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QL User Manual - Dilwyn Jones Sinclair QL Pages

1. H H HH HH fat A IB ICID HEF HGHHIHH J HH HH Given the above values the following are array slices flat 1 3 Means a single array element with value N flat 1 1 TO 6 Means six elements with values LMNOPQ Array Element Value flat 1 1 L flat 1 6 Q flat 1 Means flat 1 0 TO 9 ten elements with values KL MNOPQRST In these examples a range of values of a subscript can be given instead of a single value Ifa subscript is missing completely the complete range is assumed In the third example the second subscript is missing and it is assumed by the system to be 0 TO 9 The techniques of array slicing and string slicing are similar though the latter is more widely applicable PROBLEMS ON CHAPTER 13 1 SORTING Place ten numbers in an array by reading from a DATA statement Search the array to find the lowest number Make this lowest number the value of the first element of a new array Replace it in the first array with a very large number Repeat this process making the second lowest number the second value in the new array and so on until you have a sorted array of numbers which should then be printed 2 SNAKES AND LADDERS Represent a snakes and ladders game with a 100 element numeric array Each element should contain either zero or a number in the range 10 to 90 meaning that a player should transfer to that number by going up a ladder or dow
2. vi ae ee ee I F gt i THT METET SORTED PART UNSORTED PART We take the leftmost item of the unsorted part and compare it with each item from right to left in the sorted part until we find its right place As we compare we shuffle the sorted items to the right so that when we find the right place to insert we can do so immediately without further shuffling Suppose we have reached the point where four items are sorted and we now focus on green the leftmost item in the unsorted part 1234 5678 black blue magenta red green cyan yellow white sorted part unsorted part A 1 We place green in the variable comp and set a variable p to 5 2 The variable p will eventually indicate where we think green should go When we know that green should move left then we decrease the value of p 3 We compare green with red If green is greater than nearer to Z or equal to red we exit and green stays where it is Otherwise we copy red in to position 5 thus and decrease the value of p thus 1234 5678 black blue magenta red red cyan yellow white 4 We now repeat the process but this time we are comparing green with magenta and we get 12345 678 black blue magenta magenta red cyan yellow white 5 Finally we move left again comparing green with blue This time there is no need to move or change anything We exit from the l
3. If the string cannot be converted then an error is reported LOGICAL VARIABLES AND SIMPLE PROCEDURES There is one other type of variable in SuperBASIC or rather the SuperBASIC system makes it seem so Consider the SuperBASIC statement IF windy THEN fly_kite In other BASICs you might write IF w 1 THEN GOSUB 300 In this case w 1 is a condition or logical expression which is either true or false If itis true then a subroutine starting at line 300 would be executed This subroutine may deal with kite flying but you cannot tell from the above line A careful programmer would write IF w 1 THEN GOSUB 300 REM fly_kite to make it more readable But the SuperBASIC statement is readable as it stands The identifier windy is interpreted as true or false though it is actually a floating point variable A value of 1 or any non zero value is taken as true Zero is taken as false Thus the single word windy has the same effect as a condition of logical expression The other word fly_kite is a procedure It does a job similar to but rather better than GOSUB 300 The following program will convey the idea of logical variables and the simplest type of named procedure 100 INPUT windy 110 IF windy THEN fly_kite 120 IF NOT windy THEN tidy_shed 130 DEFine PROCedure fly_kite 140 PRINT See it in the air 150 END DEFine 160 DEFine PROCedure tidy_shed 170 PRINT Sort out rubbish 180 END DEFine INPUT OUTPUT O Sort out rubbish
4. 1 See it in the air 2 See it in the air 2 See it in the air You can see that only zero is taken as meaning false You would not normally write procedures with only one action statement but the program illustrates the idea and syntax in a very simple context More is said about procedures later in this chapter LET STATEMENTS In SuperBASIC LET is optional but we use it in this manual so that there will be less chance of confusion caused by the two possible uses of The meanings of in LET count 3 and in IF count 3 THEN EXIT are different and the LET helps to emphasise this However if there are two or a few LET statements doing some simple job such as setting initial values an exception may be made For example 100 LET first 0 110 LET second 0 120 LET third 0 may be re written as 100 LET first 0 second 0 third 0 without loss of clarity or style It is also consistent with the general concept of allowing short forms of other constructions where they are used in simple ways The colon is a valid statement terminator and may be used with other statements besides LET THE BASIC SCREEN In a later chapter we will explain how other graphics facilities such as drawing circles can be handled but here we outline the pixel oriented features There are two modes which may be activated by any of the following Low resolution MODE 256 8 Colour Mode MODE 8 256 pixels across 256 down High resolution M
5. Strictly speaking a numeric expression is an expression which evaluates to a number and there are more possibilities than we need to discuss here SuperBASIC allows you to do complex things if you want to but it also allows you to do simple things in simple ways In this section we concentrate on those usual straightforward uses of mathematical features Basically numeric expressions in SuperBASIC are the same as those of mathematics but you must put the whole expression in the form of a sequence N B Some of these mathematical expressions are a little hard to represent using standard ASCII notation DJ 5 3 6 4 becomes in SuperBASIC or other BASIC 5 3 6 4 In secondary school algebra there is an expression for one solution of a quadratic equation 2 ax bx c 0 due to ASCII limitations the above line reads a x squared plus bx c 0 One solution in mathematical notation is 12 x b Nb 4ac 2a f we start with the equation 2 2x 3x 1 0 Example 1 The following program will find one solution 100 READ a b c 110 PRINT Root is b SQRT b 2 4 a c 2 a 120 DATA 2 3 1 Example 2 In problems which need to simulate the dealing of cards you can make cards correspond to the numbers 1 to 52 as follows 1 to 13 Ace two king of hearts 14 to 26 Ace two king of clubs 27 to 39 Ace two king of diamonds 40 to 52 Ace two king of spades A particular card can be ide
6. The same result could be achieved entirely with absolute graphics but it would require a little more effort CIRCLES AND ELLIPSES f you want to draw a circle you need to specify position say 50 50 radius say 40 The statement CIRCLE 50 50 40 will draw a circle with the centre at position 50 50 and radius or height 40 units see figure due to the limitations of ASCII characters this is the best possible representation or see Chapt11e_PIC 40 lt 50 50 I A circle E EEEE EEEE If you add two more parameters e g CIRCLE 50 50 40 5 You will get an ellipse The keywords CIRCLE and ELLIPSE are interchangeable Chapt11f_PIC 40 lt 50 50 II Anellipse E o PESES EEEE EEE The height of the ellipse is 40 as before but the horizontal radius is now only 0 5 of the height The number 0 5 is called the eccentricity If the eccentricity is 1 you get a circle if it is less than 1 and greater than zero you get an ellipse If you want to tilt an ellipse you can change the fith parameter for example CIRCLE 50 50 40 5 1 This will tilt the ellipse anti clockwise by one radian about 57 degrees as shown in figure or in Chapt11g_PIC 40 JAAN lt 50 50 _ Ellipse at angle one radian ee oe a a A straight angle is 180 degrees or PI radians so you can make a pa
7. b The SHIFT key affects all the letter digit and symbol keys but the CAPS LOCK key affects only letters one point 5 The CTRL lt CTRL left arrow keys delete the previous character just left of the cursor 6 The ENTER key causes a message or instruction to be entered for action by the computer 7 We use ENTER for the ENTER key 8 CLS ENTER causes part of the screen to be cleared 9 RUN ENTER causes a stored program to be executed 10 LIST ENTER causes a stored program to be displayed on the screen 11 NEW ENTER clears the main memory ready for a new program 12 Keywords of SuperBASIC are recognised in upper or lower case 13 The part of a keyword displayed in upper case is the allowed abbreviation CHECK YOUR SCORE 14 to 16 is very good Carry on reading 12 or 13 is good but re read some parts of chapter one 10 or 11 is fair but re read some parts of chapter one and do the test again Under 10 You should work carefully through chapter one again and repeat the test ANSWERS TO SELF TEST ON CHAPTER 2 1 Aninternal number store is like a pigeon hole which you can name and put numbers into 2 A LET statement which uses a particular name for the first time will cause a pigeon hole to be created and named for example LET count 1 ENTER 1 point A READ statement which uses a name for the first time will have the same effect for example READ count ENTER 1 point 3 You can find the v
8. 110 FOR row 1 TO 4 120 PRINT Row number row 130 FOR cross 1 TO 10 140 PRINT X 150 END FOR cross 160 PRINT 170 PRINT End of row number row 180 END FOR row output is Row number 1 XXXXXXKX XXX End of row number 1 Row number 2 XXX XXXX XXX End of row number 2 Row number 3 XXX XXXX XXX End of row number 3 Row number 4 XXXXXXXXK XX End of row number 4 A big advantage of SuperBASIC is that it has structures for all purposes not just FOR loops and they can all be nested one inside the other reflecting the needs of a task We can put a REPeat loop in a FOR loop The program below produces scores of two dice in each row until a seven occurs instead of crosses 100 REMark Dice rows 110 FOR row 1 TO4 120 PRINT Row number row 130 REPeat throws 140 LET die1 RND 1 TO 6 150 LET die2 RND 1 TO 6 160 LET score die1 die2 170 PRINT score 180 IF score 7 THEN EXIT throws 190 END REPeat throws 200 PRINT End of row row 210 END FOR row sample output Row number 1 811637 End of row number 1 Row number 2 462945127 End of row number 2 Row number 3 7 End of row number 3 Row number 4 624997 End of row number 4 The third feature of loops in SuperBASIC allows more flexibility in providing the range of values ina FOR loop The following program illustrates this by printing all the divisible numbers from 1 to 20 A divisible number is divisible evenly by a number
