Character Expressions

Range membership:
while ('0' <= *cp && *cp <= '9')
Case conversion:
if ('a' <= *s && *s <= 'z')
*s -= ('a' - 'A');
Both examples above illustrate non-portable code.
A more complex example:
        i = 0;
        while (*cp >= '0' && *cp <= '9')
                i = i * 10 + *cp++ - '0';