Error CS0029

I have 2 different games… Text based and all that (because I’m learning the basics).

using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class TextController : MonoBehaviour {
	
	public Text text;
	private enum States {
		cell, mirror, sheets_0, lock_0, cell_mirror, sheets_1, lock_1, corridor_0,
		
	};
	private States myState;
	
	// Use this for initialization
	void Start () {
		//text.text = "Hello World.";
		myState = States.cell;
	}
	
	// Update is called once per frame
	void Update () {
		print(myState);
		if (myState == States.cell) 			{cell();}
	
		
	}
	void cell() {
		text.text = "You are in a prison cell and you want to escape. There are " +
				"some dirty sheets on the bed, a mirror on the wall, and the door " +
				"is locked from the outside. 

" +
“Press S to view Sheets, M to view Mirror or L to view Lock.”;

		if(Input.GetKeyDown (KeyCode.S)) 			{myState = States.sheets_0;}

and this script works perfectly fine. On the other hand I have this script:

using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class Gametext : MonoBehaviour {

	public Text text;
	private enum States {
		enter, room_0
	};
	private States mystate;

	// Use this for initialization
	void Start () {
		text.text = "Just a game";
					
					
		if(Input.GetKeyDown(KeyCode.S)){
			text.text = "Just a game";
		mystate = States.enter;
		}
		
	}
	
	// Update is called once per frame
	void Update () {
		print(mystate);
		if (mystate = States.enter) {
			enter ();	
		}
		else if(mystate = States.room_0)		{room_0();}
	
	}
	
	void enter(){
			text.text = "'Ding ding'. 

Hmm… Nu raspunde nimeni… " ;
if(Input.GetKeyDown (KeyCode.I)) {mystate = States.room_0;}
}

	void room_0() {
		text.text = "Te afli in camera de zi si incerci intrerupatoarele, dar afli ca nu exista curent in casa ";
				
	}
}

And this gives me the CS0029 Error. Why and what is wrong here?

line : 31 of the second script (Gametext). You need to use a double equal for comparing the values, a single is assignment.

//.. snip
 else if(mystate = States.room_0)
  {room_0();}

should be:

// .. snip
 else if(mystate == States.room_0)
 {
   room_0();
 }