Implement Next, Previous, First and Last on Button click using C# in ASP.Net

Hi! I used Problem in Search it's worked. But btnNext and btnPrevious not work have error.

protected void btnNext_Click(object sender, EventArgs e)
{
    ArrayList dt = GetInfo(Name.Text);
    btnPrevious.Enabled = true;
    index = index + 1;
    string[] pos = dt[index].ToString().Split(';');
    ID.Text = pos[0].ToString();
    FirstName.Text = pos[1].ToString();
    Name.Text = pos[2].ToString();
    LastName.Text = pos[3].ToString();
    Birthday.Text = pos[4].ToString();
    Adress.Text = pos[5].ToString();
    if (index == dt.Count - 1)
    {
        btnNext.Enabled = false;
    }
    else
    {
        btnNext.Enabled = true;
    }
}
protected void btnPrevious_Click(object sender, EventArgs e)
{
    ArrayList dt = GetInfo(Name.Text); btnNext.Enabled = true;
    index = index - 1;
    string[] pos = dt[index].ToString().Split(';');
    ID.Text = pos[0].ToString();
    FirstName.Text = pos[1].ToString();
    Name.Text = pos[2].ToString();
    LastName.Text = pos[3].ToString();
    Birthday.Text = pos[4].ToString();
    Adress.Text = pos[5].ToString();
    if (index == 0)
    {
        btnPrevious.Enabled = false;
    }
    else
    {
        btnPrevious.Enabled = true;
    }
}