 || Logical OR ?= Conditional Right to Left 9 =,*=,-=,&=,+=,^=,!=,<<=,>>= Assignment 10 , comma 11

Rules for evaluation of expression
Evaluate the sub expression from left to right if parenthesized. Evaluate the arithmetic expression from left to right using the rules of precedence. The highest precedence is given to the expressions with in parenthesis. Apply the associative rule if more operators of the same precedence occurs. Evaluate the inner most sub expression if the parenthesis are nested.

Sample Expression Exp = a - 2 * a * b + b / 4 Let us have a=10,b=20
Phase I exp = 2*10*20 , 20/4 will be evaluated. phase II exp = will be evaluated. Result exp = -395.

Expression Evaluation
Let us see some examples for evaluating expression. Let a = 5, b = 8, c = 2. x = b / c + a * c 10 4 14 Lecture Notes 1

Expression Evaluation
Let us see some examples for evaluating expression. Let a = 5, b = 8, c = 2. y = a + (b * 3) - c 24 29 27 Lecture Notes 1

TYPE CONVERSION OR TYPE CASTING

What is Type Conversion or Type Casting
Type Casting means One data type converted into another data type. This is called Type conversion or Type casting. Example: 1. Integer into floating point number 2. Character into integer 3. Floating point number into Integer Number Type conversion is classified into two types. 1. Implicit Type Conversion (Automatic Type Conversion) 2. Explicit Type Conversion (Manual Type Conversion) Type Conversion Implicit Conversion Explicit Conversion Automatic Conversion Casting Operation

Type Conversion Hierarchy
long double Implicit Type Conversion double float unsigned long int long int unsigned int int short char Explicit Type Conversion

Implicit Type Conversion
The Implicit Type Conversion is known as Automatic Type Conversion. C automatically converts any intermediate values to the proper type so that the expression can be evaluated without loosing any significance. Implicit type Conversion also known as Converted Lower order data type into Higher order data type. Implicit Type Conversion also known as Widening. Example: int a, b; float c; c = a + b; Print c; float a,b; int c; c = a + b; // This is Wrong

Explicit Type Conversion
The Explicit Type Conversion is, there are instances when we want to force a type conversion in a way that is different from the automatic conversion. The Explicit Type Conversion is Converted Higher order data type into Lower order data type. The Explicit type Conversion is also known as borrowing. The Explicit type conversion forces by a casting operator. Disadvantage of Explicit Type Conversion float to int causes truncation of the fractional part. double to float causes rounding of digits. Long int to int causes dropping of the excess higher order bits. The general form of the casting is (type_name) expression; Where type_name is one of the standard C data type. The expression may be a constant, variables or an expression. For Example: float a, b; int c; c = (int) a + (int) b; Print c;

Use of Casts Example Action x = (int) 7.5
7.5 is converted to integer by truncation. a = (int) 21.3 / (int) 4.5 Evaluated as 21 / 4 and the result would be 5. b = (double) sum / n Division is done in floating point mode. y = (int) (a + b) The result of a + b is converted to integer. z = (int) a + b a is converted to integer and then added to b. p = cos ((double) x) Converts x to double before using it.

Input And Output Functions

Ip / Op Statements We have two methods for providing data to the program. a) Assigning the data to the variables in a program. b) By using the input/output statements. ‘c’ language supports two types of Ip / Op statements This operations are carried out through function calls. Those function are collectively known as standard I / O library

Ip / Op Statements cont.

Unformatted Ip / Op statements
These statements are used to input / output a single / group of characters from / to the input / output device. Single character Input/output function getch() function Syntax char variable = getch(); Description char is the data type of the variable; getch() is the function Example char x = getch(); putch (x); putch() function Syntax putch (character variable); Description char variable is the valid ‘c’ variable of the type of char data type. Example char x ; putch (x);

Unformatted Ip / Op statements cont.
Group of character Input / output function. Gets() and puts are used to read / display the string from / to the standard input / output device. gets() function Syntax gets (char type of array variable); Description valid ‘c’ variable declared as one dimensional array. Example char s[10]; gets (s); puts() function Syntax puts (char type of array variable) Description valid ‘c’ variable declared as one dimensional array. Example char s[10]; gets (s); puts (s);

Sample Program #include<stdio.h> Void main() { char name[10];
char address[20]; Puts(“Enter the name : ”); gets(name); puts(“Enter the address : ”); gets(address); puts(“Name = “) puts(name); puts(“Address = “); puts(address); }

Formatted Ip / Op statements
It refers to Input / Output that has been arranged in a particular format. Using this statements, the user must specify the type of data, that is going to be accessed. scanf() (This function is used to enter any combination of input). Syntax scanf (“control strings”,var1,var2…..var n); Description control strings is the type of data that user going to access via the input statements. var1,var2 are the variables in which the data’s are stored. Example int n; scanf (“%d”, &n);

Formatted Ip / Op statements
Control strings i) It is the type of data that user is going to access via the input statement ii) These can be formatted . iii) Always preceded with a ‘%’ symbol. Format code Variable type Display %c Char Single character %d Int Decimal integer to 32768 %s Array of char Print a Strings %f Float or double Float point value without exponent %ld Long int Long integer to 65535 %u Unsigned decimal integer %o Octal integer number without leading zero %x Hexadecimal integer number without leading 0x %e Float point values in exponent form %h int Short integer

Rules for scanf() The control strings must be preceded with ‘%’ sign and must be within quotations. If there is a number of input data items, items should be separated by commas and must be preceded with ‘&’ sign except for char data types. The control strings and the variables going to input should match with each other. It must have termination. The scanf() reads the data values until the blank space in numeric input. Apart from ‘%’ it can have ‘*’ sign. This is used to ignore the values inputted. eg: scanf(“%d%d%*d%*d%d”,&I,&j,&k); if the input is The output will be i = 10, j = 20, k = 50;

Printf() printf() (This function is used to display the result or the output data on to screen) Syntax printf (“control strings”,var1,var2…..var n); Description Control strings can be anyone of the following Format code character code Execution character set Character/strings to be displayed Var1,var2 are the variables in which the data’s are stored. Example printf (“this is computer fundamental class”); printf (“/n computer fundamental class”);

Rules for printf() variables should be separated by commas and need not be preceded with ‘&’ sign. The control strings and the variables must match with each other. The control string must be in quotations and there we can also use any other text to print with data.

Formatted IO / OP Writing integers numbers Syntax Printf (%w.pd”,var1)
Description W is used to specify the minimum field width for the output. P is the precession value. D is the control string specification Example Printf ( “%5.4d”,23); The output will be $0023. Printf (“%05d”,23); The output will be

Formatted IO / OP Writing Real Numbers Syntax Printf (%w.p.f”,var1)
Description W is used to specify the minimum field width for the output. P is the number of digits to be displayed after the decimal point. f is the control string for float. Example Printf ( “%5.2.f”, ); The output will be $ Printf (“%10.2e”, ); The output will be 4.8e+01

Sample Program include<stdio.h> include<conio.h>
void main() { int r,t; char u,y; float a,b,c,d; clrscr(); scanf("%d%d",&r,&t); printf("enter the char value"); scanf("%c",&y); printf("\n%9c%9c",r,t); printf("\n\t%d\t\%d",r,t); printf("\n the value of u is %c",y); getch(); }

Control Statements (Decision Making)

Control Statements A program consists of a number of statements which are usually executed in sequence. Programs can be much more powerful if we can control the order in which statements are run. Statements fall into three general types; Assignment, where values, usually the results of calculations, are stored in variables. Input / Output, data is read in or printed out. Control, the program makes a decision about what to do next.

Control Statements Control statements in C are used to write powerful programs by; Repeating important sections of the program. Selecting between optional sections of a program.

Control Statements

Control Statements cont.
Structure Meaning Example Sequential It means the instructions are carried out in sequence a+=5; a=a+b; Selection Sequence of the instruction are determined by the result of the condition if (x>y) a = a+1; else a= a-1; Iteration Here the statements are repeatedly executed while (a<=10) printf (“%d” , a); Encapsulation Here the an iteration statement can have selection inside it or vice versa { if(a>5) printf (%d” , a); } ‘C’ language provides four general structure by which statements can be executed

SELECTION STATEMENT

Types of Selection Statement
Simple if Selection statement if else Selection statement Nested if else Selection statement else if ladder Selection statement

Simple if Selection statement
It is used to control the flow of execution of the statements and also to test logically whether the condition is true or false. if the condition is true then the statement following the “if “ is executed if it is false then the statement is skipped. Syntax: if ( condition ) { statement ; } Test Condition True Executable X - Statement

Selection Statement Properties of an if statement
if the condition is true then the simple or compound statements are executed. If the condition is false it will skip the statement. The condition is given in parenthesis and must be evaluated as true or false. If a compound structure is provided, it must be enclosed in opening and closing braces

//Biggest of Two Numbers
#include <stdio.h> void main() { int a, b; clrscr(); printf(“Enter the A and B Value:\n”); scanf(“%d”, &a); if (a > b) printf(“A is Big”); } getch();

Basic Relational Operators
Basic Relational Operators can be used in C to make “if” statement conditions more useful The 6 Basic Relational Operators are > , <, >= , <= , == , != (greater than, less than, greater than or equal to, less than or equal to, equal to, not equal to) Basic Logic Operators Basic Logic Operators can be used to combine more than one condition in an “if” statement or invert the result of a condition The 3 Basic Logic Operators are && , || , ! (and, or, not)

Executable Y - Statement Executable X - Statement
The if else statement It is used to execute some statements when the condition is true and execute some other statements when the condition is false depending on the logical test. Syntax: if ( condition ) { statement 1 ; (if the condition is true this statement will be executed) } else statement 2 ; (if the condition is false this statement will be executed) Test Condition False True Executable Y - Statement Executable X - Statement

if else statements if (result >= 45) { printf ( “ Passed\n “ ) ;
printf ( “ Congratulations\n “ ) } else printf ( “ Failed\n “ ) ; printf ( “ Good luck in the resits\n “ ) ;

// Biggest of Two Numbers
#include <stdio.h> void main() { int a, b; clrscr(); printf(“Enter the A and B Value:\n”); scanf(“%d”, &a); if (a > b) printf(“A is Big”); } else printf(“B is Big”); getch();

// Given Number is ODD or EVEN Number
#include <stdio.h> void main() { int n; clrscr(); printf(“Enter the Number:\n”); scanf(“%d”, &n); if (n % 2 == 0) printf(“Given Number is Even Number”); } else printf(“Given Number is Odd Number”); getch();

Nested if….. else statement
when a series of if…else statements are occurred in a program, we can write an entire if…else statement in another if…else statement called nesting Syntax: if ( condition 1) { if ( condition 2) statement 1 ; else statement 2 ; } if (condition 3) statement 3; statement 4;

Executable X2 - Statement Executable X1 - Statement
Test Condition_1 FALSE TRUE Test Condition_2 FALSE TRUE Executable X2 - Statement Executable X1 - Statement Test Condition_3 FALSE TRUE Executable X4 - Statement Executable X3 - Statement

