factorial.cpp

#include <iostream>

using namespace std;

int multiply(int x, int res[], int res_size);
 
void factorial(int n)
{
    int MAX = 500;
    int res[MAX];
 
    // Initialize result
    res[0] = 1;
    int res_size = 1;
 
    for (int x = 2; x <= n; x++)
        res_size = multiply(x, res, res_size);
 
    cout << "Factorial of given number is \n";
    for (int i = res_size - 1; i >= 0; i--)
        cout << res[i];
}
 

int multiply(int x, int res[], int res_size)
{
    int carry = 0; // Initialize carry
 
    // One by one multiply n with individual digits of res[]
    for (int i = 0; i < res_size; i++) {
        int prod = res[i] * x + carry;
 
        // Store last digit of 'prod' in res[]
        res[i] = prod % 10;
 
        // Put rest in carry
        carry = prod / 10;
    }
 
    // Put carry in res and increase result size
    while (carry) {
        res[res_size] = carry % 10;
        carry = carry / 10;
        res_size++;
    }
    return res_size;
}

int main()
{
    factorial(1000);

    return 0;
}