9. 130 FOR num 0 TO 9 140 READ flat floor num REMark Golfer goes in 150 END FOR num 160 END FOR floor 170 REMark End of input 180 FOR floor 0 TO 2 190 PRINT Floor number floor 200 FOR num 0 TO 9 210 PRINT Flat num flat floor num 220 END FOR num 230 END FOR floor 240 DATA A B C D E F G H I J 250 DATA K L M N O P Q R S T 260 DATA U V W X Y Z Sn The output starts Floor number 0 FLat 0 A FLat 1 B FLat2 C and continues giving the thirty occupants ARRAY SLICING You may find this section hard to read though it is essentially the same concept as string slicing You will probably need string slicing if you get beyond the learning stage of programming The need for array slicing is much rarer and you may wish to omit this section particularly on a first reading We now use the golfers flats to illustrate the concept of array slicing The flats will be numbered 0 to 9 to keep to single digits and names will be single characters for space reasons 2 0 2 1 2 2 2 2 2 4 2 5 2 6 2 7 2 8 2 9 H HH fat UIV IWHXIYIZI I 1S 11 H HH 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 H H HH fat IK ILIIM INI O IP HIQIIR ISIIT H H HH 0 0 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9
10. DIM a 2 3 4 i PRINT DIMN A 1 will print 2 ii PRINT DIMN A Z will print 3 iii PRINT DIMN A 3 will print 4 iv PRINT DIMN A will print 2 v PRINT DIMN A 4 will print 0 DIR microdrives DIR will obtain and display in the window attached to the specified or default channel Microdrives the directory of the cartridge in the specified Microdrive syntax DIR device The device specification must be a valid Microdrive device The directory format output by DIR is as follows free_sectors the number of free sectors available_sectors the maximum number of sectors on this cartridge file_name a SuperBASIC file name screen format Volume name free_sectors available_sectors sectors file_name file_ name example i DIR mdv1_ ii DIR mdv2_ iii DIR mdv amp microdrive_number amp _ screen format BASIC 183 221 sectors demo_1 demo_1_old demo_2 DN operator DNV is an operator which will perform an integer divide syntax numeric_expression DIV numeric_expression example i PRINT 5 DIV 2 will output 2 ii PRINT 5 DIV 2 will output 3 DLINE BASIC DLINE will delete a single line or a range of lines from a SuperBASIC program syntax range line_number TO line_number 1 line_number TO 2 TO line_number 3 line_number 4 DLINE range range where 1 will delete a range of lines 2 will delete from the specified line to the end 3 will delete from the start to
11. EXIT bandit We can conceive of no more complex type of problem than this with a single loop SuperBASIC can easily handle it if you want it to NESTED LOOPS Consider the following FOR loop which PLOTS a row of points of various randomly chosen colours not black 100 REMark Row of pixels 110 PAPERO CLS 120 LET up 50 130 FOR across 20 TO 60 140 INK RND 2 TO 7 150 POINT across up 160 END FOR across This program plots a row of points thus If you want to get say 51 rows of points you must plot a row for values up from 30 to 80 But you must always observe the rule that a structure can go completely within another or it can go properly around it It can also follow in sequence but it cannot mesh with another structure Books about programming often show how FOR loops can be related with a diagram like gt gt gt II HII HII Right gt gt nested Right Wrong Sequence Meshed In SuperBASIC the rule applies to all structures You can solve all problems using them properly We therefore treat the FOR loop as an entity and design a new program FOR up 30 TO 80 FOR across 20 TO 60 INK RND 2 TO 7 POINT across up END FOR across END FOR up When we translate this into a program we are entitled not only to expect it
12. RND 100 ENTER 80 END REPeat star ENTER The important thing to note here is that the program continues until colour becomes 6 Control then escapes from the loop to the point just after line 80 Since there are no program lines after 80 the program stops Another important concept has been introduced It is the idea of a decision IF colour 6 THEN EXIT star This is another very useful structure because it is a choice of doing something or not we call it a simple binary decision Its general form is IF condition THEN statement s You will see later how the two concepts of repetition or looping and decision making or selection are the main structures for program control You can stop the program by pressing the break keys hold down CTRL and then press the space bar SELF TEST ON CHAPTER 3 You can score a maximum of 13 points from the following test Check your score with the answers in the Answers to self test section at the end of this Beginner s Guide 1 What is a pixel 2 How many pixels fit across the screen in the low resolution mode 3 How many pixels fit from bottom to top in low resolution mode 4 What are the two numbers which determine the address or position of a graphics point on the screen 5 How many colours are available in the low resolution mode 6 Name the keywords which do the following i draw a line ii select a colour for drawing iii select a background colour iv draw a border 5 poin
13. RND O TO 1 120 IF rain THEN 130 PRINT Take a bus 140 ELSE 150 PRINT Walk 160 END IF All these are binary decisions The first two examples are simple either something happens or it does not The third is a general binary decision with two distinct possible courses of action both of which must be defined You can omit THEN in the long forms if you wish In the short form you can substitute for THEN EXAMPLE Consider a more complex example in which it seems natural to nest binary decisions This type of nesting can be confusing and you should only do it if it seems the most natural thing to do Careful attention to layout particularly indenting is especially important Analyse a piece of text to count the number of vowels consonants and other characters Ignore spaces For simplicity the text is all upper case Data COMPUTER HISTORY WAS MADE IN 1984 Design Read in the data FOR each character IF letter THEN IF vowel increase vowel count ELSE increase consonant count END IF ELSE IF not space THEN increase other count END IF END FOR PRINT results Program 100 REMark Character Counts 110 RESTORE 290 120 READ text 130 LET vowels 0 cons 0 others 0 140 FOR num 1 TO LEN text 150 LET ch text num 160 IF ch gt A AND ch lt Z 170 IF ch INSTR AEIOU 180 LET vowels vowels 1 190 ELSE 200 LET cons cons 1 210 END IF 220 ELSE 230 IF ch lt gt THEN
14. address numeric_expression PEEK address byte access PEEK_W address word access PEEK_L address long word access example i PRINT PEEK 12245 byte contents of location 12245 ii PRINT PEEK_W 12 word contents of locations 12 and 13 iii PRINT PEEK_L 1000 long word contents of location 1000 Warning For word and long word access the specified address must be an even address PENUP PENDOWN turtle graphics Operates the pen in turtle graphics If the penis up then nothing will be drawn If the pen is down then lines will be drawn as the turtle moves across the screen The line will be drawn in the window attached to the specified or default channel The line will be drawn in the current ink colour for the channel to which the output is directed syntax PENUP channel PENDOWN channel example i PENUP will raise the pen in the default channel ii PENDOWN 2 will lower the pen in the window attached to channel 2 PI maths function Plis a function which returns the value of x syntax Pl example PRINT PI POINT POINT_R graphics POINT plots a point at the specified position in the window attached to the specified or default channel The point is plotted using the graphics coordinates system relative to the graphics origin If POINT_Ris used then all points are specified relative to the graphics cursor and are plotted relative to each other Multiple points can be plotted with a single call to POINT s
15. called windows as shown below Note that in order to fit these windows into the area covered by a television screen some pixels around the border are not used in Television mode 0 to 511 gt 0 to 511 gt HITT HTT HITT 2 1 1 and 2 olol to to 255 255 HITT HITT 0 0 HT Ne ee V Monitor Television This windows are indentified by 0 1 and 2 so that you can relate various effects to particular windows For example CLS will clear window 1 the system chooses so if you want the left hand area cleared you must type CLS 2 f you want a different paper background colour type for green PAPER4 CLS or PAPER 2 4 CLS 2 If you want to clear window 2 to the background colour green The numbers 0 1 and 2 are called channel numbers In this particular case they enable you to direct certain effects to the window of your choice You will discover later that channel numbers have many other uses but for the moment note that all of the following statements may have a channel number The third column shows the default channel the one chosen by the system if you do not specify one Note that windows may overlap If you use a TV screen the system automatically overlaps wi
16. come 0 210 END FOR item 220 FOR k 1 TO 7 send k come k 230 END DEFine The following additional lines will test the sort procedure First type AUTO 10 to start the line numbers from 10 onwards 10 REMark Test Sort 20 DIM row 7 3 back 7 3 30 LET row 0 7 40 FORk 1 TO7 READ row k 50 sort row back 60 PRINT back 70 DATA EEL DOG ANT GNU CAT BUG FOX Output ANT BUG CAT DOG EEL FOX GNU COMMENT This program illustrates how easily you can handle arrays in SuperBASIC All you have to do is use the array names for passing them as parameters or for printing the whole array Once the procedure is saved you can use MERGE mdv1_sort to add it to a program in main memory You now have enough understanding of techniques and syntax to handle a more complex screen layout Suppose you wish to represent the hands of four card players A hand can be represented by something like H A37Q C 59J D 610K 24Q To help the presentation the Hearts and Diamonds will be printed in red and the Clubs and Spades in black A suitable STRIP colour might be white The general background could be green and a table may be a colour obtained by mixing two colours METHOD Since a substantial amount of character printing is involved it is best to start planning in terms of the pixel screen You can see that you need to provide for twelve lines of characters with some space between lines and a total screen height of 256 p
17. get day from clock DAY numeric_expression get day from supplied parameter example i PRINT DAY output the day ii PRINT DAY 234567 output the day represented by 234567 seconds DEFine FuNction END DEFine functions and procedures DEFine FuNction defines a SuperBASIC function The sequence of statements between the DEFine function and the END DEFine constitute the function The function definition may also include a list of formal parameters which will supply data for the function Both the formal and actual parameters must be enclosed in brackets If the function requires no parameters then there is no need to specify an empty set of brackets Formal parameters take their type and characteristics from the corresponding actual parameters The type of data returned by the function is indicated by the type appended to the function identifier The type of the data returned in the RETURN statement must match An answer is returned from a function by appending an expression to a RETurn statement The type of the returned data is the same as type of this expression A function is activated by including its name ina SuperBASIC expression Function calls in SuperBASIC can be recursive that is a function may call itself directly or indirectly via a sequence of other calls Syntax formal_parameters expression expression actual_parameters expression expression type DEF FuNction identifier typ
