if checkbox in gridview is checked then textbox will visible in gridview else invisible

You can use template field or any bount field and then us JS to display or hide textbox

<asp:gridview id="GridView1" runat="server" xmlns:asp="#unknown">
        <columns>
        <asp:templatefield>
        <itemtemplate>
        <asp:checkbox id="chk" runat="server" onclick="cknunck(this)" />
        <asp:textbox id="tbx" runat="server" style="display:none;"></asp:textbox>
        </itemtemplate>
        </asp:templatefield>
        </columns>
        </asp:gridview>

 function cknunck(ck)
        {
            var dis="none";
            if(ck.checked)
                dis="";
            ck.nextSibling.style.display=dis;

        }
// nextSibling use to access next element after current element
// if you use bound field then you can use 
// ch.parentElement.nextSibling.children[0] 
// if text box is in next cell of table

you can use style.visibility="hidden" tag also in place of style.display

if this will help you then please mark as solution

You Can Try This one......

<asp:gridview id="GridView1" runat="server" xmlns:asp="#unknown">
<columns> <ItemTemplate>
<asp:CheckBox ID ="chkAdd" AutoPostBack="true" runat="server" oncheckedchanged="chkAdd_CheckedChanged" Enabled="True" />
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField>
<ItemTemplate>
<asp:TextBox ID="Txtgrd" Visible="false" runat ="server" " />
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>


0n .cs Use this....
foreach (GridViewRow row in GridView1.Rows)
{
checkBox chkadd = (CheckBox)row.FindControl("chkAdd");
TextBox txtf = (Button)row.FindControl("btngrd");
if (chkadd.Checked == true)
{txtf.visible=true;}
if (chkadd.Checked == false)
{
txtf.Visible = false;
}

if U don't want use JS then u sholud try this one..