C++ Primer Plus, Fourth Edition

The cctype Library of Character Functions

C++ has inherited from C a handy package of character-related functions, prototyped in the cctype header file (ctype.h, in the older style), that simplify such tasks as determining whether a character is an uppercase letter or a digit or punctuation, and the like. For example, the isalpha(ch) function returns a nonzero value if ch is a letter and a zero value otherwise. Similarly, the ispunct(ch) returns a true value only if ch is a punctuation character, such as a comma or period. (These functions have return type int rather than bool, but the usual bool conversions allow you to treat them as type bool.)

Using these functions is more convenient than using the AND and OR operators. For example, here's ...