C Recursive Functions

A recursive function in C is a function that calls itself in order to solve a problem. It breaks a problem into smaller versions of the same problem until it reaches a simple case, known as the base case, which stops the recursion.

A recursive function generally has two parts

1. Base case: This defines the stopping condition for the recursion.

2. Recursive case: This part breaks down the problem into smaller sub-problems and calls the function itself.

General Structure of Recursive Function:


return_type function_name(parameters) {
    if (base_case_condition) {
        // Return result (or handle the simplest case)
    } else {
        // Recursive case (call the function itself)
        return function_name(smaller_sub_problem);
    }
}

Example: Factorial Program


#include <stdio.h>

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

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    
    printf("Factorial of %d is %d\n", num, factorial(num));
    return 0;
}

Output:

Enter a number: 5
Factorial of 5 is 120

Explanation:

The function factorial checks if n is 0. If true, it returns 1 (base case).
Otherwise, it multiplies n by the factorial of n – 1, recursively calling the factorial function until the base case is reached.

C Recursive Functions – Interview Questions

Q 1: What is a recursive function?

Ans: A function that calls itself to solve a problem.

Q 2: What is a base condition in recursion?

Ans: A condition that stops the recursive calls.

Q 3: Why is a base condition important?

Ans: To prevent infinite recursion.

Q 4: What are the disadvantages of recursion?

Ans: Higher memory usage and slower execution compared to loops.

Q 5: Where is recursion commonly used?

Ans: In problems like factorial, Fibonacci, and tree traversal.