#use <conio>
#use <string>

char char_tolower(char c) {
  int ccode = char_ord(c);
  if (char_ord('A') <= ccode && ccode <= char_ord('Z')) {
    int shift = char_ord('a') - char_ord('A');
    return char_chr(ccode + shift);
  } else {
    return c;
  }
}

string string_lower(string s)
//@ensures string_length(s) == string_length(\result);
{
  int len = string_length(s);
  char[] A = string_to_chararray(s);
  char[] B = alloc_array(char, len+1);
  for (int i = 0; i < len; i++)
    B[i] = char_tolower(A[i]);
  B[len] = '\0';  /* redundant */
  return string_from_chararray(B);
}

int main() {
  print (string_lower("HEllo There!?"));
  return 0;
}