This month Peter Phillips gets to grips with HiSoft Power 
                     
BASIC in the first of his tutorial series on BASIC.
                     
                     
                     
                       FirST STeps in BASIC 
                     
                     
                     
     Before you begin to program any computer, it is important to 
                     
grasp one fact. THE COMPUTER DOES NOT THINK. No matter how 
                     
intelligent your ST may seem at times, it is not an intelligent 
                     
system in the same way humans are intelligent. It cannot reach 
                     
logical conclusions about anything without being given a precise 
                     
series of instructions. The ST may give the impression of thinking 
                     
on it's own, but all its really doing is following a series of 
                     
instruction - a program.
                     
     
                     
     In order for a computer to be able to do anything, no matter 
                     
how simple it may appear to us, the task must be broken down into 
                     
a series of precise steps for the computer to follow. Try making a 
                     
list of all the steps you would expect to follow when you go to 
                     
make a cup of tea. You list should look something like this:
                     
                     
                     
     1.   Fill Kettle
                     
     2.   Boil Kettle
                     
     3.   Put Teabag In Pot
                     
     4.   Pour On Boiling Water
                     
     5.   Pour Milk Into Cup
                     
     6.   Pour The Tea
                     
                     
                     
     These six steps are simple enough for a child of a bout six 
                     
to follow and make a cup of tea. These instructions only appear 
                     
simple to us because we have learned some basic knowledge of the 
                     
world around us a s we've been growing up. A computer has no 
                     
knowledge at all, so every single step in the tea making process 
                     
must be set out, like this:
                     
                     
                     
     1.   Grasp Kettle By Handle
                     
     2.   Take Kettle To Sink
                     
     3.   Grasp And Remove Lid
                     
     4.   Place Kettle Under Cold Tap
                     
     5.   Turn On Cold Tap
                     
     6.   Wait Until Kettle Is Full
                     
     7.   Turn Off Cold Tap
                     
     8.   Replace Lid
                     
     
                     
     ... and so it would go on, each step carefully laid out. Even 
                     
these steps above can be broken down still further in terms of 
                     
precise distances and angles of movement, amount of pressure and
                     
volume of water.
                     
                     
                     
                        Before you Start... 
                     
                     
                     
     Assuming you haven't already done so, make a copy of which 
                     
ever BASIC you intend to use to follow this series. If you're 
                     
using the version of PowerBASIC included on the CoverDisk then 
                     
copy all the files to a blank disk and de-archive them. This will 
                     
give you room to store some of the tutorial files on the same 
                     
disk.
                     
     If you're using another BASIC such as GFA then set up a new 
                     
work disk to hold the files from the tutorial series. This will 
                     
help to keep them separate from any other work or example files 
                     
you may have.
                     
                     
                     
     Reboot your ST and load up your chosen BASIC. It doesn't 
                     
matter which sort of BASIC you're using since the examples in this 
                     
Tutorial have been designed to work with most of the common 
                     
programs. However, they are intended to work with the HiSoft BASIC 
                     
dialects, specifically: 
                     
                     
                     
     * FirST BASIC  - bundled with may of the newer ST packs such 
                     
       as the Turbo Pack and the Discovery Pack.
                     
     * PowerBASIC   - a demo version of this program is included on 
                     
       the CoverDisk with this issue of ST User.
                     
     * HiSoft Basic - the full version of HiSoft's implementation 
                     
       of the BASIC language.
                     
                     
                     
     * ST BASIC     - all HiSoft BASIC's are downwardly compatible 
                     
       with the original ST BASIC supplied on the Language disks 
                     
       of older machines.
                     
                     
                     
                     
                     
     BASICcanbeoperatedintwoways.Aprogramcanbetypedin
                     
linebylinethensavedtodiskforfutureuse.Asavedprogram
                     
cantheneitherbeexecutedbytheBASICprogramitselfor
                     
compiledintoaPRGfilethatcanberunfromthedesktop.
                     
     TheotherwaytouseBASICistypeinasinglelineandthen
                     
runittoseetheresult.Thisdoesn'tallowproperlargeprograms
                     
tobebuiltup,butitdoesallowyoutoexperimentwiththe
                     
facilitiesofferedbyBASIC.HiSoftBASIC'salsohavea"Direct
                     
Mode"whenanycommandtypedincanbeexecutedbypressing
                     
Alternate-X.
                     
                     
                     
     In all the following examples, all the text in bold are BASIC 
                     
statements and should be typed exactly as they appear. Remember to 
                     
press 'Return' at the end of each line so BASIC will act on the 
                     
instruction. If you make a mistake, don't worry about it, just try 
                     
again.WithHiSoftBASICs,includingtheDemoofPowerBASIConthe
                     
CoverDisk,whenyou'vetypedinthelinesasshown,gouptothe
                     
PROGRAMmenuandselectRUNtoseetheresults.
                     
                     
                     
     In Directmode, type the following, and see what the ST does 
                     
in response. 
                     
                     
                     
      PRINT "Hello World!" 
                     
                     
                     
     What you have just done is to issue a direct command to the 
                     
computer. The PRINT statement is a BASIC 'keyword' or a word that 
                     
instructs BASIC to perform a particular action. PRINT tells the 
                     
machine to print what every follows to the screen. Now try:
                     
 
                     
     PRINT "The ST"
                     
     PRINT "is the best computer available"
                     
                     
                     
      You'll see that the sentence has been split over two lines, 
                     
in exactly the same way as it was typed with the keywords. This 
                     
happens because when BASIC reaches the closing quote as any PRINT 
                     
statement, it automatically goes to the start of the next line. If 
                     
you want it to continue on the same line, you have to add a semi-
                     
colon (;) after the end quotes, like this:
                     
 
                     
     PRINT "The ST ";
                     
     PRINT "is the best computer available"
                     
 
                     
     Note that an extra space has been added at the end of the 
                     
first line. This is because BASIC will print exactly what it finds 
                     
so if the space wasn't there, BASIC wouldn't put a space between 
                     
the words 'ST' and 'is'. Try the line again but without the extra 
                     
space, just to see what happens.
                     
                     
                     
     InBASICthecomma(,)alsohasause.MostBASIC'ssetupa
                     
tabstop,usuallyeveryfourorfivecharacters.PowerBASICallows
                     
youtochangethetabstops.
                     
     Toseehowtabswork,trythis:
                     
                     
                     
      PRINT"TheST",,,"isthebestcomputerintheworld" 
                     
                     
                     
     The"is..."willbeseparatedby12spacesfromtheendof
                     
thepreviousword.Thisdemonstrateshowtabscanbeusedto
                     
arrangeonscreentextinamoreattractivemanner.
                     
                     
                     
     TryexperimentingwiththePRINTstatementtofindoutwhat
                     
itcandoandhowitcanbeusedtoputtextonthescreen.More
                     
BASICprogrammingnextmonthwhenI'llbelookingatthewayBASIC
                     
dealswithnumbersandhowarithmeticaloperationsareperformed.

Takaisin

(C) Marko, Suomen Atari-sivut / ArkiSTo 2003