// Biggest of Three Numbers
#include<stdio.h> void main() { int a, b, c; clrscr(); printf(“Enter the Three Numbers:\n”); scanf(“%d%d%d”,&a,&b,&c); if (a > b) if (a > c) printf(“A is Big”); else printf(“C is Big”); } if (b > c) printf(“B is Big”); getch();

else if Ladder or Multiple if else Statements
When a series of decisions are involved we have to use more than one if – else statement called as multiple if’s. Multiple if – else statements are much faster than a series of if – else statements, since theif structure is exited when any one of the condition is satisfied. Syntax: if (condition_1) executed statement_1; else if (condition_2) executed statement_2; else if (condition_3) executed statement_3; else if (condition_n) executed statement_n; else executed statement_x;

Test Condition_1 Exec. Stat_1 Test Condition_2 Exec. Stat_2
FALSE TRUE Exec. Stat_1 Test Condition_2 FALSE TRUE Exec. Stat_2 Test Condition_3 FALSE TRUE Exec. Stat_3 Test Condition_n FALSE TRUE Exec. Stat_X Exec. Stat_n

else if Ladder if (result >= 75) printf ( “ Passed: Grade A\n “ ) ; else if (result >= 60) printf ( “ Passed: Grade B\n “ ) ; else if (result >= 45) printf ( “ Passed: Grade C\n “ ) ; else printf ( “ Failed\n “ ) ;

/*This program reads in a simple expression with a very restricted format and prints out its value. */ main() { int n1,n2; int val; char op; printf("Enter a simple expression "); scanf("%d%c%d",&n1,&op,&n2); if(op == '+') val = n1 + n2; else if(op == '-') val = n1 - n2; else if(op == '/') val = n1 / n2; else if(op == '*') val = n1 * n2; else { printf(“?? operator %c\n",op); exit(1); } printf("%d%c%d = %d\n",n1,op,n2);

Sample Program Write a program to calculate the sales commission for the data given below: Sales value (Rs) Commission(%) Less than No commission Above 1000 but below % of sales Above 2000 but below % of sales Above % of sales

#include<stdio.h>
#include<conio.h> Void main() { float sales, com; printf(“Enter the sales value :”); scanf(“%f”, &sales); if(sales<=1000) com = 0; else if(sales>1000 && sales <=2000) com = sales*5/100; else if(sales>2000 && sales <=5000) else com = sales * 10/100; printf(“The commission for the sales value %f is %f”, sales, com); }

THE SWITCH STATEMENT The control statements which allow us to make a decision from the number of choices is called switch (or) Switch-case statement. It is a multi way decision statement, it test the given variable (or) expression against a list of case value. switch (expression) { case constant 1: simple statement (or) compound statement; case constant 2: case constant 3: } switch (expression) { case constant 1: simple statement (or) compound statement; case constant 2: default : }

Example Without Break Statement
Example With Break Statement #include<stdio.h> void main () { int num1,num2,choice; printf(“Enter the Two Numbers:\n”); scanf(“%d%d”,&num1,&num2); printf(“1 -> Addition\n””); printf(“2->Subtraction\n”); printf(“3->Multiplication\n”); printf(“4->Division\n”); printf(“Enter your Choice:\n”); scanf(“%d”,&choice); switch(choice) case 1: Printf(“Sum is %d\n”, num1+num2); case 2: Printf(“Diif. is %d\n”, num1-num2); case 3: Printf(“Product is %d\n”, num1*num2); case 4: Printf(“Division is %d\n”, num1/num2); default: printf (“Invalid Choice…..\n”); } getch(); #include<stdio.h> void main () { int num1,num2,choice; printf(“Enter the Two Numbers:\n”); scanf(“%d%d”,&num1,&num2); printf(“1 -> Addition\n””); printf(“2->Subtraction\n”); printf(“3->Multiplication\n”); printf(“4->Division\n”); printf(“Enter your Choice:\n”); scanf(“%d”,&choice); switch(choice) case 1: printf(“Sum is %d\n”, num1+num2); break; case 2: printf(“Diif. is %d\n”, num1-num2); case 3: printf(“Product is %d\n”, num1*num2); case 4: printf(“Division is %d\n”, num1/num2); default: printf (“Invalid Choice…..\n”); } getch();

Fall through Statement in C

Rules for Switch The expression in the switch statement must be an integer or character constant. No real numbers are used in an expression. The default is optional and can be placed anywhere, but usually placed at end. The case keyword must be terminated with colon (:); No two case constant are identical. The values of switch expression is compared with case constant in the order specified i.e from top to bottom. The compound statements are no need to enclose within pair of braces. Integer Expression used in different case statements can be specified in any order. A switch may occur within another switch, but it is rarely done. Such statements are called as nested switch statements. The switch statement is very useful while writing menu driven programs.

Limitations of using a switch statement
Only One variable can be tested with the available case statements with the values stored in them (i.e., you cannot use relational operators and combine two or more conditions as in the case of if or if – else statements). Floating – point, double, and long type variables cannot be used as cases in the switch statement. Multiple statements can be executed in each case without the use of pair of braces as in the case of if or if – else statement.

Iteration Statements 2. do….while loops 3. for Loop
Iteration statements is also known as Looping statement. A segment of the program that is executed repeatedly is called as a loop. Some portion of the program has to be specified several number of times or until a particular condition is satisfied. Such repetitive operation is done through a loop structure. The Three methods by which you can repeat a part of a program are, 1. while Loops 2. do….while loops 3. for Loop Loops generally consist of two parts : Control expressions: One or more control expressions which control the execution of the loop, Body : which is the statement or set of statements which is executed over and over

Any looping statement , would include the following steps:
Initialization of a condition variable Test the control statement. Executing the body of the loop depending on the condition. Updating the condition variable.

While Loop A while loop has one control expression, and executes as long as that expression is true. The general syntax of a while loop is A while loop is an entry controlled loop statement. initialize loop counter; while (condition) { statement (s); increment or decrement loop counter }

Increment or Decrement
Start Initialize Test Condition False Stop True Body of Loop Increment or Decrement

Example: // Summation of the series 1 + 2 + 3 + 4 + …….
#include <stdio.h> void main() { int i, sum; clrscr(); i = 1; sum = 0; while(i<=10) sum = sum + i printf(“The Sum Value is:%d\n”,i); ++I; } getch(); // Print the I Values #include <stdio.h> void main() { int i; clrscr(); i = 0; while(i<=10) printf(“The I Value is :%d\n”,i); ++I; } getch();

//Summation of the series 11 + 22 + 33 + …..
Example: //Summation of the series ….. #include <stdio.h> #include<math.h> void main() { int i, sum; clrscr(); i = 1; sum = 0; while(i<=10) sum = sum + pow(i,i) printf(“The Sum Value is:%d\n”,i); ++I; } getch(); } //Summation of the series ….. #include <stdio.h> #include<math.h> void main() { int i, sum; clrscr(); i = 1; sum = 0; while(i<=10) sum = sum + i*i; //or I ^2 or pow(i, 2) printf(“The Sum Value is:%d\n”,i); ++I; } getch(); }

Wap to print the summation of digits of any given number.
#include<stdio.h> void main() { int number=0, rem=0, sum=0; clrscr(); printf(“Enter the value for number”); scanf(“%d”,&n); while(number > 0) rem = number % 10; sum = sum + rem; number = number / 10; } printf(“the summation value of the given number %d is = %d”,number,sum);

THE do-while LOOP initialize loop counter; do { statement (s);
The body of the loop may not be executed if the condition is not satisfied in while loop. Since the test is done at the end of the loop, the statements in the braces will always be executed at least once. The statements in the braces are executed repeatedly as long as the expression in the parentheses is true. Make a note that do while ends in a ; (semicolon) Note that Do… While Looping statement is Exit Controlled Looping statement initialize loop counter; do { statement (s); increment or decrement loop counter } while (condition);

Increment or Decrement
Start Initialize Body of Loop Increment or Decrement Test Condition True False Stop

Difference Between While Loop and Do – While Loop
Sl.No. while loop do-while loop 1. The while loop tests the condition before each iteration. The do – while loop tests the condition after the first iteration. 2. If the condition fails initially the loop is Skipped entirely even in the first iteration. Even if the condition fails initially the loop is executed once.

Example: // Print the I Values #include <stdio.h> void main() {
int i; clrscr(); i = 0; do printf(“The I Value is :%d\n”,i); ++I; } while(i<=10); getch(); // Print the I Values #include <stdio.h> void main() { int i; clrscr(); i = 11; do printf(“The I Value is :%d\n”,i); ++I; } while(i<=10); getch();

Wap to print the Fibonacci series for any given number Using Do…
Wap to print the Fibonacci series for any given number Using Do….While Loop #include <stdio.h> void main() { int i, f1,f2,f3; clrscr(); f1 = 0; f2 = 1; printf(“The Fibonacci Series is:\n”) printf(“%d\n”,f1); printf(“%d\n”,f2); do f3 = f1 + f2; printf(%d\n”,f3); f1 = f2; f2 = f3; ++i; } while(i <= 10); getch();

for Loop for( expr1; expr2 ;expr3) { Body of the loop; }
The for loop is another repetitive control structure, and is used to execute set of instruction repeatedly until the condition becomes false. To set up an initial condition and then modify some value to perform each succeeding loop as long as some condition is true. The syntax of a for loop is The three expressions : expr1 - sets up the initial condition, expr2 - tests whether another trip through the loop should be taken, expr3 - increments or updates things after each trip. for( expr1; expr2 ;expr3) { Body of the loop; }

Initialize; test_condition; Increment / Decrement
Start Initialize; test_condition; Increment / Decrement Body of Loop Stop

Given example will print the values from 1 to 10.
#include<stdio.h> void main() { for (int i = 1; i <= 10; i++) printf("i is %d\n", i); } There is no need of { } braces for single line statement and for multiple line it is essential else it will consider only next line of for statement.

Given example of Multiplication Table
#include<stdio.h> #include<conio.h> void main() { int mul,limit,c,i; clrscr(); printf("Enter the Multiplication Number:\n"); scanf("%d",&mul); printf("Enter the Limits:\n"); scanf("%d",&limit); for(i=1;i<=limit;i++) c = i * mul; printf("%d * %d: %d\n",i,mul,c); } getch();

Additional Features of for Loop
Case 1: The statement p = 1; for (n = 0; n < 17; ++ n) can be rewritten as for (p = 1, n = 0; n < 17;++n) Case 2: The second feature is that the test – condition may have any compound relation and the testing need not be limited only to the loop control variable. sum = 0; for (i = 1; i < 20 && sum < 100; ++ i) { sum = sum + i; printf(“%d %d\n”, i, sum); }

Additional Features of for Loop Conti…
Case 3: It also permissible to use expressions in the assignment statements of initialization and increments sections. For Example: for (x = (m + n) / 2; x > 0; x = x / 2) Case 4: Another unique aspect of for loop is that one or more sections can be omitted, if necessary. m = 5; for ( ; m ! = 100 ;) { printf(“%d\n”,m); m = m + 5; } Both the initialization and increment sections are omitted in the for statement. The initialization has been done before the for statement and the control variable is incremented inside the loop. In such cases, the sections are left ‘blank’. However, the semicolons separating the sections must remain. If the test – condition is not present, the for statement sets up an ‘infinite’ loop. Such loops can be broken using break or goto statements in the loop.

