factorial in cpp of big numbers
// C++ program to compute factorial of big numbers
#include<iostream>
using namespace std;
// Maximum number of digits in output
#define MAX 500
int multiply(int x, int res[], int res_size);
// This function finds factorial of large numbers
// and prints them
void factorial(int n)
{
int res[MAX];
// Initialize result
res[0] = 1;
int res_size = 1;
// Apply simple factorial formula n! = 1 * 2 * 3 * 4...*n
for (int x=2; x<=n; x++)
res_size = multiply(x, res, res_size);
cout << "Factorial of given number is
";
for (int i=res_size-1; i>=0; i--)
cout << res[i];
}
// This function multiplies x with the number
// represented by res[].
// res_size is size of res[] or number of digits in the
// number represented by res[]. This function uses simple
// school mathematics for multiplication.
// This function may value of res_size and returns the
// new value of res_size
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;
}
// Driver program
int main()
{
factorial(100);
return 0;
}