Why Is Comparing if an Unsigned Int >= 0 a "Pointless Comparison"?

c++ c for-loop comparison unsigned
Josh picture Josh · Feb 21, 2011 · Viewed 38.1k times · Source

I got warning:

Pe186 "Pointless comparison of unsigned int with zero"

when I tried to compile the following code: 

for(clLoop = cpLoopStart; clLoop >= 0; clLoop--)                                  
{
    //Do something
}

I don't understand why. I could understand, if I were looking for a value less than zero, since an unsigned int can never be negative. But all I am looking for here is if it is equal to zero, which an unsigned int certainly can be.

I could even see this error if in this loop I tried to pre-decrement instead of post-decrement, but again that is not the case.

Answer

Timbo picture Timbo · Feb 21, 2011

You check whether the unsigned int is greater than or equal (>=) zero. This expression will always be true, because unsigned integers will never be less than zero.

The compiler tries to warn you that you are about to program an infinite loop.

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