Modulo operator gives different results with leading zeroes

Question

Why does:

int test() {
    return 00101 % 10;
}

return 5, while:

int test() {
    return 101 % 10;
}

returns 1? I can't think of an explanation.

score 23 · Answer 1 · answered Sep 26 '14 at 17:30

23

Integer literals beginning with 0 like

is actually an octal constant.

answered Sep 26 '14 at 17:30

Yu Hao

2

This is the most confusing convention ever, it's totally contradictory to the way humans look at numbers. – Mark Ransom Sep 26 '14 at 17:31
Thanks a lot! Is there a way to work around this? I'm receiving values and I don't know how many leading zeroes there will be. – Kosmas Katsoulotos Sep 26 '14 at 17:33
2

@KosmasKatsoulotos How did you receive the values? You don't encounter this problem much other than dealing with literals. – Yu Hao Sep 26 '14 at 17:40
2

If you `fscanf` or whatever, `%d` in the format string will ignore/strip/interpret as decimal the leading zeroes. (`%o` is octal). – OJFord Sep 26 '14 at 18:29

score 5 · Answer 2 · answered Sep 26 '14 at 17:35

5

00101 is octal value which is 65 in decimal so it returns 5.

answered Sep 26 '14 at 17:35

Rustam

score 0 · Answer 3 · answered Sep 26 '14 at 17:36

0

00101 is in octal which is equal to 65 in decimal, so that is why the modulus operator will always give us 5. You can do octal to decimal converstion on this link http://www.rapidtables.com/convert/number/octal-to-decimal.htm

answered Sep 26 '14 at 17:36

Taimour

1

You said "hex", but meant "octal", and anyway all the other answers before you got it right. – AndyG Sep 26 '14 at 17:39
2

hex means it should start with 0x. – Rustam Sep 26 '14 at 17:40
@AndyG Its now corrected and I was already going to correct it – Taimour Sep 26 '14 at 17:43
@Rustam yes you are right hex starts with 0x – Taimour Sep 26 '14 at 17:44

3 Answers3