C Programming

MARWARI COLLEGE, RANCHI

(AN AUTONOMOUS UNIT OF RANCHI UNIVERSITY FROM 2009)

- Prakash Kumar, Dept. of CA

______________________________________________________________________

C is a general-purpose, high-level language that was originally developed by Dennis M. Ritchie to develop the UNIX operating system at Bell Labs. C was originally first implemented on the PDP-11 computer in 1972.

Some facts about C:

·         C was invented to write an operating system called UNIX.

·         C is a successor of B language which was introduced around the early 1970s.

·         The language was formalized in 1988 by the American National Standard Institute (ANSI).

·         The UNIX OS was totally written in C.

·         Today C is the most widely used and popular System Programming Language.

·         Most of the state-of-the-art software has been implemented using C.

·         Today's most popular Linux OS and RDBMS MySQL have been written in C.

Take a NOTE:

[C is a programming language that is powerful, efficient and compact. C combines the features of high level language with element of the assembler.

C is the offspring of “Basic Combine Programming Language” called ‘B’ was developed in 1960 at “Cambridge University”  

The ‘B’ language was modified by “Dennis Ritchie” at “Bell Laboratory” in 1972. ]

A C program basically consists of the following parts:

 Preprocessor Commands

 Functions

 Variables

 Statements & Expressions

 Comments

#include <stdio.h>

int main()

{

printf("Hello, World! \n");

return 0;

}

Character Set 

It is helpful to run any type of program by the ‘words’, number’, and ‘expression’.

There are four character sets in C:-

·         Letter

·         Digit

·         Special character

·         White space

Tokens in C

A C program consists of various tokens and a token is a keyword, an identifier, a constant, a string literal, or a symbol.

Semicolons

In a C program, the semicolon is a statement terminator. That is, each individual statement must be ended with a semicolon. It indicates the end of one logical entity.

Comments

Comments are like helping text in your C program and they are ignored by the

compiler. They start with /* and terminate with the characters */ as shown

below:

/* my first program in C */

Identifiers

A C identifier is a name used to identify a variable, function, or any other userdefined item. An identifier starts with a letter A to Z, a to z, or an underscore ‘_’ followed by zero or more letters, underscores, and digits (0 to 9).

C does not allow punctuation characters such as @, $, and % within identifiers.

C is a case-sensitive programming language. Thus, Marwari and marwari are two different identifiers in C.

Rules for Identifiers:-

• The character must be an alphabet and underscore.
• It must consist of only letters, digit or underscore.
• Only 31 characters are significant.
• It cannot use keywords.
• It must not contain white space.

Keywords

The following list shows the reserved words in C. These reserved words may not be used as constants or variables or any other identifier names(32 keywords).

Data Types

Data types in C refer to an extensive system used for declaring variables or functions of different types. The type of a variable determines how much space it occupies in storage and how the bit pattern stored is interpreted.

VARIABLES

A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

The name of a variable can be composed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Upper and lowercase letters are distinct because C is case-sensitive.

Lvalues and Rvalues in C

There are two kinds of expressions in C:

·         lvalue : Expressions that refer to a memory location are called "lvalue" expressions. An lvalue may appear as either the left-hand or right-hand side of an assignment.

·         rvalue : The term rvalue refers to a data value that is stored at some address in memory. An rvalue is an expression that cannot have a value assigned to it which means an rvalue may appear on the right-hand side but not on the left-hand side of an assignment.

Constants and literals

Constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals.

Character literals

Character literals are enclosed in single quotes, e.g., 'x' can be stored in a simple variable of char type.

String literals

String literals or constants are enclosed in double quotes "". A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters.

Eg: “ Marwari College”

Defining Constants

There are two simple ways in C to define constants:

 Using #define preprocessor

#include<stdio.h>

#define  a 10

#define  b 20

void main()

{

     printf("Value=%d",a*b);

}

 Using const keyword

#include<stdio.h>

void main()

{

    const int a;

    const int b;

    int x;

    printf("Enter the value:");

    scanf("%d",&a);

    printf("Enter the value:");

    scanf("%d",&b);

    a=a+2;//Assignment of read only variable a

    scanf("%d",&a);

    printf("Value=%d",a*b);

}

Storage class

A storage class defines the scope (visibility) and life time of variables and/or functions within a C Program.

