Dart equivalent of \n

Is there a Dart equivalent to C++'s "\n"?

In the following example:

for(int j=0;j<readLines.length;j++)
{
    outputFile.writeAsStringSync(readLines[j], mode: FileMode.APPEND);
}

I would like to have the text that's in "readLines[j]" in separate lines. How could this be done?

For example:

readLines is a List of Strings, and it contains: "Hey my name is Cheshie", and "Thanks guys for trying to help".

In the code above, I am trying to write the content of the list into a file, using "outputFile", and I would like it to be written as follows:

Hey my name is Cheshie

Thanks guys for trying to help

That is, every readLines[j] should be written in a separate line.

Thanks.

The code:

import 'dart:io';

void func (String foldername)
{
  Directory thisFolder = new Directory (foldername);

  List<File> files = thisFolder.listSync(recursive:false);
  int number=1;
  String oldContent='';
  String newContent='';
  String concatenate='';
  String name='';
  int nameStart;
  int nameLength;
  for (int i=0; i<files.length; i++)
  {
    if (files[i].name.endsWith('.in'))
    {
      oldContent=files[i].readAsStringSync(Encoding.UTF_8);
      newContent=number.toString();

      var Strings=[newContent, oldContent];
      concatenate=Strings.join();

      files[i].writeAsStringSync(concatenate);
      number++;
    }   

// =====================Here begins the relevant part==================

    nameLength=files[i].name.length;
    nameStart=files[i].name.lastIndexOf('\\', nameLength);
    name=files[i].name.slice(nameStart+1, nameLength);
    if (name.compareTo('hello.in')==0)
    {
      File outputFile=new File('hello.out');
      if (outputFile.existsSync())
      {
        outputFile.deleteSync();
      }
      outputFile.createSync();
      List<String> readLi