I don't understand a challenge answer in C

Question

Here is the code of the question. I tried it with C tutor but unfortunately, it didn't help me to understand :

#define prod(i, j) i*j
int main() {
int x = 3; int y = 4;
printf("%d", prod(x+2,y-1));
 return 0;
}
I don't understand why the answer isn't 15 since :
x + 2 = 5
y - 1 = 3
5 * 3 = 15

Can someone explain this ?

Answer 1

So it was only about the brackets.

Thank you :)

Answer 2

[BusyTheseDays] I agree with your answer (although your first example has a mistake in the y substitution). Let me add to your answer and show that it is necessary to surround the whole macro with parentheses as well as the parameters. Else, division gives a wrong result:

x=3, y=4
15/prod(x+2,y-1) //15/15 = 1, yes?
15/(x+2)*(y-1) //!!!
15/(3+2)*(4-1)
15/5*3
3*3
9 /* Expected 1 :-( */

Final macro fix:
#define prod(i,j) ((i)*(j))