`<ctype.h>`

`_ctype`	An array of character attribute information.
`_tolower`	Translates characters to lowercase.
`_toupper`	Translates characters to uppercase.
`isalnum`	Character classification macro.
`isalpha`	Character classification macro.
`isascii`	Character classification macro.
`iscntrl`	Character classification macro.
`isdigit`	Character classification macro.
`isgraph`	Character classification macro.
`islower`	Character classification macro.
`isprint`	Character classification macro.
`ispunct`	Character classification macro.
`isspace`	Character classification macro.
`isupper`	Character classification macro.
`isxdigit`	Character classification macro.
`toascii`	Translates characters to ASCII format.
`tolower`	Translates characters to lowercase.
`toupper`	Translates characters to uppercase.