Introduction to Function

Function

• A function is a block of code design to perform some specific task.
• Functions are used to divide program into logical modules.
• They are used to avoid repetition of code in different part of program.
• Once a function is designed it can be used anywhere in program whenever required.

Types of Functions

Standard Library functions

• The standard library functions is defined are built in function in C programming to handle task such as
• mathematical computations ( sin( ) , cos( ), sqrt( ) , pow( )..)
• I/O processing ( printf( ) , scanf( ) , gets( ), puts( ). . . )
• String processing ( strupr( ) , strrev( ) , strlen( ), . . . )
• Graphical Operations ( line( ) , circle( ) , rect( ) . . . ) etc

User defined functions

• C allow programmers to define functions.
• Such functions created by the user are called user defined functions.

Function Categories

• Functions with arguments and return value
For ex: Z = 100 + sqrt( 10 ) ;
• Functions with arguments and no return value
For ex: circle (200, 100,50);
• Function without arguments and no return value
For ex: clrscr( ) ;
• Function without arguments and return value
For ex: ch = getchar( ) ;

According to return type function are of two type

• Functions returning value
• Such functions when called always return us some value.
• e.g.:-
• Z = 100 + fact( 5 ) ;
• P = sqrt( 10 ) ;
• As such functions returns an value So such function must be used in an expression
• Functions not returning values
• Such functions are called just to perform some task.
• e.g.:-
• clrscr( ) ;
• circle( 200 , 100 , 50 ) ;
• Such function doesn’t return any values so they can’t be used in an expression

General Format of Function

returntype functionName(datatype args1,datatype args2,...)
{
    Statements 
    ---------------
    return value ;
}

return type

• It indicates the datatype of value the function is going to return.
• If function is returning a value then it can be any datatype such as int, long, float, double, char, pointer, structure etc.
• If function is not returning any value then return type must be void.
• if no return type is specified then by default return type is int.

  #include⁢stdio.h>
  void address()
  {
    printf("CCIT\n");
    printf("Rajapeth\n");
    printf("Amravati\n");
  }
  main()
  {
    printf("Address of CCIT is ");
    address();
    printf("Address of Choudhari Sir is\n");
    address();
  }

Address of CCIT is
CCIT
Rajapeth
Amravati
Address of choudhari sir is
CCIT 
Rajapeth
Amravati
  

Calling functions

• It transfers program control to specified function.
• It executes all statements of function.
• Then it return program control to the point from where the function was call.

  #include⁢stdio.h>
  void star()
  {
    int i;
    for(i=0;i<=25;i++)
        printf("*");
  }
  main()
  {
    printf("CCIT\n");
    star();
    printf("\nAmravati\n");
    star();
  }

CCIT
*************************
Amravati
*************************
  

  #include⁢stdio.h>
  void display()
  {
    int i;
    for(i=1;i<=100;i++)
        printf("%d ",i);
  }
  main()
  {
    printf("Number is \n");
    display();
  }

  #include⁢stdio.h>
  void odd()
  {
    int i;
    for(i=1;i<=100;i=i+2)
        printf("%d ",i);
  }
  main()
  {
    printf("Odd nos. are \n");
    odd();
  }