How do I modify animation parameters from script (C#)

Okay I’m a beginner, and I am making a basic click-based attack system. I have made “Attack” and “Idle” animations in Unity 5, and I am trying to write a C# script that will tell Unity to transition from “Idle” to “Attack”, then back to “Idle” when I click the left mouse button.

I have set up the transitions in the Animator window and created a bool parameter (“Slice”) that must be true in order to invoke the transition, but I cannot figure out how to change this parameter from my script.

Here is what I have:
public class Weapon : MonoBehaviour {

Animator ani;

void Start()
ani = GetComponent();
ani.enabled = true; // this starts the “Idle” animation

void Update()

   bool attack = ani.GetBool("Slice"); //this bool defaults to false

   if (Input.GetMouseButtonDown(0)) 
       attack = true;
   attack = false;  // I tried removing this but it made no difference

Do I need to create a helper class?

You want…

 ani.SetBool("Slice", true);