Notice that what is considered a letter may depend on the locale being used; In the default C locale, what constitutes a letter is what returns true by either isupper or islower.
For a detailed chart on what the different ctype functions return for each character of the standard ANSII character set, see the reference for the <cctype> header.
In C++, a locale-specific template version of this function (isalpha) exists in header <locale>.
- Character to be checked, casted to an int, or EOF.
Return ValueA value different from zero (i.e., true) if indeed c is an alphabetic letter. Zero (i.e., false) otherwise.
character C is alphabetic character + is not alphabetic character + is not alphabetic
|isalnum||Check if character is alphanumeric (function)|
|isdigit||Check if character is decimal digit (function)|