#include <stdexcept>
#include "calculate.h"
double calculate(double x, double y, char op) {
  switch(op) {
      default:
        throw std::runtime_error("unknown sign");
      case '*':
        return x * y;
      case '+':
        return x + y;
      case '-':
        return x - y;
      case '/':
        if (y == 0) {
          throw std::runtime_error("cannot divide by 0");
        }
        return x / y;
    }
}