ctype

• The ctype.h library helps you classify char variables in a machine independent way. It is part of the built-in C library, so all you have to do is have a #include <ctype.h> at the beginning of your program to use them.

• Here are the library routines provided in ctype.h :

  extern int isalnum(int);
  extern int isalpha(int);
  extern int iscntrl(int);
  extern int isdigit(int);
  extern int isgraph(int);
  extern int islower(int);
  extern int isprint(int);
  extern int ispunct(int);
  extern int isspace(int);
  extern int isupper(int);
  extern int isxdigit(int);
  extern int tolower(int);
  extern int toupper(int);
  extern int isascii(int);
  extern int toascii(int);
  

• All these do pretty much what they say they do. The is functions return TRUE or FALSE, and the to functions return the converted character (which as we discussed last time, is "the same" as an int).

• The extern keyword just tells C compiler that these functions won't be defined in the current file.