by Dinesh Thakur

 
#include <ctype.h>

#include <stdio.h>
int main(void)
{
    char ch;
    clrscr();
    printf(". to exit:");
    for(;;)
        {
           ch = getc(stdin);
           if(ch == '.')
             break;
           if(isalnum(ch))
             printf("%c is alphanumeric\n", ch);
        }
             getch();
             return 0;
  }