由于某种原因，我的代码将2加到了变量而不是1上，我不知道为什么

我使用C＃在Unity中进行编码，并且设置了与变量相等的不同精灵i。当A被按下它应该加1 i，并且当D它被按下应该减去1，改变依赖于子画面i的值。直到昨天我再次打开它时，它一直运行良好，现在由于某种原因它只会加减2而不是1。在开始执行此操作之前，我在代码中没有做任何更改，但我不知道为什么。我的代码在下面。

public void Start()
{
    //Sets i to 4 and spriteRenderer to the current Sprite Rendered.
    i = 4;
    d = 1;
    Score1 = 0;
    spriteRenderer = this.GetComponent<SpriteRenderer>();
}

void OnTriggerEnter2D(Collider2D Death)
{
    //Detects if there is a collision and sets d to 0.
    d = 0;
}

public void Update()
{
    //A bunch of if statements to detect the input key and if the input key is set to GunAngleDown then adds 1 to i or if the input key is set to GunAngleUp the subtracts 1 from i.
    if (Input.GetKeyDown(GunAngleDown))
    {
        i++;
    }
    else if (Input.GetKeyDown(GunAngleUp))
    {
        i--;
    }

    //If i is equal to 8 then subtracts 1 from i or if i is equal to 0 then adds 1 to i.
    if (i == 8)
    {
        i--;
    }
    else if (i == 0)
    {
        i++;
    }

    //checks the current i value and sets the current sprite rendered to the respective sprite.
    if (i == 1)
    {
        spriteRenderer.sprite = SpriteGunAngleUp3;
    }
    else if (i == 2)
    {
        spriteRenderer.sprite = SpriteGunAngleUp2;
    }
    else if (i == 3)
    {
        spriteRenderer.sprite = SpriteGunAngleUp1;
    }
    else if (i == 4)
    {
        spriteRenderer.sprite = SpriteGunAngleStraight;
    }
    else if (i == 5)
    {
        spriteRenderer.sprite = SpriteGunAngleDown1;
    }
    else if (i == 6)
    {
        spriteRenderer.sprite = SpriteGunAngleDown2;
    }
    else if (i == 7)
    {
        spriteRenderer.sprite = SpriteGunAngleDown3;
    }

    //Checks if d2 is equalt to 0 and sets the rendered sprite to the dead sprite.
    if (d == 0)
    {
        spriteRenderer.sprite = Dead;
    }
}