C Factorial large numbers approximate method

#include <iostream>

#include <math.h>

double factorial(int n)

{

    double result=1;

    if(n>30)

        result=pow(n/M_E,n)*sqrt(2*M_PI*n);        //FOR BIG NUMBERS

    else

        for(int i=1;i<=n;i++)                                       //FOR SMALL NUMBERS

        {

            result*=i;

        }

        return result;

}

Returning

Hi,
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