Testing for a maximum unsigned value

Question

Is this the correct way to test for a maximum unsigned value in C and C++ code:

if(foo == -1)
{
    // at max possible value
}

where foo is

Answer 1

I would define a constant that would hold the maximum value as needed by the design of your code. Using "-1" is confusing. Imagine that someone in the future will change the type from unsigned int to int, it will mess your code.