How to add a coin sytem to my game?

Hello everyone, I'm trying to make a coin system to my game but I'm facing these two problems: 1) The text doesn't display anyt$$anonymous$$ng in the game screen, but i can see it when i'm in build mode 2) It doesn't show anyt$$anonymous$$ng until i pickup a coin, and when i do, it only says 1 no matter how many coins i pick up. My coins are all tagged with cointag I've double checked, and they do get destroyed, but it doesn't make the int coin go up. I also added using UnityEngine.UI. I'd appreciate if someone could answer my question. Thanks

public class SnowmanController : MonoBehaviour { // Update is called once per frame public int coin; public Text coinText;

 void Update ()
 {
     coin = 0;

     if (Input.GetKey (KeyCode.RightArrow)) {
         transform.position += new Vector3 (0.1f, 0, 0);
     } else if (Input.GetKey (KeyCode.LeftArrow)) {
         transform.position -= new Vector3 (0.1f, 0, 0);
     } if (Input.GetKey (KeyCode.UpArrow) | Input.GetKey (KeyCode.Space)) {
         transform.position += new Vector3 (0, 0.1f, 0);
     } else if (Input.GetKey (KeyCode.DownArrow)) {
         transform.position -= new Vector3 (0, 0.1f, 0);
     } else if (Input.GetKey (KeyCode.R)) {
         SceneManager.LoadScene ("Level1");
     }


 }
 void OnCollisionEnter2D(Collision2D other){
     if (other.gameObject.tag == "cointag") {
         Destroy (other.gameObject);
         coin = coin + 1;
         coinText.text = "Coin: " + coin.ToString ();
     } else if (other.gameObject.tag == "treetag") {
         SceneManager.LoadScene ("Level 2");
     }
 }

}