Object-Oriented Programming in C++

// PL10/exceptiondemo.cpp
// illustrates exception usage for user defined exception
// Niels Walet. Last edited 03/12/2019
#include<iostream>
#include<cstdlib> //for exit
const int divide_flag(-1);
double divide(double x, double y)
{
  if(x==0) throw divide_flag;
  return y/x;
}
int main()
{
  double x{3.},y{4.};
  double result;
  try {
      result=divide(x,y);
      std::cout<<"y/x = "<<result<<std::endl;
      x=0;
      result=divide(x,y);
      std::cout<<"y/x = "<<result<<std::endl;
    }
  catch(int error_flag) {
      if(error_flag == divide_flag) {
	  std::cerr<<"Error: divide by zero"<<std::endl;
          exit(error_flag);
        }
    }
  return 0;
}