Chapter 8 The +3 BASIC programmer's guide Part 1 Introduction Whether you read chapter 6 first, or came straight here, you should be aware that... Commands are obeyed straight away. Instructions begin with a line number and are stored away for later use. This guide to BASIC starts by repeating some of the information given in chapter 6 (Introducing +3 BASIC), but in greater detail. You may also find exercises at the end of some sections - don't ignore these, as many of them illustrate points that are hinted at in the text. Look through them, and do any that interest you or that seem to cover ground that you don't understand properly. The Keyboard +-----------------------------------------------------------------------------+ |TRUE |INV. | | | | | | | | | | | | |VIDEO|VIDEO| 1| 2| 3| 4| 5| 6| 7| 8| 9| 0|SPACE| |-----------------------------------------------------------------------------| | | | | | | | | | | | | | | | DELETE|GRAPH| Q| W| E| R| T| Y| U| I| O| P| | |-------------------------------------------------------------------------+ | | EXTEND | | | | | | | | | | | | | MODE | EDIT| A| S| D| F| G| H| J| K| L| ENTER | |-----------------------------------------------------------------------------| | |CAPS | | | | | | | | | | | CAPS SHIFT | LOCK| Z| X| C| V| B| N| M| .|CAPS SHIFT| |-----------------------------------------------------------------------------| |SYMB | | | /-- | --\ | | || | /\ | |SYMB | |SHIFT| ;| "| \-- | --/ | SPACE | \/ | || | ,|SHIFT| +-----------------------------------------------------------------------------+ The characters used on the +3 comprise not only single symbols (letters, digits, etc.) but also compound tokens (keywords, function names, etc.). Everything must be typed in full, and in most cases it doesn't matter whether capital letters (known as UPPER CASE) or small letters (lower case) are used. There are three sorts of keys on the keyboard: letter and number keys (called alphanumeric keys); symbol keys (punctuation marks); and control keys (things like CAPS SHIFT, DELETE and so on). The most commonly used keys for BASIC are the alphanumeric keys. When a letter key is pressed, a lower case letter will appear on the screen with a flashing blue and white blob called the cursor. To get an upper case letter, the CAPS SHIFT key should be held down while the letter is typed. If you wish to continuously type upper case letters, then pressing the CAPS LOCK key once will make all subsequent letters typed upper case. To return to lower case letters, simply press CAPS LOCK again. To type the symbols which appear on the alphanumeric keys on the keyboard, i.e.... ! @ # $ % & ' ( ) _ < > ^ - + = :? / * ...simply hold down the SYMB SHIFT key while the alphanumeric key with the required symbol on it is pressed (see the following diagram)... +-----------------------------------------------------------------------------+ | | | ! | @ | # | $ | % | & | ' | ( | ) | _ | | | | | 1| 2| 3| 4| 5| 6| 7| 8| 9| 0| | |-----------------------------------------------------------------------------| | | | | | | < | > | | | | | | | | | | | | | R| T| | | | | | | |-------------------------------------------------------------------------+ | | | | | | | | | ^ | - | + | = | | | | | | | | | | H| J| K| L| | |-----------------------------------------------------------------------------| | | | : |pound| ? | / | * | | | | | | | | Z|signX| C| V| B| | | | | =======-----------------------------------------------------------------======= =SYMB== | | | | | | | =SYMB== =SHIFT= | | | | | | | =SHIFT= =======-----------------------------------------------------------------======= Symbols available using SYMB SHIFT Additionally, the symbols... [ ] (C) ~ | \ { } ...can be obtained by first pressing the EXTEND MODE key once, then holding down SYMB SHIFT while pressing the appropriate alphanumeric key (see the following diagram)... +-----------------------------------------------------------------------------+ | | | | | | | | | | | | | | | | | | | | | | | | | | | | |-----------------------------------------------------------------------------| | | | | | | | | [ | ] | | |(C) | | | | | | | | | | Y| U| | | P| | ===========---------------------------------------------------------------+ | = EXTEND == | ~ | | | \ | { | } | | | | | | == MODE === | A| S| D| F| G| | | | | | ===========-------------------------------------------------------------------| | | | | | | | | | | | | | | | | | | | | | | | | =======-----------------------------------------------------------------======= =SYMB== | | | | | | | =SYMB== =SHIFT= | | | | | | | =SHIFT= =======-----------------------------------------------------------------======= Symbols available using SYMB SHIFT in EXTEND MODE To enter graphics mode, the GRAPH key is pressed once. Mosaic graphics (see the following diagram) can then be produced by pressing the number keys (except 9 and 0). Pressing the letter keys (except T, U, V, W, X, Y and Z) produce user-defined graphics (if set up). +-----------------------------------------------------------------------------+ | | |..