C Programs | IT Developer
IT Developer

C Programs

Share with a Friend
Previous
HOME
Next

Functions in C

Factorial (recursion)

A recursive function is a function which calls itself

C Program: Factorial (recursion)

C 
#include <stdio.h>


 


// Function declaration


int factorial(int n);


 


int main() {


    int num, result;


 


    // Input from user


    printf("Enter a positive integer: ");


    scanf("%d", &num);


 


    // Check for invalid input


    if (num < 0) {


        printf("Error: Factorial of a negative number doesn't exist.\n");


    } else {


        result = factorial(num);   // Function call


        printf("Factorial of %d = %d\n", num, result);


    }


 


    return 0;


}


 


// Recursive function definition


int factorial(int n) {


    if (n == 0 || n == 1)


        return 1;               // Base case


    else


        return n * factorial(n - 1);  // Recursive case


}

Output

 
OUTPUT 1 :
Enter a positive integer: 5
Factorial of 5 = 120

OUTPUT 2 :
Enter a positive integer: -3
Error: Factorial of a negative number doesn't exist.

Explanation

  1. Recursion Concept
    • The function calls itself with a smaller value (n - 1) until it reaches the base case (n == 0 or n == 1).
  2. Base Case
    • Prevents infinite recursion and provides the stopping point.
  3. Example for n = 5

          factorial(5)

          = 5 * factorial(4)

          = 5 * 4 * factorial(3)

          = 5 * 4 * 3 * factorial(2)

          = 5 * 4 * 3 * 2 * factorial(1)

          = 5 * 4 * 3 * 2 * 1 = 120

 

Previous
Next