CombinacionesRecursivos

#include <iostream>
#define assertdomjudge(x) if(!(x)){std::cout<<"ERROR"<<std::endl;}

using namespace std;


int calcularResta(int x, int y){
    int resta;
    resta = x -y;
    return resta;
}

int calcularFactorial(int x){
    if(x > 1){
        return x * calcularFactorial(x-1);
    }else{
        return 1;
    }
}

int calcularCombinacion(int x, int y, int z){
  int combinacion;
  combinacion = x / (y * z);
  return combinacion;
}


int main()
{
    int n, r, resta, combinacion;
    do
      {
        cin >> n >> r;
        if(n < 0){
            return 0;
        }
        else if(r > n){
            cout<<"ERROR"<<endl;
        }else{
            resta = calcularResta(n, r);
            n = calcularFactorial(n);
            r = calcularFactorial(r);
            resta = calcularFactorial(resta);
            combinacion = calcularCombinacion(n, r, resta);
            cout << combinacion << endl;
        }

 }while(n >= 0);
 return 0;
}