Not able to understand output

Question

#include <stdio.h>
#define prod(i,j) i*j

int main()
{
int x=3,y=4;
printf("%d",prod(x+2,y-1));
return 0;
}
Output is 10

#include <stdio.h>
#define prod(i,j) i*j

int main()
{
int x=3,y=4;
printf("%d",prod((x+2),(y-1)));
return 0;
}
Output is 15

Answer 1

It's because of operation precedence and because "define" simply substituted i with x+2 and j with y-1. Using the parentheses in the second program you force multiplication to follow addition/subtraction.

In the first program:
x+2*y-1=3+2*4-1=10
In the second program:
(x+2)*(y-1)=5*3=15