code:

private string input;
private string keyboardInput;

private bool returnPressed = false;

void Start () 
{
	//initialize stuff
	StartCoroutine(StartGame());
}

void Update() 
{
	//Capture keyboard input (abbreviated for clarity)
	keyboardInput += Input.inputString;
}

private IEnumerator StartGame()
{
	WriteSomeText("Enter a value: ");
	yield return StartCoroutine(Read());
	string userInput = input;

	//Do stuff

	WriteSomeText("Enter another value: ");
	yield return StartCoroutine(Read());
	string userInput = input;

	//Do more stuff
}

private IEnumerator Read()
{
	input = "";
	keyboardInput = "";

	while(!returnPressed)
	{
		if(Input.GetKeyDown(KeyCode.Return))
		{
			returnPressed = true;
			input = keyboardInput;
		}
		yield return 0;
	}

	returnPressed = false;
}