Question

Why should we use inline functions, why not to use macros #define?

Answer 1

Inline functions do not have double calculation errors. For example if we have a macro #define absolute(i)((i)>=0 ? (I) : (-i)) and inline function inline int absolute_f(int i) (return i>=0 ? i:-i;), then when you call absolute(f ()) function f() will be called twice; that will not happen when you call inline function.