18. ii PRINT EXP 3 141592654 FILL graphics FILL will turn graphics fill on or off FILL will fill any non re entrant shape drawn with the graphics or turtle graphics procedures as the shape is being drawn Re entrant shapes must be split into smaller non re entrant shapes When you have finished filling FILL 0 should be called syntax switch numeric_expression range 0 1 FILL channel switch example i FILL 1 LINE 10 10 TO 50 50 TO 30 90 TO 10 10 FILL O will draw a filled triangle ii FILL 1 CIRCLE 50 50 20 FILL O will draw a filled circle FILL string arrays FILL is a function which will return a string of a specified length filled with a repetition of one or two characters syntax FILL string_expression numeric_expression The string expression supplied to FILL must be either one or two characters long example i PRINT FILL a 5 will print aaaaa ii PRINT FILL 00 7 will print O000000 iii LET a a amp FILL 10 FLASH windows FLASH turns the flash state on and off FLASH is only effective in low resolution mode FLASH will be effective in the window attached to the specified or default channel syntax switch numeric_expression range 0 1 FLASH channel switch where switch 0 will turn the flash off switch 1 will turn the flash on example 100 PRINT A 110 FLASH 1 120 PRINT flashing 130 FLASH 0 140 PRINT word Warning Writing over part of a flashing cha
19. parameter is specified the parameter is taken to be the new seed If no parameter is specified then the generator is reseeded from internal information syntax RANDOMISE numeric_expression example i RANDOMISE set seed to internal data ii RANDOMISE 3 2235 set seed to 3 2235 RECOL windows RECOL will recolour individual pixels in the window attached to the specified or default channel according to some preset pattern Each parameter is assumed to specify in order the colour in which each pixel is recoloured i e the first parameter specifies the colour with which to recolour all black pixels the second parameter blue pixels etc The colour specification must be a solid colour i e it must be in the range O to 7 syntax c0 new colour for black c1 new colour for blue c2 new colour for red c3 new colour for magenta c4 new colour for green c5 new colour for cyan c6 new colour for yellow c7 new colour for white RECOL channel cO cl c2 c3 c4 c5 c6 c7 example RECOL 2 3 4 5 6 7 1 0 recolour blue to magenta red to green magenta to cyan etc REMark RE Mark allows explanatory text to be inserted into a program The remainder of the line is ignored by SuperBASIC syntax REMark text example REMark This is a comment ina program REMark is used to add comments to a program to aid clarity RENUM RENUM allows a group or a series of groups of SuperBASIC line numbers to be changed If no
20. 0 whole screen default is no parameter part 1 top excluding the cursor line part 2 bottom excluding the cursor line SCROLL channel distance part If the distance is positive then the contents of the screen will be shifted down example i SCROLL 10 scroll down 10 pixels ii SCROLL 70 scroll up 70 pixels iii SCROLL 10 2 scroll the lower part of the window up 10 pixels SDATE clock The SDATE command allows the QCs clock to be reset syntax year numeric_expression month numeric_expression day numeric_expression hours numenc_express on minutes numeric_expression seconds numeric_expression SDATE year month day hours minutes seconds example i SDATE 1984 4 2 0 0 0 ii SDATE 1984 1 12 9 30 0 iii SDATE 1984 3 21 0 0 0 SELect END SELect conditions SELect allows various courses of action to be taken depending on the value of a variable define select_variable numeric_variable select_item expression expression TO expression select_list select_item select_item LONG Allows multiple actions to be selected depending on the value of a selectvariable The select variable is the last item on the logical line A series of SuperBASIC statements follows which is terminated by the next ON statement or by the END SELect statement If the select item is an expression then a check is made within approximately 1 partin 10 otherwise for expression TO expression the ra
21. 10 will add a 10 pixel thick transparent border to the current window transparent because no colour was specified and BORDER 2 0 7 0 will add a 2 pixel thick black and white stipple border BLOCK You can specify a block s size position and colour with a single statement It is placed in the pixel co ordinate system relative to the current window or screen For example BLOCK 5 10 20 50 100 2 would create a block in the 5 window ata position 50 units across and 100 units down It would be 10 units wide and 20 units high Its colour would be red It is worth noting that WINDOW and BLOCK statements work without alteration in 4 and 8 colour mode though the colours may vary because the across values are always ona 0 to 511 scale and there are always 256 pixel positions down SPECIAL PRINTING CSIZE You can alter the size of characters For example CSIZE 3 1 will give the largest possible characters and CSIZE 0 0 will give the smallest The first number must be 0 1 2 or 3 and determines the width The second must be 0 or 1 and determines the height The normal sizes are MODE 4 CSIZE 0 0 MODE 8 CSIZE 2 0 The number of lines and columns available for each character size is dependent on whether the output is viewed on a monitor or ona television set the row and column sizes given are for a monitor those for a television set will be smaller and also will vary between different televisions If you are using low resolution
22. 160 DEFine PROCedure item num price 170 IF num lt 3 THEN LET price 300 10 num 180 IF num gt 4 THEN LET price 12 num 190 END DEFine Output 448 The parameters num and price are both automatically local so there can be no problems The diagrams show how information passes from main program to procedure and back Menu numbers Main Procedure Program Item lI prices That is enough about procedures and parameters for the present FUNCTIONS You already know how a system function works For example the function SQRT 9 computes the value 3 which is the square root of 9 We say the function returns the value 3 A function like a procedure can have one or more parameters but the distinguishing feature of a function is that it returns exactly one value This means that you can use it in expressions that you already have You can type PRINT 2 SQRT 9 and get the output 6 Thus a function behaves like a procedure with one or more value parameters and exactly one variable parameter holding the returned value that variable parameter is the function name itself The parameters need not be numeric LEN string has a string argument but it returns the numeric value 6 EXAMPLE Re write the program of the last section which used price as a variable parameter Let price be the name of the function The value to be returned is defined by the RET
23. 2 whichis less thanthe square root then 8 2 must be greater than it It follows that if we take any guess and computer number guess we have two numbers one too small and one too big We take the average of these numbers as our next approximation and thus get closer to the correct answer We repeat this process until successive approximations are so close as to make little difference 100 REMark Square Roots 110 LET number 8 120 LET approx number 2 130 REPeat root 140 LET newval approx number approx 2 150 IF newval approx THE EXIT root 160 LET approx newval 170 END REPeat root 180 PRINT Square root of number is newval sample output Square root of 8 is 2 828427 Notice that the conditional EXIT from the loop must be in the middle The traditional structures do not cope with this situation as well as SuperBASIC does The signin line 150 means approximately equal to that is equal to within 0000001 of the values being compared NUMERIC OPERATIONS SuperBASIC allows th eusual mathematical operations You may notice that they ar elike functions with exactly two operands each It is also conventional in these cases to put an operand on each side of the symbol Sometimes the operation is denoted by a familiar symbol such as or Sometimes the operation is denoted by a keyword like DIV or MOD but there is no real difference Numeric operations have an order of priority For example the result of
24. 23 b ROMOEH A3 a 24b A1 DBGL a 25 b A2 SP2 a 26 b SP3 DSMCL a 27 b IPLOL SP1 a 28 b BERRL SPO a 29 b IPL1L VP12 a 30 b EXTINTL VM12 a 31 b VIN VIN a 32 b VIN The connector on the QL is a 64 way male DIN 41612 indirect edge connector An L appended to a signal name indicates that the signal is active low A0 A19 68008 address lines RDWL Read Write ASL Address Strobe DSL Data Strobe BGL Bus Grant DSMCL Data Strobe Master Chip CLKCPU CPU Clock E 6800 peripherals clock RED Red BLUE Blue GREEN Green CSYNCL Composite Sync VSYNCH Vertical Sync ROMOEH ROM Output Enable FCO Processor status FC1 Processor status FC2 Processor status RESETCPUL Reset CPU DTACKL Data acknowledge BRL Bus request VPAL Valid Peripheral Address IPLOL Interrupt Priority Level 5 IPL1L Interrupt Priority Level 2 BERRL Bus Error EXTINTL External Interrupt DBGL Data bus grab SP0 SP3 Select peripheral 0 to 3 VIN 9V DC nominal 500mA max VM12 12V VP12 12V GND ground Miscellaneous itis not intended that the following description of the QL peripheral expansion mechanism be sufficient to implement an actual expansion device but rather be read to gain a basic understanding of the expansion mechanism Single or multiple peripherals may be added to the QL up to a maximum of 16 devices A single peripheral can be plugged directly into the QL Expansion Slot while multiple peripheral
25. 9 0 identifier letter letter number _ example i a ii limit_1 iii current_guess iv counter An identifier must begin with a letter followed by a sequence of letters numbers and underscores and can be up to 255 characters long Upper and lower case characters are equivalent Identifiers are used in the SuperBASIC system to identify Variables Procedures Functions Repetition loops etc WARNING NO meaning can be attributed to an identifier other than its ability to identify constructs to SuperBASIC SuperBASIC cannot infer the intended use of an identifier from the identifier s name JOYSTICK The joystick ports marked CTL1 and CTL2 allow two joysticks to be attached to the QL The joysticks are arranged to generate specific key depressions when moved ina specific way and any program which uses a joystick must be able to adapt to these keys The QL keyboard can be read directly using the KEYROW function CTL1 CTL2 moe key key up cursor up F4 down cursor down F2 left cursor left F1 right cursor right F3 fire space F5 The joystick ports can be used for adding other more general purpose control devices to the QL Joysticks for other computers using a 9 way D connector require an adaptor to be used with the QL Such an adaptor is available from Sinclair Research KEYWORD SuperBASIC keywords are identifiers which are defined in the SuperBASIC Keyword Reference Guide Keywords have the same form as a S
