Factorial Finding Source code

Tutorial Link : http://www.geeksforgeeks.org/factorial-large-number/

Source Code :

#include<bits/stdc++.h>
#define ll long long
using namespace std;

#define MAX 800

ll int multiply(ll int x,ll int res[],ll int res_size);

void factorial(ll int n)
{
    ll int res[MAX];

    res[0] = 1;
    ll int res_size = 1;

    for (ll int x=2; x<=n; x++)
        res_size = multiply(x, res, res_size);

    cout << "Factorial of given number is \n";
    for (ll int i=res_size-1; i>=0; i--)
        cout << res[i];
}

ll int multiply(ll int x,ll int res[],ll int res_size)
{
   ll int carry = 0;

       for (ll int i=0; i<res_size; i++)
    {
        ll int prod = res[i] * x + carry;
        res[i] = prod % 10;
        carry  = prod/10;
    }

    while (carry)
    {
        res[res_size] = carry%10;
        carry = carry/10;
        res_size++;
    }
    return res_size;
}


int main()
{
    factorial(100);
    return 0;

}