Example: Factorial using Recursion in C++

C
C++
C#
Java
Python
PHP
// Factorial using Recursion
#include <iostream>
using namespace std;

// Function to calculate factorial using recursion
long long factorial(int n) {
    // Base case: if n is 0 or 1, factorial is 1
    if (n == 0 || n == 1) {
        return 1;
    }
    // Recursive case: n * factorial(n-1)
    else {
        return n * factorial(n - 1);
    }
}

int main() {
    // Step 1: Declare a variable to store the input number
    int number;

    // Step 2: Prompt the user to enter a non-negative integer
    cout << "Enter a non-negative integer: ";
    cin >> number;

    // Step 3: Check for invalid input (negative number)
    if (number < 0) {
        cout << "Factorial is not defined for negative numbers." << endl;
    }
    // Step 4: Calculate and display the factorial for valid input
    else {
        long long result = factorial(number);
        cout << "Factorial of " << number << " is: " << result << endl;
    }

    return 0;
}