Differences Between Functions and Programs

A function defined in the Program Editor is similar to the functions built into the TI-Nspire™ Software.

Functions must return a result, which can be graphed or entered in a table. Programs do not return a result.
You can use a function (but not a program) within an expression. For example: 3 ¦ func1(3) is valid, but not 3 ¦ prog1(3).
You can run programs from Calculator and Notes applications only. However, you can evaluate functions in Calculator, Notes, Lists & Spreadsheet, Graphs & Geometry, and Data & Statistics.
A function can refer to any variable; however, it can store a value to a local variable only. Programs can store to local and global variables.

Note: Arguments used to pass values to a function are treated as local variables automatically. If you want to store to any other variables, you must declare them as Local from within the function.

A function cannot call a program as a subroutine, but it can call another user-defined function.
You cannot define a program within a function.
A function cannot define a global function, but it can define a local function.