I do not understand the behaviour of #define macro in C++

Question

I need to understand how this code works:

#define foo1( a ) (a * a)              // How does this work?
inline int foo2(         


        

Answer 1

Macros are not functions.

Macros do TEXT replacement. So when you have

#define foo1( a )   (a * a)

any instance of foo1( ... ) with anything between then parenthesis will be expanded AS TEXT, not as an expression. So when you have foo1( 1 + 2 ) it turns into ( 1 + 2 * 1 + 2 )