26. PAPER 5 4 CLS 5 130 CLOSE 5 Notice that each window can have its own features such as paper ink etc The fact that a window has been opened does not mean that it is the current default window You can change the position or shape of an opened window without closing it and reopening it Try adding two lines to the previous program 124 WINDOW 5 300 100 110 65 126 PAPER 5 2 CLS 5 Re run the program and you will find a red window within the original green one This red window is now the one associated with channel 5 see figure GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG I6Gt CC IGGIRRRRRRRRRRRRRRRRRRRRRRRRRRIGG IGGIRRRRRRRRRRRRRRRRRRRRRRRRRRIGG IGGIRRRRRRRRRRRRRRRRRRRRRRRRRRIGG IGGIRRRRRRRRRRRRRRRRRRRRRRRRRRIGGI GG GG GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG BORDER You can place a border round the edge of the screen or a window For example BORDER 5 6 would create a border round the channel 5 window It would be 6 units thick and the size of the window would be correspondingly reduced The border would be transparent protecting anything that was under it You can specify a coloured border by the usual method BORDER 5 6 2 would produce a red border You can make a border of other colours and textures by the usual methods For example BORDER
27. PRINT 7 3 2 is 13 because the multiplication has a higher priority However PRINT 7 3 2 will output 20 because brackets over ride the usual priority As you will see later so many things can be done with SuperBASIC expressions that a full statement about priority cannot be made at this stage see the Concept Reference Guide if you wish but the operations we now deal with have the following order of priority highest raising to a power multiplication and division including DIV MOD lowest add and subtract The symbols and are also used with only one operand which simply denotes positive or negative Symbols used in this way have the highest priority of all and can only be over ridden by the use of brackets Finally if two symbols have equal priority the leftmost operation is performed first so that PRINT 7 2 5 will cause the subtraction before the addition This might be important if you should ever deal with very large or very small numbers Operation Symbol Examples Results Note Add 7 6 6 13 6 Subtract 7 6 6 0 4 Multiply 3 2 16 3 2 1 3 6 3 Divide 7 2 3 5 Do not divide by zero 17 5 3 4 Raise to power 441 5 8 Integer divide DIV 8 DN 2 4 Integers only 7 DN 2 3 Do not divide by zero Modulus MOD 13 MOD 5 3 21 MOD 70 17 MOD 87 Modulus returns the remainder part of a division Any attempt to divide by zero will generate an error and terminate program exection NUMERIC EXPRESSIONS
28. TO 400 140 LET die1 RND I TO 6 150 LET die2 RND I TO 6 160 LET score diel die2 170 IF score 2 THEN LET two two 1 180 IF score 3 THEN LET three three 1 190 IF score 4 THEN LET four four 1 200 IF score 5 THEN LET five five 1 210 IF score 6 THEN LET six six 1 220 IF score 7 THEN LET seven seven 1 230 IF score 8 THEN LET eight eight 1 240 IF score 9 THEN LET nine nine 1 250 IF score 10 THEN LET ten ten 1 260 IF score 11 THEN LET eleven eleven 1 270 IF score 12 THEN LET twelve twelve 1 280 END FOR throw 290 PRINT two three four five six 300 PRINT seven eight nine ten eleven twelve In the above program we establish eleven simple variables to store the tally of the scores If you plot the tallies printed at the end you find that the bar chart is roughly triangular The higher tallies are for scores six seven eight and the lower tallies are for 2 and 12 As every dice player knows the reflects the frequency of the middle range of scores six seven eight and the rarity of twos or twelves 100 REMark Dice2 110 DIM tally 12 120 FOR throw 1 TO 400 130 LET die_1 RND 1 TO 6 140 LET die_2 RND 1 TO 6 150 LET score die_1 die 2 160 LET tally score tally score 1 170 END FOR throw 180 FOR number 2 TO 12 PRINT tally number In the first FOR loop using throw the subscript of the array variable is score This mea
29. act as an automatic stop STRIP windows STRIP will set the current strip colour in the window attached to the specified or default channel The strip colour is the background colour which is used when OVER 1 is selected Setting PAPER will automatically set the strip colour to the new PAPER colour syntax STRIP channel colour example i STRIP 7 set a white strip ii STRIP 0 4 2 set a black and green stipple strip Comment The effect of STRIP is rather like using a highlighting pen TAN maths functions TAN will compute the tangent of the specified argument The argument must be in the range 30000 to 30000 and must be specified in radians syntax TAN numeric_expression range 30000 30000 example i TAN 3 print tan 3 ii TAN 3 141592654 2 print tan PI 2 TURN TURNTO turtle graphics TURN allows the heading of the turtle to be turned through a specified angle while TURNTO allows the turtle to be turned to a specific heading The turtle is turned in the window attached to the specified or default channel The angle is specified in degrees A positive number of degrees will turn the turtle anti clockwise and a negative number will turn it clockwise Initially the turtle is pointing at 0 degrees that is to the right hand side of the window syntax angle numeric_expression angle in degrees TURN channel angle TURNTO channel angle example i TURN 90 turn through 90 degrees ii TURNTO 0 turn
30. array variable name All the variables in an array share one name but each has a different subscript 3 You must declare an array giving its size dimension in a DIM statement usually placed near the beginning of a program before the declared array is used 4 The distinguishing number of an array variable is called the subscript 5 Houses ina street share the same street name but each has its own number Beds ina hospital ward may share the name of the ward but each bed may be numbered Cells in a prison block may have a common block name but a different number Holes on a golf course e g the fifth hole at Royal Birkdale 6 A FOR loop terminates when the process corresponding to the last value of the loop variable has been completed 7 A FOR loop s name is also the name of the variable which controls the loop 8 The two phrases for this variable are loop variable or control variable 9 The values of a loop variable may be used as subscripts for array variable names Thus as the loop proceeds each array variable is visited once 10 Both FOR loops and REPeat loops a have an opening keyword REPeat FOR b have a closing statement END REPeat name END FOR name c have a loop name Only the FOR loop has d a loop variable or control variable four points CHECK YOUR SCORE This test is more searching than the previous ones 15 or 16 is excellent Carry on reading 13 or 14 is ve
31. can either be relative to this cursor or can be absolute i e relative to the graphics origin 0 Ee S 100 III III Ily II II II II II III III III 0 0 x gt a EE E EEEN EEA E The Graphics Coordinate System The scaling factor is such that the full distance in the vertical direction in the specified or default window has length 100 by default and can be changed with the SCALE command The scale in the x direction is equal to the scale in the y direction However the length of line which can be drawn in the x direction is dependent on the shape of the window Increasing the scale factor increases the maximum size of the figure which can be drawn before the window size is exceeded If the graphics output is switched to a different size of window then the subsequent size of the output is adjusted to fit the new window If the figure exceeds its output window then the figure is clipped It is useful to consider the window to be a window onto a larger graphics space in which the figures are drawn The SCALE command allows the graphics origin to be set so allowing the window to be moved around the graphics space The graphics procedures are output to the window attached to the specified or default channel and the output is drawn in the INK colour for that channel CIRCLE draw an ellipse or a circle LINE draw a line absolute ARC draw an arc o
32. can write LET pet1 CAT LET pet2 DOG IF pet1 lt pet2 THEN PRINT Meow The output will be Meow because in this context the symbol lt means earlier nearer to A in the alphabet SuperBASIC makes comparisons sensible For example you would expect cat to come before DOG and ERD98L to come before ERD746L A simplistic approach blindly using internal character coding would give the wrong result in both the above cases but try the following program which finds the earliest of two character strings 100 INPUT item1 item2 110 IF item1 lt item2 THEN PRINT item1 120 IF item1 item2 THEN PRINT Equal 130 IF item1 gt item2 THEN PRINT item2 cat dog cat cat DOG cat ERD98L ERD746L ERD98L ABC abc ABC The Concept Reference Guide section will give full details about the way comparisons of strings are made in SuperBASIC VARIABLES AND NAMES IDENTIFIERS Most BASICs have numeric and string variables As in other BASICs the distinguishing feature of a string variable name in SuperBASIC is the dollar sign on the end Thus numeric count string word sum high_st total day_of_week You may not have met such meaningful variable names before though some of the more recent BASICs do allow them The rules for identifiers in SuperBASIC are given in the Concept Reference Guide The maximum length of an identifier is 255 characters Your choice of identifiers is a personal one Sometimes
33. colour refers to the colour coding used on the 8 way cable and connector available from Sinclair Research Limited Pin designation is as shown in the diagram below sleeve colour pin function signal on QL RGB colour lead 1 PAL composite PAL 4 orange 2 GND ground green 3 VIDEO composite monochrome video 3 brown 4 CSYNC composite sync 2 yellow 5 VSYNC vertical sync 1 blue 6 GREEN green 1 red 7 RED red 1 white 8 BLUE blue 1 purple A monochrome monitor can be connected using a screened lead with a 3 way or an 8 way DIN plug at the QL end Only pins 2 ground and 3 composite video need to be connected via the cable to the monitor The connection at the monitor end will vary according to the monitor but is usually a phono plug The monitor must have a 75 ohm 1V pk pk composite video non inverting input which is the industry standard Both 3 way DIN plugs and phono plugs are available from audio shops RGB CONNECTOR 8 blue POWER CONNECTOR 7 red 6 green 76 I 3 composite 3 8 1 1 composite PAL monochrome IIS 47 ll 5 vertical synch 4 composite synch II 27 2 ground Diagram of Monitor Connector as viewed from rear of QL showing pin numbers and functions An RGB colour monitor can be connected using a lead with an
34. enable the rows to be easily readable The program thus works well in either graphics mode CONCLUSION We have tried to show how you can use SuperBASIC to solve problems We have shown how simple tasks can be performed in simple ways When the task is inherently complex like manipulating arrays or designing screen graphics SuperBASIC enables it to be handled efficiently with maximum possible clarity If you were a beginner and you have worked through a fair proportion of this guide you will have started well on the road to good programming If you were already experienced we hope that you will appreciate and exploit the extra features offered by SuperBASIC So enormous is the range of tasks which can be done with SuperBASIC that we have only been able to touch a fraction of them in this guide We cannot guess at which of the thousands of possibilities you will attempt but we hope that you will find them fruitful stimulating and fun ANSWERS TO SELF TEST ON CHAPTER 1 1 Use the BREAK sequence to abandon a running program because a something is wrong and you do not understand it b itis longer of interest c any other problem three points 2 The RESET button is on the right hand side of the computer 3 The effect of the RESET button is rather like switching the computer off and on again 4 The SHIFT key a is only effective while you hold it down whereas the CAPS LOCK key stays effective after you have pressed it one point
