Given a number we have to calculate the factorial of number .

so what is **factorial number**?

factorial of a number n is the product of all number from 1 upto the number n.

n!=(n-1)*(n-2)*(n-3)….*1

```
5!=5*4*3*2*1
=120
3!=3*2*1
=6
```

**Example**

```
input: 5
output:120
input:4:
output:24
```

Logic:

`the logic behind this question is just to multiply all number which are smaller than or equal to them.`

#include<iostream> using namespace std; int main() { int num; cout<<"Enter a number : "<<endl; cin>>num; int factorial=1; for(int i=1;i<=num;i++) { factorial=factorial*i; } cout<<"factorial of a number is "<<factorial<<endl; }

**Output**

Enter a number : 5 factorial of a number is 120

Time complexity:O(N)

Space Complexity:O(1)