求救字符转化DateTime

确保方法参数的格式正确。
将一个字符串转化成为DateTime时，先分析该字符串以获取日期，然后再将每个变量放置到DateTime对象中。我的程序是这样子的： for (int i = 0; i < GridView1.Rows.Count; i++)
        {DateTime DT = Convert.ToDateTime( GridView1.Rows[i].Cells[5].Text); if (DT.AddDays(3) < DateTime.Today)
            {
                Image img1 = (Image)GridView1.Rows[i].FindControl("Image1");
                img1.Visible = false;
            }
            if (Convert.ToInt32(GridView1.Rows[i].Cells[4].Text) < 5)
            {
                Image img2 = (Image)GridView1.Rows[i].FindControl("Image2");
                img2.Visible = false;
            }}这怎么改了