How to pass a textbox value from view to a controller in MVC 4?

Question

Here i am fetching the value from database and showing it in a input field

<input type="text" id="ss" value="@item.Quantity"/>

and the value fetching from database is 1.Then i am changing the input field value to 2 and passing that value to the controller in a action click

 <a id="imgUpdate"  href="@Url.Action("Update", "Shopping", new { id = Request.QueryString["UserID"], productid = item.ProductID, qty = item.Quantity, unitrate = item.Rate })"> 

But in the controller part i am getting that old value1 for qty.But i need that updated value 2 in qty

public ActionResult Update(string id, string productid, int qty, decimal unitrate)
        {
            if (ModelState.IsValid)
            {
                int _records = UpdatePrice(id,productid,qty,unitrate);
                if (_records > 0)
                {
                    return RedirectToAction("Index1", "Shopping");
                }
                else
                {
                    ModelState.AddModelError("","Can Not Update");
                }
            }
            return View("Index1");
        }

Any suggestion?

EDIT:

     @using (Html.BeginForm("Update", "Shopping", FormMethod.Post))
     {

                @Html.Hidden("id", @Request.QueryString["UserID"] as string)
                @Html.Hidden("productid", item.ProductID as string)
                @Html.TextBox("qty", item.Quantity)
                @Html.Hidden("unitrate", item.Rate)

                <input type="submit" value="Update" />
     }

Answer 1

I'll just try to answer the question but my examples very simple because I'm new at mvc. Hope this help somebody.

    [HttpPost]  ///This function is in my controller class
    public ActionResult Delete(string txtDelete)
    {
        int _id = Convert.ToInt32(txtDelete); // put your code           
    }

This code is in my controller's cshtml

  >   @using (Html.BeginForm("Delete", "LibraryManagement"))
 {
<button>Delete</button>
@Html.Label("Enter an ID number");
@Html.TextBox("txtDelete")  }  

Just make sure the textbox name and your controller's function input are the same name and type(string).This way, your function get the textbox input.