Function Parameters and Variables are Local

Function p arameters and variables only exist inside their own functions. Within the confines of Scene1 , there is no such thing as sMessage . If you try to use it, the compiler will complain. Similarly, inside ShowTextTwice there is no such thing as sWarning . Variables like this are said to be local . In order to keep track of parameters and local variables, it is useful to draw a stack diagram. Like state diagrams, stack diagrams show the value of each variable, but the variables are contained in larger boxes that indicate which function they belong to.

For example, the state diagram for ShowTextTwice looks like this:

Whenever a function is called, it creates a new instance of that function. Each instance of a function contains the parameters and local variables for that function. In the diagram an instance of a function is represented by a box with the name of the function on the outside and the variables and parameters inside.

In the example, Scene1 has one local variable, sWarning, and no parameters. ShowTextTwice has no local variables and one parameter, named sMessage.