Question

First, defining two constant expressions without parentheses is my fault:

#define BIG_INTERVAL 60 * 60 * 1000
#define SMALL_INTERVAL 1 * 1000

int i = 1;

if (i >= BIG_INTERVAL / SMALL_INTERVAL - 1)
{
    printf("Oops!\n");
}

The if statement after the macro expansion is if(i >= 60 * 60 * 1000 / 1 * 1000 - 1).

That is not my intention. But I find something strange if I write if (i >= 3600000000 - 1). It is false.

What type is 60 * 60 * 1000 / 1 * 1000 - 1 ? int?

Answer 1

All operators on ints return int. So yes, 60 * 60 * 1000 / 1 * 1000 - 1 is an int. But the expected result of 3599999999 is too big for an int, so the expression actually evaluates to -694967297 (assuming 32-bit int and two’s complement).

This doesn’t happen with a literal 3600000000 because integer literals larger than INT_MAX are of a type that can hold the full value.