Confused by squaring macro SQR in c [duplicate]

Answer 1

SQR(1+1) expands to 1+1*1+1 which is 3, not 4, correct?

A correct definition of the macro would be

#define SQR(x) ((x)*(x))

which expands to (1+1)*(1+1) and, more important, shows you one of the reasons you shouldn't use macros where they aren't needed. The following is better:

inline int SQR(int x)
{
    return x*x;
}

Furthermore: SQR(i++) would be undefined behavior if SQR is a macro, and completely correct if SQR is a function.

Answer 2

The problem is that macros are doing textual substition before it is compiled, so the macro expands to 1+1*1+1

Answer 3

That is why you always put arguments to macros into ():

#define SQR(x) ((x)*(x))