C++ FAQ Celebrating Twenty-One Years of the C++ FAQ!!!
(Click here for a personal note from Marshall Cline.)
Section 29:
29.1 What is this "newbie section" all about?
29.2 Where do I start? Why do I feel so confused, so stupid?
29.3 Should I use void main() or int main()?
29.4 Should I use f(void) or f()?
29.5 What are the criteria for choosing between short / int / long data types?
29.6 What the heck is a const variable? Isn't that a contradiction in terms?
29.7 Why would I use a const variable / const identifier as opposed to #define?
29.8 Are you saying that the preprocessor is evil?
29.9 What is the "standard library"? What is included / excluded from it?
29.10 How should I lay out my code? When should I use spaces, tabs, and/or newlines in my code?
29.11 Is it okay if a lot of numbers appear in my code?
29.12 What's the point of the L, U and f suffixes on numeric literals?
29.13 I can understand the and (&&) and or (||) operators, but what's the purpose of the not (!) operator?
29.14 Is !(a < b) logically the same as a >= b?
29.15 What is this NaN thing?
29.16 Why is floating point so inaccurate? Why doesn't this print 0.43?
29.17 Why doesn't my floating-point comparison work?
29.18 Why is cos(x) != cos(y) even though x == y? (Or sine or tangent or log or just about any other floating point computation)
29.19 What is the type of an enumeration such as enum Color? Is it of type int?
29.20 If an enumeration type is distinct from any other type, what good is it? What can you do with it?
29.21 What other "newbie" guides are there for me?
[29.8] Are you saying that the preprocessor is evil?

Yes, that's exactly what I'm saying: the preprocessor is evil.

Every #define macro effectively creates a new keyword in every source file and every scope until that symbol is #undefd. The preprocessor lets you create a #define symbol that is always replaced independent of the {...} scope where that symbol appears.

Sometimes we need the preprocessor, such as the #ifndef/#define wrapper within each header file, but it should be avoided when you can. "Evil" doesn't mean "never use." You will use evil things sometimes, particularly when they are "the lesser of two evils." But they're still evil :-)