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 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.

```
#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`

.