Additional Features of for Loop Conti…
Case 5: We can set up time delay loops using the null statement as follows: for ( j = 1000; j > 0; j = j – 1) 1. This is loop is executed 1000 times without producing any output; it simply causes a time delay. 2. Notice that the body of the loop contains only a semicolon, known as a null statement. Case 6: This implies that the C compiler will not give an error message if we place a semicolon by mistake at the end of a for statement. The semicolon will be considered as a null statement and the program may produce some nonsense.

Nesting of for Loop Syntax:
The One for statement within another for statement is called Nesting for Loop. Syntax: for (initialize; test_condi; incre. / decre.) { } Outer for Loop Inner for Loop

// Print the I and J Value
Example // Print the I and J Value #include<stdio.h> #include<conio.h> void main() { int I, j; clrscr(); for (i = 1; I < = 10 ; I ++) printf (“The I Value is %d \n", i); for (j = 1; j < = 10; j ++) printf (“The J Value is %d \t", j); } getch();

Example #include<stdio.h> #include<conio.h> void main() {
// Multiplication Table #include<stdio.h> #include<conio.h> void main() { int sum = 1,a,b; clrscr(); for (a=1;a<=5;a++) printf ("the multiplication table for %d\n",a); for (b=1;b<=12;b++) sum=a*b; printf("%d*%d=",a,b); printf("%d\n",sum); } sum = 0; getch();

Exercise Write a program that will read in N numbers and print out their average. Wap to print the following series for N given number 1+(1+2)+(1+2+3)+( )……… + ++ +++ ++++ +++++ ……….. 1 111 11111

JUMPS IN LOOPS

Loops perform a set of operations repeatedly until the control variable fails to satisfy the test – condition. The number of times a loop is repeated is decided in advance and the test condition is written to achieve this. Sometimes, when executing a loop it becomes desirable to skip a part of the loop or to leave the loop as soon as a certain condition occurs. Jumps out of a Loop is Classified into three types 1. break; 2. continue; 3. goto;

The break Statement break;
A break statement is used to terminate of to exit a for, switch, while or do – while statements and the execution continues following the break statement. The general form of the break statement is The break statement does not have any embedded expression or arguments. The break statement is usually used at the end of each case and before the start of the next case statement. The break statement causes the control to transfer out of the entire switch statement. break;

#include <stdio.h>
void main() { int i; clrscr(); i = 1; while (i < = 10) printf (“The I Value is: %d \n”, i); if (i = = 6) printf (“The I value is Reached 6, So break of the programs\n”); break; } ++ i

void main () { int num1,num2,choice; printf (“Enter the Two Numbers:\n”); scanf(“%d%d”,&num1,&num2); printf(“1 -> Addition\n””); printf(“2->Subtraction\n”); printf(“3->Multiplication\n”); printf(“4->Division\n”); printf (“Enter your Choice:\n”); scanf (“%d”, &choice); switch (choice) case 1: printf (“Sum is %d \n”, num1+num2); break; case 2: printf (“Diif. is %d \n”, num1-num2); case 3: printf (“Product is %d \n”, num1*num2); case 4: printf (“Division is %d \n”, num1/num2); default: printf (“Invalid Choice…..\n”); } getch(); }

The continue Statement
The continue statement is used to transfer the control to the beginning of the loop, there by terminating the current iteration of the loop and starting again from the next iteration of the same loop. The continue statement can be used within a while or a do – while or a for loop. The general form or the syntax of the continue statement is The continue statement does not have any expressions or arguments. Unlike break, the loop does not terminate when a continue statement is encountered, but it terminates the current iteration of the loop by skipping the remaining part of the loop and resumes the control tot the start of the loop for the next iteration. continue;

void main() { int i; clrscr(); i = 1; while (i < = 10) printf (“The I Value is: %d \n”, i); if (i = = 6) printf (“The I value is Reached 6, But Continue this Programs\n”); continue; } ++ i

Differences Between Break and Continue Statement
Sl.No. break continue 1. Used to terminate the loops or to exit loop from a switch. Used to transfer the control to the start of loop. 2. The break statement when executed causes immediate termination of loop containing it. Continue statement when executed causes Immediate termination of the current iteration of the loop.

The goto Statement The goto statement is used to transfer the control in a loop or a function from one point to any other portion in that program. If misused the goto statement can make a program impossible to understand. The general form or the syntax of goto statement is The goto statement is classified into two types a. Unconditional goto b. Conditional goto goto label; Statement (s); ……………. label: statement (s);

Unconditional Goto The Unconditional goto means the control transfer from one block to another block without checking the test condition. Example: #include <stdio.h> void main() { clrscr(); Start: printf(“Welcome\n”); goto Start; getch(); }

Conditional Goto The Conditional goto means the control transfer from one block to another block with checking the test condition. #include <stdio.h> void main() { int a, b; clrscr(); printf (“Enter the Two Value:\n”); scanf (“%d”, &a, &b); if (a > b) goto output_1; else goto output_2; output_1: printf (“A is Biggest Number”); goto Stop; output_2: printf (“B is Biggest Number”); Stop: getch(); }

UNIT IV ARRAYS AND FUNCTIONS

Arrays

Definition of Array An array is a fixed – size sequenced collection of elements of the same data type. It is simply a grouping of like – type data. In its simplest form, an array can be used to represent a list of numbers, or list of names. (OR) Array is a Collection of Homogenous Data Items Example 1. List of temperatures recorded every hour in a day, or a month, or a year. 2. List of employees in an organization. 3. List of products and their cost sold by a store. 4. Test Scores of a class of students.

Types of Array. 1. One Dimensional Array. 2. Two Dimensional Array. 3
Types of Array One Dimensional Array Two Dimensional Array Multi Dimensional Array

One Dimensional Array Y X Z
One Dimensional Array is defined any one of axis (X or Y or Z) in the graph

Arrays So far, we've been declaring simple variables int i;
It is also possible to declare an array of Several elements. an array is a variable that can hold more than one value , The declaration int a[10]; declares an array, named a, consisting of ten elements, each of type int. We can represent the array a above with a picture like this: Arrays are zero-based: the ten elements of a 10-element array are numbered from 0 to 9.

Arrays An array uses a single identifier, together with an integer index, to create one variable that can hold many values An array is created the same as a “normal” variable, but with the addition of square brackets indicating the size of the array Each value in an array is accessed using the identifier and a valid index in square brackets Each value in the array is called an element, and the identifier by itself resolves to the address of where the array is in memory

One Dimensional Arrays
Syntax data_type array_name[size]; Description Data_type valid data type in C language Array_name name given to the array Size1 are the size of the dimensions Example Int a[3]; Float b[4];

Initializing Arrays An array is initialized using a code block containing comma-delimited values which match in position the elements in the array If there are values in the initialization block, but not enough to fill the array, all the elements in the array without values are initialized to 0 in the case of float or int, and NULL in the case of char If there are values in the initialization block, an explicit size for the array does not need to be specified, only an empty Array Element Operator. C will count the values and size the array for you

Initializing Arrays int x [ 5 ] = { 1,2,3,4,5 }; size 10 bytes
creates array with elements 0-4 values 1-5 int x [ 5 ] = { 4,3 }; size 10 bytes creates array with elements 0-4 values 4,3,0,0,0 int x [ ] = { 1,2,3 }; size 6 bytes creates array with elements 0-2 values 1,2,3 char c [ 4 ] = { ‘M’ , ‘o’ , ‘o’ }; size 4 bytes creates array with elements 0-3 values M o o NULL

Arrays Cont’ The first element of the array is x[0], the second element is x[1].. e.g x[0] = 10; x[1] = 20; x[2] = 30 x[3] = 40 x[4] = 50 Total = 150; This loop sets all ten elements of the array a to 0. int a[i]; int i; for(i = 0; i < 10; i = i + 1) a[i] = 0; To copy the contents of one array to another, you must again do so one by one: int b[10]; b[i] = a[i]; Printing Array Values for(i = 0; i < na; i = i + 1) printf("%d\n", a[i]);

Array Basics An array has a fixed number of elements based on its creation The elements are ALWAYS numbered from 0 to 1 less than the array’s size Referencing an element outside of the created bounds is possible but not recommended

Visual Representation of an Array
Offset Address int x[4]; x[2]=23; ? 342901 X Identifier ? 342905 1 23 342909 2 ? 342913 3 Value

The Array Element Operator [ ]
The Array Element Operator is used to reference a specific array element The expression inside the Array Element must resolve to type int. This value is known as an index The value of the index can be any number, but care should be taken that the index falls within the bounds of the array. The bounds of an array are defined as 0 to 1 less than the size of the array

Array Example #include <stdio.h> int main(void) { int x[5];
x[0]=23; valid x[2.3]=5; invalid: index is not an int x[6]=45; valid but not recommended return 0; }

A Simple Array Example #include <stdio.h> int main(void) {
int i , x[ 5 ] , total = 0 ; for ( i = 0 ; i < 5 ; i++ ) printf( “Enter mark %d” , i ); scanf ( “%d” , &x[ i ] ); } total = total + x[ i ]; printf ( “The average is %d” , total / 5 ); return 0;

ARRAYS DON'T declare arrays with subscripts larger than you will need; it wastes memory. DON'T forget that in C, arrays are referenced starting with subscript 0, not 1.