35. how the actual parameters must be processed and so have no type associated with them The items in each list of parameters are paired off in order when the function or procedure is called and the formal parameters become equivalent to the actual parameters There are three distinct ways of using parameters If the actual parameter is a single variable and if data is assigned to the formal parameter in the function or procedure then the data is also assigned to the corresponding actual parameter If the actual parameter is an expression then assigning data to the corresponding formal parameter will have no effect outside the procedure Note that a variable can be turned into an expression by enclosing it within brackets if the actual parameter is a variable but has not previously been set then assigning data to the corresponding formal parameter will set the variable specified as the actual parameter Variables can be defined to be local to a function or procedure with the LOCal statement Local variables have no effect on similarly named variables outside the function or procedure in which they are defned and so allow greater freedom in choosing sensible variable names without the risk of corrupting external variables A local variable is available to any inside function or procedure called from the procedure function in which it is declared to be local unless the function or procedure called contains a further local declaration of the same v
36. it ina way which moves all the time from known ideas to new ones or new uses of old ones The movement is also towards greater economy f you understand the first two or three methods perfectly well you may prefer to move straight onto methods 4 and 5 But if you are in any doubt methods 1 2 and 3 will help to clarify things Program 1 100 DIM high_st 4 3 110 LET high_st I VAL 120 LET high_st 2 HAL 130 LET high_st 3 MEL 140 LET high st 4 DEL 150 PRINT high_st 1 high st 2 160 PRINT high_st 3 high st 4 Program 2 100 DIM high st 4 3 110 READ high_st 1 high_st 2 high_st 3 high_st 4 120 PRINT high_st 1 high_st 2 130 PRINT high_st 3 high_st 4 140 DATA VAL HAL MEL DEL This shows how to economise on variable names but the constant repeating of high_st is both tedious and the cause of the cluttered appearance of the programs We can again use a known technique the REPeat loop to improve things further We set up a counter number which increases by one as the REPeat loop proceeds Program 3 100 RESTORE 190 110 DIM high_st 4 3 120 LET number 0 130 REPeat houses 140 LET number number 1 150 READ high_st number 160 IF num 4 THEN EXIT houses 170 END REPeat houses 180 PRINT high_st 1 high_st 2 high_st 3 high_st 4 190 DATA VAL HAL MEL DEL This special type of loop in which something has to be done a c
37. mdvi_guess iii LOAD neti_3 iv LOAD serl_e LN LOG10 maths functions LN will return the natural logarithm of the specified argument LOG10 will return the common logarithm There is no upper limit on the parameter other than the maximum number the computer can store syntax LOG10 numenic_expression range greater than zero LN numeric_expression range greater than zero example i PRINT LOG10 20 ii PRINT LN 3 141592654 LOCal functions and procedures LOCal allows identifiers to be defined to be LOCal to a function or procedure Local identifiers only exist within the function or procedure in which they are defined or in procedures and functions called from the function or procedure in which they are defined They are lost when the function or procedure terminates Local identifiers are independent of similarly named identifiers outside the defining function or procedure Arrays can be defined to be local by dimensioning them within the LOCal statement The LOCal statement must precede the first executable statement in the function or procedure in which it is used syntax LOCal identifier identifier example i LOCal a b c 10 10 ii LOCal temp_data comment Defining variables to be LOCal allows variable names to be used within functions and procedures without corrupting meaningful variables of the same name outside the function or procedure LRUN devices microdrives LRUN will load and run a SuperBASIC program
38. numeric_expression angle numeric_expression range 2 to Ph parameters x y 1 radius eccentricity angle 2 where 1 will draw a circle 2 will draw an ellipse of specified eccentricity and angle CIRCLE channel parameters parameters x horizontal offset from the graphics origin or graphics cursor y vertical offset from the graphics origin or graphics cursor radius radius of the circle eccentricity the ratio between the major and minor axes of an ellipse Angle the orientation of the major axis of the ellipse relative to the screen vertical The angle must be specified in radians example i CIRCLE 50 50 20 a circle at 50 50 radius 20 ii CIRCLE 50 50 20 0 5 0 an ellipse at 50 50 major axis 20 eccentricity 0 5 and aligned with the vertical axis CLEAR CLEAR will clear out the SuperBASIC variable area for the current program and will release the space for Qdos syntax CLEAR example CLEAR Comment CLEAR can be used to restore to a known state the SuperBASIC system For example if a program is broken into or stops due to an error while it is ina procedure then SuperBASIC is still in the procedure even after the program has stopped CLEAR will reset the SuperBASIC See CONTINUE RETRY CLOSE devices CLOSE will close the specified channel Any window associated with the channel will be deactivated syntax channel numeric_expression CLOSE channel example i CLOSE 4 ii CLOSE inp
39. other Write a program to simulate this entirely with LET and PRINT statements Use a third person Sue to hold Bill s money while he accepts Ben s 7 Re write the program of problem 6 so that a DATA statement holds the two numbers to be exchanged CHAPTER 3 DRAWING ON THE SCREEN In order to use either a television set or monitor with the QL two different screen modes are available MODE 8 permits eight colour displays with a graphics resolution of 256 by 256 pixels and large characters for display on a television set MODE 4 allows four colours with a resolution of 512 by 256 pixels and a maximum of eighty character lines for which a monitor must be used for successful display However it would be unfortunate if a program was written to draw circles or squares in one mode and produced ellipses or rectangles in another mode as some systems do We therefore provide a system of scale graphics which avoids these problems You simply choose a vertical scale and work to it The other type of graphics pixel oriented is also available and is described fully ina later chapter Suppose for example that we choose a vertical scale of 100 and we wish to draw a line from position 50 60 to position 70 80 This diagram is Chapt3A_pic in the file compilations 100 70 across 80 up 50 across 60 up 0 Scale Graphics A COLOURED LINE We need to specify thr
40. other than the total memory capacity of the computer An array of data is stored such that the last index defined cycles round most rapidly the array defined by DIM array 2 4 will be stored as 0 0 low address 2 3 2 4 high address The element referred to by array a b c is equivalent to the element referred to by array a b c DIM dimension an array DIMN find out about the dimensions of an array SuperBASIC includes most of the functions procedures and constructs found in other dialects of BASIC Many of these functions are superfluous in SuperBASIC but are included for compatibility reasons GOTO use IF REPEAT etc GOSUB use DEFine PROCedure ON GOTO use SELect ON GOSUB use SELect Some commands appear not to be present They can always be obtained by using a more general function For example there are no LPRINT or LLIST statements in SuperBASIC but output can be directed to a printer by opening the relevant channel and using PRINT or LIST LPRINT use PRINT LLIST use LIST VAL not required in SuperBASIC STR not required in SuperBASIC IN not applicable to 68008 processor OUT not applicable to 68008 processor Almost all forms of BASIC require the VAL x and STR x functions in order to be able to convert the internal codified form of the value of a string expression to or from the internal codified form of the value of a numeric expression These functions are redundant in SuperBASIC because of the prov
41. others others 1 240 END IF 250 END FOR num 260 PRINT Vowel count is vowels 270 PRINT Consonant count is cons 280 PRINT Other count is others 290 DATA COMPUTER HISTORY WAS MADE IN 1984 Output Vowel count is 9 Consonant count is 15 Other count is 4 MULTIPLE DECISIONS SELect Where there are three or more possible actions and none is dependant ona previous choice the natural structure to use is SELect which enables selection from any number of possibilities EXAMPLE A magic snake grows without limit by adding a section to its front Each section may be up to twenty units long and may be a new colour or it may remain the same Each new section must grow in one of the directions North South East or West The snake starts from the centre of the window Method At any time while the snake is still on the screen you choose a random length and ink colour easily The direction may be selected by a number 1 2 3 or 4 as shown North 1 West 4 East 2 South 3 Design Select PAPER Set snake to centre of window REPeat Choose direction colour length of growth FOR unit 1 to growth Make snake grow north south east or west IF snake is off window THEN EXIT END FOR END REpeat PRINT end message Program 100 REMark Magic Snake 110 PAPERO CLS 120 LET across 50 up 50 130 REPeat snake 140 LET direction RND I TO 4 colour RND 2 TO 7 150 LET g
42. parameters are specified then RENUM will renumber the entire program The new listing will begin at line 100 and proceed in steps of 10 f a start line is specified then line numbers prior to the start line will be unchanged If an end line is specified then line numbers following the end line will be unchanged f a start number and stop are specified then the lines to be renumbered will be numbered from the start number and proceed in steps of the specified size If a GOTO or GOSUB statement contains an expression starting with a number then this number is treated as a line number and is renumbered syntax startline numeric_expression start renumber end_line numeric_expression stop renumber start_number numeric_expression base line number step numeric_expression step RENUM start_line TO end_line startnumber step example i RENUM renumber whole program from 100 by 10 ii RENUM 100 TO 200 renumber from 100 to 200 by 10 Comment No attempt must be made to use RENUM to renumber program lines out of sequence ie to move lines about the program RENUM should not be used in a program REPeat END REPeat repetition REPeat allows general repeat loops to be constructed REPeat should be used with EXIT for maximum effect REPeat can be used in both long and short forms SHORT The REPEAT keyword and loop identifer are followed on the same logical line by a colon and a sequence of SuperBASIC statements EXIT wil
