Programming Commands
Every command on the calculator is useful for programming, but some are expressly designed for that purpose. These are roughly divided into three categories: commands to control the flow of a program, commands to manage variables, and commands that provide input and output.
Control Flow
Any program is just a sequence of commands; but usually, it's not enough to just run through them all one by one in order and be done. Changes to this order have to be made: some commands should only be followed in certain situations, others might be repeated several times, still others might be a last resort in case of an error. Control flow commands are those that determine this order.
The simplest control flow commands are 68k:Goto and 68k:Lbl, which simply involve jumping around in the program. This isn't always the best way of doing things, though, and there are many alternatives:
Conditionals
A common situation is when certain commands depend on a condition being met. The following commands address this situation:
- The 68k:If statement simply places a condition on a command or block of commands.
- The 68k:Else statement, used with If, provides an alternative branch if the condition is not met.
- The 68k:ElseIf statement, also used with If, allows for several mutually exclusive conditions.
Conditions are typically created by combining equality relations (=, ≠, >, ≥, <, ≤) with logical operators (68k:and, 68k:or, 68k:xor, 68k:not).
Loops
Loops allow commands to be repeated over and over. The following types of loops exist:
- 68k:Loop..EndLoop blocks just keep repeating forever.
- 68k:While..EndWhile blocks repeat as long as a condition is satisfied.
- 68k:For..EndFor blocks repeat a fixed number of times.
To deal with these loops, we have a couple auxiliary commands:
- 68k:Cycle prematurely goes back to the beginning of a loop.
- 68k:Exit leaves a loop ahead of time.
Subroutines
If a task has to be done several times inside a program, the code for it can be removed to a subroutine: this routine can then be "called" whenever necessary. Subroutines in TI-Basic are essentially programs of their own. They can be defined inside a program with the 68k:Define command, and are of two types:
- Functions (defined with 68k:Func..EndFunc) return a value, and can't affect the overall state of the calculator.
- Programs (defined with 68k:Prgm..EndPrgm) can do anything, but don't return a value directly.
Two commands exist specifically for use with subroutines.
- 68k:Return exits a subroutine, returning to the program that called it.
- 68k:Stop exits every program currently running, subroutine or not.
Error Catching
Error catching provides a last resort if an error occurs. A portion of the program, or even the entire program itself, can be put into a 68k:Try..Else..EndTry block. The code after Else will only run in case of an error, and has the option to 68k:ClrErr — go on as though nothing happened — or 68k:PassErr — handle the error normally, with an OS error message.
Variable Management
Another part of programming is managing variables. This means:
- Defining them — with → or 68k:Define.
- Deleting them — with 68k:DelVar, 68k:DelType, 68k:DelFold, or 68k:NewProb.
- Protecting them — with 68k:Lock, 68k:Unlock, 68k:isLocked(), 68k:Archive, 68k:Unarchiv, or 68k:isArc().
- Dealing with names and folders — with 68k:CopyVar, 68k:MoveVar, 68k:Rename, or 68k:NewFold, 68k:setFold().
There is also the 68k:Local command, which designates certain variables as local to the program they are used in.
Input and Output
Finally, a program has to be able to get input from the user and give some output in response. For games, this usually means using the 68k:graphics commands, and reading keys with the 68k:getKey() command. There are other alternatives, however.
On the Program I/O screen:
- 68k:Input, 68k:InputStr, and 68k:Prompt read in typed text.
- 68k:Disp, 68k:Output, and 68k:Pause display text.
- 68k:ClrIO clears the I/O screen.
A more stylish method is to use 68k:dialogs, wrapped in a 68k:Dialog..EndDlog box.
- Input here is accomplished with 68k:Request and 68k:DropDown.
- The 68k:Text command, appropriately, displays text. A 68k:Title is also handy.
Some miscellaneous commands remain. 68k:Custom..EndCustm and 68k:Toolbar..EndTBar both create toolbar menus with the help of the 68k:Title and 68k:Item commands. And 68k:PopUp displays a popup menu.
Input and output also refers to interacting with other calculators. There are five commands for the purpose:
- 68k:Get and 68k:GetCalc read data from a connected calculator.
- 68k:Send, 68k:SendCalc, and 68k:SendChat send data to a connected calculator.