C library: ctype <ctype.h>

The ctype library in C programming language provides functions that handle character values. With functions inside this C library, we can convert character values and identify their types. This C library is included with most C compilers.

Note: to use functions inside ctype library, we need to include the header file ctype.h into our program (#include <ctype.h>).

We can find 13 functions in this standard C library:

• C function: isalnum
  Determines if the received value is an alphanumeric character
• C function: isalpha
  Determines if the received value is an alphabetic character
• C function: iscntrl
  Determines if the received value is a control character
• C function: isdigit
  Determines if the received value is a digit character
• C function: isgraph
  Determines if the received value is a graphically representable character
• C function: islower
  Determines if the received value is a lowercase alphabetic character
• C function: isupper
  Determines if the received value is an uppercase alphabetic character
• C function: ispunct
  Determines if the received value is a punctuation character
• C function: isspace
  Determines if the received value is a whitespace character
• C function: isprint
  Determines if the received value is a printable character
• C function: isxdigit
  Determines if the received value is a hexadecimal character
• C function: tolower
  Converts uppercase alphabetic character to lowercase
• C function: toupper
  Converts lowercase alphabetic character to uppercase