Sample program #include<stdio.h> main() { int a[5],i;
printf(‘enter the array elements”); for(i = 0;i<5;i++) scanf(“%d”,&a[i]); printf(“Array in the reverse order”); for(i = 5;i>0;i--) printf(“%d”,a[i]; }

#inlcude<stdio.h>
#define Max 5; main(); { int a[Max], i, min; int pos = 0; printf(“Enter the array elements”); for(i=0;i<5;i++) scanf(‘%d”,&a[i]); min = a[0]; for(i=1;i<Max;i++) if(a[i] < min) min = a[i]; pos = i; } printf(“ Minimum Value = %d” , min); printf(“ Position of the Minimum Value = %d” , pos);

Exercise Identify the errors if any, #define Max 1.5; main() {
int a[Max]; } int i,a[5]; for(i=0;i<5;i++); a[i] = 0;

main() { int size; scanf(“%d”,&size); int arr[size]; for(int i=1;i<size;i++) scanf(“%d”,&arr[i]); printf(“%d”,arr[i]); }

State whether the following are true or false
The array int num[26] has twenty-six elements. The expression num[1] designates the first element in the array. The expression num[27] designates the twenty-eighth element in the array. What is the difference between the 5’s in these two expressions int num[5]; num[5] = 200;

Two-Dimensional Arrays
Two-dimensional Array: a collection of a fixed number of components arranged in two dimensions All components are of the same type The syntax for declaring a two-dimensional array is: dataType arrayName[intexp1][intexp2]; where intexp1 and intexp2 are expressions yielding positive integer values

Two-Dimensional Arrays (continued)
The two expressions intexp1 and intexp2 specify the number of rows and the number of columns, respectively, in the array Two-dimensional arrays are sometimes called matrices or tables

Two Dimensional Array Y X Z
Two Dimensional Array is defined any Two of axis of XY or YZ or ZX in the graph

Two Dimensional Arrays
Syntax data_type array_name[size_1][size_2]; Description Data_type valid data type in C language Array_name name given to the array Size_1 is the row size of the array Size_2 is the column size of the array Example int a[3][3]; float b[4][4]; Int a[3][2];

Two Dimensional Array Initializing
int table [2][3] = {0,0,0,1,1,1}; int table [2][3] = {{0,0,0},{1,1,1}}; int table [2][3] = { {0,0,0}, {1,1,1} }; int table [ ][3] = { {0,0,0}

Two Dimensional Array Initializing
If the values are missing in an initializer, they are automatically set to zero. For instance, the statement int table [2][3] = { {1,1}, {2} }; will initialize the first two elements of the first row to one, the first element of the second row to two , and all other elements to zero. When all the elements are to be initialized to zero, the following short – cut method may be used. int m[3][5] = { {0},{0},{0} }; The first element of each row is explicitly initialized to zero while other elements are automatically initialized to zero, The following statement will also achieve the same result: int m[3][5] = {0,0};

Accessing Array Components
The syntax to access a component of a two-dimensional array is: arrayName[indexexp1][indexexp2] where indexexp1 and indexexp2 are expressions yielding nonnegative integer values indexexp1 specifies the row position and indexexp2 specifies the column position

1 2 3 4 25.75

Multi – Dimensional Arrays
Three or More Dimensional Array is called the Multi – Dimensional Arrays. Y X Z Three Dimensional array defined in any three of axis of XYZ OR YZX OR ZXY in the graph

Multi Dimensional Arrays
This arrays have more than one dimensions. Syntax data_type array_name[size1][size2]…….[sizen]; Description Data_type valid data type in C language Array_name name given to the array Size1,size2 are the sizes of the dimensions Example Int a[3][3][3]; Float b[4][4][4];

CHARACTER ARRAYS AND STRINGS

Character and Strings An char array is a group of characters that store related data A String is a special char array that does not store related data, but a single piece of data made up of a number of characters OR A string is a sequence of character that is treated as a single data item. Any group of characters defined between double quotation marks is a string constant. Example: Grades can be stored in a char array with the values A,B,C,D,F; when we want to print a specific grade we use only 1 element of the array Example: But for grades like “Pass” and “Fail” we must print ALL the elements

String Conti… Most Computers languages have a string data type; C does NOT There are 3 ways to store strings in memory Fixed Length Stored Length Terminated C adopts the Terminated String approach A string is C is an array of chars terminated by the String Terminator or NULL character \0

Common String Operation
Reading and Writing Strings Combining strings together Copying one string to another Comparing strings for equality Extracting a portion of a string

Declaring and Initializing of String
The General form of String is char string_name [size]; Example: char city [10]; char name[30]; When the complier assigns a character string to a character array, it automatically supplies a multicharacter (‘\0’) at the end of the string. Therefore, the size should be equal to the maximum number of characters in the string plus one. C Permits a character array to be initialized in either of the following two forms: char city [9] = “ NEW YORK”; char city [9] = {‘N’.’E’,’W’,’ ‘,’Y’,’O’,’R’,’K’,’\0’); C also permits us to initialize a character array without specifying the number of elements. In such cases, the size of the array will be determined automatically, base on the number of elements initialiazed. For Example, the statement char string [ ] = {‘G’,’O’,’O’,’D’,’\0’};

DeclaringConti…. G O O D \0 \0 \0 \0 \0
We can also declare the size much larger than the string size in the initializer. That is, the statement. char str[9] = “GOOD”; G O O D \0 \0 \0 \0 \0 The following declaration is illegal. (I) char str[5]; str = “GOOD”; This will result in a compile time error. Also note that we cannot separate the initialization from declaration. (II) char s1[4] = “abc”; char s2[4]; s2 = s2; /* Error */ is not allowed. An array name cannot be used as the left operand of an assignment operator.

Creating a String in C 1820 h array 2820 h string 1821 i 2821 i 1822 !
2822 ! 2823 /0

READING STRINGS FROM TERMINAL
The familiar input function scanf can be used with %s format specification to read in a string of characters. Example: char address [10]; scanf(“%s”,address); The problem with the scanf function is that it terminates its input on the first white space it finds. Therefore, if the following line of text is typed in at the terminal, NEW YORK then only the string “NEW” will be read into the array address, since the blank space after the word ‘NEW’ will terminate the string reading. The scanf calls in the case of character arrays, the ampersand (&) is not required before the variable name. The address array is created in the memory as shown below: N E W \O ? ? ? ? ? ? Note that the unused locations are filled with garbage. If we want to read the entire line “NEW YORK”, then we may use two character arrays of approximate sizes. That is, char adr1[5], adr2[5]; scanf(“%s %s”,adr1,adr2); With the line of text NEW YORK

READING STRINGS FROM TERMINAL
We can also specify the field width using the form %ws in the scanf statement for reading a specified number of characters from the input string. Example: scanf(“%ws”,name); Here two things may happen. 1. The width w is equal to or grater than the number of characters typed in. The entire string will be stored in the string variable. 2. The width w is less than the number of characters in the string. The excess characters will be truncated and left unread. Consider the following statements: char name [10]; scanf(“%5s”,name); The input string RAM and KRISHNA will be stored as: R A M \0 ? ? ? ? ? ? K R I S H \0 ? ? ? ?

Using getchar and gets Functions
Reading a Line of Text We have seen just now that scanf with %s or %ws can read only strings without white spaces. That is, they cannot be used for reading a text containing more than one word. However, C Supports a format specification known as the edit set conversion code % [..] that can be used to read a line containing a variety of characters, including white spaces. Recall that we have used this conversion code in the program segment char line [80]; scanf (“%[^\n]”,line); printf(“%s”,line); will read a line of input from the keyboard and display the same on the screen. We would very rarely use this method. Using getchar and gets Functions To read a single character from the terminal, using the function getchar. We can use this function repeatedly to read successive single characters from the input and place them into a character array. Thus, an entire line of text can be read and stored in an array. The reading is terminated when the newline character (‘\n’) is netered and the null character is then inserted at the end of the string. The getchar function call takes the form: char ch; ch = getchar ( ); Note that the getchar function has no parameters.

void main() { char line[81], character; int c; c = 0; printf("Enter text. Press <Return> at end\n"); do character = getchar( ); line[c] = character; c++; } while(character != '\n'); c = c - 1; line [c] = '\0'; printf("\n%s\n", line);

getchar and gets Conti….
Another and more convenient method of reading a string of text containing white spaces is to use the library function gets available in the <stdio.h> header file. This is a simple function with one string parameter and called as under. gets (str); str is string variable declared properly. It reads characters into str from the keyboard until a new line character is encountered and then appends a null character to the string. Unlike scanf, it does not skip white spaces. For example the code segment char line [80]; gets (line); printf(“%s”,, line); reads a line of text from the keyboard and displays it on the screen. The last two statements may be combined as follows: printf(“%s”,gets(line)); C does not provide operators that work on strings directly. For instance we cannot assign one string to another directly. For example, the assignment statements. string = “ABC” string1 = string2; are not valid.

void main() { char string1[80],string2[80]; int i; printf("Enter a string \n"); printf("?"); scanf("%s",string2); for(i=0;string2[i] != '\o'; i++) string1[i] = string2[i]; string1[i] = '\o'; printf("\n"); printf("%s\n", string1); printf("Number of characters = %d\n",i); }

WRITING A STRINGS TO SCREEN
We have used extensively the printf function with %s format to print strings to the screen. The format %s can be used to display an array of characters that is terminated by the null character. For example, the statement printf(“%s”, name); can be used to display the entire contents of the array name. We can also specify the precision with which the array is displayed. For instance, the specification %10.4 Indicates that the first four characters are to be printed in a field width of 10 columns. However, if we include the minus sign in the specification (e.g., %-10.4s), the string will be printed left-justified. Using putchar and puts Functions Like getchar, C supports another character handling function putchar to output the values of character variables. It takes the following form: char ch = ‘A’; putchar (ch); The function putchar requires one parameter. This statement is equivalent to: printf(“%c”,ch); We have used putchar function to write characters to the screen. We can use this function repeatedly to output a string of characters stored in an array using a loop:

Using putchar and puts Functions Conti…
Example: char name[6] = “PARIS”; for(i=0;i<5;i++) putchar (name[i]); putchar(‘\n’); Another and more convenient way of printing string values is to use the function puts declared in the header file <stdio.h>. This is a one parameter function and invoked as under: puts (str); Where str is a string variable containing a string value. This prints the value of the string variable str and then moves the cursor to the beginning of the next line on the screen. For example, the program segment char line [80]; gets (line); puts (line); Reads a line of text from the keyboard and displays it on the screen. Note that the syntax is very simple compared to using the scanf and printf statements

Function Action STRING HANDLING FUNCTIONS
The C Library supports a large number of string – handling function that can be used to carry out many of the string manipulations. The most commonly used string – handling functions. Function Action strcat ( ) Concatenates two strings strcmp ( ) Compares two strings strcpy ( ) Copies one strings over another strlen ( ) Finds the length of a string

Function

Introduction C function can be classified into two categories, namely, library functions and user – defined functions. main is an example of user – defined functions. printf and scanf belong to the category of library functions. We have also used other library functions such as sqrt, cos, strcat, etc. The main distinction between these two categories is that library functions are not required to be written by us whereas a user – defined function has to be developed by the user at the time of writing a program. Some Characteristic of modular programming are: 1. Each module should do only one thing. 2. Communication between modules is allowed only by a calling module. 3. A module can be called by one and only one higher module 4. No communication can take place directly between modules that do not have calling – called relationship 5. All modules are designed as single – entry, single – exit systems using control structures

Need for User – Defined Functions
1. Every program must have a main function to indicate where the program has to begin its execution. While it is possible to code any program utilizing only main function. It leads to a number of problems. 2. The program may become too large and complex and as a result the task of debugging, testing, and maintaining becomes difficult. 3. If a program is divided into functional parts, then each part m ay be independently coded and later combined into a single unit. These subprograms called ‘functions’ are much easier to understand, debug, and test. 4. The length of a source program can be reduced by using functions at appropriate places. This factor is particularly critical with microcomputers where memory space is limited. 5. It us easy to locate and isolate a faulty function for further investigations. 6. A function may be used by many other programs.

DEFINITION A function is a named, independent section of C code that performs a specific task and optionally returns a value to the calling program. A function is named A function is independent. A function performs a specific task. A function can return a value to the calling program.

