Why is the return value not what I expected in this C program with macro? [duplicate]

Answer 1

Needs more parentheses. This:

#define SQR(a) a*a

expands to this:

i+2*i+2

which is:

3+2*3+2

which is 11 because * has precedence over +.

You need to define your macro like this:

#define SQR(a) ((a)*(a))

to ensure that this kind of thing doesn't happen.