A Little C Primer/C Character Class Test Library

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These functions perform various tests on characters. They require the declaration:

   #include <ctype.h>

The character is represented as an "int" and the functions return an "int". They return 0 if the test is false and non-0 if the test is true:

   isalnum( c )     Character is alpha or digit.
   isalpha( c )     Character is alpha.
   iscntrl( c )     Character is control character.
   isdigit( c )     Character is decimal digit.
   isgraph( c )     Character is printing character (except space).
   islower( c )     Character is lower-case.
   isprint( c )     Character is printing character (including space).
   ispunct( c )     Character is printing character but not space/alpha-digit.
   isspace( c )     Character is space, FF, LF, CR, HT, VT.
   isupper( c )     Character is upper-case.
   isxdigit( c )    Character is hex digit.

The library also contains two conversion functions that also accept and return an "int":

   tolower( c )    Convert to lower case.
   toupper( c )    Convert to upper case.