Implicit conversion trouble

[Guzfraba]

Why aren't this codes the same?

inline Fract operator+(const Fract& f1,const Fract& f2){
		Fract rez;
		return rez.add(f1,f2);
		
	}
//....
Fract Fract::add(const Fract& f1,const Fract& f2) {
	int lcmb=gcf_or_lcm(f1.den,f2.den,2);
	int mult1=lcmb/f1.den;
	int mult2=lcmb/f2.den;
	Fract rez(f1.num*mult1+f2.num*mult2,lcmb); 
	return rez;  //here

}

inline Fract operator+(const Fract& f1,const Fract& f2){
		Fract rez;
		return rez.add(f1,f2);
		
	}
//...
Fract Fract::add(const Fract& f1,const Fract& f2) {
	int lcmb=gcf_or_lcm(f1.den,f2.den,2);
	int mult1=lcmb/f1.den;
	int mult2=lcmb/f2.den;
	return (f1.num*mult1+f2.num*mult2,lcmb); //and here

}

The "num" and "den" variables are of type int.You can see the difference at line 11
I mention that the class "Fract" has got a constructor that takes two ints.
But anyway,the result is different,where is the problem ?

[Guzfraba]

...any idea ?

[jlb]

,where is the problem ?

Right here:

return (f1.num*mult1+f2.num*mult2,lcmb); //and here

First you can only return one item from a function, not two.

Second what exactly do you want to return from this function, what type of variable?

[ResidentBiscuit]

Interesting, I didn't know you could use the comma operator like that. I definitely don't recommend doing it the second way as I'm sure a lot of people are going to read that and not have a clue what you just did. The first way at least makes sense as to what you're going after.

Anyways, how are they different?

EDIT:

jlb wrote:

First you can only return one item from a function, not two.

Actually, from what I just read this is actually legal.
http://stackoverflow.com/questions/2539458/c-return-x-y-what-is-the-point

[jlb]

It may be legal but it is still only returning one item, and I guarantee it is not what the OP is trying to accomplish.

When you return an item from a function it must be the same type of variable as in the function signature. In this case a Fract. Do you see this return statement returning a Frac?

[ResidentBiscuit]

I believe what's it doing is creating a Fract object implicitly, using the values in the return statement for the constructor.

I could be entirely wrong here though, I've never seen this before.

[jlb]

using the values in the return statement for the constructor.

What constructor? I don't see the use of any constructor in that return statement.

[ResidentBiscuit]

The function returns a Fract object. I think you're missing the implicit word I keep using. ie, you're not going to see it in the code. The compiler does it in the background.

EDIT:
After further reading, I believe I am wrong here. Although it would be interesting behavior.

[jlb]

No I'm not missing the implicit word. The compiler will not do it in the background, you must return the proper type.

[Guzfraba]

ok...so simplifying my code i realized that actually the one int constructor is called there...i was sure that Frameworks respond on this topic was corect http://www.cplusplus.com/forum/beginner/94383/ ... he does exactly what i tried to do but now i realize that there are some mistakes.