Thread: Infinite 'for' loop

Code:

int i = 1;
for ( ; ; )
     if (i >= 10)
          break;
     else
     if (i % 2)
          i += 2;
     else
          i -= 2;
printf("%d", i);

I don't know how this code works, but the output is 11 so I guess the condition (i%2) is true so i is incremented by 2 until it's 11, which is >=10 and then the loop exits with the break statement.
Can anyone give me some details about how this code is executed please?

Originally Posted by laserlight

You seem to have the basic idea right though. What exactly are you having problems with?

Thanks for clarifying my guess. I just don't know what (i%2) means, and why it's true in this case.

Originally Posted by grumpy

i%2 is the remainder on dividing the integer i by 2. If i is a multiple of 2, i%2 is zero. Otherwise it is 1.

Depending on age of your compiler, there are some caveats if i is negative (since some aspects of integer division involving negative values were implementation-defined in the 1989 C standard and earlier, although this was changed in the 1999 C standard).

Yes, but I still don't understand the if statement, I've seen if (i%2 == 0) .... but not if(i%2)

Originally Posted by grumpy

When doing any logical test, a zero value is false, and a non-zero value is true.

So "if (i%2)" is shorthand for "if (i%2 != 0)". This is true in all conditionals (loop conditions, ternary ?:, etc).

Great explanation, thank you!