how to code a button in unity code example

Example 1: unity assign button onclick

public Button yourButton;	

void Start () 
{
	Button btn = yourButton.GetComponent(); //Grabs the button component
	btn.onClick.AddListener(TaskOnClick); //Adds a listner on the button
}	
void TaskOnClick()
{
	Debug.Log ("You have clicked the button!");
}

Example 2: how to declare an button in unity

using UnityEngine.UI;

public class PlayerDash : MonoBehaviour
{
public Button your_button;