C++ Programming Languages Sharif University of Technology C++ Programming Languages Lecturer: Omid Jafarinezhad Spring 2014 Lecture 1 c programming language overview Department of Computer Engineering

Review Of Course Materials Overview of the C-portions of C++ e.g., loops, structs, arrays, basic data types, etc. A quick tour through C++, focusing primarily on classes, templates, inheritance, and dynamic binding An in-depth look at defining abstract data types in C++ focusing primarily on classes, templates, and exception handling single and multiple inheritance dynamic binding pointer-to-member functions in C++ dynamic memory management in C++ container classes in C++ Traps and pitfalls of using C++ and how to workaround them Thread and Graphic (2D and 3D) programming, Refactoring, TDD, Qt, …

References P. Deitel, H. Deitel, C++: How to Program, 9th Edition, Prentice Hall, 2011.  J. Soulie, C++ Language Tutorial, 2009. Available at http://www.cplusplus.com/doc/tutorial/  M. Fowler, K. Beck, J. Brant, W. Opdyke, D. Roberts, Refactoring: Improving the Design of Existing Code, Addison Wesley, 1999.

Grading policy Assignments : 4 pts Projects: 4 pts Quizzes: 2 pts Midterm: 4 pts Final Exam: 6 pts Programming Contest: +1 pt (bonus)

C History BCPL ,1967, Martin Richards B, 1969, Ken Thomson writing operating-systems software and compiler B, 1969, Ken Thomson based on BCPL C, 1972, Dennis Ritchie based on BCPL and B at Bell Laboratories originally implemented on a DEC PDP-11

C++ Programming Language early 1980s, Bjarne Stroustrup at Bell Labroratory C++ a superset of C object-oriented programming Objects are essentially reusable software components that model items in the real world filename.cpp

Simple C Program Examples: // int is return data type // main is entrance function int main() { statement 1; // …. return 0; } // Simplest c program int main() { return 0; } /* Objective: print on screen */ #include <stdio.h> // preprocessor statements have not ; int main() { printf("welcome to c!!!"); return 0; // indicate that program ended successfully } welcome to c!!!

Example #include <stdio.h> // (preprocessor ) Header file Constant Main function Variables Input and output Process #include <stdio.h> // (preprocessor ) #define PI 3.14 // PI constant (preprocessor ) // calculating area of circle int main() { /* variable definition */ float Radius; float Area = 0; // get radius of circle form user printf("Enter Radius :\n"); scanf("%f", &Radius); // calculating area of circle Area = PI * Radius * Radius; printf(“Area = %f", Area ); system("Pause"); return 0; }

Variable declaration Before using a variable, you must declare it Data_Type Identifier; int width; // width of rectangle float area; // result of calculating area stored in it char separator; // word separator Data_Type Identifier = Initial_Value; int width = 10; // width of rectangle float area = 255; // result of calculating area stored in it char seperator = ‘,’; // word separator Data_Type Identifier, Identifier, Identifier ,….; int width, length, temporary; float radius, area = 0;

Data types Minimal set of basic data types primitive data types int float double char Void The size and range of these data types may vary among processor types and compilers

Data type qualifiers Modify the behavior of data type to which they are applied: Size qualifiers: alter the size of the basic data types: short: multiply by 0.5 long: multiply by 2 short can be applied to: int long can be applied to: int and double Sign qualifiers: can hold both positive and negative numbers, or only positive numbers.: signed: + and - unsigned: + they can be applied to : int and char

Data type size and range Example Qualifier Data type -128 .. 127 0 .. 255 8 signed char c; unsigned char c; char c; signed unsigned char signed (16): -32768 .. 32767 unsigned (16): 0 .. 65535 signed (32): -2147483648 .. 2147483647 unsigned (32): 0 .. 4294967295 16 16 or 32 32 64 signed short i; signed short int i; unsigned int i; int i; signed int i; short i; short int i; long i; long int i; signed long i; signed long int i; long long i; long long int i; signed long long i; signed long long int i; short long int +/- 3.4e +/- 38 (~7 digits) float f; float +/- 1.7e +/- 308 (~15 digits) 80 double d; long double d; double

Overflow and Underflow /* The # character indicate a pre-processor directive; it's an instruction to the compiler to make it do something The <> character tell C to look in the system area for the file stdio.h. If I had given the name #include "stdio.h" instead it would tell the compiler to look in the current directory /* #include <stdio.h> * Function main begins program execution * Semi-colon is statement terminator, so it is as a signal to the compiler for end of line */ int main() { /* The 2 curly brackets { }, are used to specify the limits of the program block */ char letter = 'A'; // char variable to show ASCII code short shortVariable = 32769; // short variable for test overflow // printf command display string on the monitor printf("current value of shortVariable is = %d\n", shortVariable); printf("current value of letter is = %d", letter); printf("current value of letter is = %c", letter); system("PAUSE"); // pause the execution to show press any key … return 0; // indicate that program ended successfully } current value of shortVariable is = -32767 current value of letter is = 65 current value of letter is = A

Program Error Compile-time or syntax Run-time Logical is caused when the compiler cannot recognize a statement Run-time E.g. division by zero Logical E.g. Overflow and Underflow

Integer constant value Base 10: 1 915 +8 -90 Base 8: 074 0123 084 Base 16: 0x1 0X5 0x7fab unsigned: 5000u 4U long: 123456789l 56L unsigned long: 536489ul long long : 5361254865LL 25lL Example : 0xABu 0123uL 017LL

floating-point constant value A floating-point value contains a decimal point 33.5 0.0 -657.983 .2 6. For example, the value 150.4582 is represented in scientific notation as 1.504582 X 102 and is represented in exponential notation (by the computer) as 1.504582E+02 This notation indicates that 1.504582 is multiplied by 10 raised to the second power (E+02) The E stands for “exponent”

Char and string constant value char c; c = 'A'; // d = 65; String printf("string is array of char!!!"); printf("example of escape sequence is \n");

Constant Constants provide a way to define a variable which cannot be modified by any other part in the code #define: without memory consume const: memory consume #define Identifier constant_value #define PI 3.14 #define ERROR "Disk error " #define ERROR "multiline \ message" #define ONE 1 #define TWO ONE + ONE

Constant const [Data_Type] Identifier = constant_value; const p = 3; // const int p = 3; const p; p = 3.14; // compile error const p = 3.14; // p = 3 because default is int const float p = 3.14;

Operators Arithmetic Operators Assignment Operators unary operators operators that require only one operand binary operators operators that require two operands Assignment Operators Equality and Relational Operators Logical Operators Bitwise Operators Conditional Operator Comma Operator sizeof Operator Width * High Operand

Arithmetic Operators Unary Operator C operation Operator Expression Explanation Positive + a = +3; Negative - b = -4; Increment ++ i++; Equivalent to i = i + 1 Decrement - - i - -; Equivalent to i = i - 1

Arithmetic Operators Binary Operators C operation Operator Expression Addition + b = a + 3; Subtraction - b = a – 4; Multiplication * b = a * 3; Division / b = a / c; Modulus (integer) % b = a % c;

Division The division of variables of type integer will always produce a variable of type integer as the result Example int a = 7, b; float z; b = a / 2; z = a / 2.0; printf("b = %d, z = %f\n", b, z); Since b is declared as an integer, the result of a/2 is 3, not 3.5 b = 3, z = 3.500000

