Are these two loops equivalent: off-by-one

Question

Are these two loops the same? For some reason the second loop is off-by-one and I cannot figure out why.

while ( !b && ++n < WORD_COUNT ) b = mWords[n];

n++;
while ( !b && n < WORD_COUNT ) {
    b = mWords[n];
    n++;
}

duplicate: https://stackoverflow.com/questions/25705000/the-difference-between-n-and-n-at-the-end-of-a-while-loop-ansi-c — OrenIshShalom, Aug 03 '20 at 06:17

score 2 · Accepted Answer · answered Aug 03 '20 at 06:27

When the predicate b was not successful, then a logic short-circuit may apply in the first form and the final increment of n may be skipped.

In the second form, the increment happens before predicate b is evaluated, so n is off-by-one when the loop exits.

1 Answers1