Question

greeting all
i am working on school project and i have a problem with my cod , what i am trying to do is returning two values.
any help appreciated 🙂

 #include <iostream>
 #include <string>
 using namespace std;

 // class for rational number 
class rational
  {
public:
// input & output the fraction 
void output(ostream& out);
void set(int num, int den);
int get_numerator();
int get_denominator();
// the operations
rational add(rational number);
rational sub(rational number);
rational mul(rational number);
rational div(rational number);
rational comp(rational number );

  private:
int numerator;
int denominator;
  };

  rational rational1, rational2; // global veriables to use at comparing operations 

rational rational::add(rational number) // addition operation 
 {
rational sum;
sum.numerator = numerator*number.denominator + denominator*number.numerator;
sum.denominator = denominator*number.denominator;
return sum ;
   }
 rational rational::sub(rational number) // subtract operation 
  {
rational sum2;
sum2.numerator =numerator*number.denominator - denominator*number.numerator;
sum2.denominator = denominator*number.denominator;
return sum2 ;
}
rational rational ::div(rational number) // divede operation 
{
rational sum3 ;
sum3.numerator =numerator*number.denominator ;
sum3.denominator = denominator*number.numerator;
return sum3 ;

}
 rational rational::mul(rational number) // multiply operation 
 {
rational sum4;
sum4.numerator =numerator*number.numerator;
sum4.denominator = denominator*number.denominator;
return sum4 ;
}
 rational rational::comp (rational number ) // compare operation 
 {
rational compare1 , compare2 ;
compare1.denominator = numerator*number.denominator ;
compare2.numerator = denominator*number.numerator;
if (compare1.denominator > compare2.numerator)
{ cout << endl ;
    cout << "the biggest fraction is  ";
    return rational1;

} else if (compare1.denominator < compare2.numerator ) 
{
    cout << endl ;
    cout << "the biggest fraction is  ";
    return rational2 ;
} else { 
    cout << " both fractions are equal ..." << rational2 << " = "; // here                                                                                                              
         is the error 
    return rational1  ;

}

   }
       void rational::set( int num, int den)
   {
numerator = num;
denominator = den;
}

   void rational::output(ostream& out = cout)
    {
out << numerator << "/" << denominator;
     }


    int main ()
   {
rational result ;
char salsh ;

cout << "please enter the numerator and denominator for the 1st fraction : ";
int num, den;
cin >> num >> salsh >> den;
if (den ==0)
{
    cout << "the denominator can't be zero " << endl ;
    system("pause");
    return 0;
}

else 
{
    rational1.set(num, den);

    cout << "please enter the numerator and denominator for the 2nd fraction :           
                    " ;
    cin >> num >>salsh >> den;
    if (den ==0)
    {
        cout << "the denominator can't be zero " << endl ;
        system("pause");
        return 0;

    }
    else {
        rational2.set(num, den);
        result = rational1.add(rational2);
        cout << "The result of adding them is: ";
        result.output(cout);
        cout << endl ;

        result = rational1.sub(rational2);
        cout << "The result of subtracting them is: ";
        result.output(cout);
        cout << endl ;

        result = rational1.div(rational2);
        cout << "The result of diveding them is: ";
        result.output(cout);
        cout << endl ;


        result = rational1.mul(rational2);
        cout << "The result multiplying them is: ";
        result.output(cout);
        cout << endl ; 

        result = rational1.comp(rational2) ;
        result.output(cout);
        cout << endl;
    }

}

system ("pause");
return 0;
     }

Error 1 error C2679: binary ‘<<‘ : no operator found which takes a right-hand operand of type ‘rational’ (or there is no acceptable conversion) c:\users\mike\documents\visual studio 2008\projects\mik\mik\michael shokery.cpp 73

here is the code

   inline ostream& operator<<(ostream& stream,  rational& rational)
{
 rational.output(stream);
 return stream;
} 

Answer 1

The difference is that in one place you do

cout << " both fractions are equal ..." << rational2 << " = "; // error here     

while in the other places you do

    cout << "The result of adding them is: ";
    result.output(cout);   

To have the << operator work for rational you need to define the operator for that type

inline ostream& operator<<(ostream& stream, const rational& value)
{
     value.output(stream);
     return stream;
}   

---

And to have the output function callable with the const parameter to operator<<, the function has to be constas well:

class rational
{
public:
    // input & output the fraction
     void output(ostream& out) const;      // Add const here

…

void rational::output(ostream& out = cout) const   // and here!
{ 
    out << numerator << "/" << denominator;
}