Modulus You could only use modulus (%) operation on integer variables (int, long, char) z = a % 2.0; // error z = a % 0; // error Example int a = 7, b, c; b = a % 2; c = a / 2; printf("b = %d\n", b); printf("c = %d\n", c); Modulus will result in the remainder of a/2. 7 2 6 3 1 - a/2 integral a%2 remainder

Assignment Operators lvalue = rvalue; int i; float f; i = 2; // *&i = 2; 2 = i; // error: invalid lvalue in assignment f = 5.6; i = f; // i = 5; i = -5.9; // i = -5;

Assignment Operators Assignment operators are used to combine the '=' operator with one of the binary arithmetic or bitwise operators Example : c = 9; Operator Expression Equivalent Statement Results += c += 7; c = c + 7; c = 16 -= c -= 8; c = c – 8; c = 1 *= c *= 10; c = c * 10; c = 90 /= c /= 5; c = c / 5; %= c %= 5; c = c % 5; c = 4 &= c &= 2 ; c = c & 2; c = 0 ^= c ^= 2; c = c ^ 2; c = 11 |= c |= 2; c = c | 2; <<= c <<= 2; c = c << 2; c = 36 >>= c >>= 2; c = c >> 2; c = 2

Equality and Relational Operators Equality Operators: Relational Operators: Operator Example Meaning == x == y x is equal to y != x != y x is not equal to y Operator Example Meaning > x > y x is greater than y < x < y x is less than y >= x >= y x is greater than or equal to y <= x <= y x is less than or equal to y

Logical Operators Logical operators are useful when we want to test multiple conditions AND OR NOT C has not bool data type, but: 0: evaluate to false If(0) printf(" …"); other: evaluate to true If(1) printf(" …"); If(-13) printf(" …");

&& - Logical AND All the conditions must be true for the whole expression to be true Example: if (a == 1 && b == 2 && c == 3) means that the if statement is only true when a == 1 and b == 2 and c == 3 If (a = 5) … e1 e2 Result = e1 && e2 1 e1 e2 Result = e1 && e2 false true

|| - Logical OR The truth of one condition is enough to make the whole expression true Example: if (a == 1 || b == 2|| c == 3) means the if statement is true when either one of a, b or c has the right value e1 e2 Result = e1 || e2 1 e1 e2 Result = e1 || e2 false true

! - Logical NOT Reverse the meaning of a condition Example: if (!(radius > 90)) Means if radius not bigger than 90. e1 Result = !e1 1 e1 Result = !e1 false true

Bitwise Operators Apply to all kinds of int and char types: signed and unsigned char, short, int, long, long long Operator Name Description & AND Result is 1 if both operand bits are 1 | OR Result is 1 if either operand bit is 1 ^ XOR Result is 1 if operand bits are different ~ Not (Ones Complement) Each bit is reversed <<  Left Shift Multiply by 2 >>  Right Shift Divide by 2

Bitwise Operators Applicable for low level programming, e.g.: Usually: Port manipulation I/O programming Usually: &: set OFF one bit |: set ON one bit ^: reverse one bit

Conditional Operator The conditional operator (?:) is used to simplify an if/else statement Condition ? Expression1 : Expression2; The statement above is equivalent to: if (Condition) Expression1; else Expression2; Which are more readable?

Comma Operator (Expression1 ,Expression2,…); Example: int x, y, z; z = (x = 2, y = x + 1); printf("z = %d", z); int x, y, z; x = 2; y = x + 1; z = y; printf("z = %d", z);

sizeof The sizeof keyword returns the number of bytes of the given expression or type returns an unsigned integer result sizeof variable_Identifier; sizeof (variable_Identifier); sizeof (Data_Taype); Example: int x; printf("size of x = %d", sizeof x); printf("size of long long = %d", sizeof(long long)); printf("size of x = %d", sizeof (x));

Type Casting Explicit Type cast: carried out by programmer using casting int k, i = 7; float f = 10.14; char c = 'B'; k = (i + f) % 3; // error k = (int)(i + f) % 3; Implicit Type cast: carried out by compiler automatically f = 65.6; i = f; //f = (int)f; c = i; // c = (int)i;

Precedence Rules Primary Expression Operators () [] . -> () [] . -> left-to-right Unary Operators * & + - ! ~ ++expr --expr (typecast) sizeof right-to-left Binary Operators * / % + - >> << < > <= >= == != & ^ | && || Ternary Operator ?: Assignment Operators = += -= *= /= %= >>= <<= &= ^= |= Post increment expr++ expr-- - Comma ,

Control Structures Sequence Decision selection statement Repetition The if statement is called a single-selection statement because it selects or ignores a single action. The if…else statement is called a double-selection statement because it selects between two different actions. The switch statement is called a multiple-selection statement because it selects among many different actions Repetition while do…while for

Compound Statements A statement is a specification of an action to be taken by the computer as the program executes Compound Statements is a list of statements enclosed in braces, { }

Decision Structure One of two possible actions is taken, depending on a condition Selection structures are used to choose among alternative courses of action YES NO YES NO x < y? Process B Process A

C programming language Decision Structure The flowchart segment below shows how a decision structure is expressed in C as an if/else statement Flowchart C programming language YES NO x < y? Calculate a as x times 2. Calculate a as x plus y. if (x < y) a = x * 2; else a = x + y;

C programming language Decision Structure The flowchart segment below shows a decision structure with only one action to perform Flowchart C programming language YES NO x < y? Calculate a as x times 2. if (x < y) a = x * 2;

Combining Structures YES NO if (x > min) { if (x < max) Display “x is within limits.” Display “x is outside the limits.” YES NO x > min? x < max? if (x > min) { if (x < max) printf("x is within the limits"); else printf("x is outside the limits"); }

Example if(x) if(x) if(x) if(y) { { printf("Yes"); if(y) if(y) else printf("No"); if(x) { if(y) printf("Yes"); else printf("No"); } if(x) { if(y) printf("Yes"); } else printf("No"); if (x < 0.25) count1++; else if (x >= 0.25 && x < 0.5) count2++; else if (x >= 0.5 && x < 0.75) count3++; else count4++; if (x < 0) sign = -1; else if (x == 0) sign = 0; else sign = 1;

Case Structure One of several possible actions is taken, depending on the contents of a variable

Case Structure indicates actions to perform depending on the value in years_employed If years_employed = 2, bonus is set to 200 If years_employed = 3, bonus is set to 400 CASE years_employed 1 2 3 Other bonus = 100 bonus = 200 bonus = 400 bonus = 800 If years_employed = 1, bonus is set to 100 If years_employed is any other value, bonus is set to 800

switch A switch statement allows a single variable (integer or char) to be compared with several possible constants A constant can not appear more than once, and there can only be one default expression

switch switch (variable) { case const: statements...; default: } switch (c = toupper(getch())) { case ‘R’: printf("Red"); break; case ‘G’: printf("Green"); default: printf("other"); }

Example switch(betty) { case 1: printf("betty = 1\n"); case 2: case 3: break; case 3: printf("betty=3\n"); default: printf("Not sure\n"); } CASE betty? 1 2 3 Other betty = 1 betty = 2 betty = 3 Not sure

Repetition Structure A loop tests a condition, and if the condition exists, it performs an action. Then it tests the condition again. If the condition still exists, the action is repeated. This continues until the condition no longer exists x < y? Process A YES

C programming language Repetition Structure The flowchart segment below shows a repetition structure expressed in C as a while loop Flowchart C programming language x < y? Add 1 to x YES while (x < y) x++;

