C/ctype.h/isxdigit
int isxdigit(int ch)
//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;
}