static const char *codes[] = {
  ".-", /* A */
  // FIXME more
};

for (int i = 0; str[i] != NULL; i++)
{
  char c = str[i];

  /* make character upper case if required */
  if (c >= 'a' && c <= 'z')
    c += -'a' + 'A'

  if (c < 'A' || c > 'Z')
    continue; // FIXME: support numbers?

  code = codes[c - 'A'];

  for (int j = 0; code[j] != NULL; j++)
  {
    if (code[j] == '.') dot();
    if (code[j] == '-') dash();
    else /* bad, do something */
  }
}