While while (loop_repetition_condition) statement; OR //Compound statement { statement1; statement2; // … }

Controlling a Repetition Structure The action performed by a repetition structure must eventually cause the loop to terminate. Otherwise, an infinite loop is created In this flowchart segment, x is never changed. Once the loop starts, it will never end How can this flowchart be modified so it is no longer an infinite loop? x < y? Display x YES

Controlling a Repetition Structure Adding an action within the repetition that changes the value of x x < y? Display x Add 1 to x YES

A Pre-Test Repetition Structure This type of structure is known as a pre-test repetition structure. The condition is tested BEFORE any actions are performed if the condition does not exist, the loop will never begin x < y? Display x Add 1 to x YES

Example int counter = 0; while (counter < 1000) ; while (1); printf("%d\n", counter ++); int counter = 9; while (counter > 0) printf("%d\n", counter --); int counter = 0; while (counter < 9) { printf("%d\n", counter); counter++; } int counter = 0; while (counter < 9) { printf("%d\n", counter ++); }

A Post-Test Repetition Structure The condition is tested AFTER the actions are performed A post-test repetition structure always performs its actions at least once Display x Add 1 to x YES x < y? C programming language do { printf(…); x++; } while (x < y);

do-while do statement; while (loop_repetition_condition) OR do //Compound statement { statement1; statement2; // … }

For for (initial_value ; condition; update_counter) statement; OR // Compound statement for (initial_value ; condition; update_counter) { statement; // … }

Array Generic declaration: typename variablename[size]; typename is any type variablename is any legal variable name size is a number the compiler can figure out For example : int a[10]; Defines an array of ints with subscripts ranging from 0 to 9 There are 10*sizeof(int) bytes of memory reserved for this array. You can use a[0]=10; x=a[2]; a[3]=a[2]; etc. You can use scanf("%d",&a[3]); 9 8 7 6 5 4 3 2 1 10 a

Array Representation int A[3]; A[2] 0x1008 A[1] 0x1004 A[0] 0x1000 All elements of same type – homogenous Last element (index size - 1) First element (index 0) array[0] = 3; array[2] = 4; array[10] = 5; array[-1] = 6; sizeof(A)? sizeof(A[0]) = sizeof(A[1]) = sizeof(A[2])? No bounds checking! 3 * 4 = 12 4

Using Constants to Define Arrays It is useful to define arrays using constants: #define MONTHS 12 float a [MONTHS]; However, in ANSI C, you cannot int n; scanf(“%d”, &n); float a[n]; In GNU C, the variable length array is allowed.

Initializing Arrays Initialization of arrays can be done by a comma separated list following its definition For example: int array [4] = { 100, 200, 300, 400 }; This is equivalent to: int array [4]; array[0] = 100; array[1] = 200; array[2] = 300; array[3] = 400; You can also let the compiler figure out the array size for you: int array[] = { 100, 200, 300, 400};

Initializing Arrays For example: Also can be done by int array [4] = { 100, 200 }; Also can be done by int array [4] = { 100, 200, 0, 0 }; This is equivalent to int array [4]; array[0] = 100; array[1] = 200; array[2] = 0; array[3] = 0;

Multidimensional Arrays Arrays in C can have virtually as many dimensions as you want Definition is accomplished by adding additional subscripts when it is defined For example: int a [4] [3] ; 2-dimensional array 4 * 3 * sizeof(int) int a[4][3][2] 3-dimention array 4 * 3 * 2 * sizeof(int)

Multidimensional Arrays Representation Row 0 Row 1 Row 2 Column 0 Column 1 Column 2 Column 3 a[ 0 ][ 0 ] a[ 1 ][ 0 ] a[ 2 ][ 0 ] a[ 0 ][ 1 ] a[ 1 ][ 1 ] a[ 2 ][ 1 ] a[ 0 ][ 2 ] a[ 1 ][ 2 ] a[ 2 ][ 2 ] a[ 0 ][ 3 ] a[ 1 ][ 3 ] a[ 2 ][ 3 ] Row subscript Array name Column subscript int a[n][m] ; &a[i][j] = [(m * i) + j] * (sizeof(int)) + &a[0]

Initializing Multidimensional Arrays The following initializes a[4][3]: int a[4] [3] = { {1, 2, 3} , {4, 5, 6} , {7, 8, 9} , {10, 11, 12} }; Also can be done by: int a[4] [3] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 }; is equivalent to a[0][0] = 1; a[0][1] = 2; a[0][2] = 3; a[1][0] = 4; ... a[3][2] = 12;

Examples Initialization Example: short b[ 2 ][ 2 ] = { { 1, 2 }, { 3, 4 } }; If not enough, unspecified elements set to zero short b[ 2 ][ 2 ] = { { 1 }, { 3, 4 } }; 2 1 4 3 1 4 3

Examples int a[10]; // Ok int a[2.5]; // Syntax error int a[-5]; // Syntax error int a[0]; // Logical error a[3.6] = 10; // Syntax error or a[3] = 10; a[3.2] = 10; // Syntax error or a[3] = 10; int b[2][3] = { {1, 2}, {3, 4}, {5, 6} }; // Syntax error

Strings are Character Arrays Strings in C are simply arrays of characters Example: char s [10]; This is a ten (10) element array that can hold a character string consisting of  9 characters This is because C does not know where the end of an array is at run time By convention, C uses a NULL character '\0' to terminate all strings in its library functions For example: char str [10] = {'u', 'n', 'I', 'x', '\0'}; It’s the string terminator (not the size of the array) that determines the length of the string

Accessing Individual Characters The first element of any array in C is at index 0. The second is at index 1, and so on ... char s[10]; s[0] = 'h'; s[1] = 'i’; s[2] = '!'; s[3] = '\0'; This notation can be used in all kinds of statements and expressions in C: For example: c = s[1]; if (s[0] == '-') … switch (s[1]) ... ? \0 ! i h [9] [8] [7] [6] [5] [4] [3] [2] [1] [0] s

String Literals String literals are given as a string quoted by double quotes printf("Long long ago."); Initializing char array ... char s[10] = "unix"; /* s[4] is '\0'; */ char s[ ] = "unix"; /* s has five elements */

Pointer Fundamentals When a variable is defined the compiler (linker/loader actually) allocates a real memory address for the variable int x; // &x = 22f54; &x = 22f54; // Error When a value is assigned to a variable, the value is actually placed to the memory that was allocated x = 3; // * (&x) = 3; *x = 3; // Error * & 00000000 22F54 22F55 22F56 00000011 22F57 x

Pointer Fundamentals When the value of a variable is used, the contents in the memory are used y = x; y = *(&x); &x can get the address of x (referencing operator &) The address can be passed to a function: scanf("%d", &x); The address can also be stored in a variable … * & 00000000 22F54 22F55 22F56 00000011 22F57 x

Pointers To declare a pointer variable For example: int x; type * PointerName; For example: int x; int * p; //p is a int pointer // char *p2; p1 = &x; /* Initializing p1 */ * & ? 22F50 x 22F51 22F52 22F53 00 22F54 p 02 22F55 2F 22F56 50 22F57 …

Initializing Pointers Like other variables, always initialize pointers before using them!!! void main() { int x; int *p; scanf("%d", p); /* */ p = &x; scanf("%d", p); /* Correct */ } * & ? 22F50 x 22F51 22F52 22F53 00 22F54 p 02 22F55 2F 22F56 50 22F57 … Compiler Developer Don’t

Using Pointers You can use pointers to access the values of other variables, i.e. the contents of the memory for other variables To do this, use the * operator (dereferencing operator) Depending on different context, * has different meanings For example: int n, m = 3, *p; p = &m; // Initializing n = *p; printf("%d\n", n); // 3 printf("%d\n", *p); // 3 *P = 10; printf("%d\n", *p); // 10 * & n 3 m p * & n 3 m p * & 3 n m p * & 3 n 10 m p

Pointer Assignment int a = 2, b = 3; int *p1, *p2; p1 = &a; p2 = &b; printf("%p %p", p1 ,p2); *p1 = *p2; printf("%d %d", *p1, *p2); p2 = p1; printf("%p %p", p1, p2); printf("%p %p", &p1, &p2); * & 3 b 2 a p1 p2 * & 3 b a p1 p2

Constant Pointers A pointer to const data does not allow modification of the data through the pointer const int a = 10, b = 20; a = 5; // Error const int *p; int *q; p = &a; *p = 100; // Error : p is (const int *) p = &b; q = &a; *q = 100; // OK !!!

