The names of variables are built up by composing letters, digits, and the underscore `_'. The type of a variable, iconic or control variable, depends on its position in the parameter list in which the variable identifier is used for the first time, see also section “Basic Types of Parameters”, and is determined during the input of the operator parameters. Whenever a new identifier appears, a new variable with the same identifier is created. Control and iconic variables must have different names. The value of a variable is undefined until the first assignment defines it, note that the variable has not been instantiated yet. A read access to an undefined variable leads to a runtime error.
Instantiated variables contain tuples of values. Depending on the kind of the variable, the data items are either iconic objects or control data. The length of the tuple is determined dynamically by the performed operation. A variable can get new values any number of times, but once a value has been assigned the variable will always keep being instantiated, unless you select the menu item Menu Execute ▹ Reset Program Execution. The content of the variable is deleted before the variable is assigned new values.