On 15/09/2008, at 2:15 PM, Alex Reynolds wrote:
I'm wondering if I'm using unsigned integers (specifically
NSUInteger) properly or not.
I was under the impression that unsigned integers run from 0 to
MAX_INT, but when I use them in a "for" loop within these bounds,
the loop does not seem to always obey these constraints.
For example:
for (NSUInteger counter = 5; counter >= 0; --counter)
{
NSLog(@"NSUInteger: %d", counter);
}
keeps running well after the "counter" variable turns negative:
First problem: %d is for signed integers; if you want to see the
value, you want %u.
Second problem (which you'll see if you change the NSLog): counter is
unsigned, so it *never* "turns negative".
The values of counter in your loop will be 5,4,3,2,1,0,MAX_UINT,
MAX_UINT-1, etc
(Note that the range of values for unsigned integers is 0..MAX_UINT,
not MAX_INT.)
However, the following does *not* run, starting from a negative
integer (as I would expect):
for (NSUInteger counter = -5; counter <= 0; ++counter)
{
NSLog(@"NSUInteger: %d", counter);
}
counter can't have a value of -5 because it's unsigned; the value you
are getting here will be MAX_UINT-5. And that's not <=0, so the loop
invariant fails the first time.
Also, the following works properly:
for (NSUInteger counter = 0; counter <= 5; ++counter)
{
NSLog(@"NSUInteger: %d", counter);
}
That works properly because this time you're not assigning values that
you think should be negative to an unsigned int.
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