🔢 Factorial of a Number Using Loop in C++

🔢 Factorial of a Number Using Loop in C++

A factorial is a mathematical operation that multiplies a number by every positive number below it. In C++, calculating a factorial using a loop is one of the simplest and most common programming exercises for beginners.

📘 What Is a Factorial?

The factorial of a non-negative integer n, written as n!, is defined as:

n! = n × (n - 1) × (n - 2) × ... × 1
Example: 5! = 5 × 4 × 3 × 2 × 1 = 120
  

Factorials are used in mathematics, especially in permutations, combinations, and other algorithmic problems.

📄 C++ Code to Find Factorial Using Loop

#include <iostream>
using namespace std;

int main() {
    int number;
    unsigned long long factorial = 1;

    // Input from user
    cout << "Enter a positive integer: ";
    cin >> number;

    // Error check
    if (number < 0) {
        cout << "Factorial is not defined for negative numbers." << endl;
    } else {
        for (int i = 1; i <= number; ++i) {
            factorial *= i;
        }

        // Output result
        cout << "Factorial of " << number << " = " << factorial << endl;
    }

    return 0;
}
    

✅ Sample Output

Enter a positive integer: 6  
Factorial of 6 = 720
  

🧠 Explanation

• Step 1: Take input from the user.
• Step 2: Check if the number is negative (factorials aren't defined for negatives).
• Step 3: Use a for loop to multiply the number down to 1.
• Step 4: Display the result.

📘 Definition: Factorial Using Loop

Calculating a factorial using a loop in C++ is a method where a repeated multiplication is performed using a for or while loop. It avoids recursion and is generally easier to implement and understand for beginner-level programmers. This technique is especially useful for iterative computations and number-based logic tasks.

🎯 Final Thoughts

The factorial loop program is not only a classic beginner example but also a practical one used in real-world algorithms. By learning how to compute factorials using loops, programmers strengthen their foundation in iteration, logic, and algorithm design.