An easy way to swap 2 variables without using another variable:

a=a+b;
b=a-b;
a=a-b;

Two guidelines from Thinking in C++ by Bruce Eckel:

Avoid the preprocessor. Always use const for value substitution and inlines for macros.
Avoid global variables. Always strive to put data...

I totally agree with sunnypalsingh. I am reading this book now and its really a great deal. You can find this book for free at:
http://www.pythoncriticalmass.com/

It's in 2 volumes.