[c-prog] output explanation

[mohit_dreamer]

#include<stdio.h>
#include<conio.h>
#define PRODUCT(x) (x*x)
void main()
{
int i=3,j,k,l;
clrscr();
j=PRODUCT(i+1);
printf("%d",j);
k=PRODUCT(i++);
printf("\n%d",k);
l=PRODUCT(++i);
printf("\n%d",l);
getch();
}
output:
7
9
49
can u plz expln the output...??

any help will be thankful.

thanx.