How do I PROPERLY implement a high score script in my game?

Questions & Answers
1

I’m expanding on the 3D Space Shooter project from the tutorial, but I’m having some difficulty with saving and loading a high score IF the regular score variable is set to 0 in the Start Function. In other words, what happens is… the high score only gets successfully saved/loaded if I set my variable “start” to PlayerPrefs.GetInt(“High Score”).
However, the problem with this is that is that my regular score counts up to what my high score was: If my high score was 1080 for example, I reload the scene, and then as soon as I shoot one asteroid, I gain 1080 points when I’m only supposed to gain 10. This seems to be the only way I can use a previously saved high score though.
I’ve tried creating a separate variable in the Start function called “highscore” and setting THAT to PlayerPrefs.GetInt(“High Score”), while also setting score to 0 but that doesn’t enable the high score to save and load the next time I reload the scene. Could somebody tell me what’s wrong with my GameController script (script where the high score is supposed to fit in)?
BEFORE ANYONE ASKS ME IF I READ THE DOCUMENTATION OR LOOKED AT SIMILAR QUESTIONS ON HERE, I DID. I looked at how one puts PlayerPrefs.GetInt and PlayerPrefs.SetInt but for whatever reason, it’s not working. I’d much appreciate some help with this. Thank you.

using UnityEngine;
using UnityEngine.UI;
using System.Collections;
using UnityEngine.SceneManagement;

public class GameController : MonoBehaviour
{
    public GameObject[] hazards;
    public Vector3 spawnValues;
    public int hazardCount;
    public float spawnWait;
    public float startWait;
    public float waveWait;
 
    public GUIText scoreText;
    public GUIText restartText;
    public GUIText gameOverText;
    public GUIText highScoreText;

    private bool gameOver;
    private bool restart;
    private int score;
    private int highscore;

    
    

    void Start ()
    {
        gameOver = false;
        restart = false;
        restartText.text = "";
        gameOverText.text = "";
        highscore = PlayerPrefs.GetInt("High Score");
        score = 0;
        UpdateScore();
        StartCoroutine (SpawnWaves());
        
        
    }  
    
    void Update ()
    {
        if (restart)
        {
            if (Input.GetKeyDown (KeyCode.R))
            {
                SceneManager.LoadScene("Main");
            }
        }

        if (score > highscore)
        {
            highscore = score;
            highScoreText.text = "High Score: " + PlayerPrefs.GetInt("High Score");
            print(PlayerPrefs.GetInt("High Score"));
            
        }

    } 

    IEnumerator SpawnWaves ()
    {
        yield return new WaitForSeconds(startWait);
        while (true)
        {
            for (int i = 0; i < hazardCount; i++)
            {
                GameObject hazard = hazards[Random.Range(0, hazards.Length)];
                Vector3 spawnPosition = new Vector3(UnityEngine.Random.Range(-spawnValues.x, spawnValues.x), spawnValues.y, spawnValues.z);
                Quaternion spawnRotation = Quaternion.identity;
                Instantiate(hazard, spawnPosition, spawnRotation);
                yield return new WaitForSeconds(spawnWait);
            }
            yield return new WaitForSeconds(waveWait);

            if (gameOver)
            {
                restartText.text = "Press 'R' for Restart";
                restart = true;
                break;
            }
        }    
    }

    public void AddScore(int newScoreValue)
    {
        score += newScoreValue;
        UpdateScore();
        PlayerPrefs.SetInt("High Score", score);
        
    }

    void UpdateScore ()
    {
        scoreText.text = "Score: " + score;
        highScoreText.text = "High Score: " + score;
        //print(PlayerPrefs.GetInt("High Score"));
        
    }

    public void GameOver()
    {  
        gameOverText.text = "Game Over";
        gameOver = true;
        PlayerPrefs.SetInt("High Score", score);
        PlayerPrefs.Save();
    }
}
2

This should work for you

using UnityEngine;
using UnityEngine.UI;
using System.Collections;
using UnityEngine.SceneManagement;

public class GameController : MonoBehaviour
{
    public GameObject[] hazards;
    public Vector3 spawnValues;
    public int hazardCount;
    public float spawnWait;
    public float startWait;
    public float waveWait;
 
    public GUIText scoreText;
    public GUIText restartText;
    public GUIText gameOverText;
    public GUIText highScoreText;

    private bool gameOver;
    private bool restart;
    private int score;
    private int highscore;

    void Start ()
    {
        gameOver = false;
        restart = false;
        restartText.text = "";
        gameOverText.text = "";

        // default "highscore" to 0 if the key does not exist in PlayerPrefs
        highscore = PlayerPrefs.GetInt("High Score", 0);
        score = 0;
        UpdateScore();
        StartCoroutine (SpawnWaves());
    }  
    
    void Update ()
    {
        if (restart)
        {
            if (Input.GetKeyDown (KeyCode.R))
            {
                SceneManager.LoadScene("Main");
            }
        }
    } 

    IEnumerator SpawnWaves ()
    {
        yield return new WaitForSeconds(startWait);
        while (true)
        {
            for (int i = 0; i < hazardCount; i++)
            {
                GameObject hazard = hazards[Random.Range(0, hazards.Length)];
                Vector3 spawnPosition = new Vector3(UnityEngine.Random.Range(-spawnValues.x, spawnValues.x), spawnValues.y, spawnValues.z);
                Quaternion spawnRotation = Quaternion.identity;
                Instantiate(hazard, spawnPosition, spawnRotation);
                yield return new WaitForSeconds(spawnWait);
            }
            yield return new WaitForSeconds(waveWait);

            if (gameOver)
            {
                restartText.text = "Press 'R' for Restart";
                restart = true;
                break;
            }
        }    
    }

    public void AddScore(int newScoreValue)
    {
        score += newScoreValue;
        if (score > highscore)
        {
            highscore = score;

            // save the "High Score" since it has changed
            PlayerPrefs.SetInt("High Score", highscore);
            
        }
        UpdateScore();
    }

    void UpdateScore ()
    {
        scoreText.text = "Score: " + score;
        highScoreText.text = "High Score: " + highscore;
        print("Current High Score = " + highscore);
    }

    public void GameOver()
    {  
        gameOverText.text = "Game Over";
        gameOver = true;
        PlayerPrefs.SetInt("High Score", highscore);
        PlayerPrefs.Save();
    }

    public void OnApplicationQuit()
    {  
        GameOver();
    }
}