int count on collision enter not working

Questions & Answers
1

public var touchCount : int;

function Update()
{
	if (touchCount >= 4)
		renderer.material.color = Color.red;
		
	if (touchCount < 4)
       	renderer.material.color = Color.gray;
}

function OnCollisionEnter () 
{
	touchCount + 1;
	Debug.Log ("+ 1");
}
        
function OnCollisionExit () 
{
	touchCount - 1;
	Debug.Log ("- 1");
}
2

it should be:
touchCount++ or touchCount += 1