C Recursion

Recursion is a powerful technique in programming that involves a function calling itself. In C programming language, a recursive function is a function that calls itself either directly or indirectly to solve a problem. Recursive functions are used in problems where the solution depends on solutions to smaller instances of the same problem.

The general idea of recursion is to break a problem into smaller sub-problems that can be solved by calling the same function again and again until the sub-problems become simple enough to be solved directly. The recursion continues until a base case is reached, which is a problem that can be solved without further recursion.

A recursive function in C must have two parts: a base case and a recursive case. The base case specifies the problem that can be solved without further recursion, and the recursive case specifies the problem that can be broken down into smaller sub-problems.

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

int factorial(int n) {
    if (n == 0) {
        return 1; // base case
    } else {
        return n * factorial(n - 1); // recursive case
    }
}

This function takes an integer n as input and calculates the factorial of n using recursion. The base case is when n is equal to 0, in which case the function returns 1. The recursive case is when n is greater than 0, in which case the function calls itself with n - 1 as the argument and multiplies the result with n.

For example, factorial(5) would call itself with factorial(4), which in turn would call itself with factorial(3), and so on, until factorial(0) is reached, at which point the recursion stops and the function returns 1. The final result would be the product of all the numbers from 1 to 5, which is 120.