Recursion

Recursion is a programming technique in which a function calls itself repeatedly until a certain condition is met. Recursion is a powerful tool that allows you to solve problems by breaking them down into smaller and simpler subproblems.

Recursion is often used to solve problems that can be naturally divided into smaller subproblems, such as sorting and searching algorithms, tree traversals, and mathematical calculations.

Here is an example of a recursive function in C that calculates the factorial of a number:

#include <stdio.h>
int factorial(int n)
{
   if (n == 0) {
       return 1;
   }
   else {
       return n * factorial(n - 1);
   }
}
int main()
{
   int result = factorial(5);
   printf("Result: %d\n", result);
   return 0;
}

In this example, we have defined a recursive function factorial that calculates the factorial of a given number n. The function has a base case that is triggered when n is 0, in which case it returns 1. For all other values of n, the function calls itself with n - 1 as the argument, and it returns the product of n and the result of the recursive call.

The function is called from the main function with the argument 5, and it calculates the factorial of 5 by calling itself repeatedly until the base case is reached. The final result is then printed to the console.

Recursion can be a useful technique for solving problems, but it is important to carefully consider the efficiency and complexity of recursive algorithms and to ensure that they terminate correctly. Recursive functions should always have a base case that stops the recursion, or they may enter an infinite loop.