i had a program to swap variables, which was working fine but when i tried to put it into functions it went crazy i dont even know what is going on anymore please help :< #include int x, y; void input(int x,int y) { cout << "Enter X\n"; cin >> x; cout << "\nEnter Y\n"; cin >> y; } void swap(int x,int y) { x ^= y; y ^= x; x ^= y; return; } void output(int x,int y) { cout << "\n\nX is now " << x << "\nY is now " << y << "\n"; return; } int main() { input(x,y); swap(x,y); output(x,y); return 0; }

You''re swapping copies of the integers. To swap the integers themselves, swap''s parameters will need to be pointers or references.
Alternatively, #include <algorithm> and use std::swap instead.

Beer Hunter is, of course, right. Beyond that, I rather wonder how good that swapping algorithm is ... the XOR method is often described as overly clever. It is not extensible to anything but basic types, for instance, and won''t work for cases when x == y.

Well, that was the first thing I saw, anyway. Upon re-reading it, I see some others.
Try this:

quote: Original post by Miserable
and won''t work for cases when x == y.

Sure it will...


Update GameDev.net system time campaign: ''date ddmmHHMMYYYY''

Correction : it doesn't work when x and y are the same variable - which may happen when variable aliasing is involved. A robust function would essentially do a no-op. But here the code becomes :

x ^= x; // zeroes x
x ^= x; // zeroes x
x ^= x; // zeroes x

Given that flaw, the fact that it only works with basic types and that it is no faster than using a temporary, this 'trick' is strongly advised against.

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[edited by - Fruny on January 27, 2003 4:07:03 AM]

Directly from std::swap

quote:




end quote:

Notice the pointers.


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[edited by - MichaelT on January 27, 2003 4:21:55 AM]

MichaelT-

Not to be picky, but I think you mean references (not pointers )... just don't want anyone to get confused!

-Glyph

[edited by - Glyph on January 28, 2003 10:28:26 AM]

Both references and pointers can be used to implement a swap algorithm. Check out Sam''s Teach Yourself C++ in 21 days for the code.

Brendan

quote: Original post by Glyph
MichaelT-

Not to be picky, but I think you mean references (not pointers )... just don''t want anyone to get confused!

-Glyph

[edited by - Glyph on January 28, 2003 10:28:26 AM]

Quite right. ;-)


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