Constant Pointers int x; /* define x */ int y; /* define y */ /*ptr is a constant pointer to an integer that can be modified through ptr, but ptr always points to the same memory location */ int * const ptr = &x; *ptr = 7; /* allowed: *ptr is not const */ ptr = &y; /* error: cannot assign new address */

Constant Pointers int x = 5; /* initialize x */ int y; /* define y */ /*ptr is a constant pointer to a constant integer. ptr always points to the same location; the integer at that location cannot be modified */ const int * const ptr = &x; *ptr = 7; /* error: cannot assign new value */ ptr = &y; /* error: cannot assign new address */

Multiple indirection int a = 3; int *b = &a; int **c = &b; int ***d = &c; int ****f = &d; * & 3 a b c d f

NULL Pointer Special constant pointer NULL Points to no data Dereferencing illegal To define, include <stdlib.h> or <stdio.h> int *q = NULL;

Generic Pointers: void * void *: a pointer to anything Lose all information about what type of thing is pointed to Reduces effectiveness of compiler’s type-checking Can’t use pointer arithmetic type cast: tells the compiler to change an object’s type (for type checking purposes – does not modify the object in any way) void *p; int i; char c; p = &i; p = &c; putchar(*(char *)p);

Arithmetic Operations A pointer may be incremented or decremented An integer may be added to or subtracted from a pointer. Pointer variables may be subtracted from one another int a, b; int *p = &a, *q = &b; p = p + q ; // Error p = p * q; // Error p = p / q; // Error p = p - q; // OK p = p + 3; p += 1.6; // Error p %= q; // Error

Arithmetic Operations When an integer is added to or subtracted from a pointer, the new pointer value is changed by the integer times the number of bytes in the data variable the pointer is pointing to For example, if the pointer p contains the address of a double precision variable and that address is 234567870, then the statement: p = p + 2; // 234567870 + 2 * sizeof(double) would change p to 234567886

Logical Operations Pointers can be used in comparisons int a[10], *p, *q , i; p = &a[2]; q = &a[5]; i = q - p; /* i is 3*/ i = p - q; /* i is -3 */ a[2] = a[5] = 0; i = *p - *q; // i = a[2] – a[5] if (p < q) ...; /* true */ if (p == q)...; /* false */ if (p != q) ...; /* true */ * & p q ? [0] [1] [2] [3] [4] [5] [6] [7] [8] [9]

Pointers and Arrays int a[ 10 ], *p; p = &a[2]; p[0] = 10; p[1] = 10; Array  pointer to the initial (0th) array element a  &a[0] a[i]  *(a+i) &a[i]  a + i int a[ 10 ], *p; p = &a[2]; p[0] = 10; p[1] = 10; printf("%d", p[3]); int a[ 10 ], *p; a[2] = 10; a[3] = 10; printf("%d", a[5]); Example: int a, *p; p=&a; *p = 1; p[0] = 1; p p[7] p[6] p[5] p[4] p[3] p[2] p[1] p[0] [9] [8] [7] [6] [5] [4] [3] [2] [1] [0] a

These two blocks of code are functionally equivalent Pointers and Arrays Array  pointer to the initial (0th) array element a  &a[0] a[i]  *(a+i) &a[i]  a + i 3 2 1 a + 3 a + 2 a + 1 a int i; int array[10]; for (i = 0; i < 10; i++) { array[i] = …; } int *p; int array[10]; for (p = array; p < &array[10]; p++) { *p = …; } These two blocks of code are functionally equivalent

An Array Name is Like a Constant Pointer Array name is like a constant pointer which points to the first element of the array int a[10], *p, *q; p = a; /* p = &a[0] */ q = a + 3; /* q = &a[0] + 3 */ a ++; /* Error !!! */ int * const a

Example int a[10], i; int *p = a; // int *p = &a[0]; for (i = 0; i < 10; i++) scanf("%d", a + i); // scanf("%d", &a[i]); for (i = 9; i >= 0; --i) printf("%d", *(p + i)); // printf("%d", a[i]); //printf("%d", p[i]); for (p = a; p < &a[10]; p++) printf("%d", *p);

An example int a[10], *p, *q; p = &a[2]; q = p + 3; p = q – 1; p++; printf("%d", *q); * & p q ? [0] [1] [2] [3] [4] [5] [6] [7] [8] [9] * & p q ? [0] [1] [2] [3] 123 [4] [5] [6] [7] [8] [9]

An Example int a[10], *p; a++; //Error a--; // Error a += 3; //Error p = a; // p = &a[0]; p ++; //OK p--; // Ok P +=3; // Ok

Strings In C, strings are just an array of characters Terminated with ‘\0’ character Arrays for bounded-length strings Pointer for constant strings (or unknown length) char str1[15] = "Hello, world!“; \0 ! d l r o w , e H char str1[] = "Hello, world!"; char *str2 = "Hello, world!"; \0 ! d l r o w , e H

An Example void copy1(char * const s1, const char * const s2) { int i; /* counter */ /* loop through strings */ for ( i = 0; ( s1[ i ] = s2[ i ] ) != '\0'; i++ ); /* do nothing in body */ } void copy2(char *s1, const char *s2) for ( ; ( *s1 = *s2 ) != '\0'; s1++, s2++ ); /* do nothing in body */

Multi-Dimensional Arrays int a[row][col]; a[row][col]  *(*(a + row) + col) a[row][col]  *(a[row] + col) &a[row][col]  a[row] + col a  a[0][0]  a[0] scanf(" %d ", &a[0][0])  scanf(" %d ", a[0]) printf (" %d ", a[0][0])  printf(" %d ", *a[0]) scanf(" %d ", &a[2][2])  scanf(" %d ", a[2]+ 2) printf (" %d ", a[2][2])  printf(" %d ", *(a[2] + 2)) a[0] + 2 [0][9] [0][8] [0][7] [0][6] [0][5] [0][4] [0][3] [0][2] [0][1] [0][0]  a[0] [1][9] [1][8] [1][7] [1][6] [1][5] [1][4] [1][3] [1][2] [1][1] [1][0] a[1] [2][9] [2][8] [2][7] [2][6] [2][5] [2][4] [2][3] [2][2] [2][1] [2][0] a[2] [3][9] [3][8] [3][7] [3][6] [3][5] [3][4] [3][3] [3][2] [3][1] [3][0] a[3] [4][9] [4][8] [4][7] [4][6] [4][5] [4][4] [4][3] [4][2] [4][1] [4][0] a[4]

