Boss Health Bar

Okey, so basically I am trying to create a boss health bar that follows the enemy (above his head) and if player collides, it drops down from 100 to 80. The script should be c# and it’s 2D.
This is my current script

		if(col.gameObject.name == "BossBody"){
			gameObject.transform.position = respawnPoint.position;
			bossDamage = 0;
			AudioSource.PlayClipAtPoint(BossDeath, transform.position);
		}

		if(col.gameObject.name == "Boss"){
			bossDamage +=1;
			Debug.Log ("Current bossDamage is: " + bossDamage);
			AudioSource.PlayClipAtPoint(BossHit, transform.position);
			}
		
		if(col.gameObject.name == "Boss" && bossDamage == 5) {
			Destroy(col.gameObject);
			score+= 5;
			AudioSource.PlayClipAtPoint(BossKill, transform.position);
			GetComponent<AudioSource>().Stop();
			audio2.Play ();
		}

This makes the music stop, play and so on aswell as makes the boss die after 5 hits.
I have tried to add a boss health bar to the script by impementing this code that I found online, but I simply cannot get it working. All help and tips is much appreaciated. Thanks in advance

public int maxHealth = 100;
    public int curHealth = 100;
   
    public float healthBarLength;
   
    // Use this for initialization
    void Start () {
        healthBarLength = Screen.width / 6;
    }
   
    // Update is called once per frame
    void Update () {
        AddjustCurrentHealth(0);   
    }
   
    void OnGUI() {
        GUI.Box(new Rect(700, 10, healthBarLength, 20), curHealth + "/" + maxHealth);
    }
   
    public void AddjustCurrentHealth(int adj) {
        curHealth += adj;
       
        if (curHealth < 0)
            curHealth = 0;
       
        if (curHealth > maxHealth)
            curHealth = maxHealth;
       
        if(maxHealth < 1)

Well, really you should create the bosses max health and then have a variable for the current health.

 private float bossMaxHp = 100f;
 private float bossHp;
 public Image hpBarBackground; // Add your background image here(inside Unity)
 public Image hpBarForeground; // add the HP image that will be affected by Damage here

Somewhere inside your code:
bossHp = bossMaxHp;

When using Unity UI, or images you’ve created for HP bar, you can have your images accessed like this:

 void Update(){

hpBarForeground.fillAmount = bossHp / bossMaxHp;

 }

As far as your bosses damage and detection, you should use OnCollisionEnter()

 void OnCollisionEnter(Collision collision){

if(collision.tag == "Boss"){
`}
// Insert your code here

  `}

And you can pretty much keep adding your IF statements inside this function.
I think this will clean your code up quite a bit.