购物车里的加减号功能的实现代码

int num;
    protected void Page_Load(object sender, EventArgs e)
    {
        num = Convert.ToInt32(((TextBox)(FormView1.FindControl("txtNum"))).Text);
        FormView1.DataBind();      
    }
    protected void jianbtn_Click(object sender, EventArgs e)
    {
        num--;
        if (num <= 0)
            num = 0;   
        ((TextBox)(FormView1.FindControl("txtNum"))).Text = num.ToString();
    }
    protected void Addbtn_Click(object sender, EventArgs e)
    {
        num++;
        ((TextBox)(FormView1.FindControl("txtNum"))).Text = num.ToString();