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# C++ Program to Find Factorial

### What is the factorial of a number?

Factorial of a non-negative integer is the multiplication of all positive integers smaller than or equal to n, i.e. factorial of 5 is 5*4*3*2*1 which is 120.

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

## Program to find the factorial of a given number using for loop

``````#include <iostream>
using namespace std;

int main() {
int n;
long factorial = 1.0;

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

if (n < 0)
cout << "Error! Factorial of a negative number doesn't exist.";
else {
for(int i = 1; i <= n; ++i) {
factorial *= i;
}
cout << "Factorial of " << n << " = " << factorial;
}

return 0;
}``````

## Output

```Enter a positive integer: 4
Factorial of 4 = 24```

In the above program, we take a positive integer from the user and compute the factorial using `for` loop. We print an error message if the user enters a negative number.

## Program to find the factorial of a given number using recursion

``````#include <iostream>
using namespace std;

int fact(int n){
if(n>0)
{
return n*fact(n-1);
}
else
return 1;
}
int main() {
int num;
cin>>"Enter an integer to compute the factorial "
cout<<fact(num);
return 0;
}``````

A factorial is represented by a number and a  ” ! ”  mark at the end. It is widely used in permutations and combinations to calculate the total possible outcomes. A French mathematician Christian Kramp firstly used the exclamation.

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