isalnum

determines if the argument is alpha-numeric

isalpha

determines if the argument is alphabetic

iscntrl

determines if the argument is an ASCII control character

isdigit

determines if the argument is a decimal digit

isgraph

determines if the argument is a printing character but not a space

islower

determines if the argument is a lower-case letter

isprint

determines if the argument is a printing character

ispunct

determines if the argument is a punctuation character

isspace

determines if the argument is a space, horizontal or vertical tab, carriage return, form-feed or newline

isupper

determines if the argument is an upper-case letter

isxdigit

determines if the argument is a hexadecimal digit

tolower

converts upper-case characters to lower case; returns other characters unchanged

toupper

converts lower-case characters to upper case; returns other characters unchanged