for (i=3; i>=1; i--) printf("%d\n", i);
3 2 1
for (i=0; i<=3; i++) printf("%d\n", i);
0 1 2 3
i=3; while(i>=1) { printf("%d\n", i); i--; } i=0; while(i<=1) { printf("%d\n", i); i++; }