HP Prime Graphing NW280AAABA manual Programming in HP PPL 557

variables represent the definitions and settings you make when working with apps interactively. As you work through an app, the app functions may store results in app variables as well. In a program, app variables are used to edit an app’s data to customize it and to retrieve results from the app’s operation.

CAS variables are similar to the Home real variables A–Z, except that they are lowercase and designed to be used in CAS view and not Home view. Another difference is that Home and App variables always contain values, while CAS variables can be simply symbolic and not contain any particular value. The CAS variables are not typed like the Home and App variables. For example, the CAS variable t may contain a real number, a list, or a vector, etc. If a CAS variable has a value stored in it, calling it from Home view will return its contents.

User variables are variables created by the user, either directly or exported from a user program. They provide one of several mechanisms to allow programs to communicate with the rest of the calculator and with other programs. User variables created in a program may be either local to that program or global. Once a variable has been exported from a program, it will appear among the user variables in the Variables menu, next to the program that exported it. User variables may be multi- character, but must follow certain rules; see “Variables and visibility” on page 511 for details.

User variables, like CAS variables, are not typed and thus may contain objects of different types.

The following sections deal with using app variables in programs, providing descriptions of each app variable by name and its possible contents. For a list of all the Home and app variables, see chapter 22, “Variables”, beginning on page 423. For user variables in programs, see “The HP Prime programming language”, beginning on page 511.

Programming in HP PPL 557