C ctype.h

Functions

isalnum()
Checks if the given character is an alphanumeric character (a letter or a digit). Returns a nonzero value if true.
isalpha()
Determines whether the given character is an alphabetic letter (either uppercase or lowercase). Returns a nonzero value if true.
isblank()
Checks if the given character is a blank space, including space (‘ ‘) and tab (‘\t’). Returns a nonzero value if true.
iscntrl()
Identifies whether the given character is a control character (e.g., newline, backspace). Returns a nonzero value if true.
isdigit()
Determines if the given character is a decimal digit (0-9). Returns a nonzero value if true.
isgraph()
Checks if the given character has a graphical representation (any printable character except space). Returns a nonzero value if true.
islower()
Checks if the given character is a lowercase letter (a-z). Returns a nonzero value if true.
isprint()
Determines whether the given character is a printable character, including spaces but excluding control characters. Returns a nonzero value if true.
ispunct()
Checks if the given character is a punctuation character (not alphanumeric or space). Returns a nonzero value if true.
isspace()
Determines whether the given character is a whitespace character (space, tab, newline, carriage return, vertical tab, or form feed). Returns a nonzero value if true.
isupper()
Checks if the given character is an uppercase letter (A-Z). Returns a nonzero value if true.
isxdigit()
Determines if the given character is a valid hexadecimal digit (0-9, A-F, a-f). Returns a nonzero value if true.
tolower()
Converts an uppercase letter to its lowercase equivalent if applicable; otherwise, returns the character unchanged.
toupper()
Converts a lowercase letter to its uppercase equivalent if applicable; otherwise, returns the character unchanged.