Modulo operator gives different results with leading zeroes [duplicate]

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.

Answer 1

Integer literals beginning with 0 like

00101

is actually an octal constant.