what does the signed/unsigned comparison warning mean?

Question

auto.cpp: In function ‘int autooo(unsigned int)’:
auto.cpp:33:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]

Answer 1

You are getting this warning about comparing signed and unsigned types because the ranges of signed and unsigned ints are different. If you have to make such a comparison, you should explicitly cast one of the values to be compatible with the other, but a check is required to make sure value your cast is valid.

For e.g:-

int i = someIntValue();

if (i >= 0)
{
    // i is non-negative, so it is safe to compare to unsigned value
    if ((unsigned)i >= u)
        // do something
}