c

gistfile1.c

  while (acc < UINT_MAX / 16) {
    if ( s[i] >= '0' && s[i] <= '9' ) {
      acc *= 16;
      acc += s[i] - '0';
     } else if (s[i] >= 'A' && s[i] <= 'F') {
      acc *= 16;
      acc += s[i] - 'A' + 10;
     } else if (s[i] >= 'a' && s[i] <= 'f') {
      acc *= 16;
      acc += s[i] - 'a' + 10;
     } else {
      putchar('\n'); 
      return acc; /* end */
     }
     putchar(s[i]);
     ++i;
}