timjpriebe — Wed, 14 Feb 2007 14:29:33 +0000

Not a problem! Sorry I didn't explain it better in my first reply.

teammatt3 — Wed, 14 Feb 2007 14:24:10 +0000

Quote: While it's tedious, I sometimes find that if I get a white board (or paper) and calculator out and track each of the variables involved manually through the loop, I can figure out what's going on.

Great advice Tim, now it makes perfect sense what's going on in there. Thanks!

timjpriebe — Wed, 14 Feb 2007 13:07:43 +0000

The for loop is just evaluating the same thing at the same time. Remember, you're checking the last variable that was put into factorial. The computer has no way of knowing what's ABOUT TO be put in there.

If you want it in the condition, your condition (assuming it's a while loop) should read like this:

while ( (number * factorial <= factor) && (factor > 0) )

Does that make sense?

While it's tedious, I sometimes find that if I get a white board (or paper) and calculator out and track each of the variables involved manually through the loop, I can figure out what's going on.

teammatt3 — Tue, 13 Feb 2007 20:12:20 +0000

EDIT

Now it should work if I throw it in a for loop like the following, right?

unsigned long long int factorial = 1, number = 1, factor = ULONG_MAX;

for(; factorial <= factor; number++)
{
factorial = number * factorial;

printf("llu        llu\n", number factorial);
}

A for loop evaluates the expression before it gives the printf() output, right?. Apparently it doesn't, that gives me the same result (number goes up to 13) (that is without the if in it).

Arggg, I just don't get what is going on...

Tim, the if solves my problem . It is good enough with my experiments but if it were graded I would get knocked for inefficiency. I asked my professor about it, and his answer totally confused me, which is why I turned to you guys .

timjpriebe — Tue, 13 Feb 2007 13:17:15 +0000

Simple, the loop checks factorial at the beginning, before factorial gets recalculated. So the last time it does the check, factorial is, indeed, less than (or equal to) ULONG_MAX. Then factorial is recalculated, at which point it is then printed, being greater than ULONG_MAX.

If you're just looking to change the output, change

printf("%llu %llu\n", number, factorial);

if (factorial <= factor)
{
  printf("%llu     %llu\n", number, factorial);
}