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Programming in C– An Overview

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1 Programming in C– An Overview

2 C-Programming General Purpose Language Developed by Dennis Ritchie of Bell Labs (1972). First used as The Systems Language for The UNIX operating system. Why ‘C’ 1. C is a SMALL Language Small is beautiful in programming Fewer key words but powerful 2. C is the Standard Developmental Language for personal computers. Much of : MS-DOS & OS/2 Many windowing packages, Data Base PGMS, Graphic Libraries & other Large Application Packages are written in ‘C’

3 3. ‘C’ is Portable - easily moved from machine to machine.
Provides a standard library of functions that work the same on all machines. Built in Preprocessor - helps isolate any system dependent code. 4. ‘C’ is Terse - very powerful set of operators. Can accomplish in 1 statement what might require many statements in another language. A Terse language explicitly magnifies the underlying productivity of the programmers. 5. ‘C’ is Modular - Supports Structured Programming. Functions - Internal - External Supports user - Defined Libraries of Functions Supports Privacy by using “Static” storage Class within files.

4 Lexical Elements C is a language. Characters + Punctuators + Rules.
C Program is viewed as a sequence of Tokens separated by White Space (i.e., spaces, tabs, new lines). Keywords. Identifiers. Constants. String constants. Operators. Punctuators.

5 Keywords Reserved words.
Cannot be redefined or used in other contexts. Case sensitive. See pg. 46 in your text.

6 Identifiers The names of variables, functions, labels and other user-defined items are called identifiers. May be any length. ANSI C – First 31 characters are recognized. Cannot be the same as a keyword or library function. Case sensitive. E.g., count, Count and COUNT are three separate identifiers.

7 Identifiers should be chosen to reflect their use in the program.
The first character must be a letter or an underscore, and subsequent characters must be either letters, digits or underscores. Correct Incorrect Count1 1count test23 hi!there high_balance high . . . Balance Identifiers should be chosen to reflect their use in the program.

8 Constants Integer A) Decimal B) Octal C) Hexidecimal F

9 Character: Any single printable character in single
Floating Point: Need . Or E format e e-05 Character: Any single printable character in single

10 String Constants Character(s) enclosed in Double Quotes
“A” and ‘A’ or not the same. “A” is actually followed by the Null character. “Hello” is really “Hello\0”

11 “a string of text” “” // the null string “ ” // a string of a blank character “ a = b + c; ” // nothing is executed

12 Operators Arithmetic Addition + Subtraction - Multiplication *
Division / { int/int – int} Modulus % 5%3 = Integer Remainder 3%9 = 3

13 Relational Operators:
< <= > >= != == Allow us to create Boolean expressions which can control program execution. Logical Operators: Not ! And && Or ||

14 Sometimes the meaning of the operator must be its determined by context.
a) scanf (“% d”, variable); b) x = y % z; a) % a conversion character b) % a modulus operator

15 Punctuators They are located by the compiler as tokens and are used to separate language elements. Parentheses ( ) Braces { } Commas , Semicolons ; int main(void) { int a, b=3, c=6; a = 17 * (b + c); }

16 Terms Source code Object code Linker Text of a program.
The input to the C compiler. Object code Translation of the source code of a program into machine code. Output from the Compiler. The input to the linker. Linker A program that links separately compiled modules into one program. The output is an executable program.

17 Library Compile time Run time
The file containing the standard functions that a program can use. Compile time The time during which a program is being compiled. Run time The time during which a program is executing.

18 Compilation A compiler translates source code into machine code.
One high-level instruction can correspond to several machine instructions. Ex: x = (y + 3) / z; Control structures while, repeat, if-then-else, case, …

19 Procedures/subroutines/functions.
Must create machine language code to: Copy input parameter values . Save return address. Start executing at beginning of invoked routine. Copy output parameter values at end of procedure. Set PC to return address.

20 Ex: total=sum + 55.32 contains five tokens,
Lexical Analysis: Break up command syntax into logical components, called tokens, and discard comments, spaces, etc. Ex: total=sum contains five tokens, total, =, sum, +, and 55.32 Parsing: Decide how tokens are related. Ex: sum is an arithmetic expression, total = sum is an assignment statement.

21 Code generation: Generating machine instructions to implement each high-level command. It is important to optimize the code.

22 X = Y+Z; W =X+Z; After line 1, X and Z are already in registers, so no need to re- load the registers for line 2, therefore execution is faster. Less retrieval time. The resulting machine language program,called object code, is written to disk.

