C Program to Find the Factorial of a Number using Recursion

This C program calculates the factorial of a given number using recursion.

Problem Statement

The program asks the user to enter a positive integer for which they want to calculate the factorial. It then calls the factorial function, which uses recursion to find the factorial. Finally, the program prints the factorial of the given number.

C Program to Find the Factorial of a Number using Recursion

#include <stdio.h>

// Function prototype
int factorial(int n);

int main() {
    int num;
    
    // Introduction
    printf("Factorial Calculator\n");
    printf("===================\n");
    
    // Problem Statement
    printf("Enter a positive integer: ");
    scanf("%d", &num);
    
    // Calculate and print the factorial
    printf("The factorial of %d is %d.\n", num, factorial(num));
    
    return 0;
}

// Recursive function to calculate factorial
int factorial(int n) {
    // Base case: factorial of 0 is 1
    if (n == 0) {
        return 1;
    }
    // Recursive case: multiply n with factorial of (n-1)
    else {
        return n * factorial(n - 1);
    }
}

How it works

1. The program defines a recursive function factorial that takes an integer num as a parameter and returns the factorial of num.
2. In the factorial function, if the input number num is 0 or 1, it returns 1, as the factorial of 0 and 1 is defined to be 1.
3. If the input number is not 0 or 1, the function recursively calls itself with the parameter num - 1 and multiplies the current num with the result of the recursive call.
4. The main function serves as the entry point of the program.
5. The program starts with an introduction, printing the title of the factorial calculator.
6. It then prompts the user to enter a number to calculate its factorial.
7. The user’s input is read using scanf and stored in the variable number.
8. The program calls the factorial function with the number and stores the result in the variable result.
9. Finally, the program displays the calculated factorial by printing the number and result using printf.

Input / Output