how to get textbox value in placeholder on code behind?

Question

I created some textbox and I want to get their value dynamically. Briefly, ı explain my page:

I have dropDown list has number 1 to 15.When the user select number and I

Answer 1

protected void btnSave_Click(object sender, EventArgs e)
            {

               for (int a = 1; a <= int.Parse(ddlUserSelected.SelectedItem.Text); a++)
                {              
                     string value = Request.Form["txtDate" + a];
                }

            }