#include <iostream>

using namespace std;


class bad_thing: public exception
{ public:
    string explanation;
    bad_thing(string expl);
    virtual const char * what() const noexcept; };

bad_thing::bad_thing(string expl): explanation(expl)
{ }

const char * bad_thing::what() const noexcept
{ return explanation.c_str(); }


int compute(int x, int y)
{ int total = 0;
  for (int i = 0; i < x; i += 1)
    total += 1;
  for (int i = 0; i < y; i += 1)
    total -= 1;
  if (total == 7)
    throw bad_thing("It isn't supposed to be seven!");
  return total; }


int main()
{ int a[] = { 3, 11, 8, 15 };
  int v = 15;

  try
  { cout << "The results are:\n";
    for (int i = 0; i < 4; i += 1)
      cout << "  " << compute(v, a[i]) << "\n";
    cout << "That's it.\n"; }

  catch (bad_thing & bt)
  { cout << "\nFailed because of a bad thing,\n";
    cout << "  the explanation is \"" << bt.what() << "\"\n"; }

  cout << "But the program safely continues.\n"; }