What problems might the following macro bring to the application?

Question

Can the following macro bring problems?

#define sq(x) x*x

If yes, then how and why?please help.

Answer 1

As pointed out, you should wrap each use of the argument in parentheses to ensure correct behavior, for example, when the argument is something like i * 2:

#define sq(x) ((x)*(x))

But there is another potential issue. Consider the following:

result = sq(++i);

This is translated to:

result = ((++i)*(++i))

Where as the intention was likely to increment i only once, it gets incremented twice. This is a common side effect for macros.

One approach is just to be aware of this when calling it, but a better one is to put sq() in its own inline function.