Function COND… FUNCTION DECLARATION FUNCTION DEFINITION
FUNCTION INVOCATION (FUNCTION CALL)

FUNCTION DEFINITION SYNTAX
A function definition, also known as function implementation shall include the following elements. 1. Function Name 2. Function Type 3. List of Parameters 4. Local variable declarations 5. Function Statements 6. A Return statement All the six elements are grouped into two parts, namely, 1. Function header (First three Elements) 2. Function Body (Second three Elements) function_type function_name(parameter_list) { local variable declaration; executable statement_1; executable statement_2; return statement; } Example: float mul ( float x, float y) float result; result = x * y; return (result); }

FUNCTION PROTYPING OR FUNCTION DECLARATION
A function prototype is a very important feature of modern C programming It must be added to a C program just before the main function, if we call that function before defining it It tells the compiler what type of value the function returns, numbers and types of parameters, and order in which these parameters are expected. There is no need for a prototype if the function is called after its definition

FUNCTION DECLARATION SYNTAX
Like variables, all functions in a C program must be declared, before they are invoked, A function declaration (also known as function prototype) consists of four parts. 1. Function type (return type) 2. Function name 3. Parameter list 4. Terminating semicolon The general format is Function_type function_name(parameter_list); Example: float mul (float x, float y);

Function Prototype Function Definition
A simple format of a C function definition is as follows: return-value-type function-name(parameters) { Declarations; Statements; Return (expression); }

Difference Between Function Prototyping and Function Definition
Sl.No. Function prototype Function definition 1. It declares the function. It defines the function 2. It ends with a semicolon. It doesn’t end with a semicolon. 3. Declaration need not include parameters. Declaration should include names for the parameters.

WORKING PRINCIPLES

Function Terminologies
Local and global variables Local: a variable defined inside a function Global: a variable defined outside of functions Sl.No. Local Variables Global Variables 1. These are declared within the body of the function. These are declared outside the function. 2. These variables can be referred only within the function in which it is declared. The values of the variables disappear once the function finishes its execution. These variable can be referred from any part of the program value of variables disappear only after the entire execution or the program.

Formal and Actual Parameters
In C, there are two types of parameters Formal parameters appear in the prototype and definition, and are representative of the data types the function expects to receive Actual parameters appear only in a function call and are the actual data passed

Example #include <stdio.h> void MyFun( int ); Formal Parameter
int main( void ) { int x=3; printf( “x has a value of %d”, x); MyFun( x ); Actual Parameter return 0; Parameter Passing } void MyFun( int x ) Formal Parameter x = 77;

Function prototype and definition
#include <stdio.h> int mod(int , int); /* Function Prototype */ void main() { printf("The mod is: %d ", mod(4,5)); } /* Function Definition */ int mod(int x, int y) return x % y;

CATEGORIES OF FUNCTIONS
Category 1: Functions with no arguments and no return values. Category 2: Functions with arguments and no return values. Category 3: Functions with arguments and return a value. Category 4: Functions with no arguments but return a value. Category 5: Functions that return multiple values.

Function with No return type and No arguments
void main() { ……. func1(); } void func1() { ……. }

void add(); void main() { add(); } void add() int a,b,c; printf(“enter any two numbers”) scanf(“%d%d”,&a,&b); c= a+b; printf(“the addition of %d and %d is %d”,a,b,c);

Function with No return type and with arguments
Void main() { ……. func1(x,y); } func1(a,b) { ……. }

void add(int,int); void main() { int x,y,c; printf(“enter any two numbers”) scanf(“%d%d”,&x,&y); add(x,y); } void add(int a,int b) int c; c= a+b; printf(“the addition of %d and %d is %d”,a,b,c);

Function with return type and with arguments
void main() { ……. int c = func1(x,y); } int func1(a,b) { ……. }

int add(int,int); Void main() { int x,y,c; printf(“enter any two numbers”) scanf(“%d%d”,&x,&y); c = add(x,y); printf(“The Result = %d ”,c); } int add(int a ,int b) int c; c= a+b; return (c);

Function with return type and No arguments
void main() { ……. int func1(); } int func1() { ……. }

int add(); Void main() { int c; c = add(); printf(“The Result = %d ”,c); } int add() int a,b,c; printf(“enter any two numbers”) scanf(“%d%d”,&a,&b); c= a+b; return (c);

Functions that return multiple values
#include <stdio.h> void interchange (int *a , int *b) void main() { int i=5,j=10; printf(“Before : I and J value is %d and %d”,I,j); interchange(&i,&j); printf(“After : I and J value is %d and %d”,I,j); } void interchange (int *a, int *b) int t; t=*a *a=*b *b=t O/p: Before : I and J value is 5 and 10 After : I and J value is 10 and 5

Function without a prototype
#include <stdio.h> int sum(int x, int y) { return x+y; } void main() printf("The sum is: %d ", sum(4,5));

Parameter Passing Methods
In C there are two ways of passing parameters to a function Call by Value Call by Reference

Call by value Copy of data passed to function
Changes to copy do not change original Prevent unwanted side effects This Method copies the value of actual parameters(calling program) into the formal parameters(called program) of the functions. Here the changes of the formal parameters cannot affect the actual parameters. Because only the copy of actual arguments were passed. A function can return only one value per call.

Example #include <stdio.h> int cube (int) void main() { int n=5;
printf(“Cube of %d is %d”,n,cube(n)); } int cube (int x); x=x*x*x; return x; O/p: Cube of 5 is 125

Function can directly access data Changes affect original
Call by reference Function can directly access data Changes affect original It is another way of passing parameter to the functions here the address of arguments are copied into the parameters inside the functions. The address is used to access the actual arguments used in the call. By using this we can make a function to return more the one value(indirectly).

Example #include <stdio.h> void interchange (int *a , int *b)
void main() { int i=5,j=10; printf(“Before : I and J value is %d and %d”,I,j); interchange(&i,&j); printf(“After : I and J value is %d and %d”,I,j); } void interchange (int *a, int *b) int t; t=*a *a=*b *b=t O/p: Before : I and J value is 5 and 10 After : I and J value is 10 and 5

Call by value Vs Call by reference
Copy of data passed to function Changes to copy do not change original Prevent unwanted side effects Call by reference Function can directly access data Changes affect original

void swap(int, int); void main() { int num1, num2; num1 = 10; num2 = 20; swap ( num1, num2 ); printf("%d %d\n", num1, num2); } void swap(int val1, int val2) int temp; temp = val1; val1 = val2; val1 = temp;

Swap two integers using call by value(cont.)
In the above example, we passed parameters by value, a copy is made of the variable and thus any change made to the parameters val1 and val2 will not be passed back to the main function The main function will not know anything about the swapping of val1 and val2 Therefore, the output of the above program will be ….? Normally if we wished to pass back a value we would use return or we would pass the parameters by reference

Nested Functions In C , it provides a facility to write one function with in another function. This is called nesting of functions Main() { func1(); } func1() { func2(); } func2() { }

Recursion

Recursion Recursion is a process of calling the same function itself again and again until same condition is satisfied. This is used for repetitive computation in which each action is satisfied in terms of a previous result A function can call itself Directly Indirectly Function1() { ----- Function1(); }

Recursion vs. Iteration
Repetition Iteration: explicit loop Recursion: repeated function calls Termination Iteration: loop condition fails Recursion: base case recognized Both can have infinite loops Balance between performance (iteration) and good software engineering (recursion)

Difference Between Iteration and Recursion
Sl.No. Iteration Recursion 1. Iteration explicitly user a repetition structure. Recursion achieves repetition throught repeated function calls. 2. Iteration terminates when the loop continuation condition fails. Recursion terminates when a base case is reached. 3. Iteration keeps modifying the counter until the loop continuation condition fails. Recursion keeps producing simple versions of the original problem until the base case is 4. An infinite loop occurs when the loop step continuation test never becomes false. An infinite loop occurs if the recursion doses not reduce the problem each time in a manner that converges the base case. 5. Iteration normally occurs within a loop so extra memory assignment is omitted. Recursion causes another copy of the function & hence a considerable memory space is occupied. 6. It reduces the processor operating time. It increases the processor operating time.

Example: fibonacci.c function Fibonacci ( n ) {
if ( n is less than or equal to 1 ) then return n else return Fibonacci ( n - 2 ) + Fibonacci ( n - 1 ) } /* Compute the n-th Fibonacci number, when=0,1,2,... */ long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); }

Example: Computation of fib(4)
long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 4 4 4 4 fib(4) fib(2) fib(3) +

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 2 2 2 2 fib(4) fib(2) + fib(3) fib(0) fib(1) +

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } fib(4) fib(2) + fib(3) fib(0) + fib(1)

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } fib(4) fib(2) + fib(3) + fib(1)

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 2 fib(4) fib(2) + fib(3) + fib(1)

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 1 1 1 fib(4) fib(2) + fib(3) + fib(1)

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 1 1 1 fib(4) fib(2) + fib(3) + 1

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 2 1 fib(4) fib(2) + fib(3) + 1

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 2 2 1 2 fib(4) 1 + fib(3) + 1

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 4 1 fib(4) fib(3) 1 + + 1

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 3 3 3 3 fib(4) fib(3) 1 + fib(1) fib(2) + 1 +

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 1 1 1 fib(4) fib(3) 1 + fib(1) fib(2) + 1 +

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 1 1 1 fib(4) fib(3) 1 + fib(2) + 1 1 +

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 3 1 fib(4) 1 + fib(3) fib(2) + 1 1 +

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 2 2 2 2 fib(4) 1 + fib(3) + 1 1 + fib(2) fib(0) fib(1) +

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } fib(4) 1 + fib(3) + 1 1 + fib(2) fib(0) fib(1) +

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } fib(4) 1 + fib(3) + 1 1 + fib(2) fib(1) +

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 2 fib(4) 1 + fib(3) + 1 1 + fib(2) fib(1) +

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 1 1 1 fib(4) 1 + fib(3) + 1 1 + fib(2) + fib(1)

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 1 1 1 fib(4) 1 + fib(3) + 1 1 + fib(2) + 1

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 2 1 fib(4) 1 + fib(3) + 1 1 + fib(2) + 1

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 2 2 2 1 2 fib(4) 1 + fib(3) + 1 1 + 1 + 1

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 3 1 1 fib(4) 1 + fib(3) + 1 1 + 1 + 1

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 3 3 1 3 1 3 fib(4) 1 + 2 + 1 1 + 1 + 1

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 4 1 2 fib(4) 1 + 2 + 1 1 + 1 + 1

long fib ( int n ) { if ( n <= 1 ) return n ; else return fib( n - 2 ) + fib( n - 1 ); } 4 4 1 4 2 4 3 1 + 2 + 1 1 + 1 + 1

Thus, fib(4) returns the value 3 3 1 + 2 + 1 1 + 1 + 1

Sample main() for testing the fib() function:
Example: fibonacci.c Sample main() for testing the fib() function: int main(void) { int number; printf("Enter number: "); scanf("%d", &number); printf("Fibonacci(%d) = %ld\n", number, fib(number)); return 0; }

Where can you use a variable which is declared in a function?
Scope Where can you use a variable which is declared in a function? In that function only Not in a calling function Not in a called function

Scope: Local Variables
Formal parameters: only accessible whilst a function is executing Variables declared in a function body: only accessible whilst the function is executing In fact, this is true of every block in a program

Exercise Write a program to find the factorial using a functions.
Write a program to find the value of xn. For any given values of x and n .

