Numero factorial C++

Numero factorial C++

#include <iostream.h>
using namespace std;
unsigned int factorial(int);
int permutacion(int);
int combinacion(int);
int main(){
int x,y;
cin>>x;
y=factorial(x);
cout<<"n El factorial de "<<x<<" es: "<<y;


return 0;

}
unsigned int factorial(int n){

if(n==0||n==1)
return 1;
return n*factorial(n-1);
}

int permutacion(int n, int r){
return factorial(n)/factorial(n-1);
}

int combinacion(int n, int r){
return factorial(n)/(factorial(n-1)*factorial(r));
}