Event Variables are number or text values which are either global to the project or local to a range of events. They are modified using the Event Variable dialog. To add an event variable, right-click on an event, another variable, or an empty space in the event sheet, and select Add global variable or Add local variable. Variables at the root level of the event sheet (not indented beneath anything else) become global variables, whereas variables in groups or sub-events become local variables.
Event variables are modified with the system actions in the Global & local variables category. They can be retrieved by simply using their name in expressions.
Global variables show a globe icon. They are always at the top level of an event sheet - they are not sub-events or inside any groups.
Global variables store their values between layouts. Events in any layout can access any global variable, even if it was created in a different event sheet that is not included.
Global variables can be moved to another event sheet by cutting and pasting them. After being cut, references to the global variable will disappear because it has been removed; this is normal and nothing to worry about. When you paste the global variable, the references that disappeared will reappear again.
Local variables are variables placed nested under other events, or inside a group. They also show with a different icon to global variables.
The main difference between global and local variables is local variables can only be accessed in their scope. A local variable's scope is its level of sub-events. All other events at the same level of indentation, or lower levels, can access the local variable. Events above it (less indented) cannot access the local variable.
For example, if an event variable is in a group of events, it becomes a local variable. Then, it will only appear as an option for a variable in events inside that group. In other groups or in other event sheets it does not appear at all and cannot be accessed. This makes the variable local to the scope in which it is placed.
Local variables convenient for temporarily holding variables over a short range of events, such as to calculate an average value (where a temporary 'sum' variable may be necessary). It also helps keep the project simple, since it prevents the need to create more global variables, which appear everywhere in the project even if they are not needed everywhere.
The scope of local variables is designed to mimic how the scope of variables works in real programming languages.
Static and constant variables
By default, local variables reset to their initial value whenever entering their scope (usually every tick), like local variables in programming languages. If the variable is marked static in the Event Variable dialog it will persist its value permanently, like a global variable.
Both global and local variables can be marked constant. This makes them read-only: they can be retrieved and compared, but not changed.