Question

I have recently started using the -Wall compiler switch in an attempt to improve the quality of my code. It is giving (correctly) a warning about this little snippet…

    int i;

    for (i = start - 1; i >= 0; i--)
    {
        if (i >= number1.array.size())
        {
            one_value = 0;
        }

because number1.array.size is unsigned (it’s the size method on a std::vector). Since the test in the loop is i >= 0, i has to be signed or it doesn’t work. It seems I have three choices; to refrain from using -Wall, to ignore the warning, or to introduce an ancillary element…

    int          i;
    unsigned int j;

    for (i = start - 1; i >= 0; i--)
    {
        j = i;

        if (j >= number1.array.size())
        {
            one_value = 0;
        }

None of these seems particularly desirable. Can you suggest any alternative, or make a recommendation as to what I should do in this case?

Answer 1

“Since the test in the loop is i >= 0, i has to be signed or it doesn’t work.” Just change your test like this:

for(unsigned i = start; i--;) {
    // ...
}

Gives you the same value of i in the loop body.