c#初学者问题

代码如下，希望你好好学习，加油！！！

public partial class MyAutoExp : Form
    {
    int index = 0;   //定义图片的初始下标
    public MyAutoExp()
    {
    InitializeComponent();
    }

    //“上一张图片”功能按钮
    private void button1_Click(object sender, EventArgs e)
    {
    if (index == 0)   //如果小标为0时，下标等于imageBox里面最后一张图片的下标；
    {
    index = imageList1.Images.Count - 1;
    }
    if (index > 0)    //如果下标大于0，下标-1；
    {
    index--;
    pictureBox1.Image = imageList1.Images[index];
    }
    }

    //“下一张图片”功能按钮
    private void button2_Click(object sender, EventArgs e)
    {
    if (index < imageList1.Images.Count - 1)    //如果下标小于集合里最后一张图片的下标；
    {
    index++;    //下标+1；
    pictureBox1.Image = imageList1.Images[index];
    }
    if (index == imageList1.Images.Count - 1)  //如果下标等于集合里最后一张图片的下标；
    {
    index = 0;    //下标为集合里第一张图片的下标
    }
    }

    private void MyAutoExp_Load(object sender, EventArgs e)
    {
    pictureBox1.Image = imageList1.Images[0];
    }

    //“自动播放”功能按钮
    private void button3_Click(object sender, EventArgs e)
    {
    if (timer1.Enabled == false)    //如果在自动播放中的时候
    {
    timer1.Enabled = true;
    button3.Text = "播放中...";
    }
    else    //如果在暂停的时候
    {
    timer1.Enabled = false;
    button3.Text = "暂停";
    }
    
    
    }

    private void timer1_Tick(object sender, EventArgs e)
    {
    if (index < imageList1.Images.Count - 1)
    {
    index++;
    }
    else
    {
    index = 0;
    }
    pictureBox1.Image = imageList1.Images[index];

    }

    //任务栏
    private void MyAutoExp_SizeChanged(object sender, EventArgs e)
    {
    if (this.WindowState==FormWindowState.Minimized)
    {
    this.ShowInTaskbar = false;   //任务栏不显示
    this.notifyIcon1.Visible = true;   //托盘任务栏
    }
    }

    private void notifyIcon1_MouseDoubleClick(object sender, MouseEventArgs e)
    {
    if (this.WindowState == FormWindowState.Minimized)
    {
    this.ShowInTaskbar = true;  //显示在系统任务栏
    this.WindowState = FormWindowState.Normal;  //还原窗体
    notifyIcon1.Visible = false;  //托盘图标隐藏
    }

    }
    }