C/ctype.h/isxdigit

int isxdigit(int ch)

<source lang="cpp">

//Declaration: int isxdigit(int ch); //Return: returns nonzero if ch is a hexadecimal digit;

               otherwise zero is returned. 
 #include <ctype.h>
 #include <stdio.h>
 int main(void)
 {
   char ch;
   for(;;) {
     ch = getchar();
     if(ch == "."){
         break;
     }
     if(isxdigit(ch))(){
         printf("%c is hexadecimal digit\n", ch);
     }
   }
   return 0;
 }
          
      </source>