Question

Possible Duplicate:
“static const” vs “#define” in C

I started to learn C and couldn’t understand clearly the differences between macros and constant variables.

What changes when I write,

#define A 8

and

const int A = 8

?

Answer 1

Macros are handled by the pre-processor – the pre-processor does text replacement in your source file, replacing all occurances of ‘A’ with the literal 8.

Constants are handled by the compiler. They have the added benefit of type safety.

For the actual compiled code, with any modern compiler, there should be zero performance difference between the two.