Passing arrays to Functions

Arrays to the function in One dimensional
An entire array can be transferred to a function as a parameter. Actual parameter : the array name is enough without subscripts to transfer an array. Formal parameter : must be declared as an array to receive the values from main program. syntax : void func(int,int[]) main() void func(int x, int arr[10]) { { int a[10],i; ………… func(i,a); ………… } }

Three Rules of Pass an Array to a Function
1. The function must be called by passing only the name of the array. 2. In the function definition, the formal parameter must be an array type; the size of the array does not need to be specified. 3. The function prototype must show that the argument is an array.

Sample program void add(int a[]) #include<stdio.h> {
int i,sum = 0; for(i = 0;i<10;i++) sum = sum+a[i]; printf(“ the value of sum is %d”, sum); } #include<stdio.h> #inlcude<conio.h> void add(int[]) void main() { int i,arr[10]; printf(“Enter 10 elements of the array”); for(i = 0;i<10;i++) scanf(‘%d”,&arr[i]); add(arr); }

Changing an Array in a Function
#include <stdio.h> void fun ( int [ ] ) int main(void) { int array[ ] = { 1 , 2 , 3 , 4 , 5 }; fun ( array ); printf ( “%d” , array [ 3 ] ); Will print 20 return 0; } void fun ( int x[ ] ) x[3] = 20; return;

Largest of Given Numbers
#include<stdio.h> void main() { float largest(float a[ ], int n); float value [4] = {2.5,-4.75,1.2,3.67}; printf("%f\n",largest(value,4); } float largest(float a[ ], int n) int i; float max; max = a[0]; for(i=1; i<n; i++) if(max < a[i]) max = a[i]; return(max);

Sorting of Given Numbers
#include<stdio.h> void main() { int i; int mark[5] = {40,90,73,81,35}; printf("Marks before sorting\n"); for(i = 0;i<5;i++) printf("%d",marks[i]); printf("\n\n"); sort(5,marks); printf("Marks after sorting\n"); printf("%4d",mark[i]); printf("\n"); }

Sorting of Given Numbers Conti….
void sort(int m,int x[]) { int i,j,t; for(i=0;i<m-1;i++) for(j=i+1;j<m;j++) if (x[i] > x[j]) t = x[i]; x[i] = x[j]; x[j] = t; }

Arrays to the function in Two dimensional
Like simple arrays, we can also pass multidimensional array to functions. The approach is similar to the one we did with one – dimensional arrays. The rules are simple. 1. The function must be called by passing only the array name. 2. In the function definition, we must indicate that the array has two dimensions by including two sets of brackets. 3. The size of the second dimension must be specified. 4. The prototype declaration should be similar to the function header.

Calculates the average of the values in a two – dimensional matrix
#include<stdio.h> void main() { int M = 3, N = 2; double average (int [] [N],int,int); double mean; int matrix [M][N] = {{1,2},{3,4},{5,6}}; mean = average(matrix, M, N); printf("The Mean of the Two Dimensional Array is: %f",mean); } double average(int x [ ] [N],int M,int N) int i,j; double sum = 0.0; for(i=0;i<m;i++) for(j=1;j<N;j++) sum = sum + x[i][j]; return (sum / (M * N);

Passing Strings to Functions
The Strings are treated as character arrays in C, the rules for passing strings to functions are very similar to those for passing arrays to functions. Basic Rules are: 1. The string to be passed must be declared as a formal argument of the function when it is defined. Example: void display(char item_name[]) { } 2. The function prototype must show that the argument is a string. For the above function definition, the prototype can be written as void display(char str[ ]) 3. A call to the function must have a string array name without subscripts as its actual arguments. display(names); where names is a properly declared string array in the calling function.

Storage class

Storage class Storage_class data_type v1,v2,v3,………………..vn.
Every variable or constant possesses a data type In addition to the data type, a variable possesses an attribute called storage class. where v1,v2 are the variables data_type is the valid data type in c language storage_class gives information regarding lifetime and scope. Storage_class data_type v1,v2,v3,………………..vn.

Storage class cont’ Lifetime
Lifetime or Longetivity of a variable refers to the duration for which the variable retains a given value during the execution of a program. Scope It is the portion of the program in which the variable may be visible or available .It can classified into two types Type 1: Local variable (or) private variable (or) internal variable. Type 2: Global variable (or) public variable (or) external variable.

Types Sl.No Types of Storage Class Reserved words 1 Automatic auto 2
Register register 3 Static static 4 External extern

Automatic variables By default all variables are automatic storage class. Their memory space is automatically allocated as the variable is declared. These variables are given only temporary memory space and after the execution all the automatic variables will get disposed. It can not be accessed directly by other functions.

Sample Program #include<stdio.h> Void main() { float f1 = 10.2;
printf(“the value of f1 in block 3 is %f”,f1); } printf(“the value of f1 in block 2 is %f”,f1); printf(“the value of f1 in block 1 is %f”,f1);

Static Variables The variables are declared with static keyword.
It can be internal static (or) external static based on the place of its declaration. Both are declared using the keyword static. The storage used by an static variable in a block is not lost after the completion of the execution. Even after the termination of the block, the value of the static variable is available. If the value is changed during the execution the recent value is retained. When the execution enters the next time the same block, the initialiser is neglected and the recently stored value is retained.

Sample Program #include<stdio.h> #include<conio.h>
int fun(int); void main() { int i,x; clrscr(); for(i=1;i<=10;i++) x = fun(i); printf(“The I Value is:%d”, x); } getch(); int fun(int a) { auto int sum = 100; sum = sum + a; return(sum); }

Output When sum is static When sum is auto The I Value is:101

Register Variables The variables are declared using register keyword.
The scope and lifetime is same as that of automatic variables. For any given operation the data available in the memory should be transferred to the CPU registers. So if the data are stored in register itself then the time for data transfer from the memory to the register is saved. Only a few values can be placed at a time and hence it is advisable to use limited register variables. main() { register int i; for(i=0;i<10;i++) printf(“%d”,i); }

External variables It refers to the location outside a block i.e., prior to the main() or beyond the closing braces ( } ) of the outermost block in a program . The value is available throughout the program because of its global scope. Whenever an external variable is modified in a block, the effect is propagated to all places where ever it is used.

Sample Program main() { extern int x=5; int y = 10,z; z = y/x;
printf(“x = %d, y = %d, z = %d”, x, y, z); }

C Standard Library

C Standard Library Every implementation of C comes with a standard library of predefined functions. Note that, in programming, a library is a collection of functions. The functions that are common to all versions of C are known as the C Standard Library.

C Standard Library Function Examples
Name Math Value Example abs(x) absolute value |x| abs(-1) returns 1 sqrt(x) square root x0.5 sqrt(2.0) 1.414… exp(x) exponential ex exp(1.0) 2.718… log(x) natural logarithm ln x log(2.718…) 1.0 sin(x) sine sin x sin(3.14…) 0.0 cos(x) cosine cos x cos(3.14…) -1.0 tan(x) tangent tan x tan(3.14…) ceil(x) ceiling ┌ x ┐ ceil(2.5) 3.0 floor(x) floor └ x ┘ floor(2.5) 2.0

Using the C Standard Math Library
If you’re going to use functions like cos that are from the part of the C standard library that has to do with math, then you need to do two things: In your source code, immediately below the #include <stdio.h> you must also put #include <math.h> When you compile, you must append -lm to the end of your compile command: gcc -o funcargs funcargs.c –lm (Note that this is hyphen ell em, NOT hyphen one em.)

UNIT V STRUCTURES AND FILES

User Defined Data types
STRUCTURES

User Defined Data types
C has several mechanisms for creating data types other than the basic ones (int, float, etc.) provided by the language. structs – a collection of named variables unions – a types that can hold one of a set of variables enum – a set of named integers typedef – define a name for a user type These tools are especially useful when combined with pointers and dynamic memory allocation.

Structure A structure is derived type usually representing a collection of variables of same or different data types grouped together under a single name. The variables or data items in a structure are called as members of the structure. A structure may contain one or more integer variables, floating – point variables character variables, arrays, pointers , and even other structures can also be included as members. Structures help to organize data, particularly in large programs, because they allow a group of related variables to be treated as a single unit.

Why use structs? The last example is one of the main reasons. Rather than having four arrays of items, we have one array of structs. When combined with dynamic memory allocation, we can create many different data structures (trees, lists, heaps, etc.). Structs help to keep code organized logically.

Declaring a Structure Structure declarations are somewhat more complex than array declarations since a structure must be defined in terms of its individual members. The general form of the Structure is: struct <structure_name> { data_type member_1; ………………………….. data_type member_n; };

struct is keyword. Structure_name is the user defined name, usually referred as a tag, which is used to identify the structure. Member_1 to Member_n is the list of members with its data type in structures. The list of member declarations is enclosed in a pair of flower braces. The closing brace of the structure and the semicolon ends the structure declaration. Example: // Declare a person struct struct person { char name[50]; int age; char phone[15]; float height; }; Usually declare structs in global scope, often in a separate file.

A field is an individual variable in the struct. It is accessed by var
A field is an individual variable in the struct. It is accessed by var. field where var is the struct variable and field is the field name. // Declare a person struct struct person { char name[50]; int age; char phone[15]; float height; }; tag name or structure name fields Each field has its own memory location.