Array of Pointers char *suit[ 4 ] = { "Hearts", "Diamonds", "Clubs", "Spades" }; \0 s t r a e H  suit[0] d n o m i D suit[1] b u l C suit[2] p S suit[3]

Array of Pointers int a=1, b=2, c=3, d=4; int *k[4] = {&a, &b, &c, &d}; printf("%d %d %d %d", *k[0], *k[1],*k[2],*k[3]); * & k[0] k[1] k[2] k[3] 1 a 2 b 3 c 4 d 1 a  k[0] 2 b k[1] 3 c k[2] 4 d k[3]

Functions Every C program starts with main() function Functions could be Pre-defined library functions e.g., printf, sin, tan Programmer-defined functions e.g., my_printf, area int main() { … }

Functions - Definition Structure Function 'header' Return data type (if any) Name Descriptive Arguments (or parameter list) Notice: data type and name Statements Variable declaration Operations Return value (if any) type function_name (type arg1, type arg2 ) { statements; } A function that calculates the product of two numbers double product(double x, double y) { double result; result = x * y; return result; } The function definition declares the return data type, its name, and the data types of its parameters. Any parameter names included in the list are actually ignored by the compiler. The names are included to help document the function. Contrast this with the function prototype.

An Example printf("var1 = %.2f\n" #include <stdio.h> /* function prototype */ double product(double x, double y); int main() { double var1 = 3.0, var2 = 5.0; double ans; ans = product(var1, var2); printf("var1 = %.2f\n" "var2 = %.2f\n",var1,var2); printf("var1*var2 = %g\n", ans); return 0; } /* function definition */ double product(double x, double y) double result; result = x * y; return result; Function prototype Like a variable declaration Tells compiler that the function will be defined later Helps detect program errors Note semicolon!! Function definition See previous slide Note, NO semicolon Function return return statement terminates execution of the current function Control returns to the calling function if return expression; then value of expression is returned as the value of the function call Only one value can be returned this way Function call main() is the 'calling function' product() is the 'called function' Control transferred to the function code Code in function definition is executed Show structure from the template: miles_to_kilometers.c The function prototype declares the return data type, the function's name, and the data types of its parameters. Any parameter names included in the list are actually ignored by the compiler. The names are included to help document the function. Function prototype helps reduce program errors, because by using it, the compiler can then detect the wrong number or the wrong type of data items that are passed to the function

Formal and Actual Parameters #include <stdio.h> int calSum(int,int); /*function prototype*/ int main(void) { ….. sum = calSum(num1,num2); /* function call */ } int calSum(int val1, int val2) /*function header*/ …… Formal Parameters Actual Parameters Formal Parameters

An Example If the function requires some arguments to be passed along, then the arguments need to be listed in the ( ) according to the specified order void Calc(int, double, char, int); int main(void) { int a, b; double c; char d; … Calc(a, c, d, b); return (0); } Function Call

Functions that do not return a value Use the return type of void void functionName( DataType arg_1,…) void functionName() void functionName( void)

Function Call – An Example 1 2 3 4 #include <stdio.h> //function prototype //global variable declaration int main(void) { local variable declaration; statements; fn1( ); fn2( ); return (0); } void fn1(void) { local variable declaration; statements; } void fn2(void) return;

Call by value And Call by reference In this method, only the copy of variable’s value (copy of actual parameter’s value) is passed to the function. Any modification to the passed value inside the function will not affect the actual value In all the examples that we have seen so far, this is the method that has been used Call by reference In this method, the reference (memory address) of the variable is passed to the function. Any modification passed done to the variable inside the function will affect the actual value To do this, we need to have knowledge about pointers and arrays

Call by value – An Example #include <stdio.h> int calSum(int,int); /*function protototype*/ int main(void) { int sum, num1, num2; printf("Enter two numbers to calculate its sum:\n"); scanf("%d%d",&num1,&num2); sum = calSum(num1,num2); /* function call */ printf("\n %d + %d = %d", num1, num2, sum); return(0); } int calSum(int val1, int val2) /*function definition*/ int sum; sum = val1 + val2; val2 = 100; return sum; 4 num2 9 num1 13 sum 4 num2 9 num1 ? sum ? num2 num1 sum 100 val2 9 val1 13 sum 4 val2 9 val1 13 sum 4 val2 9 val1 ? sum Enter two numbers to calculate its sum: 4 9 4 + 9 = 13 Press any key to continue

Call by reference 10 b a 5 b 1 a b a main -5 b a main 5 b 1 a #include <stdio.h> void CalByVal(int a, int b) { a = 0; b = 10; } void CalByRef(int *a, int *b) // CalByRef(int *p, int *q) *a = 0; *b = -5; // a = 0; !!!! int main(void) int a = 1, b = 5; printf("Before cal CalByVal: a = %d, b = %d\n", a, b); CalByVal(a, b); printf("After cal CalByVal: a = %d, b = %d\n", a, b); printf("Before cal CalByRef: a = %d, b = %d\n", a, b); CalByRef(&a, &b); printf("After cal CalByRef: a = %d, b = %d\n", a, b); getch(); return 0; /* Exit program. */ CalByVal 10 b a CalByVal 5 b 1 a CalByRef b a main -5 b a main 5 b 1 a

Pointers and Arrays Recall that the value of an array name is also an address void main() { int x[10]; ReOrder(x); // ReOrder(&x); } void ReOrder(int *x) int i, j, t; for(i = 0; i < 9; i++) for(j = i + 1; i < 10; ++j) if(x[i] < x[j]) t = x[i]; x[i] = x[j]; x[j] = t;

Organizing Multi-File Programs A large C program should be divided into multiple files // main.c #include <stdio.h> void Test() { // … } int main() // … return 0; } // math.c double mathVar; double sin() { double tempSin; // … return tempSin; }

YES! --> concept of ‘scope’ Identifiers and Scope Identifier The name of a variable, function, label, etc. int my_var1; /* a variable */ pow_table(); /* a function */ start: /* a label */ Question: Does it make a difference where in a program an identifier is declared? YES! --> concept of ‘scope’

Scope of Identifiers Scope of a declaration of an identifier The region of the program that the declaration is active (i.e., can access the variable, function, label, etc.) Five types of scope: Program (global scope) File Function prototype Function Block ("between the { } scope")

Scope of Identifiers - Program Scope Program (global) scope if declared outside of all functions "Visible" to all functions from point of declaration Visible to functions in other source files Use only when necessary and then very carefully!! If there exist a local variable and a global variable with the same name, the compiler will refer to the local variable #include <stdio.h> int a = 10; double product(double x, double y); int main() { double var1 = 3.0, var2 = 5.0; double ans; ans = product(var1, var2); // … } /* function definition */ double product(double x, double y) double result; a = 20; result = x * y; return result; a = 10 a = 20 Switch to ChIDE and show a modified version of the program with printf() statements included (var_scope.c) that show variable a is 'visible' throughout the program. Assign a new value in function to show how variable a is accessible and changeable. Beware!! Try to avoid using global variables. The temptation is that the variable is visible to all modules - simple and fast … But, it makes maintenance more difficult. Enables potential conflicts between modules where two programmers working on separate modules might use the same name for different global variables. Can introduce bugs that are hard to find. Any time you see a source file with global variables defined, you need to go through all source files that are part of the program to make sure there are no conflicts. Adds other restrictions like the ANSI standard only guaranteeing that a compliant compiler recognize the first 6 characters of a global variable, and may suspend case sensitivity. Better to pass data directly or via pointers.

