C++ Program to Find Factorial

The factorial of a positive integer n is equal to 1*2*3*...n. You will learn to calculate the factorial of a number using for loop in this example.

To understand this example, you should have the knowledge of the following C++ programming topics:

For any positive number n, it's factorial is given by:

factorial = 1*2*3...*n

Factorial of negative number cannot be found and factorial of 0 is 1.

In this program below, user is asked to enter a positive integer. Then the factorial of that number is computed and displayed in the screen.

Example: Find Factorial of a given number

#include <iostream>
using namespace std;

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

    cout << "Enter a positive integer: ";
    cin >> n;

    for(int i = 1; i <=n; ++i)
    {
        factorial *= i;
    }

    cout << "Factorial of " << n << " = " << factorial;    
    return 0;
}

Output

Enter a positive integer: 12
Factorial of 12 = 479001600

Here variable factorial is of type unsigned long long.

It is because factorial of a number is always positive, that's why unsigned qualifier is added to it.

Since the factorial a number can be large, it is defined as long long.