Recursion in C

Recursion is a programming technique that allows the programmer to express operations in terms of themselves. In C, this takes the form of a function that calls itself.

In programming languages, if a program allows you to call a function inside the same function, then it is called a recursive call of the function.

 void recursion( ) {

   recursion();
/* function calls itself */

}

int main( ) { 

recursion( );

}

While using recursion, programmers need to be careful to define an exit condition from the function, otherwise it will go into an infinite loop.

Recursive functions are very useful to solve many mathematical problems, such as calculating the factorial of a number, generating Fibonacci series, etc.

The following example calculates the factorial of a given number using a recursive function –

 #include <stdio.h>

 int factorial(int i) {

    if(i <= 1) {

return 1;

   }

   return i * factorial(i - 1);

}

 int  main()
{

   int i = 12;

printf("Factorial of %d is %d\n", i, factorial(i));

  return 0;

}

The following example generates the Fibonacci series for a given number using a recursive function –

 #include <stdio.h>

 int fibonacci(int i) {

    if(i == 0) {     

return 0;

   }   

   if(i ==1) { 

return 1;

   }

return fibonacci(i-1) + fibonacci(i-2);

}

 int  main()
{

    int i;      

   for (i = 0; i < 10; i++) {     

printf("%d\t\n", fibonacci(i));

   }

   return 0;

}