C++ Program To Find Factorial Of A Number

In this example, you will learn to calculate the factorial of a number entered by the user.

The factorial of a positive number n is given by:

factorial of n (n!) = 1 * 2 * 3 * 4....n

The factorial of a negative number doesn't exist. And, the factorial of 0 is 1.

Factorial of a Number

#include <iostream>
using namespace std;

int main() {
    int n, i;
    unsigned long long fact = 1;
    cout<<"Enter an integer: ";
    cin>>n;

    // shows error if the user enters a negative integer
    if (n < 0)
        cout<<"Error! Factorial of a negative number doesn't exist.";
    else {
        for (i = 1; i <= n; ++i) {
            fact *= i;
        }
        cout<<"Factorial of "<< n<<"is"<<fact;
    }

    return 0;
}

Output

Enter an integer: 10
Factorial of 10 = 3628800