title: Edit variables in my main form, from my sub forms
body: <p>This is my first time posting, so please tell me if I'm doing anything wrong!</p>
  
  <p>I've made a WPF form, which is a small RPG text based game. 
  I have a button that opens a new form, which is supposed to be a shop. 
  I use <code>var ShopWindow = new Shop(); ShopWindow.ShowDialog();</code> to open the sub form. </p>
  
  <p>My question is, how do I edit my variables on the main form? 
  Let's say I buy something for 10 units, then I want to withdraw 10 units from the main form, and add an item. </p>
  
  <p>I hope I've given enough information, please tell me if you need anything! </p>