string c;		//implicitly assigned an empty string
if (length(c) == 0) {
  write("Empty string");
} else {
  write("Non empty string");
}

string s = "";		//explicitly assigned an empty string
if (s == "")  {
  write("Empty string");
}
if (s != "")  {
  write("Non empty string");
}

string t = "not empty";
if (t != "")  {
  write("Non empty string");
} else {
  write("Empty string");
}