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

i wondering if there's way add (in case) 120 degrees everytime push 'buttona', , subtract 120 degrees everytime push 'buttonb', z-axis rotation of 2d sprite (prefab).

this code i'm using @ moment, rotates once left, , 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 can, i'm pretty new coding , unityscript know far.

from online documentation shown signature of function is

static function lerp(from: quaternion, to: quaternion, t: float): quaternion;  

that means second parameter new rotation of object not rotation offset

you should use of 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 second parameter transform.rotation + quaternion.euler(0,0,120) (current rotation + offset right)

i'm not expert on unity engine (i started toying free version yesterday, literally)