Unity - How can I add or subtract a chosen number of degrees from an angle? - unity3d

Question

I was wondering if there's a way to add (in my case) 120 degrees everytime I push 'ButtonA', and subtract 120 degrees everytime I push 'ButtonB', from the Z-axis rotation of a 2d sprite (prefab).
This is the code I'm using at the moment, but it only rotates once left, and once right:
function TouchOnScreen ()
{
if (Input.touchCount > 0)
{
var touch = Input.touches[0];
if (touch.position.x < Screen.width/2)
{
var RSpeed = 10.0f
transform.rotation = Quaternion.Lerp ( transform.rotation,Quaternion.Euler(0,0,120), Time.deltaTime*RSpeed);
Debug.Log("RotateRight");
}
else if (touch.position.x > Screen.width/2)
{
var LSpeed = 10.0f
transform.rotation = Quaternion.Lerp ( transform.rotation,Quaternion.Euler(0,0,-120), Time.deltaTime*LSpeed);
Debug.Log("RotateLeft");
}
}
}
Thanks in advance!
Note: Please use unityscript if you can, I'm pretty new to coding and unityscript is all I know so far.

Answer 1

From the online documentation it is shown that the signature of the function is
static function Lerp(from: Quaternion, to: Quaternion, t: float): Quaternion;
that means the second parameter is the new rotation of the object not the rotation offset
you should use something of the sort
function TouchOnScreen ()
{
if (Input.touchCount > 0)
{
var touch = Input.touches[0];
if (touch.position.x < Screen.width/2)
{
var RSpeed = 10.0f
transform.rotation = Quaternion.Lerp ( transform.rotation,transform.rotation + Quaternion.Euler(0,0,120), Time.deltaTime*RSpeed);
Debug.Log("RotateRight");
}
else if (touch.position.x > Screen.width/2)
{
var LSpeed = 10.0f
transform.rotation = Quaternion.Lerp ( transform.rotation,transform.rotation + Quaternion.Euler(0,0,-120), Time.deltaTime*LSpeed);
Debug.Log("RotateLeft");
}
}
}
note the second parameter is transform.rotation + Quaternion.Euler(0,0,120) (current rotation + offset to the right)
I'm not an expert on unity engine (I only started toying with the free version yesterday, literally)

Answer 2

Try this one
function TouchOnScreen ()
{
if (Input.touchCount > 0)
{
var touch = Input.touches[0];
if (touch.position.x < Screen.width/2)
{
var RSpeed = 10.0f
transform.Rotate(0,0,120);
Debug.Log("RotateRight");
}
else if (touch.position.x > Screen.width/2)
{
var LSpeed = 10.0f
transform.Rotate(0,0,-120);
Debug.Log("RotateLeft");
}
}
}
If this not works try with Gameobject. I didn't check this