C isalnum()
checks alphanumeric character
C isalpha()
checks whether a character is an alphabet or not
C iscntrl()
checks control character
C isdigit()
checks numeric character
C isgraph()
checks graphic character
C islower()
checks lowercase alphabet
C isprint()
checks printable character
C ispunct()
checks punctuation
C isspace()
check white-space character
C isupper()
checks uppercase alphabet
C isxdigit()
checks hexadecimal digit character
C tolower()
converts alphabet to lowercase
C toupper()
converts to uppercase alphabet