// IfFilterGuard.C
// (c) Burt Rosenberg 1997

// This program illustrates use of the if/else statement
// as a FILTER to coerce the world into a comfortable 
// state, defined as one in which the ASSERTION is satisfied,
// and as a GUARD to protect code from being used under
// conditions adverse to the code's health.

#include<iostream.h>

void main()
{
    // Create two integers
    int numerator ;
    int denominator ;
 
    // input values
    cout << "Enter numerator: " ;
    cin >> numerator ;
    cout << "Enter denominator: " ;
    cin >> denominator ;

    // FILTER the input, boy we wish those
    // values were positive ...
    if ( numerator<0 )
    {
       numerator = -numerator ;
    }
    if ( denominator<0 )
    {
       denominator = -denominator ;
    }

    // ASSERT, numerator >= 0 AND denominator >=0

    // GUARD against division by zero
    if ( denominator != 0 ) 
    {
        // ASSERT, denominator > 0 
        cout << "numerator/denominator = " 
             << (numerator/denominator) ;
    }
    else
    {
        cout << "Illegal division by zero." ;
     }

    cout << "\n" ;   // I need a newline.
    cout << "Good bye." << endl ;

}