There are following storage classes which can be used in a C Program

• auto
• register
• static
• extern

auto - auto is the default storage class for all local variables.

                int main()

{                     int Count;                     auto int Month;                     return 0;           }

The example above defines two variables with the same storage class. auto can only be used within functions, i.e. local variables.

register -

register is used to define local variables that should be stored in a register instead of RAM. This means that the variable has a maximum size equal to the register size.

NOTE: It cannot have the unary '&' operator applied to it (as it does not have a memory location).

                int main()

{             register int  Miles;              return 0;           }

Register should only be used for variables that require quick access - such as counters.

static -

static is the default storage class for global variables. The two variables below (count and road) both have a static storage class.

static int Count;

Static variables can be 'seen' within all functions in this source file. Static can also be defined within a function. If this is done the variable is initialized at run time but is not reinitialized when the function is called. Inside a function static variable retains its value during various calls.

NOTE : Here keyword void means function does not return anything and it does not take any parameter. You can memoriese void as nothing. static variables are initialized to 0 automatically.

extern -

extern is used to give a reference of a global variable that is visible to ALL the program files. When you use 'extern' the variable cannot be initialized as all it does is point the variable name at a storage location that has been previously defined.

When you have multiple files and you define a global variable or function which will be used in other files also, then extern will be used in another file to give reference of defined variable or function. Just for understanding extern is used to declare a global variable or function in another files.

File 1: main.c

int count=5;    main()    {      write_extern();    }

File 2: write.c

void write_extern(void);    extern int count;    void write_extern(void)    {      printf("count is %i    \n", count);    }

Operator

An operator is a symbol that tells the compiler to perform specific mathematical or logical functions. C language is rich in built-in operators and provides the following types of operators:

 Arithmetic Operators

 Relational Operators

 Logical Operators

 Bitwise Operators

 Assignment Operators

 Misc Operators

 

Operators Precedence in C

Decision-making structures

if(boolean_expression)

{

/* statement(s) will execute if the boolean expression is true */

}

eg: To find greatest between 3 numbers

#include<stdio.h>

int main()

{

int num1,num2,num3;

printf("\n Enter number1:");

scanf("%d",&num1 );

printf("\n Enter number2:");

scanf("%d",&num2);

printf("\n Enter number3:");

scanf("%d",&num3);

if(num1>num2 && num1>num3)

{

printf("\n Num1 is the largest");

}

else

{

  if(num2>num3)

  {

    printf("\n Num2 is the largest");

  }

  else

  {

    printf("\n Num3 is the largest");

  }

}

return 0;

}

Switch Statement

A switch statement allows a variable to be tested for equality against a list of values. Each value is called a case, and the variable being switched on is checked for each switch case.

Syntax

The syntax for a switch statement in C programming language is as follows:

switch(expression){

case constant-expression :

statement(s);

break;                       /* optional */

case constant-expression :

statement(s);

break;                       /* optional */

default :                                             /* Optional */

statement(s);

}

eg:

#include<stdio.h>

main()

{

char ch;

float A1,A2,x,y,r;

printf("\n1 to find Area of rectangle or 2 to find Area of circle :");

scanf("%c",&ch);

switch(ch)

{

case'1':

    printf("\n Enter the length x:");

    scanf("%f",&x);

    printf("\n Enter the breath y:");

    scanf("%f",&y);

    A1=x*y;

    printf("Area of rectangle=%f",A1);

    break;

case'2':

    printf("\n Enter the radius r:");

    scanf("%f",&r);

    A2=3.14*r*r;

    printf("Area of Circle=%f",A2);

    break;

default:

        printf("\n Wrong Choice");

}

}

The   ? :   Operator:

Conditional operator ? :  can be used to replace if...else statements. It has the following general form:

Exp1? Exp2: Exp3;

Where Exp1, Exp2, and Exp3 are expressions.

#include<stdio.h>

int main()

{

    int a,b;

    printf("\n Enter the value of a:");

    scanf("%d",&a);

    printf("\n Enter the value of b:");

    scanf("%d",&b);

    ((a>b?printf("\n A is greater"):printf("\nB is greater")));

    return 0;

}