function in C - Computer science fundamentals tutorial

Functions in C

Functions are subprogram which are used to compute a value or perform a task. They can't be run independently and are always called by main() program or by some other function.

Types of function : - 

1. Library or built in function : - Library function are used to perform  standard operation. Example printf(), scanf(), etc.

2. User defined Function : - User defined function are self contain block of statement which are written by user to compare a value or to perform a task. They can be called by the main program repeatedly as per requirements.

Uses of function : - 

1. Functions are very much useful when a block of sentences has to be executed again and again.

2.When the program is to long or complex function are called to perform each task sequence from  main program.  

3. Functions are also used to reduced the different during debugging a program

Function declaration :- 

type name(arg 1,arg 2,.......,arg n)

{

  (local declaration)

   ............................

   (statement block)

.................................

   return(variable or expression)

}

Calling a function : -

A function is called by calling program using the function with the required number of arguments in parentheses. The function called appears in an assignment statement or in an output statement.

example of C program using function

#include<stdio.h>
void Fact(int);//function prototype declearation
int i,fact=1;//global variable declearation
int main() 
{
int n;
printf("\n enter the  number:");
scanf("%d",&n);
Fact(n);//function call
}
//function definition
void Fact(int n) 
{
for(i=1; i<=n; i++) 
{
fact=fact*i;
}
printf("\n factorial of %d is=%d",n,fact);
}
Program explanation:
1. for example we take 5 as input.
2.we declare the void Fact(int) function globally.
3.after taking function call we give the function definition outside the main function.
4. in function definition for loop started.In for loop i=1 & fact=1 then fact=1. after this loop is continue and incremented by1 until the n is grater than equal to i. 
OUTPUT

**NOTES**

Actual arguments & Formal arguments

the arguments listed in the function calling statement are referred to as Actual arguments.

the arguments listed in the function declaration are referred  to as Formal arguments.  

Recursion

A function calling it self again and again to compute a value is preferred to as recursion or recursive function. Normally a function is called by the main function or by other function but in recursion same function is called by itself repeatedly.

Example of recursion

#include<stdio.h>

main() 

{

int k,f;

int Fact(int);

printf("\n enter the  number:");

scanf("%d",&k);

printf("\n factorial of %d is=%d",k,Fact(k));

}

//function definition

int Fact(int k) 

{

  if(k==0)

  return(1);

  else 

  return(k*Fact(k-1));

}

Output

Uses of Recursive functions: -

1. Recursive functions are retain with less number of statement             compared to function.

2. Recursion is effective where terms are generated successively to      compute value.

3.  Recursion is useful for branching processes recursion helps to         create short code that would other wise be impossible. 

Void function

A function which does not return a value directly to the calling program is referred as a void function. The void function commonly used to perform a task and they declaration. It is declared with the keyword instead of data type of the function.

A void function can also use a return statement without a return value.