An Example extern int a = 10; // File name: main.c #include <stdio.h> int a = 10; /* function definition */ double product(double x, double y) { double result; // … a = 70; return result; } int main() a = 80; // File name: ExternFile.c extern int a = 10; /* function definition */ void TestExtern() { // … a = 90; }

Scope of Identifiers - File Scope #include <stdio.h> static int a = 10; double product(double x, double y); int main() { double var1 = 3.0, var2 = 5.0; double ans; ans = product(var1, var2); // … } /* function definition */ double product(double x, double y) double result; result = x * y; return result; File scope Keyword static Makes variable a ‘visible’ only within this source file Use file scope to avoid naming conflict if multiple source files are used

An Example extern int a = 10; static int a = 10; // File name: main.c #include <stdio.h> static int a = 10; /* function definition */ double product(double x, double y) { double result; // … a = 70; return result; } int main() a = 80; // File name: ExternFile.c extern int a = 10; /* function definition */ void TestExtern() { // … a = 90; }

Scope of Identifiers - Function Prototype Scope #include <stdio.h> double product(double x, double y); int main() { int a = 10; double var1 = 3.0, var2 = 5.0; double ans; ans = product(var1, var2); printf("var1 = %.2f\n" "var2 = %.2f\n",var1,var2); printf("var1*var2 = %g\n", ans); } /* function definition */ double product(double A, double B) double result; result = A * B; return result; Function prototype scope Identifiers x and y are not visible outside the prototype Thus, names in the prototype do not have to match names in the function definition MUST match types, however! double product(double x, double x); will produce an error double product(double, double); will also work

Scope of Identifiers - Function Scope Active from the beginning to the end of a function #include <stdio.h> int main() { int a; // … return 0; } int FunctionScopeTest() int b;

Scope of Identifiers - Block Scope Block (local) scope A block is a series of statements enclosed in braces { } The identifier scope is active from the point of declaration to the end of the block ( } ) Nested blocks can both declare the same variable name and not interfere #include <stdio.h> double product(double x, double y); int main() { int a = 10; double var1 = 3.0, var2 = 5.0; double ans; ans = product(var1, var2); // … } /* function definition */ double product(double x, double y) double result; // a = 60; Error result = x * y; return result; Show how this works in ChIDE using var_scope_block.c Show also scope_nested_blocks.c Note: a variable declared in a block that also contains a block (nested block) is active within the contained block, but not vice-versa.

An Example a = ? a = 70 a = 100 a = 70 a = 10 a = 80 #include <stdio.h> int a = 10; int f1() { int a; a = 70; a = 100; } return a; void main() a = 80; f1(); a = ? a = 70 a = 100 a = 70 a = 10 a = 80

Storage Classes Refers to the lifetime of a variable Local variables only exist within a function by default. When calling a function repeatedly, we might want to Start from scratch – reinitialize the variables The storage class is ‘auto’ Continue where we left off – remember the last value The storage class is ‘static’ Another two storage classes (seldomly used) register (ask to use hardware registers if available) extern (global variables are external)

Auto storage class Variables with automatic storage duration are created when the block in which they are declared is entered, exist when the block is active and destroyed when the block is exited. The keyword auto explicitly declares variables of automatic storage duration. It is rarely used because when we declare a local variable, by default it has class storage of type auto. int a, b; // is the same as auto int a, b;

Static storage class However the static keyword can be applied to a local variable so that the variable still exist even though the program has gone out of the function. As a result, whenever the program enters the function again, the value in the static variable still holds

Auto - Example #include <stdio.h> void auto_example(void); int main(void) { int i; printf("Auto example:\n"); auto_example( ); return(0); } void auto_example(void) auto int num = 1; printf(" %d\n",num); num = num + 2; Auto example: 1 Press any key to continue

Static - Example #include <stdio.h> void auto_example(void); int main(void) { int i; printf("Static example:\n"); static_example( ); return(0); } void static_example(void) static int num = 1; printf(" %d\n",num); num = num + 2; Static example: 1 3 5 Press any key to continue

Recursion if (stopping case) solve it else Recursion is a technique that solves a problem by solving a smaller problem of the same type A recursive function is a function invoking itself, either directly or indirectly Recursion: A → B → C → D → A Concept of recursive function (generally): A recursive function is called to solve a problem The function only knows how to solve the simplest case of the problem. When the simplest case is given as an input, the function will immediately return with an answer However, if a more complex input is given, a recursive function will divide the problem into 2 (or more) pieces: a part that it knows how to solve and another part that it does not know how to solve if (stopping case) solve it else reduce the problem using recursion

Recursion solution of xy #include <stdio.h> double XpowerY(double, int); int main(void) { double power, x; int y; printf("Enter the value of x and y:\n"); scanf("%lf%d", &x, &y); power = XpowerY(x, y); printf("%.2f to the power of %d is %.2f\n\n", x, y, power); return(0); } double XpowerY(double x, int y) if (y ==1) return x; else return x * XpowerY(x, y-1); Enter the value of x and y: 2 3 2.00 to the power of 3 is 8.00 Press any key to continue

Recursive Steps of xy x = 2; y = 2; return x; x = 2; y = 2; #include <stdio.h> double XpowerY(double, int); int main(void) { double power, x; int y; printf("Enter the value of x and y:\n"); scanf("%lf%d", &x, &y); power = XpowerY(x, y); printf("%.2f to the power of %d is %.2f\n\n", x, y, power); return(0); } double XpowerY(double x, int y) if (y ==1) return x; else return x * XpowerY(x, y-1); x = 2; y = 2; return x; 2 x = 2; y = 2; x * XpowerY(2, 1) 2 * 2 x = 2; y = 3; x * XpowerY(2, 2) 2 * 4 x = 2; y = 4; x * XpowerY(2, 3) 2 * 8

Pointer to Function #include <stdio.h> void f1(float a){ printf("F1 %g", a);} void f2(float a){ printf("F2 %g", a);} int main(){ void (*ptrF)(float a); ptrF = f1; ptrF(12.5); ptrF = f2; getch(); return 0; } A function pointer is defined in the same way as a function prototype, but the function name is replaced by the pointer name prefixed with an asterisk and encapsulated with parenthesis Example: int (*fptr)(int, char) fptr = some_function; (*ftpr)(3,'A'); some_function(3,'A');

Array of Functions #include<stdio.h> void func1() { printf("Function 1 Called\n"); } void func2() { printf("Function 2 Called\n"); } void func3() { printf("Function 3 Called\n"); } int main(int argc, char *argv[]) { void (*ptr[3]) () = {func1, func2, func3}; int k = 0; for(k = 0; k < 3; k++) ptr[k](); getch(); return 0; }

Passing Arrays to Functions #include <stdio.h> void display(int a) { printf("%d",a); } int main() int c[] = {2,3,4}; display(c[2]); //Passing array element c[2] only return 0;

Passing Arrays to Functions #include <stdio.h> float average(float a[], int count); // float average(float *a, int count) int main(){ float avg, c[]={23.4, 55, 22.6, 3, 40.5, 18}; avg=average(c, 6); /* Only name of array is passed as argument */ printf("Average age=%.2f", avg); return 0; } float average(float a[], int count){ // float average(float *a) int I; float avg, sum = 0.0; for(I = 0;I < count; ++i) sum += a[i]; avg = (sum / 6); return avg; void func (int* x); /* this is a pointer */ void func (int x[]); /* this is a pointer */ void func (int x[10]); /* this is a pointer */