## |##.. |#### |.... |..## |##.. |#### |.... |graph| | | | | |....1|....2|....3|..##4|..##5|..##6|..##7|....8|off 9| | | |-----------------------------------------------------------------------------| | | | | | | | | | | | | | | | |GRAPH| | | | | | | | | | | | |-------------------------------------------------------------------------+ | | | | | | | | | | | | | | | | | | | | | | | | | | | |-----------------------------------------------------------------------------| | | | | | | | | | | | | | | | | | | | | | | | | |-----------------------------------------------------------------------------| | | | | | | | | | | | | | | | | | | | | | | +-----------------------------------------------------------------------------+ Mosaic graphics available using GRAPH To obtain inverted mosaic graphics, press the above number keys while holding down CAPS SHIFT. [See (near the end of) chapter 7 for a diagram showing them.] General keyboard notes If any key is held down for more than 2 or 3 seconds, it will start repeating. As keys are pressed, a line will be built up on the screen. A line, by the way, means a line of BASIC, and may easily be several lines long on the screen. The cursor keys can be used to move about the line, and if the part of the line that the cursor is moved to is off screen, then the text on screen will scroll up or down to display it. Any characters typed will be inserted at the cursor, and pressing DELETE causes the character to the left of the cursor to be removed. As soon as ENTER is pressed or any attempt is made to move the cursor off the line, the +3 checks to see if the line makes sense. If it does, then there is a high-pitched bleep, and the line is either acted upon immediately or stored away as part of a program. If the line contains an error, then the +3 generates a low-pitched bleep and moves the cursor to the area where it thinks the error is (the colour of the cursor also changes to red to indicate the error). It is impossible to move off a line which contains an error [or even some which contain no error - see imc's ROM bugs list] - the +3 will always move the cursor back. The monitor screen This has 24 lines (each being 32 characters long) and is divided into two parts. The larger (top) part of the screen is at most 22 lines and displays either a listing or program output. It is the one used most often for editing. When printing in the top part has reached its bottom limit, the contents scroll up by one line. If, however, scrolling would mean losing a line that you haven't yet had a chance to see, then the +3 stops with the message... scroll? Pressing any key (except N, BREAK or the space bar) will let scrolling continue. Pressing one of the keys N, BREAK or the space bar will make the program stop with the report... D BREAK - CONT repeats The smaller (bottom) part of the screen is used for editing short programs, entering input data, entering direct commands (where the main screen must not be used, e.g. graphics programs), and also for displaying reports. Program entry If the program being entered gets bigger than the screen size, then the +3 attempts to display the area of most interest (usually the last line entered together with its surrounding lines). You may, however, specify a different area of the program to be displayed using the command... LIST xxx ...where xxx is a line number, telling the +3 to bring a specified area of the program into view. When a command is executed or a program is run, output is displayed in the top part of the screen and remains there when the program finishes (until a key is pressed). If the program is being edited in the bottom part of the screen, then any output in the top screen will stay there until it is either overwritten, scrolled off, or a CLS command is issued. The bottom screen may display a report giving a code (digit or letter) referred to in part 29 of this chapter. This report remains in the bottom screen until a key is pressed. While the +3 is running a BASIC program, the BREAK key is checked every so often. This happens at the end of a statement, during use of the cassette unit (if connected) or printer (if connected), or while music is being played. If the +3 finds that the BREAK key is pressed, then program execution stops and displays a report. The program may then be edited.