// B2.6.cpp : Defines the entry point for the console application.
//
// Please provide the definition of a function that accepts a pointer 
// to a function with the signature int func(X &x), invokes the function, 
// and returns the value computed if positive.  Otherwise it throws an 
// exception with an error message.

#include "stdafx.h"
#include <iostream>
using namespace std;

class X {
public:
  X(int i) : val(i) { }
  int& value() { return val; }
private:
  int val;
};

int fun1(X &x) { return x.value(); }

int fun2(X &x) { return (x.value()*x.value()); }

//// answer ///////////////////////////////////////////////
  int invoker(int(*fPtr)(X &x), X &x)
  { 
    int test = fPtr(x);
    if(test <= 0) {
      exception e("exception thrown: non positive result");
      throw e;
    }
    return fPtr(x);
  }
///////////////////////////////////////////////////////////

int _tmain(int argc, _TCHAR* argv[])
{
  std::cout << "\n  Exam B2 - Question #6 "
            << "\n =======================\n";

  try {
    cout << "\n  value returned by invoker = " << invoker(fun1,X(5));
    cout << "\n  value returned by invoker = " << invoker(fun2,X(5));
    cout << "\n  value returned by invoker = " << invoker(fun1,X(-5));
  }
  catch(exception& e) {
    cout << "\n  " << e.what();
  }

  cout << "\n\n";
	return 0;
}