Passing Arrays to Functions #include <stdio.h> void f1(float *a) { a[1] = 100;} void f2(float a[]){ a[2] = 200;} void printArrat(float a[]) { int i = 0; for(; i < 6; i++) printf("%g ", a[i]); } int main(){ float c[]={23.4, 55, 22.6, 3, 40.5, 18}; f1(c); printArrat(c); puts(""); f2(c); getch(); return 0; Passing Array By Reference 18 40.5 3 22.6 55 23.4 100 200

Passing 2D, 3D,… Array to Functions Only the first dimension may be omitted int m[5][7]; func(m); void func(int a[5][7]) { ... } void func(int a[][7]) { ... }

Allocating Memory for a Pointer // The following program is wrong! #include <stdio.h> int main() { int *p; scanf("%d", p); return 0; } // This one is correct: #include <stdio.h> int main() { int *p; int a; p = &a; scanf("%d", p); return 0; } Don’t

malloc Prototype: void *malloc(size_t size); #include <stdlib.h> function returns the address of the first byte programmers responsibility to not lose the pointer Example: #include <stdlib.h> Key previously allocated int *ptr; ptr = (int *)malloc(sizeof(int)); // new allocation new allocation 10 Memory ptr 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

free Prototype: void free(void *ptr) releases the area pointed to by ptr ptr must not be null trying to free the same area twice will generate an error #include <stdlib.h> 2 5 p2 p1 initial memory 1 2 3 4 5 6 7 NULL 2 Key free(p1); p1 p2 allocated memory after free free memory 1 2 3 4 5 6 7

Allocating Memory for a Pointer There is another way to allocate memory so the pointer can point to something: #include <stdio.h> #include <stdlib.h> int main(){ int *p; p = (int *) malloc( sizeof(int) ); /* Allocate 4 bytes */ scanf("%d", p); printf("%d", *p); // .... free(p); /* This returns the memory to the system*/ /* Important !!! */ }

Allocating Memory for a Pointer You can use malloc and free to dynamically allocate and release the memory int *p; p = (int *) malloc(1000 * sizeof(int) ); for(i=0; i<1000; i++) p[i] = i; p[999]=3; p[1000]=3; /* Wrong! */ free(p); p[0]=5; /* Wrong! */

Structures Structures Unions Bit fields Structures Enumerations Be able to use compound data structures in programs Unions Be able to share storage space of their members Bit fields Structures Be able to do simple bit-vector manipulations Enumerations Be able to use compound symbolic constants

User Defined Data Types (typedef) Winter 2005 Engineering H192 User Defined Data Types (typedef) The C language provides a facility called typedef for creating synonyms for previously defined data type names. For example, the declaration:   typedef int Length; makes the name Length a synonym (or alias) for the data type int. The data type name Length can now be used in declarations in exactly the same way that the data type int can be used: Length a, b, len ; Length numbers[10] ; typedef char String[50]; typedef int Array[10]; String name; Array ages; Instructor: Typedef acts as a macro for data types. In the given example, whenever the alias Length appears in code, the compiler automatically knows to replace this with int, thus effectively giving length the type definition of int. Lecture 23

Structures (struct) Structures—sometimes referred to as aggregates—are collections of related variables under one name Structures may contain variables of many different data types—in contrast to arrays that contain only elements of the same data type Structures are commonly used to define records to be stored in files Pointers and structures facilitate the formation of more complex data structures such as linked lists, queues, stacks and trees Structures are derived data types—they are constructed using objects of other types

Declaring Structures (struct) The name "employee" is called a structure tag Variables declared within the braces of the structure definition are the structure’s members struct employee { char firstName[ 20 ]; char lastName[ 20 ]; int age; char gender; double hourlySalary; }; struct employee Ali, emp[10]; struct employee { char firstName[ 20 ]; char lastName[ 20 ]; int age; char gender; double hourlySalary; } Ali, Sara, empDTS[20]; struct employee Reza, *emp; struct { char firstName[ 20 ]; char lastName[ 20 ]; int age; char gender; double hourlySalary; } Ali;

Declaring Structures (struct) Often, typedef is used in combination with struct to declare a synonym (or an alias) for a structure: typedef struct { char firstName[ 20 ]; char lastName[ 20 ]; int age; char gender; double hourlySalary; } employee; /* The "alias" employee Ali; /* Create a struct variable */ struct employee { char firstName[ 20 ]; char lastName[ 20 ]; int age; char gender; double hourlySalary; } Ali, Sara, empDTS[20]; struct employee Reza, *emp;

Declaring Structures (struct) Members of the same structure type must have unique names, but two different structure types may contain members of the same name without conflict Each structure definition must end with a semicolon struct employee { char Name[ 20 ]; char Name[ 20 ]; // Error!!! int age; char gender; double hourlySalary; } Ali, Sara, empDTS[20]; struct employee Reza, *emp; struct Student { char Name[ 20 ]; // OK int age; char gender; }; struct Student Ce40153[80];

Declaring Structures (struct) A structure cannot contain an instance of itself For example, a variable of type struct employee cannot be declared in the definition for struct employee A pointer to struct employee, however, may be included A structure containing a member that is a pointer to the same structure type is referred to as a self-referential structure struct employee2 { // … double hourlySalary; struct employee2 person; /* ERROR */ struct employee2 *ePtr; /* pointer */ };

Declaring Structures (struct) The structure tag name is optional If a structure definition does not contain a structure tag name, variables of the structure type may be declared only in the structure definition—not in a separate declaration struct { char firstName[ 20 ]; char lastName[ 20 ]; int age; char gender; double hourlySalary; } Ali;

Memory layout struct COST { int amount; char currency_type[2]; } struct PART { char id[2]; struct COST cost; int num_avail; Here, the system uses 4-byte alignment of integers, so amount and num_avail must be aligned Four bytes wasted for each structure! currency_type id amount num_avail cost

Memory layout struct COST { int amount; char currency_type[2]; } struct PART { struct COST cost; char id[2]; int num_avail; Implementation dependent!!! currency_type amount id num_avail cost

Accessing Struct Members Individual members of a struct variable may be accessed using the structure member operator (the dot, "."):   myEmp.firstName ; employee. firstName; // Error Or , if a pointer to the struct has been declared and initialized   employee *emp = &myEmp ; by using the structure pointer operator :   emp -> firstName; // arrow operator which could also be written as:   (* emp).firstName; struct employee { char firstName[ 20 ]; // … } myEmp;

An Example - Initialization //Create a struct but don’t reserve space struct personal { long id; // student ID float gpa; // grade point average }; struct identity { char FirstName[30]; char LastName[30]; unsigned age; struct personal person; }; struct identity js = {"Joe", "Smith", 25}, *ptr = &js ; js.person.id = 123456789 ; js.person.gpa = 3.4 ; printf ("%s %s %d %ld %f\n", js.FirstName, js.LastName, js.age, js.person.id, js.person.gpa) ; printf ("%s %s %d %ld %f\n", ptr->FirstName, ptr->LastName,ptr->age, ptr->person.id, ptr->person.gpa) ; js.personal.id Error js = {"Joe", "Smith", 25, 9, 10} strcpy(js.FirstName, "Joe");