43. problem CHAPTER 16 SOME TECHNIQUES In this final chapter we present some applications of concepts and facilities already discussed and we show how some further ideas may be applied SIMULATION OF CARD PLAYING tis easy to store and manipulate playing cards by representing them with the numbers 1 to 52 This is how you might convert such a number to the equivalent card Suppose for example that the number 29 appears You may decide that cards 1 13 are hearts cards 14 26 are clubs cards 27 39 are diamonds cards 40 52 are spades and you will know that 29 means that you have a diamond You can program the QL to do this with LET suit card 1 DV 13 This will produce a value in the range 0 to 3 which you can use to cause the appropriate suit to be printed The value can be reduced to the range 1 to 13 by writing LET value card MOD 13 IF value 0 THEN LET value 13 Program The numbers 1 to 13 can be made to print Ace 2 3 Jack Queen King or if you prefer it such phrases as two of hearts can be printed The following program will print the name of the card corresponding to your input number 100 REMark Cards 110 DIM suitname 4 8 cardval 13 5 120 LET f of 130 set_up 140 REPeat cards 150 INPUT Enter a card number 1 52 card 160 IF card lt 1 OR card gt 52 THEN EXIT cards 170 LET suit card 1 DM 13 180 LET value card MOD 13 190 IF value 0 THEN LET value 13 200 PRINT cardval
44. return immediately examples i PRINT INKEY input from the default channel ii PRINT INKEY 4 input from channel 4 iii PRINT INKEY 50 wait for 50 frames then return anyway iv PRINT INKEY 0 return immediatly poll the keyboard v PRINT INKEY 3 100 wait for 100 frames for an input from channel 3 then return anyway INPUT INPUT allows data to be entered into a SuperBASIC program directly from the QL keyboard by the user SuperBASIC halts the program until the specified amount of data has been input the program will then continue Each item of data must be terminated by the ENTER key INPUT will input data from either the specified or the default channel If input is required from a particular console channel the cursor for the window connected to that channel will appear and start to flash syntax separator TO prompt channel expression separator INPUT prompt channel variable variable example i INPUT Last guess amp guess amp New guess guess ii INPUT What is your guess guess iii 100 INPUT array size Limit 110 DIM array limit 1 120 FOR element 0 to Limit 1 130 INPUT data for element amp element array element 140 END FOR element 150 PRINT array INSTR operator INSTR is an operator which will determine if a given substring is contained within a specified string If the string is found then the substring s position is returned If t
45. side up A up ac The colour of the square is easily fixed but the square itself uses the values of side and ac and up as follows 200 DEFine PROCedure square side ac up 210 LINE ac up TO actside up 220 LINE TO ac side up tside 230 LINE TO ac up tside TO ac up 240 END DEFine In order to make this procedure work values of side ac and up must be provided These values are provided when the procedure is called For example you could add the following main program to get one green square of side 20 100 PAPER 7 CLS 110 INK 4 120 square 20 50 50 The numbers 20 50 50 are called parameters and they are passed to the variables named in the procedure definition thus square 20 50 50 II I vvv DEFine PROCedure square side ac up The numbers 20 50 50 are called actual parameters They are numbers in this case but they could be variables or expressions The variables side ac up are called formal parameters They must be variables because they receive values A more interesting main program uses the same procedure to create a random pattern of coloured pairs of squares Each pair of squares is obtained by offsetting the second one across and up by one fifth of the side length thus I HI Assuming that the procedure square is still present at line 200 then the following program will have the classical effect 100 REMark Squares Pattern 110
46. that you wish to keep in Microdrive 1 Type Irun mdv2_clone Press the ENTER key and the screen will display the message FORMAT mdvi_ type space to continue Press the space bar only when you are sure that the cartridge contains nothing that you wish to keep as everything on it will be erased The computer will format the cartridge and will then copy the program in sections displaying the name of each one as it does so Wait until the Microdrive lights go out before removing the master cartridge from Microdrive 1 LOADING You should never use any of the original program cartridges except when making a copy onto a blank cartridge All the programs are loaded similarly There are two ways of doing this Without cartridges in the Microdrives press reset Place your copy of the program cartridge in Microdrive 1 and then press either Fl or F2 as prompted Microdrive 1 will automatically run and after a short pause a title display will appear on the screen to confirm that the program is being loaded Once the program is loaded into the computer the program will start up by itself When you become more familiar with the programs and when using a printer or the network you will sometimes find that commands need to be given to the computer before the programs start You cannot switch off or reset the computer in this instance because your commands would be lost Instead place the program cartridge in Microdrive 1 and type Irun mdvl
47. the first program This facility becomes very valuable as you become proficient in handling procedures It is then quite natural to build a program up by adding procedures or functions to it GENERAL Be careful and methodical with cartridges Always keep one back up copy and if you suspect any problem with a cartridge or microdrive keep a second back up copy Computer professionals very rarely lose data They know that even with the best machines or devices there will be occasional faults and they allow for this If you want to call a program by a particular name say square it may be a good idea to use names like sq1 sq2 for preliminary versions When the program is in its final form take at least two copies called square and the others may be deleted by re formatting or by some more selective method SELF TEST ON CHAPTER 5 You can score a maximum of 14 points from the following test Check your score with the answers in the Answers To Self Tests section at the back of this Beginner s Guide 1 Why are lower case letters preferred for program words which you choose 2 What is the purpose of indenting 3 What should normally guide your choice of identifiers for variables and loops 4 Name three ways of editing a program in the computer s main memory three points 5 What should you remember to type at the end of every command or program line when you enter it 6 What should you normally type before you enter a pro
48. the specified line 4 will delete the specified line example i DLINE 10 TO 70 80 200 TO 400 will delete lines 10 to 70 inclusive line 80 and lines 200 to 400 inclusive ii DLINE will delete nothing EDIT The EDIT command enters the SuperBASIC line editor The EDIT command is closely related to the AUTO command the only difference being in their defaults EDIT defaults to a line increment of zero and thus will edit a single line unless a second parameter is specified to define a line increment If the specified line already exists then the line is displayed and editing can be started If the line does not exist then the line number is displayed and the line can be entered The cursor can be manipulated within the edit line using the standard QL keystrokes cursor right cursor left cursor up same as ENTER but automatically gives previous existing line to edit next cursor down same as ENTER but automatically gives next existing line to edit next CTRL gt delete character right CTRL lt delete character left When the line is correct pressing ENTER will enter the line into the program If an increment was specified then the next line in the sequence will be edited otherwise edit will terminate syntax increment numeric_expression EDIT line_number increment example i EDIT 10 edit line 10 only ii EDIT 20 10 edit lines 20 30 etc EOF devices EOF is a function which will determine if an end of f
49. to 18 down to positions 51 to 17 Place the chosen card from the temporary store to position 52 Deal similarly with the ranges 1 50 1 49 down to 1 2 so that the pack is well shuffled Output the result of the shuffle 6 Set up six DATA statements each containing a surname initials and a telephone number dialling code and local number Decide ona suitable structure of arrays to store this information and READ it into the arrays PRINT the data using a separate FOR loop and explain how the input format DATA the internal format arrays and output format are not necessarily all the same CHAPTER 14 PROGRAM STRUCTURE In this chapter we go again over the ground of program structure loops and decisions or selection We have tried to present things in as simple a way as possible but SuperBASIC is designed to cope properly with the simple and the complex and all levels in between Some parts of this chapter are difficult and if you are new to programming you may wish to omit parts The topics covered are Loops Nested loops Binary decisions Multiple decisions The latter parts of the first section Loops get difficult as we show how SuperBASIC copes with problems that other languages simply ignore Skip these parts if you feel so inclined but the other sections are more straightforward LOOPS In this section we attempt to illustrate the well known problems of handling repetition with simulations of some Wild West scenes The
50. to work but to know what it will do It will plot a rectangle made up of rows of pixels 100 REMark Rows of pixels 110 PAPERO CLS 120 FOR up 30 TO 80 130 FOR across 20 TO 60 140 INK RND 2 TO 7 150 POINT across up 160 END FOR across 170 END FOR up Different structures may be nested Suppose we replace the inner FOR loop of the above program by a REPeat loop We will terminate the REPeat loop when the zero colour code appears for a selection in the range 0 to 7 100 REMark REPeat in FOR 110 PAPERO CLS 120 FOR up 30 TO 80 130 LET across 19 140 REPeat dots 150 LET colour RND 7 160 INK colour 170 LET across across 1 180 POINT across up 190 IF colour 0 THEN EXIT dots 200 END REPeat dots 210 END FOR up Much of the wisdom about program control and structure can be expressed in two rules 1 Construct your program using only the legitimate structures for loops and decision making 2 Each structure should be properly related in sequence or wholly within another BINARY DECISIONS The three types of binary decision can be illustrated easily in terms of what to do when it rains i 100 REMark Short form IF 110 LET rain RND O TO 1 120 IF rain THEN PRINT Open brolly ii 100 REMark Long form IF END IF 110 LET rain RND O TO 1 120 IF rain THEN 130 PRINT Wear coat 140 PRINT Open brolly 150 PRINT Walk fast 160 END IF iii 100 REMark Long form IF ELSE END IF 110 LET rain
