how to retrieve value from input type=date textbox using c#

In ASP.NET you don't have a TextBox control you have an input field instead. You can get its properties or values on the serverside (code behind) using the Request class of ASP.NET.

First you need to make sure, that the input field you're trying to access is a part of a form. Since only forms invoke submit method inside the HTML elements. Here is an example of such HTML code

<!-- method="post" is totally unrelated, don't fall for it -->
<form method="post">
  <input name="Txtdoa" type="date"  value="Date Of Arrival" id="Txtdoa" title="Date Of Arrival" class="water" style="width:100%;">
  <input type="submit" value="Submit" />
</form>

The above form has an input field (to get the date) and a submit button. Once submitted the form will be passed on to the server, with the input fields specified inside it. In this case, the input field for the date will be sent. Youc an get the value on the serverside, using the name of the field. Like this

// get the value of the object with name Txtdoa in the Request
var date = Request["Txtdoa"];
// use date variable inside the code where required. 

This is the example code, you can learn more of this stuff at ASP.NET official website. http://asp.net/web-pages[^]. They've got a lot of cool codes for you to get started.