Recursion is the process which repeat itself until some condition is reached otherwise it gets repeated again and again.

In programming languages, if a program allows 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();
}

Recursion is used in the programming where repetition needs to be done for the same process but for the different values .

Recursion also increase the programming load of the CPU in terms of execution so its better to avoid recursion for large program manipulation.

#include <stdio.h>

int factorial(unsigned int i) {

   if(i <= 1) {
      return 1;
   }
   return i * factorial(i - 1);
}

int  main() {
   int i = 15;
   printf("Factorial of %d is %d\n", i, factorial(i));
   return 0;
}