51. top right of the command window 100 c RESPR 100 110 FOR i 0 TO 68 STEP 2 120 READ x POKE_W itc x 130 END FORi 140 SEXEC mdv2_clock c 100 256 1000 DATA 29439 29697 28683 20033 17402 1010 DATA 48 13944 200 20115 12040 1020 DATA 28691 20033 17402 74 27698 1030 DATA 13944 236 20115 8279 11314 1040 DATA 13944 208 20115 16961 16962 1050 DATA 30463 28688 20035 24794 1060 DATA 0 7 240 10 272 200 N B Line 1060 governs the position and colour of the clock window the data terms are in order border colour width paper ink colour window width height x origin y origin These are pairs of bytes entered by POKE_W as words The x origin and the y origin the last data item should be 272 and 202 in monitor mode or 240 and 216 in TV mode Generate the paper and ink word for example as 256 papertink Thus white paper red ink is 256 7 2 1794 REPETITION Repetition in SuperBASIC is controlled by two basic program constructs Each construct must be identified to SuperBASIC REPeat identifier FOR identifier range statements statements END REPeat identifier END FOR identifier These two constructs are used in conjunction with two other SuperBASIC statements NEXT identifier EXIT identifier Processing a NEXT statement will either pass control to the statement following the appropriate FOR or REPeat statement or if a FOR range has been exhausted to the statement folliwng the NEXT Prcoessing an EXIT will pass contr
52. unwanted side effect Similarly you do not want a procedure to cause unplanned changes to values of variables used in the main program Of course you could make sure that there are no double uses of variable names ina program That will work up to a point but we have shown in this chapter how to avoid trouble even if you forget what variables have been used in any particular procedure A second aim in using procedures is to make a program modular Rather than have one long main program you can break the job down into what Seymour Papert the inventor of LOGO calls Mind sized bites These are the procedures each one small enough to understand and control easily They are linked together by the procedure calls ina sequence or hierarchy A third aim is to avoid writing the same code twice Write it once as a procedure and call it twice if necessary Functions and procedures written for one program can often be directly used without change by other programs and one might create a library of commonly used procedures and functions We give below another example which shows how procedures make a program modular EXAMPLE An order is placed for six dishes at Chan s Take Away where the menu is 1 Prawns 3 50 2 Chicken 2 80 3 Special 3 30 Write procedures for the following tasks 1 Set up two three element arrays showing menu dishes and prices Use a DATA statement 2 Simulate an order for six randomly chosen dishes using a procedure
53. used to activate particular blocks of code called subroutines The GOSUB statement is unsatisfactory in a number of ways and SuperBASIC offers properly named procedures with some very useful features Consider the following programs both of which draw a green square of side length 50 pixel screen units at a position 200 across 100 down ona red background a Using GOSUB 100 LET colour 4 background 2 110 LET across 20 120 LET down 100 130 LET side 50 140 GOSUB 170 150 PRINT END 160 STOP 170 REMark Subroutine to draw square 180 PAPER background CLS 190 BLOCK side side across down colour 200 RETurn b Using a procedure with parameters 100 square 4 50 20 100 2 110 PRINT END 120 DEFine PROCedure square colour side across down background 130 PAPER background CLS 140 BLOCK side side across down colour 150 END DEFine In the first program the values of colour across down side are fixed by LET statements before the GOSUB statement activates lines 180 and 190 Control is then sent back by the RETURN statement In the second program the values are given in the first line as parameters in the procedure call square which activates the procedure and at the same time provides the values it needs In its simplest form a procedure has no parameters It merely separates a particular piece of code though even in this simpler use the procedure has the advantage over GOSUB because it is prop
54. value f suitname suit 210 END REPeat cards 220 DEFine PROCedure set_up 230 FORs 1 TO 4 READ suitname s 240 FOR v 1 TO 13 READ cardval v 250 END DEFine 260 DATA hearts clubs diamonds spades 270 DATA Ace Two Three Four Five Six Seven 280 DATA Eight Nine Ten Jack Queen King Input and Output 13 King of hearts 49 Ten of spades 27 Ace of diamonds 0 COMMENT Notice the use of DATA statements to hold a permanent file of data whlch the program always uses The other data which changes each time the program runs is entered through an INPUT statement If the input data was known before running the program it would be equally correct to use another READ and more DATA statements This would give better control SEQUENTIAL DATA FILES Numeric File The following program will establish a file of one hundred numbers 100 REMark Number File 110 OPEN NEW 6 mdv1_numbers 120 FOR num 1 TO 100 130 PRINT 6 num 140 END FOR num 150 CLOSE 6 After running the program check that the filename numbers is in the directory by typing DIR mdv1_numbers You can get a view of the file without any special formatting by copying from Microdrive to screen COPY mdv1_numbers to scr You can also use the following program to read the file and display its records on the screen 100 REMark Read File 110 OPEN_IN 6 mdv1_ numbers 120 FOR num 1 TO 100 130 INPUT 6 item 140 PRINT it
55. we automatically make procedure formal parameters local Though we have not mentioned it before parameters such as num in the above programs cannot interfere with main program variables To prove this we drop the LOCAL statement from the above program and use num for the price of lager Because num in the procedure is local everything works Program 100 REMark LOCAL parameter 110 LET num 70 120 item 3 130 item 4 140 PRINT num 150 DEFine PROCedure item num 160 IF num lt 3 THEN LET price 300 10 num 170 IF num gt 4 THEN LET price 12 num 180 PRINT price 190 END DEFine Output 330 48 70 VARIABLE PARAMETERS So far we have only used procedure parameters for passing values to the procedure But suppose the main program wants the cost of an item to be passed back so that it can compute the total bill We can do this easily by providing another parameter in the procedure call This must be a variable because it has to receive a value from the procedure We therefore call it a variable parameter and it must be matched by a corresponding variable parameter in the procedure definition EXAMPLE Use actual variable parameters cost_1 and cost_2 to receive the values of the variable price from the procedure Make the main program compute and print the total bill Program 100 REMark Variable parameter 110 LET num 70 120 item 3 cost_1 130 item 4 cost_2 140 LET bill num cost_1 cost_2 150 PRINT bill
56. which would give the answer on the screen However the ideas we have discussed are the essential starting points of programming in SuperBASIC They are so essential that they occur in many computer languages and have been given special names 1 Names such as dogs days and tins are called identifiers 2 A single instruction such as LET dogs 9 ENTER is called a statement 3 The arrangement of name and associated pigeon hole is called a variable The execution of the above statement stores the value 9 in the pigeon hole identified by the Identifier dogs A statement such as LET dogs 9 ENTER is an instruction for a highly dynamic internal process but the printed text is static and it uses the sign borrowed from mathematics It is better to think or say but not type LET dogs become 9 and to think of the process having a right to left direction do not type this dogs lt 9 The use of ina LET statement is not the same as the use of in mathematics For example if another dog turns up you may wish to write LET dogs dogs 1 ENTER Mathematically this is not very sensible but in terms of computer operations it is simple If the value of dogs before the operation was 9 then the value after the operation would be 10 Test this by typing LET dogs 9 ENTER PRINT dogs ENTER LET dogs dogs 1 ENTER PRINT dogs ENTER The output should be 9 10 proving that the final value in the p
57. writing a procedure definition before using its name in a main program 7 How can the use of procedures help a thirty line programmer to write much bigger programs 8 Some programs use more memory in defining procedures but in what circumstances do procedures save memory space 9 Name two ways by which information can be passed from a main program to a procedure two points 10 What is an actual parameter 11 What is a formal parameter PROBLEMS ON CHAPTER 7 1 Write a procedure which outputs one of the four suits Hearts Clubs Diamonds or Spades Call the procedure five times to get five random suits 2 Write another program for problem 1 using a number in the range 1 to 4 as a parameter to determine the output word If you have already done this then try writing the program without parameters 3 Write a procedure which will output the value of a card that is a number in the range 2 to 10 or one of the words Ace Jack Queen King 4 Write a program which calls this procedure five times so that five random values are output 5 Write the program of problem 3 again using a number in the range 1 to 13 as a parameter to be passed to the procedure If this was the method you used first time then try writing the program without parameters 6 Write the most elegant program you can using procedures to output four hands of five cards each Do not worry about duplicate cards You can take eleganc
58. 2 program listing channel 4 St HTT 2 1 1 amp 2 HITT HTT HTT OIIO Monitor Television OPEN open a channel for VO CLOSE close a previously opened channel PRINT output to a channel INPUT input from a channel INKEY input a character from a channel The cursorncontrols are not built in to the operating system however if these functions are to be provided by applications software they should use the keys specified also the specified keys should not normally be used for any other purpose 0 00 CTRL NULL 101 CTRL A 2 02 CTRL B 3 03 CTRL C Change input channel see note 4 04 CTRL D 505 CTRL E 6 06 CTRL F 7 07 CTRL G 8 08 CTRL H 9 09 TAB CTRL I Next field 10 0A ENTER CTRL J New line Command entry 11 0B CTRL K 12 0C CTRL L 13 0D CTRL M Enter 14 0E CTRL N 15 OF CTRL O 16 10 CTRL P 17 11 CTRL Q 18 12 CTRL R 19 13 CTRL S 20 14 CTRL T 2115 CTRL U 22 16 CTRL V 23 17 CTRL W 24 18 CTRL X 25 19 CTRL Y 26 1A CTRL Z 27 1B ESC CTRL SHIFT Abort current level of command 28 1C CTRL SHIFT 29 1D CTRL SHIFT 30 1E CTRL SHIFT 31 1F CTRL SHIFT ESC 32 20 SPACE 33 21 SHIFT 1 34 22 SHIFT 35 23 SHIFT 3 36 24 SHIFT 4 37 25 SHIFT 5 38 26 SHIFT 7 amp 39 27 40 28 SHIFT 9 41 29 SHIFT 0 42 2A SHIFT 8 43 2B SH
59. 280 FOR pick 1 TO 6 290 LET number RND 1 TO 3 300 LET dish number dish number 1 310 END FOR pick 320 END DEFine 330 DEFine PROCedure waiter dish cost 340 compute dish cost 350 cook dish 360 END DEFine 370 DEFine PROCedure compute dish total 380 LET total 0 390 FORk 1TO3 400 LET total total dish k price k 410 END FORk 420 END DEFine 430 DEFine PROCedure cook dish 440 FORc 1TO3 450 PRINT dish c item c 460 END FORc 470 END DEFine 480 REMark PROGRAM DATA 490 DATA Prawns 3 5 Chicken 2 8 Special 3 3 Output The output depends on the random choice of dishes but the following choice illustrates the pattern and gives a sample of output 3 Prawns 1 Chicken 2 Special Total cost is 20 40 COMMENT Obviously the use of procedures and parameters in such a simple program is not necessary but imagine that each sub task might be much more complex In such a situation the use of procedures would allow a modular build up of the program with testing at each stage The above example merely illustrates the main notations and relationships of procedures Similarly the next example illustrates the use of functions Note that in the previous example the procedures waiter and compute both return exactly one value Rewrite the procedures as functions and show any other changes necessary as a consequence DEFine FuNction waiter dish cook dish RETurn compute dish END DEFine DEFi
