how do you correct errors in a script?

I am using the latest version of unity and this script was taken out of a book to make the game character move. LEARNING 2D GAME DEVELOPMENT WITH UNITY BY MATTHEW JOHNSON the book is based on unity 2D version 4.5.1 and I used that at first and even that had problems.

I have created the first level and I'm stuck in chapter 5 because this script will not work and I don't know how to correct the errors that occur when I copy this script into visual studio and attach it to my game character. What is wrong with this script how should it be written to work properly.

 public class PlayerController : MonoBehaviour 
 {
     [HideInInspector]
     public bool isFacingRight = true;
 
     [HideInInspector]
     public bool isJumping = false;
 
     [HideInInspector]
     public bool isGrounded = false;
 
     public float jumpForce = 650.0f;
     public float maxSpeed = 7.0f;
 
     public Transform groundCheck;
     public LayerMask groundLayers;
 
     private float groundCheckRadius = 0,2f;
 
     void Start()
     {
     }
 
     void Update()
     {
     }
 
     void FixedUpdate()
     {
     }
 }