Day/Night circle script error

Hello,

I recive the following error after saving script. I ll provide booth texts below:

Error:

Assets/gametime.cs(30,49): error CS0201: Only assignment, call, increment, decrement, and new object expressions can be used as a statement

Script:

using UnityEngine;
using System.Collections;

public class gametime : MonoBehaviour {
public Transform sun;
public float dayCicleInMinutes =1;

private const float SECOND = 1;
private const float MINUTE = 60 * SECOND;
private const float HOUR = 60 * MINUTE;
private const float DAY = 24 * HOUR; 

private const float DEGREES_PER_SECOND = 360 / DAY;


private float _degreeRotation;

private float _timeOfDay;

// Use this for initialization
void Start () {
       _timeOfDay = 0;
	   _degreeRotation = DEGREES_PER_SECOND * DEGREES_PER_SECOND / (dayCicleInMinutes * MINUTE);
}

// Update is called once per frame
void Update () {
        sun[0].Rotate(new Vector3(_degreeRotation, 0, 0) * Time.deltaTime);
	
	    _timeOfDay +- Time.deltaTime;
	    Debug.Log(_timeOfDay);
}}

After saving the script evething is green (in script file) so I am not sure where’s the problem.
Thank you for your time and help

Filip5

(Also sorry for tags, but seems the ones I added in couldn’t be created as I have very few points yet…)

_timeOfDay += Time.deltaTime;

In the Update method.