Various ways to create a structure
Defined for variables struct { // see example: structEx0.c int month; int day; } birth, current; Defined as a new data type struct Date { // see example: structEx1.c int month; int day; } ; Defined as both a new data type and variables struct Date { // see example: structEx2.c int month; int day; } birth, current;

Defining a Structure struct <structure_name>
Declaring a structure is just a skeleton it merely describes the template. It does not reserve any memory space rather the declaration creates a new data type. So, to use the structure you have to define it. Defining a structure means creating variables to access the members in the structure. Creating a structure variable allocates sufficient memory space to hold all the members of the structure. The structure variables can be created during structure declaration or by explicitly using the structure name. The general form of the Structure is: struct <structure_name> { data_type member_1; ………………………….. data_type member_n; }structure_variable;

The memory allocation for the structure person is
Example: struct person { char name[50]; int age[5]; char phone[15]; float height; }stud; Where the structure person declares a variable stud of its type. The structure_variable is are declared like ordinary variables is used to access the members of the structure. More than one structure_variable can also be declared by placing a comma in between the variables. The memory allocation for the structure person is name bytes age bytes phone bytes height 4 bytes

The syntax for defining the structure using the structure name is
Example: struct person stud; or person stud; If you need only one structure variable, the structure name or the tag is not necessary. For example. struct structure_name structure_variable; Or structure_name structure_variable; struct{ char name[50]; int age[5]; char phone[15]; float height; }stud;

Where the structure declares and defines a variable named stud.
Note that the structure name or the structure variables may be omitted, but both, should not be omitted. The member names within a particular structure must be distinct from one another though a member name can be same as the name of the variable, which is defined outside the structure. For example, struct{ char name[50]; int age[5]; char phone[15]; float height; }stud; char phone[15]; Where character variable phone inside the structure shares the same name with the variable phone declare outside the structure. Note that a structure declaration that is not followed by a list of variables reserves not storage space, it merely describes the template (i.e., the structure is only defined not declared.

structure_variable.member_name;
Accessing Structure Members We have declared and defined the structure and how let us see how the elements of the structure can be accessed. A member of a structure is always referred and accessed by the structure variable. The general form or the syntax of accessing a member of a structure is Example: stud.name; stud.age; stud.phone stud.height To assign a value to the member of the structure use, stud.name = “sakthi vinayagam”; stud.age = “32”; structure_variable.member_name;

Structs: Example #include <stdio.h> // Declare a person struct
struct person { char name[50]; int age; char phone[15]; float height; }; int main() struct person stud; stud.name = “sakthi”; stud.age = 32; stud.phone = “ ”; stud.height = ; stud sakthi name 31 age phone 175 height char[50] int char[15] float printf(“The Stud name is:%d\n”,stud.name); printf(“The Stud age is: %d\n”,stud.age); printf(“The Stud phone is:%d\n”,stud.phone); printf(“The Stud height is:%d\n”,stud.height); getch(); }

Initializing Structure
The syntax of C language prevents the programmer from initializing individual structure members within the structure template. Structure members can be initialized only by using structure variables during structure declarations or by explicitly using the structure name. The syntax for initializing the structure during structure declaration is struct <structure_name> { data_type member_1; ……………………….. data_type member_n; }structure_variable = {value_1,value_2,……….value_n}; Example: struct{ char name[50]; int age[5]; char phone[15]; float height; }stud = {“sakthi”,31,” ”,173.86};

Example Program for structure initialization
#include <stdio.h> // Declare a person struct Struct { char name[50]; int age[5]; char phone[15]; float height; }stud = {“sakthi”,31,” ”,173.86}; int main() { printf(“The Stud name is:%d\n”,stud.name); printf(“The Stud age is: %d\n”,stud.age); printf(“The Stud phone is:%d\n”,stud.phone); printf(“The Stud height is:%d\n”,stud.height); getch(); }

Example Program for structure initialization
#include <stdio.h> // Declare a person struct struct person { char name[50]; int age; char phone[15]; float height; }; int main() struct person stud_1={“sak”,31}; struct person stud_2={“vel”}; stud_1.phone = “ ”; stud_1.height = ; stud_3 = stud_1; printf(“The Stud name is:%d\n”,stud_1.name); printf(“The Stud age is: %d\n”,stud_1.age); printf(“The Stud phone is:%d\n”,stud_1.phone); printf(“The Stud height is:%d\n”,stud_1.height); printf(“The Stud name is:%d\n”,stud_2.name); printf(“The Stud name is:%d\n”,stud_3.name); printf(“The Stud age is: %d\n”,stud_3.age); printf(“The Stud phone is:%d\n”,stud_3.phone); printf(“The Stud height is:%d\n”,stud_3.height); getch(); } Note: The information contained in one structure variable can also be assigned to another structure variable using a single assignment statement.

Difference Between Array and Structure Sl.No. Array Structures 1.
An array is an single entity representing a collection of data items of same data types. A structure is a single entity representing a collection of data items of different data types. 2. Individual entries in an array are called elements. Individual entries in a structure are called members. 3. An array declaration reserves enough memory space for its elements. The structure definition reserves enough memory space for it s members. 4. No keyword is used to represent arrays except the square braces [] preceding the variable name indicates that it is an array. The keyword struct tells us that we are dealing with structures. 5. Initialization of elements can be done during array declaration. Initialization of members can be done only during structure definition.

Difference Between Array and Structure Conti…
Sl.No. Array Structures 6. The elements of an array are stored in sequence of memory locations. The members of a structure are not stored sequences of memory locations. 7. The array elements are accessed by its followed by the square braces [] within which the index is placed. The members of a structure are accessed by the dot operator (also called as the period operator) 8. The General format is data_type variable_name [size]; Ex: int sum [100]; struct <struct_name> { data_type structure_member_1; data_type structure_member_2; data_type structure_member_3; . data_type structure_member_n; }structure_variable; struct student char studentname[20]; int rollno; }stud;

STRUCTURE WITHIN STRUCTURE OR NESTING OF STRUCTURE
Structure within a structure means nesting of structures. Example: struct salary { char name[20]; char department[10]; int basic_pay; int dearness_allowance; int house_rent_allowance; int city_allowance; }employee; This structures defines name, department, basic pay and three kind of allowance. We can group all the items related to allowance together and declare them under a substructure.

Case 1: struct employee { char name[20]; char department[10]; struct salary int basic_pay; int dearness_allowance; int house_rent_allowance; int city_allowance; }emp_salary; }emp_person;

Case 2: struct employee { char name[20]; char department[10]; }; struct salary int basic_pay; int dearness_allowance; int house_rent_allowance; int city_allowance; struct employee emp_persion; }emp_salary;

Structures and Functions

There are three methods by which the values of a structure can be transferred from one function to another. 1. The first method is to pass each member of the structure as an actual argument of the function call. The actual arguments are then treated independently like ordinary variables. The is the most elementary method and becomes unmanageable and inefficient when the structure size is large. 2. The second method involves passing of a copy of the entire structure to the called function. Since the function is working on a copy of the structure, and changes to structure members within the function are not reflected in the original structure (in the calling function). It is , therefore, necessary for the function to return the entire structure back to the calling function. All Compilers may not support this method of passing the entire structure as a parameter. 3. The third approach employs a concept called pointers to pass the structure as an argument. In this case, the address location of the structure is passed to the called function. The function can access indirectly the entire structure and work on it. This is similar to the way arrays are passed to function. This method is more eifficient as compared to the second one.

The general format of sending a copy of a structure to the called function is:
function_name (structure_variable_name); The called function takes the following form: data_type function_name(struct_type st_name) { return (expression); }

The following points are important to note:
1. The called function must be declared for its type, appropriate to the data type it is expected to return. For example, if it is returning a copy of the entire structure, then it must be declared as struct with an appropriate tag name. 2. The structure variable used as the actual argument and the corresponding formal argument in the called function must be of the same struct type. 3. The return statement is necessary only when the function is returning some data back to the calling function. The expression may be any simple variable or structure variable or an expression using simple variables. 4. When a function returns a structure, it must be assigned to a structure of identical type in the calling function. 5. The called functions must be declared in the calling function appropriately.

We can send structures to functions
#include <stdio.h> struct Date { int month; int day; } ; void callToFunction( struct Date val ); // function prototype int main( ) struct Date birth = {9, 31}; printf( "Birth date: %d/%d/\n", birth.month, birth.day ); callToFunction( birth ); printf( "Birth date after function: %d/%d/\n", birth.month, birth.day ); } void callToFunction( struct Date val ) printf(“%d\n”,val.month); printf(“%d\n”,val.day);

Function does not change original!
We can send structures to functions #include <stdio.h> struct Date { int month; int day; } ; void callToFunction( struct Date val ); // function prototype int main( ) struct Date birth = {9, 31}; printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( birth ); printf( "Birth date after function: %d/%d\n", birth.month, birth.day ); } void callToFunction( struct Date val ) val.month = 1; val.day = 28; OUTPUT: cs157> gcc structFunc.c cs157> a.out Birth date: 9/31 Birth date after function: 9/31 Function does not change original!

We can send structures to functions
#include <stdio.h> struct Date { int month; int day; } ; void callToFunction( struct Date val ); // function prototype int main( ) struct Date birth = {9, 31}; printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( birth ); printf( "Birth date after function: %d/%d\n", birth.month, birth.day ); } void callToFunction( struct Date val ) val.month = 1; val.day = 28; Function does not change original! OUTPUT: cs157> gcc structFunc.c cs157> a.out Birth date: 9/31 Birth date after function: 9/31 Val is a full copy of birth structure

We can refer to globally defined structures
#include <stdio.h> struct Date { int month; int day; } birth = {9, 31}; void callToFunction( ); int main( ) printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( ); printf( "Birth date after call to function: %d/%d\n", birth.month, birth.day ); } void callToFunction( ) birth.month = 1; birth.day = 28;

We can refer to globally defined structures
Function does change original! #include <stdio.h> struct Date { int month; int day; } birth = {9, 31}; void callToFunction( ); int main( ) printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( ); printf( "Birth date after call to function: %d/%d\n", birth.month, birth.day ); } void callToFunction( ) birth.month = 1; birth.day = 28; OUTPUT: cs157> gcc structFunc2.c cs157> a.out Birth date: 9/31 Birth date after function: 1/28 birth is a global variable, so function affects original

We can send a pointer to the structure
#include <stdio.h> struct Date { int month; int day; }; void callToFunction( struct Date * ); int main( ) struct Date birth; birth.month = 9; birth.day = 31; printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( &birth ); printf( "Birth date after function: %d/%d\n", birth.month, birth.day ); } void callToFunction( struct Date *birth ) birth->month = 1; birth->day = 28; Send the address to the function Use -> to dereference from a pointer

We can send a pointer to the structure
#include <stdio.h> struct Date { int month; int day; }; void callToFunction( struct Date * ); int main( ) struct Date birth; birth.month = 9; birth.day = 31; printf( "Birth date: %d/%d\n", birth.month, birth.day ); callToFunction( &birth ); printf( "Birth date after function: %d/%d\n", birth.month, birth.day ); } void callToFunction( struct Date *birth ) birth->month = 1; birth->day = 28; Function does change original! OUTPUT: cs157> gcc structFunc3.c cs157> a.out Birth date: 9/31 Birth date after function: 1/28 Send the address to the function Use -> to dereference from a pointer

Arrays of Structures

We use structures to describe the format of a number of related variables. For example, in analyzing the marks obtained by a class of students, we may use a template to describe student name and marks obtained in various subjects and then declare all the student as structure variables. In such cases, we may declare an array of structures, each element of the array representing a structure variable. For example: struct class student [100]; defines an array called student, that consists of 100 elements. Each element is defined to be of the type struct class. Consider the following declaration: struct marks { int subject_1;int subject_2;int subject_3; } main struct marks student [3] = {{45,68,81},{75,53,69},{57,36,71}};

We can create arrays of structs just like any other type.
name char[50] name char[50] name char[50] name char[50] age unsigned char age unsigned char age 54 unsigned char age unsigned char phone char[15] phone char[15] phone char[15] phone char[15] height 4.21 float height float height float height float int main() { struct person people[4]; people[2].age = 54; people[0].height = 4.21; ...etc... }

} #include <stdio.h> #include <string.h> struct student {
char name[50]; int age; char phone[15]; float height; }; #define NUMSTUDENTS 3 int main( ) { struct student cs157[NUMSTUDENTS] = { {"Bob", 84, " ", 6.3 }, { "Rob", 14, " ", 4.8 }, { "Zob", 4, " ", 2.7 }, } ; for( int i=0; i<NUMSTUDENTS; i++ ) printf( "Student %i: %s %d years old\n", i+1, cs157[i].name, cs157[i].age ); } OUTPUT: cs157> gcc people.c -std=c99 cs157> a.out Student 1: Bob 84 years old Student 2: Rob 14 years old Student 3: Zob 4 years old

Structures and sizeof Due to memory alignment restrictions, the size of a structure is >= the sum of the sizes of its member variables struct blah { char x; int y; char z; }; Always use sizeof to determine the size of a structure sizeof(blah)  12 bytes Memory layout x = Padding y y y y z

C Permits the use of arrays as structure members
C Permits the use of arrays as structure members. We can use single – or multi – dimensional array of type int or float. For Example, the following structure declaration is valid: struct marks { int number; float subject [3]; } student [2]; Here the member subject contains three elements, subject [0], subject [1] and subject [2]. These elements can be accessed using appropriate subscripts. For example, the name student [1] . Subject [2]; Would refer to the marks obtained in the third subject by the second student.

