doubt

[Maerle]

what's the difference between macro and functions?
What's the advantage and disadvantage of each one?
Show me an example showing the diference if possible.

[LB]

#define OPERATION(a,b) a*b

int Operation(int a, int b)
{
	return(a*b);
}

 //...

int main()
{
	cout << OPERATION(3+2, 4+5) << endl; //shows 16 
	cout << Operation(3+2, 4+5) << endl; //shows 45
}

Why? Because the macro expands it to 3+2*4+5, which is most certainly not what you wanted.

Functions are a nice thing to have because of how they can actually modify things through expressions, while that is more complicated otherwise.

[jsmith]

Macros are textual substitutions performed during the preprocessing phase.

The advantage of macros over non-inlined functions is that you avoid the overhead of a function call
and return. The disadvantage of macros are the subtle side effects that can happen. L B gave just
one example. The canonical example is this one:

#define MIN( a, b ) a < b ? a : b

int main() {
    int a = 5;
    int b = 6;

    std::cout << MIN( a++, b++ ) << std::endl;
}

What is the value of a and b at the end of the program? Hint: it is NOT 6 and 7.

For this reason alone inline functions are *always* preferred to macros.

EDIT: And for that matter, what value is output by the cout statement above?

[Disch]

Yet more reasons to avoid macros:

macros ignore language scope rules and pollute the global namespace, which can lead to some very nasty and bizarre bugs. Consider the folliowing:

#include <iostream>
#include "someheader.h"

int main()
{
  int MYVAR = 5;
  std::cout << MYVAR;
}

Seems harmless, right... but what if someheader.h looks like this:

#define MYVAR     16 

This would cause the compiler to throw all kinds of errors at you.