//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; }