An Example - Assignment //Create a struct but don’t reserve space struct personal { long id; // student ID float gpa; // grade point average }; struct identity { char FirstName[30]; char LastName[30]; unsigned age; struct personal person; }; struct identity js = {"Joe", "Smith", 25}, oj ; js.person.id = 123456789 ; js.person.gpa = 3.4 ; oj = js; printf ("%s %s %d %ld %f\n", oj.FirstName, oj.LastName, oj.age, js.person.id, oj.person.gpa) ; printf ("%s %s %d %ld %f\n", ptr->FirstName, ptr->LastName,ptr->age, ptr->person.id, ptr->person.gpa) ;

Arrays of Structures struct identity sharifC40153[80] = {"omid", "Jafarinezhad", 14, 9140153, 20, "Samad", "Shekarestani", 90, 2222222, 20} ; strcpy(sharifC40153[2].FirstName, "Khaje Nezam"); strcpy(sharifC40153[2].LastName, "Shekarestani"); sharifC40153[2]. age = 100; sharifC40153[2]. person.id = 11111111; sharifC40153[2]. person. gpa = 20; //Create a struct but don’t reserve space struct personal { long id; // student ID float gpa; // grade point average }; struct identity { char FirstName[30]; char LastName[30]; unsigned age; struct personal person; } students[4]; person age LastName FirstName gpa id 20 9140153 14 Jafarinezhad omid students[0] 2222222 90 Shekarestani Samad Students[1] 11111111 100 Khaje Nezam students[2] students[3]

Pointers to Structures Date create_date1(int month, int day, int year) { Date d; d.month = month; d.day = day; d.year = year; return (d); } void create_date2(Date *d, int month, int day, int year) { d->month = month; d->day = day; d->year = year; } Pass-by-reference Date today; today = create_date1(9, 4, 2008); create_date2(&today, 9, 4, 2008); Copies date

Pointers to Structures void create_date2(Date *d, int month, int day, int year) { d->month = month; d->day = day; d->year = year; } void foo(void) Date today; create_date2(&today, 9, 4, 2008); 0x30A8 month: 9 day: 4 year: 2008 0x30A0 0x30A4 d: 0x1000 0x3098 today.month: today.day: today.year: 0x1000 0x1004 0x1008 2008 4 9

Compression of Structures Structures may not be compared using operators == and !=, because structure members are not necessarily stored in consecutive bytes of memory struct a { int a; // OK int b; }; struct a b, c; b.a = 10; b.b = 30; c = b; if(c == b) // Error

Winter 2005 Engineering H192 Enumeration Enumeration is a user-defined data type. It is defined using the keyword enum and the syntax is: enum tag_name {name_0, …, name_n} ; The tag_name is not used directly. The names in the braces are symbolic constants that take on integer values from zero through n. As an example, the statement: enum colors { red, yellow, green } ; creates three constants. red is assigned the value 0, yellow is assigned 1 and green is assigned 2 Instructor: Enumeration is essentially a method of creating a numbered list. It allows the user to assign names to numbers which can then be used as indices in an array. An example is given on the next two slides. Lecture 23

Enumeration Values in an enum start with 0, unless specified otherwise, and are incremented by 1 The identifiers in an enumeration must be unique The value of each enumeration constant of an enumeration can be set explicitly in the definition by assigning a value to the identifier Multiple members of an enumeration can have the same constant value Assigning a value to an enumeration constant after it has been defined is a syntax error Use only uppercase letters enumeration constant names. This makes these constants stand out in a program and reminds you that enumeration constants are not variables

An Example /* enumeration constants represent months of the year */ enum months {JAN = 1, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC }; enum months month; /* initialize array of pointers */ const char *monthName[] = { "", "January", "February", "March", "April", "May", "June", "July", "August", "September", "October", /* loop through months */ for (month = JAN; month <= DEC; month++ ) { printf( "%2d%11s\n", month, monthName[month] ); }

Unions A union is a derived data type—like a structure—with members that share the same storage space For different situations in a program, some variables may not be relevant, but other variables are—so a union shares the space instead of wasting storage on variables that are not being used The members of a union can be of any data type The number of bytes used to store a union must be at least enough to hold the largest member Only one member, and thus one data type, can be referenced at a time

Unions representation c union myDataUnion { int i; char c; float f; } u1, u2; union myDataUnion u3; u1.i = 4; u1.c = ’a’; u2.i = 0xDEADBEEF; i f

Unions The operations that can be performed on a union are the following: assigning a union to another union of the same type taking the address (&) of a union variable accessing union members using the structure member operator and the structure pointer operator Unions may not be compared using operators == and != for the same reasons that structures cannot be compared

Unions In a declaration, a union may be initialized with a value of the same type as the first union member union a { int a; // OK char b[4]; }; union a b = {10}; printf("%d", b.a);

Unions ? A union value doesn’t "know" which case it contains How should your program keep track whether elt1, elt2 hold an int or a char? ? union AnElt { int i; char c; } elt1, elt2; elt1.i = 4; elt2.c = ’a’; elt2.i = 0xDEADBEEF; if (elt1 currently has a char) … Basic answer: Another variable holds that info

Tagged Unions Tag every value with its case enum Union_Tag {IS_INT, IS_CHAR}; struct TaggedUnion { enum Union_Tag tag; union { int i; char c; } data; }; Enum must be external to struct, so constants are globally visible Struct field must be named

Bit-field Structures C enables you to specify the number of bits in which an unsigned or int member of a structure or union is stored This is referred to as a bit field Bit fields enable better memory utilization by storing data in the minimum number of bits required Bit field members must be declared as int or unsigned A bit field is declared by following an unsigned or int member name with a colon (:) and an integer constant representing the width of the field (i.e., the number of bits in which the member is stored)

Bit-field Structures Notice that bit field members of structures are accessed exactly as any other structure member Padded to be an integral number of words Placement is compiler-specific struct Flags { int f1:3; unsigned int f2:1; unsigned int f3:2; } foo; foo.f1 = -2; foo.f2 = 1; foo.f3 = 2; f1 f2 f3 1 … …8 bit …

Unnamed Bit-field struct example { unsigned a : 13; unsigned : 19; unsigned b : 4; }; uses an unnamed 19-bit field as padding—nothing can be stored in those 19 bits An unnamed bit field with a zero width is used to align the next bit field on a new storage-unit boundary For example, the structure definition struct example { unsigned a : 13; unsigned : 0; unsigned b : 4; uses an unnamed 0-bit field to skip the remaining bits (as many as there are) of the storage unit in which a is stored and to align b on the next storage-unit boundary

An Example - disk drive controller Frequently device controllers (e.g. disk drives) and the operating system need to communicate at a low level. Device controllers contain several registers which may be packed together in one integer

An Example - disk drive controller struct DISK_REGISTER { unsigned ready:1; unsigned error_occured:1; unsigned disk_spinning:1; unsigned write_protect:1; unsigned head_loaded:1; unsigned error_code:8; unsigned track:9; unsigned sector:5; unsigned command:5; }; struct DISK_REGISTER *disk_reg = (struct DISK_REGISTER *) DISK_REGISTER_MEMORY; /* Define sector and track to start read */ disk_reg->sector = new_sector; disk_reg->track = new_track; disk_reg->command = READ; /* wait until operation done, ready will be true */ while ( ! disk_reg->ready ) ; /* check for errors */ if (disk_reg->error_occured) { /* interrogate disk_reg->error_code for error type */ switch (disk_reg->error_code) ...... }