+= operator overloading c++

Question

This is a code representing a fraction with an operator overloading

class Fraction
{
private:
int _counter, _denominator;
public:
Fraction(int _x, int _y);

Fraction & operator+=(int b)
{
    _counter = _counter + b*_denominator;
    return  *this;
}

Fraction & operator-=(int b)
{
    _counter = _counter - b*_denominator;
    return  *this;
}
};

Fraction::Fraction(int _x, int _y)
{
    _counter = _x;
    _denominator = _y;
}


void main()
{
    Fraction *f = new Fraction(2, 4);

    f += 5;
}

Can someone tell me why the operator += overloading doesn't work?

`f` is a pointer for absolutely no reason. That is the problem. — juanchopanza, Dec 21 '15 at 22:04
Why are you using `new`? Use variables with automatic storage (i.e. the stack) whenever possible. — Kevin, Dec 21 '15 at 22:04
Or even better, don't use `new`: `Fraction f(2, 4); f += 5;` — Jarod42, Dec 21 '15 at 22:05
When you're done with your pointer, don't forget to delete it: `delete f;`. Also, you probably [shouldn't start names with underscores](http://stackoverflow.com/questions/228783/what-are-the-rules-about-using-an-underscore-in-a-c-identifier). — Ben, Dec 21 '15 at 22:06
BTW, your implementation is wrong when denominator is negative. — Jarod42, Dec 21 '15 at 22:08
@Jarod42: I dno, is it? This is not a conventional operator overloading, so it seems to me that the semantics are pretty much up to the OP. — Lightness Races in Orbit, Dec 21 '15 at 22:18

Aganju · Answer 1 · 2015-12-21T22:24:47.973

2

You are overloading the operator for Fraction objects, but adding 5 to a Fraction * object - a pointer to Fraction.

Something like this would work:

(*f) += 5;

edited Dec 21 '15 at 22:24

answered Dec 21 '15 at 22:12

Aganju

6,295
1
12
23

score 1 · Answer 2 · edited Dec 21 '15 at 22:27

1

If you implement operator+=() you should be aware of it and use it by yourself, so this code:

_counter = _counter + b*_denominator;

Is better written as:

_counter += b * _denominator;

As it is shorter and less verbose.

About the error: Use object instead of pointer, as this is not java:

int main() // main() must return int
{
   Fraction f(2, 4);
   f += 5;
}

edited Dec 21 '15 at 22:27

Bryn McKerracher

683
6
21

answered Dec 21 '15 at 22:06

Slava

43,454
1
47
90

2

_"should be written as"_ Why? – Lightness Races in Orbit Dec 21 '15 at 22:07
@LightnessRacesinOrbit it is shorter and less verbose – Slava Dec 21 '15 at 22:09
1

@Slava: so *may* instead of *should*. – Jarod42 Dec 21 '15 at 22:10
Plus it makes sense to use `+=` on data members in the definition of `+=` for the class. – Kevin Dec 21 '15 at 22:11
2

But why are you leading with a largely irrelevant and misleading statement? Answer the question first, no? – juanchopanza Dec 21 '15 at 22:12
@Jarod42 hmm english not my first language probably I do not understand the difference. – Slava Dec 21 '15 at 22:12
@Slava: *should* is nearer than *must/have to*. *may* is for a possibility. (English is not my mother language neither) – Jarod42 Dec 21 '15 at 22:30

+= operator overloading c++

2 Answers2