I want to make a high score

Questions & Answers
1

and i have a problem at (score = null;)

using UnityEngine;
using UnityEngine.UI;

public class Column : MonoBehaviour
{
    public float score;
    public float Highscore;

    private void OnTriggerEnter2D(Collider2D obj)
    {
        if (obj.GetComponent<Bird>() != null)
        {
            GameController.Instance.Score();
            score = null;
        }
    }
    private void HighScore()
    {
        if (Highscore < score)
        {
            Highscore = score;
        }
    }
}
2

score is a number and you cant assign a null to a number, what are you trying to achiev?