#include  <stdio.h>                                         
   #include  <ctype.h>                                         
   main()                                                      
   {                                                           
       char character;                                         
       printf("Press any key\n");                              
       character = getchar();                                  
       if (isalpha(character) > 0)                             
          printf("The character is a letter.");                
       elseif (isdigit (character) > 0)                         
             printf("The character is a digit.");              
          else                                                 
             printf("The character is not alphanumeric.");     
   }  
                                                         
Output                                                      
                                                               
   Press any key                                               
   h                                                           
   The character is a letter.                                  
                                                               
   Press any key                                               
   5                                                           
   The character is a digit.                                   
                                                               
   Press any key                                               
   *                                                           
   The character is not alphanumeric.