23 Library and Linking Most programs include calls to various functions contained in C's standard library. The object code(from C compiler) contains “holes” due to these missing parts. A Linker links the object code with the code for the missing functions to produce an executable image(load module).

24 Library and Linking Linker: combines the result of compiling different pieces of the program separately. If pieces refer to each other, these references cannot be resolved during independent compilation. procedure p main Refers to x Declares x Invokes p

25 Two separate files int count;                       #include <stdio.h> void display(void);        extern int count; int main(void)    void display(void) { { count = 10; printf(“%d”, count); display(); } return 0; }

26 C’s Memory Map Stack Heap-Dynamic Global variables Program code
Separate compilation. Conceptualized memory map of a C program. Memory for the program, memory for the data. Stack Heap-Dynamic Global variables Program code

27 A Hello World Program Hello, world!
/*The traditional first program in honor of Dennis Ritchie who invented C at Bell Labs in 1972.*/ #include <stdio.h> int main(void) //main function { printf(“Hello, world!\n”); return 0; } Hello, world!

28 Format of the Function:
Preprocessor Directives //Here we include any libraries required by the program. : int main () { Declarations ; //Here we list any data variable declarations. Body of Function //Here is the source program version of the algorithm. } Main Function: Program will have 1 main function where Execution Begins & Ends. Pre-Defined Functions: Already Exist - Part of the Language Programmer uses them to do predefined Activities - Input/Output. User-Defined Functions: Functions written by the programmer. Created to do specific task(s). e.g. - Given Hours worked & payrate; Calculate Employee salary.

29 Preprocessing directives
Before compilation takes place the preprocessor modifies the source code that is input to the compiler. includes files - #include define constants - #define All preprocessor directives begin with a # sign. Each preprocessing directive must be on its own line. #include <stdio.h> #include <stdlib.h> //wrong

30 #include General Syntax:
#include <filename> e.g. #include <stdio.h> The preprocessor looks for the file only in standard places. #include “filename” e.g. #include “utility.h” The preprocessor first search the file in the current directory and then in other system-dependent places.

31 #define General Syntax: Symbolic Constant #define macro-name char-sequence e.g. #define PI The preprocessor changes all occurrence of the identifier PI to 3.14. e.g. printf(“PI = %f\n”, PI) printf(“PI = %f\n”, 3.14) A symbolic constant is easily changed later. By convention, a symbolic constant is written in capital letters.

32 xyz #define ONE 1 #define TWO ONE+ONE
#define E_MS "standard error on input\n" printf(E_MS); standard error on input #define XYZ this is a test printf("XYZ"); xyz #define LONG_STRING "this is a very long \ string that is used as an example"

33 # define: can be placed anywhere in your source code.
usually place at the beginning of your source code before main( ) function. Where you place them determines their SCOPE. SCOPE: The segment of code that “knows about” the existence of the symbolic constants and/or macros you have created. e.g., If place at the beginning of your source file, then the SCOPE is the entire file.

34 Header Files: Are joined with your source code by the Preprocessing Directive #. Why - often reason is that they contain the FUNCTIONAL PROTOTYPES (FP’s) of functions that the program wishes to call. - If the FP’s are not available then the program can’t call (use) those functions. Functional Prototype: The “Heading” of the function. Contains the Name and return type of the function. The number & type of values that may be passed to the function (Formal parameters). The Compiler needs the FP’s of invoked functions to perform its job.

35 Comments Multi-Line comments /* this is a multiline comment */
May be placed anywhere in a program. May not be nested. /* this is a multiline comment */ x = 10+ /* add the numbers */5; //correct /* this is an outer comment    x = y/a;   /* this is an inner comment - and causes an error */ */ //wrong

36 Single-Line Comments A single-line comment can be nested within a multi-line comment. All but the most obvious functions should have a comment at the top that states what the function does, how it is called, and what it returns. // this is a single-line comment /* this is a // test of nested comments. */

37 A Depth Program #include <stdio.h> int main(void) {
int inches, feet, fathoms; //declarations fathoms = 7; feet = 6 * fathoms; inches = 12 * feet; printf(“Wreck of the Hesperus:\n”); printf(“Its depth at sea in different units:\n”); printf(“ %d fathoms\n”, fathoms); printf(“ %d feet\n”, feet); printf(“ %d inches\n”, inches); } Wreck of the Hesperus: Its depth at sea in different units: 7 fathoms 42 feet 504 inches

38 Declaration A variable is declared to be of a type. This enables the compiler to: Set aside the appropriate amount of memory to hold the variable. Defines what operations are permissible with that variable. All variables must be declared before they are assigned values and used in statements. Declaration end with a semicolon.

