isalnum()               Test for Alphanumeric Character (Macro)

 #include   <ctype.h>

 int        isalnum(c);
 int        c;                           Integer to be tested

    isalnum() tests whether 'c' is an alphanumeric character; that is, if
    it is included in the set:

                  'A'-'Z', 'a'-'z', or '0'-'9'

       Returns:     True (nonzero) if the integer is in one of the sets,
                    and 0 if not.  The result is undefined if 'c' is
                    other than an ASCII character or EOF.

         Notes:     isalnum() is a macro.

   -------------------------------- Example ---------------------------------

    The following statements continue to get input from stdin until a
    non-alphanumeric character is read.

           #include <ctype.h>
           #include <stdio.h>

           int x = 0;
           char buffer[80];
           int ch;

           main()
           {
              while (isalnum(ch = getche()))
                    buffer[x++] = ch;
              printf("data input from console: %s \n",buffer);
           }