Lowercase is not working about cpplabs

[potat-dev]

I rewrote the algorithm for converting a letter to lowercase (StackOverflow)

char tolower(int c)
{
    // (int)a = 97, (int)A = 65
    // (a)97 - (A)65 = 32
    // therefore 32 + 65 = a
    return c > 64 && c < 91 ? c + 32 : c;
}

It can be written shorter:

#define tolower(c) c > 64 && c < 91 ? c + 32 : c

[potat-dev]

#define tolower(c) c > 64 && c < 91 ? c + 32 : c

not working...