// Code derived from Stroustrup's PPP2 book
// § 5.5.2 The callee deals with errors
//  -and beginning on p 143

#include <iostream>
#include <stdexcept>

using std::cout;
using std::runtime_error;

// error() simply disguises throws
void error(const char* s) { throw runtime_error(s); }

// calculate area of a rectangle
int area(int length, int width)
{
  if (length <= 0 || width <= 0)
    error("non-positive area() argument");

  return length * width;
}

// calculate area within frame
int framed_area(int x, int y)
{
  constexpr int frame_width = 2;

  if (x - frame_width <= 0 || y - frame_width <= 0)
    error("non-positive area() argument called by framed_area()");

  return area(x - frame_width, y - frame_width);
}

int main()
{
  int y = 0;  // please test out some positive values here, too
  int z = 0;  //

  int area2 = framed_area(1, z);
  int area3 = framed_area(y, z);

  cout << y << '\n'      //
       << z << '\n'      //
       << area2 << '\n'  //
       << area3 << '\n';
}