Tema: Calcular factorial de numeros grandes

Hola, bueno ahí les dejo un programa que hice en C/C++ para calcular el factorial de números grandes.

Código:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define MAX 100

struct GranNumb {
	int *v;
	int n;
};

GranNumb granprod(GranNumb fact_1, GranNumb fact_2) {
	int *v, n;
	n = (fact_1.n > fact_2.n) ? 2*fact_1.n : 2*fact_2.n;
	v = new int[n];
	
	for(int i=0; i<n; i++) v[i] = 0;
	
	for(int i=0; i<fact_1.n; i++) {
		for(int j=0; j<fact_2.n; j++) {
			int prod = fact_1.v[i] * fact_2.v[j] + v[i+j];
			int u = prod % 10;
			int d = prod / 10;
			v[i+j] = u;
			v[i+j+1] += d;
		}
	}
	
	GranNumb gn;
	gn.n = 0;
	gn.v = v;
	
	for(int i=n-1; i>=0; i--) {
		if(v[i] != 0) {
			gn.n=i+1;
			break;
		}
	}
	
	return gn;
}

GranNumb grandec(GranNumb gn) {
	int *v = new int [gn.n];
	for(int i=0; i<gn.n; i++) v[i] = gn.v[i];
	
	if(gn.n == 0) {
		return gn;
	} else {
		for(int i=0; i<gn.n; i++) {
			if(v[i] == 0) {
				v[i] = 9;
			} else {
				v[i]--;
				break;
			}
		}
	}

	GranNumb dec;
	dec.n = 0;
	dec.v = v;
	for(int i=gn.n-1; i>=0; i--) {
		if(v[i] != 0) {
			dec.n=i+1;
			break;
		}
	}
	return dec;
}


GranNumb granfact(GranNumb gn) {
	if( gn.n == 0) {
		GranNumb uno;
		uno.n = 1;
		uno.v = new int[1];
		uno.v[0] = 1;
		return uno;
	} else {
		return granprod(gn, granfact(grandec(gn)));
	}
}



int main() {
	char s[MAX];
	
	printf("Ingresar N: ");
	scanf("%s", s);

	GranNumb gn;
	gn.n = strlen(s);
	gn.v = new int[gn.n];
	for(int i=0; i<gn.n; i++) gn.v[i] = (int)s[gn.n-1-i] - 48; //convierte caracter en cifra
	
	GranNumb fact = granfact(gn);
		
	for(int i=fact.n-1; i>=0; i--) {
		printf("%d", fact.v[i]);
	}
	printf("\n");
	
	return 0;
}

Saludos.