C <ctype.h>

The C <ctype.h> header file declares a set of functions to classify (and transform) individual characters. For example, isupper() checks whether a character is uppercase or not.

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 lowercase alphabet