39 Assignment Allows the work and processing of data to achieved.
variable; Variable = constant; function call; expression; [contains any/all of above joined by operators] Multiple assignments. Right to Left Association: 1. C = 0 A = B = C = 0; 2. B = (C = 0) 3. A = (B = (C = 0))

40 Compound Assignments +=, -=, *=, /=, %= General Form:
+=, -=, *=, /=, %= General Form: Variable += Exp; Variable = Variable + Exp; Variable -= Exp Variable = Variable - Exp Variable *= Exp Variable = Variable * Exp Variable /= Exp Variable = Variable * Exp Variable %= Exp Variable = Variable % Exp x += 10; x = x +10; x -= 100; x = x - 100;

41 Data Types: See more in Chap. 6
Variables - Locations in memory we create which can hold data. Variables have a specific type. Type defines what sort of data is allowed to be stored in the variable. Integer Types: int, short int, long int Real Types: float, double, long double Text Types: Char 1 keystoke (1 symbol) String multiple characters

42 Initialization When variables are declared, they may also be initialized. Typically, constants or constant expressions are used to initialize a variable. General Syntax type variableName = constant; A) Integer Constant: e.g. x = 100; correct = x; wrong B) Real: double 1.63F float 1.63L long double e.g. float x, y; x = 1.0; y = 2.0; x/y = 0.5;

43 C) Char Single symbol in single quotes.
e.g. Char Letter; Letter = ‘A’. Letter = ‘9’; D) String Multiple symbols in double quotes. e.g. “This is a string constant”

44 Input Predefined Functions
General Syntax: scanf (“format string”, Arguments) Interactive Input: get data from user entering via keyboard. fscanf (f, “format string”, Arguments) File Input: get data that is stored in file F. sscanf (s, “format string”, Arguments) String Input: get data from string S. Return value: If error occurs, return value is EOF (usually -1), Otherwise returns the number of successful assignments of data to the arguments.

45 Unsuccessful Input: EOF (End of File) is reached before ALL arguments have been assigned data, if so the value EOF (-1) is returned. Data Mismatch: The input data does not match the control string specifications. (e.g., indicated data would be integer and the data actually entered was REAL).

46 SCANf - Interactive Input
User enters data with keyboard when program interrupt occurs. Input data treated as an input stream of characters. Arguments of the scanf are addresses. scanf(“%d”, &x);

47 String Input #include <stdio.h> int main(void) { char str[80];
printf("Enter a string: ");   scanf(''%s", str);   printf("Here's your string: %s", str);   return 0; }

48 Output Predefined Functions
General Syntax: printf (“control string”, Arguments) Writes to terminal. fprintf (f, “control string”, Arguments) Writes to another file. sprintf (s, “control string”, Arguments) Writes to string s. Return Value: If EOF occurs, return value is -1, Otherwise returns the number of successful assignments of data to the arguments.

49 Format Specifiers Contain Text: int Sum = 500;
Contain Conversion Specification Characters: e.g., d - decimal data c - character f - floating point s - string printf("I like %c %s", 'C', "very much!"); Contain Text: int Sum = 500; printf (“The Sum is %d”, Sum); New Line - printf (“hello, \n world”); Tab - printf (“hello, \t world \n”) The Sum is 500

50 Format Specifiers (cont.)
ASIDE: scanf float use %f double use %lf printf float or use %f double

51 Field Width Specification
printf (“more numbers: %7.1f %7.2f %7.3f”, 4.0, 5.0, 6.0); Field width. Precision # of columns output # of decimal digits to right including dec. pt. of decimal pt. more numbers:_ _ _ _ 4.0 _ _ _ 5.00 _ _ 6.000

52 Character Data: printf (“%c%5c/n%4c”, ‘x’, ‘y’, ‘z’); x_ _ _ _ y _ _ _z

53 Categories: Conditional Loops: while do-while Counting Loop : for
Looping - Iteration Categories: Conditional Loops: while do-while Counting Loop : for While Statement: while (Expression) { Body of Loop } while (scanf(“%d”, &d)==1) { printf(“%d”, d); }

54 How Terminate Loop? Dummy Data Logic: End-of-file Logic:
User enter a value that can’t be successfully converted. End-of-file Logic: Indicate all data has been entered by typing EOF signal. UNIX ctrl + d MS DOS ctrl + z break Exit from Loop immediately. continue - Jump to Bottom of Loop.

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