The cctype C++haracter Functions
Function Name Return Value
isalnum() This function returns true if the argument is alphanumeric (that is, a letter or a digit).
isalpha() This function returns true if the argument is alphabetic.
isblank() This function returns true if the argument is a space or a horizontal tab.
iscntrl() This function returns true if the argument is a control character.
isdigit() This function returns true if the argument is a decimal digit (0–9).
isgraph() This function returns true if the argument is y printing character other than a space.
islower() This function returns true if the argument is a lowercase letter.
isprint() This function returns true if the argument is any printing character, including a space.
ispunct() This function returns true if the argument is a punctuation character.
isspace() This function returns true if the argument is a standard whitespace character (that is, a space, formfeed, newline, carriage return, horizontal tab, vertical tab).
isupper() This function returns true if the argument is an uppercase letter.
isxdigit() This function returns true if the argument is a hexadecimal digit character (that is, 0–9, a–f, or A–F).
tolower() If the argument is an uppercase character, tolower() returns the lowercase version of that character; otherwise, it returns the argument unaltered.
toupper() If the argument is a lowercase character, toupper() returns the uppercase version of that character; otherwise, it returns the argument unaltered.
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