手动构造table

string str = "<table style='width:100%;' border=1><tr>";
        int j = 0;
        for (int i = 1; i <= 13; i++)
        {
            j = i;           
            if (i % 3 == 0)
            {
                str += "<td>" + i.ToString() + "</td></tr><tr>";
            }
            else
            {
                str += "<td>" + i.ToString() + "</td>";
            }
        }
        if (j / 3 != 0)
        {
            for (int i = 0; i < 3 - (j % 3); i++)
            {
                str += "<td>" + i.ToString() + "</td>";
            }
        }
        str += "</tr></table>";
        Response.Write(str);