2D snake game ( how to rotate snake's head with movement ?)

Question

I want to know:

1. how to rotate snake's head with movement
2. how to make tail prefabs (body) follows head direction.

public class Snake : MonoBehaviour {

    bool ate = false;
    bool isDied = false;
    public GameObject tailPrefab;
    Vector2 dir = Vector2.right;
    List<Transform> tail = new List<Transform>();

    void Start ()
    {
        InvokeRepeating("Move", 0.3f, 0.1f); 
    }

    void Update () {
        if (!isDied) {
            if (Input.GetKey (KeyCode.RightArrow))
            {
                dir = Vector2.right;
                //transform.rotation=Quaternion.Euler(0, 0, 180);
            }
            else if (Input.GetKey(KeyCode.DownArrow))
            {

                dir = -Vector2.up;    
                //transform.rotation = Quaternion.Euler(0, 0, 90);
            }
            else if (Input.GetKey(KeyCode.LeftArrow))
            {

                dir = -Vector2.right;
                //transform.rotation = Quaternion.Euler(0, 0, 0);
            }
            else if (Input.GetKey(KeyCode.UpArrow))
            {

                dir = Vector2.up;
                //transform.rotation = Quaternion.Euler(0, 0, 270);

            }
    }

    void Move() {
        if (!isDied) {
            Vector2 v = transform.position;

            transform.Translate (dir);

            if (ate) {
                GameObject g = (GameObject)Instantiate (tailPrefab,
                                  v,
                                  Quaternion.identity);

                tail.Insert (0, g.transform);

                ate = false;
            } else if (tail.Count > 0) {    
                    tail.Last ().position = v;

                    tail.Insert (0, tail.Last ());
                    tail.RemoveAt (tail.Count - 1);
            }
        }
    }

    void OnTriggerEnter2D(Collider2D coll) {
        if (coll.name.StartsWith("Food")) {

            ate = true;

            Destroy(coll.gameObject);
        } else {    
            isDied = true;
        }
    }
}

Answer 1

I can't really help with the body, since I've never played snake before, but in regard to your head rotation, the below code should help. Note that I flipped the sprite horizontally in Photoshop, because if his default direction is moving right, then he should also be facing right.

void Update()
{
    if (!isDied)
    {
        if (Input.GetKey(KeyCode.RightArrow))
        {
            transform.rotation = Quaternion.Euler(Vector3.zero);
        }
        else if (Input.GetKey(KeyCode.DownArrow))
        {
            transform.rotation = Quaternion.Euler(Vector3.forward * -90);
        }
        else if (Input.GetKey(KeyCode.LeftArrow))
        {
            transform.rotation = Quaternion.Euler(Vector3.forward * 180);
        }
        else if (Input.GetKey(KeyCode.UpArrow))
        {
            transform.rotation = Quaternion.Euler(Vector3.forward * 90);
        }
    }
}

Basically, you don't need to keep resetting the 'dir'. All you have to do is set it once (Vector2.right) so it'll move, and then you just rotate it while it's moving.