SO fiddle

Test Fiddle mainly for SO Questions

HTML

<link rel="stylesheet" href="http://ajax.googleapis.com/ajax/libs/jqueryui/1.8/themes/dot-luv/jquery-ui.css">
<input type="text" class="myclass" />
<input type="text" class="myclass" />
<input type="text" class="myclass" value="12" />
<input type="text" class="myclass" />
<input type="text" class="myclass" />

JavaScript

$(document).ready(function() {
  $('.myclass').val(function (index, value) {
    // If the element has a value, return it, else return "0"
    return value || "0";
  });
});