consolidate items in a list c#
<p>I now have two list box, lstStock and lstSupply. lstSupply consists of </p>

<pre><code>-Pen
-Pencil
-Staple
-Stapler
-Folder
-Notebook
-Eraser
-Marker
</code></pre>

<p>and i have two button, one button named btnAdd and another btnRemove.</p>

<p>when i click on btnAdd i want the selected item in lstSupply to be added into lstStock which i have done by </p>

<pre><code>    lstStock.Item.Add(lstSupply.SelectedItem);
</code></pre>

<p>if i select the same item in lstSupply twice, I want it to be consolidated in lstStock.
for instance, if i select Pen twice, the list box shall give me "Pen x 2" instead of Pen in a line and another Pen in another line. 
I got the feeling this is dealing with foreach but i dont really know how to use that.</p>
