将查询发送到同一页面

I have this form

<form action="index.php?store=<?php echo $_GET['store'];?>/" method="GET">
        <input type="text" class="form-control txt-fc" name="s" placeholder="Enter Product Name" />
</form>

The url of the current page is like this

index.php?store=gsStore

Now the problem is that when I submit the form the url becomes this

index.php?s=Graphics+Cards

Since there is no store in the url therefore php shows error! What I actually want is that it should submit the form without losing the store variable like this

index.php?store=gsStore&s=Graphics+Cards

How it is achievable?

Use hidden input element:

<form action="" method="GET">
  <input type="hidden" name="store" value="<?php echo $_GET['store'];?>">
  <input type="text" class="form-control txt-fc" name="s" placeholder="Enter Product Name" />
</form>