Structure bit fields Recall bit flags and bit masks
Useful when we need to pack several flags or objects into the smallest amount of space possible Structure bit fields make this a little easier at the cost of portability struct argb { unsigned int alpha : 8; unsigned int red : 8; unsigned int green : 8; unsigned int blue : 8; }; Implementation-dependent!

Unions

Unions A union is a type that allows several variables to be stored in the same memory location (but not at the same time). It provides a way of improving memory efficiency. On most modern desktop machines, this is not really an issue, and unions will be used less frequently.

Unions // Declare a union union int_or_float { int i; float f; }; tag name fields The declaration is similar to that of a struct, but the implementation is different. Only one field will contain data and be accessible at any given time.

Unions 14 ???? // Declare a union union int_or_float { int i; float f;
}; tag name fields q i int int main() { union int_or_float q; q.i = 14; } 14 ???? f float

Unions ???? 175.543 // Declare a union union int_or_float { int i;
float f; }; tag name fields q i int int main() { union int_or_float q; q.i = 14; q.f = ; } ???? f float

Unions 175 ???? // Declare a union union int_or_float { int i;
float f; }; tag name fields q i int int main() { union int_or_float q; q.i = 14; q.f = ; q.i = q.f; } 175 ???? f float

Unions Accessing a union member that has not been assigned most recently will produce undefined results. Unless you are really concerned about memory use (perhaps when writing code for an embedded device), stay away from unions.

Unions Syntactically similar to structures
However, all member variables occupy the same location in memory You are responsible for accessing the right members at the right time Union size is size of the largest member union UBlah { char x; int y; char z; }; Memory layout x,y,z y y y

Unions (2) union { char x; int y; char* z; } utype; utype.x = 'c';
printf("%c\n", utype.x); utype.z = "Hello"; printf("%s\n", utype.z); printf("%d\n", utype.y); /* Undefined! */

Enumerated Types

Enumerated Types The enum type allows you to specify a finite set of names to which C will automatically give values. These names can be compared which makes them useful in situations where a variable should only take on values from a small set.

Enum Values are assigned starting at zero and incrementing by 1.
tag name // Declare a enum enum r_p_s { rock, paper, scissors }; values Values are assigned starting at zero and incrementing by 1. While enums are comparable with ints, you should avoid treating them as integers.

enum Example // Declare a enum enum r_p_s { rock, paper, scissors };
player machine int main() { enum r_p_s player, machine; }

enum Example rock // Declare a enum enum r_p_s { rock, paper, scissors
}; player rock machine int main() { enum r_p_s player, machine; player = rock; }

enum Example rock scissors // Declare a enum enum r_p_s { rock, paper,
}; player rock int main() { enum r_p_s player, machine; player = rock; machine = scissors; if (machine == player) printf(“Tied.\n”); else ... } machine scissors

enumerated types example
// Declare a enum enum r_p_s { rock, paper, scissors }; // Declare a enum enum result { win, loss, tie }; enum result happened = tie; if(machine == player) happened = tie; else if((machine+1)%3 == player) happened = win; else if((player+1)%3 == machine) happened = loss; player happened rock win machine scissors

Tag Names and Declarations
The syntax for defining structs, unions, and enums is very similar. The type is either struct, unions, or enums. The tag is a name for the type. It differentiates on struct from another. After the declaration a list of variables to create can be given. type tag { ... } var1, var2, var3, ...;

typedefs Allow you to make a new “logical” name for an existing data type. Like a name-tag Makes code more readable. typedef char * string; int main ( ) { // instead of char* my_string; string name; strcpy(name,”hello”); }

Typedefs A typedef is a name for some type. Any type can be named with a typedef. struct my_struct_S { int age; char name[30]; }; typedef struct my_struct_S person; int main() // instead of struct my_struct_S people[20]; person people[20]; }

Typedefs For stucts, enums, and unions the syntax can be slightly simplified. We can combine the declaration and the typedef. This allows us to leave out the tag name. typedef struct { int age; char name[30]; } person; int main( ) person people[20]; }

Initialization of User Defined Types
We can define the values of user defined types at the declaration. The syntax is similar to that of array intialization. typedef struct { char name[50]; unsigned char age; char phone[15]; float height; } person; int main() { person company[2] = {{“Robert Smitherson”, 45, “(303) ”, 5.9}, {“Sally Robertson”, 38, “(303) ”, 5.5}}; }

Nested Types It is legal to nest the definition of user defined types. Structs, for example, can have structs (or unions or enums) as members. The members of nested types are accessed using the same ‘.’ operator. We might, for example, have something like var.stype.age.

Nested User Defined Types
typedef struct { char name[50]; unsigned char age; char phone[15]; float height; union { int num_new_teeth; // if age <= 2 int school_grade; // if age <= 18 int fake_hips; // if age >= 60 } info; } person; int main() { person bob; bob.age = 75; bob.info.fake_hips = 2; }

Anonymous Nested Types
You can leave off the type name for nested types. typedef struct { unsigned char age; union { int num_new_teeth; // if age <= 2 int school_grade; // if age <= 18 int fake_hips; // if age >= 60 }; //no name } person; int main() { person bob; bob.age = 75; bob.fake_hips = 2; }

Complex example typedef struct { enum { beverage, candy, snack } type;
char name[30]; union { float fl_ounces; int pieces; int servings; }; float cost; int count; } item; int main() { item vendmach[20]; ... vendmach[0].type = beverage; strcpy(vendmach[0].name,”Coke”); vendmach[0].fl_ounces = 12; vendmach[0].cost = 1.25; vendmach[0].count = 10; vendmach[0].type = candy; strcpy(vendmach[0].name,”KitKat”); vendmach[0].pieces = 4; vendmach[0].cost = 0.95; vendmach[0].count = 7; vendmach[0].type = snack; strcpy(vendmach[0].name,”Pringles”); vendmach[0].servings = 2; vendmach[0].cost = 1.10; vendmach[0].count = 5; ...

FILE HANDLING IN C

Files in C In C, each file is simply a sequential stream of bytes. C imposes no structure on a file. A file must first be opened properly before it can be accessed for reading or writing. When a file is opened, a stream is associated with the file. Successfully opening a file returns a pointer to (i.e., the address of) a file structure, which contains a file descriptor and a file control block.

Files in C The statement: FILE *fptr1, *fptr2 ; declares that fptr1 and fptr2 are pointer variables of type FILE. They will be assigned the address of a file descriptor, that is, an area of memory that will be associated with an input or output stream. Whenever you are to read from or write to the file, you must first open the file and assign the address of its file descriptor (or structure) to the file pointer variable.

Opening Files The statement: fptr1 = fopen ( "mydata", "r" ) ;
would open the file mydata for input (reading). fptr2 = fopen ("results", "w" ) ; would open the file results for output (writing). Once the files are open, they stay open until you close them or end the program (which will close all files.)

Modes for opening files
The second argument of fopen is the mode in which we open the file. There are three "r" opens a file for reading "w" opens a file for writing - and writes over all previous contents (deletes the file so be careful!) "a" opens a file for appending - writing on the end of the file.

The exit() function Sometimes error checking means we want an "emergency exit" from a program. We want it to stop dead. In main we can use "return" to stop. In functions we can use exit to do this. Exit is part of the stdlib.h library exit(-1); in a function is exactly the same as return -1; in the main routine

Testing for Successful Open
If the file was not able to be opened, then the value returned by the fopen routine is NULL. For example, let's assume that the file mydata does not exist. Then: FILE *fptr1 ; fptr1 = fopen ( "mydata", "r") ; if (fptr1 == NULL) { printf ("File 'mydata' did not open.\n") ; }

Reading From Files In the following segment of C language code:
int a, b ; FILE *fptr1, *fptr2 ; fptr1 = fopen ( "mydata", "r" ) ; fscanf ( fptr1, "%d%d", &a, &b) ; the fscanf function would read values from the file "pointed" to by fptr1 and assign those values to a and b.

End of File The end-of-file indicator informs the program when there are no more data (no more bytes) to be processed. There are a number of ways to test for the end-of-file condition. One is to use the feof function which returns a true or false condition: fscanf (fptr1, "%d", &var) ; if ( feof (fptr1) ) { printf ("End-of-file encountered.\n”); }

End of File There are a number of ways to test for the end-of-file condition. Another way is to use the value returned by the fscanf function: int istatus ; istatus = fscanf (fptr1, "%d", &var) ; if ( istatus == EOF ) { printf ("End-of-file encountered.\n”) ; }

Writing To Files Likewise in a similar way, in the following segment of C language code: int a = 5, b = 20 ; FILE *fptr2 ; fptr2 = fopen ( "results", "w" ) ; fprintf ( fptr2, "%d %d\n", a, b ) ; the fprintf functions would write the values stored in a and b to the file "pointed" to by fptr2.

Closing Files The statements: fclose ( fptr1 ) ; fclose ( fptr2 ) ;
will close the files and release the file descriptor space and I/O buffer memory.

Reading and Writing Files
#include <stdio.h> int main ( ) { FILE *outfile, *infile ; int b = 5, f ; float a = 13.72, c = 6.68, e, g ; outfile = fopen ("testdata", "w") ; fprintf (outfile, "%6.2f%2d%5.2f", a, b, c) ; fclose (outfile) ; infile = fopen ("testdata", "r") ; fscanf (infile,"%f %d %f", &e, &f, &g) ; printf ("%6.2f%2d%5.2f\n", a, b, c) ; printf ("%6.2f,%2d,%5.2f\n", e, f, g) ; } **************************** 13.72, 5, 6.68

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Introduction to C Generation of ‘C’ Language

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