Getting and Setting Values of GControls:
- All of the GControls have a .value that can be used from the macro.
- When the PANEL is created the /CONTROLS=GC switch can be added in.
  - This tells GCONTROL to put a reference for each control into the GC table.
```
startmacro
  pipe on
    panel/controls=gc
    
    gcontrol lval mynum "MyNum" 50 0 100 5
    
    res gc.mynum.value
  pipe off
endmacro
```
- When a user changes the value of a GControl, the control sends a message to the macro.
  - This message can be viewed in the processMessage procedure.
```
startmacro
  pipe on
    panel/controls=gc
    
    gcontrol lval     mynum "MyNum" 50 0 100 5
    gcontrol calendar mycal 
    gcontrol button   mybtn "My Buttons" "RED,WHITE,BLUE"
  pipe off
endmacro

procedure processMessage m:msg
  say "Got message name=^msg.name info=^msg.info data=^msg.data"
return
```
- NOTE: Certain message names are reserved and have special uses. These names should be avoided when composing messages. Also, since command id's become the message name when interacting with the macro, users should not assign any commands (including gcontrols) an id with one of these reserved names:
```
   EXIT
   ERROR
   EXEC
   MACRO
```