title: Grade Calculator isn't exiting
body: <p>I have a program that is supposed to approximate  a letter grade based off of an integer input.  I want it to be able to run continuously until the number "-1" is input, then quit.  However, whenever I try to run it, the program just keeps telling me my grade over and over again, and it won't do anything else.  Here is what I have so far.  </p>
  
  <pre><code>import easygui
  
  
  grade = int(easygui.enterbox(msg="Enter a grade between 0 and 100: "))
  while grade != -1:
  
      if grade &gt;= 90 and grade &lt;100:
          easygui.msgbox ("You got an A")
      if grade &gt;= 80 and grade &lt;90:
          easygui.msgbox ("You got a B")
      if grade &gt;= 70 and grade &lt;80:
          easygui.msgbox ("You got a C")
      if grade &gt;= 60 and grade &lt;70:
          easygui.msgbox ("You got a D")
      if grade &gt;= 0 and grade &lt;60:
          easygui.msgbox ("You got an F")
  
  else: raise SystemExit
  </code></pre>