Coin Pickup system carry int into void

So I’m trying to make it so when I touch a coin (Sprite, It’s a 2D game) it gets destroyed and i get a point up, but the problem is, that it says that score does not exist in the current context.

UNITY ERROR:
(Assets/_SCRIPTS/TextScore.cs(11,61): error CS0103: The name `score’ does not exist in the current context)

CODE:

     using UnityEngine;
     using System.Collections;
     using UnityEngine.SocialPlatforms.Impl;
     using UnityEngine.UI;
     using System.Security.Cryptography.X509Certificates;

     public class CodeSystem : MonoBehaviour {

// Use this for initialization
void Start () {

}

// Update is called once per frame
void Update () {

}

int score = 0;

void OnCollisionEnter ( Collider other )
{
	Debug.Log("Picked up coin!");
	if (tag == "Coin")
	{
		Debug.Log("Added score!");
		score = score + 1;
	}
  }
 }

void OnCollisionEnter ( Collider other )
Change to:

 void OnCollisionEnter ( Collision other )

http://docs.unity3d.com/ScriptReference/Collider.OnCollisionEnter.html