60. 32768 save memory 50000 length 10000 bytes on mdv1_test_program ii SBYTES mdv1_test_program 50000 10000 save memory 50000 length 1000 bytes on mdvi_test_program iii SBYTES neto_3 32768 32678 save memory 32768 length 32768 bytes on the network iv SBYTES ser1 0 32768 save memory 0 length 32768 bytes on serial channel 1 SCALE graphics SCALE allows the scale factor used by the graphics procedures to be altered A scale of x implies that a vertical line of length x will fill the vertical axis of the window in which the figure is drawn A scale of 100 is the default SCALE also allows the origin of the coordinate system to be specified This effectively allows the window being used for the graphics to be moved around a much larger graphics space syntax x numeric_expression y numeric_expression origin x y scale numeric_expression SCALE channel scale origin example i SCALE 0 5 0 1 0 1 set scale to 0 5 with the origin at 0 1 0 1 ii SCALE 10 0 0 set scale to 10 with the origin at 0 0 iii SCALE 100 50 50 set scale to 100 with the origin at 50 50 SCROLL windows SCROLL scrolls the window attached to the specified or default channel up or down by the given number of pixels Paper is scrolled in at the top or the bottom to fill the clear space An optional third parameter can be specifiedto obtain a part screen scroll syntax part numeric_expression distance numeric_expression where part
61. 8 way DIN plug at the QL end The connection at the monitor end will vary according to the monitor there is no industry standard and will often be supplied with it A suitable cable with an 8 way DIN plug at one end and bare wires at the other end is available from Sinclair Research Limited A composite PAL monitor or the composite video input on some VCRs may work witht he QL Only pins 2 ground and 1 composite PAL need to be connected via a cable to the monitor or VCR NETWORK The QL can be connected with up to 63 other QLs If there are more than 2 computers on the network then each computer or station must be assigned a unique station number On the QL this can be done using the NET command Information is transmitted over the network in blocks For normal communication between two stations the receiving station must acknowledge correct reception of the block If a block is corrupted then the receving station will request retransmission Using a network station number of zero has a special meaning Sending to neto_0 is called broadcasting any message sent in this way can be read by any station which is listening to neti_O Note that the normal verification that a message has been received is disabled for broadcasts so that broadcasting messages of length more than one block 255 bytes s unreliable A network station which listens to its own station number e g NET3 LOAD neti_3 can receive data from any station sending to it C
62. 9 These numbers are passed back to the main program to become the values of array black The values are printed to prove that the data has moved as required MAIN Screen PROGRAM row back Output I III PROCEDURE come gt 6 gt send addsix Program 100 REMark Pass Arrays 110 DIM row 3 back 3 120 FORk 1 TO 3 LET row k k 130 addsix row back 140 FORk 1TO3 PRINT back k 150 DEFine PROCedure addsix come send 160 FORk 1 TO 3 LET send k come k 6 170 END DEFine Output 789 The following procedure receives an array containing data to be sorted The zero element will contain the number of items Note that it does not matter whether the array is numeric or string The principle of coercion will change string to numeric data if necessary A second point of interest is that the array element come 0 is used for two purposes it carries the number of items to be sorted it is used to hold the item currently being placed 100 DEFine PROCedure sort come send 110 LET num come 0 120 FOR item 2 TO num 130 LET p item 140 LET come 0 come p 150 REPeat compare 160 IF come 0 gt come p 1 EXIT compare 170 LET come p come p 1 180 LETp p 1 190 END REPeat compare 200 LET come p
63. AL ARRAYS Sometimes the nature of a problem suggests two dimensions such as 3 floors of 10 flats rather than just a single row of 30 Suppose that 20 or more golfers need flats and there is a block of 30 flats divided into three floors of ten flats each A realistic method of representing the block would be with a two dimensional array You can think of the thirty variables as shown below flat 2 0 flat 2 1 flat 2 2 ss flat 2 9 a a iiesoene ne HT TT ITA II second 2 HTT TTA aa a ec LL flat 1 0 flat 1 1 flat 1 2 ss flat 1 9 a a ee t ITITI ILITI I first 1 MITI ee flat 0 0 flat 0 1 flat 0 2 flat 0 9 area a ec L HTT ITA III ground 0 HTT TTA Assuming DATA statements with 30 names a suitable way to place the names in the flats is 120 FOR floor 0 TO 2 130 FOR num 0 TO 9 140 READ flats floor num 150 END FOR num 160 END FOR floor You also need a DIM statement 20 DIM flat 2 9 8 which shows that the first subscript can be from 0 to 2 floor number and the second subscript can be from 0 to 9 room number The third number states the maximum number of characters in each array element We add a print routine to show that the golfers are in the flats and we use letters to save space 100 REMark 30 Golfers 110 DIM flat 2 9 8 120 FOR floor 0 TO 2
64. ARC 10 50 TO 50 90 1 which gives a moderate curvature in the current INK colour Chapt12h_PIC eee 50 90 I angle __ 10 50 Arc FS Re eee ee NT hea FILL You can fill a closed shape with the current INK colour by simply writing FILL 1 before the shape is drawn The following program produces a green circle CIRCLE 50 50 30 The FILL command works by drawing touching horizontal lines between suitable points The statement FILLO will turn off the FILL effect SCROLLING AND PANNING You can scroll or pan the display in a window like a film cameraman You arrange scrolling in terms of pixels A positive number of pixels indicates upwards scrolling thus SCROLL 10 moves the display in the current window or screen 10 pixels downwards SCROLL 8 Moves the display 8 pixels up You can add a second parameter to induce part scrolling SCROLL 8 1 will scroll the part above not including the cursor line and SCROLL 8 2 will scroll the part below not including the cursor line As scrolling occurs the space left by movement of the display is filled with the current paper colour A second parameter 0 has no effect You can PAN the display in the current window left or right The PAN statement works in a similar manner to SCROLL but PAN 40 moves display right PAN 40 moves display left A second parameter gives a partial PAN 0 whole screen 3 the whole of the line occupied by the cu
65. BASIC program to stop hold down the CTRL key and press the space bar The computer should then display its cursor If this doesn t work remove any Microdrive cartridges and then press reset The message Bad Line appearing in the command window means that the computer doesn t understand a command that you have typed in Delete or correct the line using the cursor keys MICRODRIVES The two QL Microdrives are called mdvi_ on the left and mdv2_ on the right Cartridges must be placed correctly into the Microdrives Hold the cartridge by the ribbed plastic handle and remove it from its protective cover The cartridge s name label or the recess for its stick on label should face upwards Cartridges should always be treated with care You should never turn the QL on or off with a cartridge in the Microdrives Take care when inserting or removing cartridges wait until the Microdrive lights have gone out before removing the cartridge be gentle but firm Never touch the tape in the cartridge and always return the cartridge to its protective cover Before a blank cartridge can be used it must go through a process called formatting This process erases any data or programs on a cartridge so always be sure that all cartridges are clearly labelled with their contents and check that cartridges to be formatted contain no useful data Instructions for formatting cartridges are contained in the Information section All magnetic storage media including Microdr
66. Bad name The file system has recognised the name but there is a syntax or parameter value error In SuperBASIC it means a name has been used out of context For example a variable has been used as a procedure 13 Xmit error RS 232 C parity error 14 Format failed Attempted format operation has failed the medium is possibly faulty usually a Microdrive cartridge 15 Bad parameter There is an error in the parameter list of a system or SuperBASIC procedure or function call An attempt was made to read data from a write only device 16 Bad or changed medium The medium usually a Microdrive cartridge is possibly faulty 17 Error in expression An error was detected while evaluating an expression 18 Overflow Arithmetic overflow division by zero square root of a negative number etc 19 Not Implemented 20 Read only There has been an attempt to write data to a shared file 21 Bad line A SuperBASIC syntax error has occurred 22 PROC FN cleared This is a message which is for information only and is not reporting an error It is reporting that the program has been stopped and subsequently changed forcing SuperBASIC to reset its internal state to the outer program level and so losing any procedure environment which may have been in effect ERROR RECOVERY After an error has occurred the program can be restarted at the nextstatement by typing CONTINUE If the error condition can be corrected without changi
67. C program to be started If a line number is specified in the RUN command then the program will be started at that point otherwise the program will start at the lowest line number syntax RUN numeric_expression example i RUN run from start ii RUN 10 run from line 10 iii RUN 2 20 run from line 40 Comment Although RUN can be used within a program its normal use is to start program execution by typing it in as a direct command SAVE devices microdrives SAVE will save a SuperBASIC program onto any QL device syntax line numeric_expression TO numeric_expression 1 numeric_expression TO 2 TO numeric_expression 3 numeric_expression 4 5 SAVE device line where 1 will save from the specified line to the specified line 2 will save from the specified line to the end 3 will save from the start to the specified line 4 will save the specified line 5 will save the whole program example i SAVE mdv1_program 20 TO 70 save lines 20 to 70 on mdv1_ program ii SAVE mdv2_test_program 10 20 40 save lines 10 20 40 on mdv1_test_program iii SAVE net3 save the entire program on the network iv SAVE ser1 save the entire program on serial channel SBYTES devices microdrives SBYTES allows areas of the QL memory to be saved ona QL device syntax start_address numeric_expression length numeric_expression SBYTES device start_address length example i SBYTES mdv1_screendata 131072
68. COPY mdv1_test_file TO seric NETd_s Serial Network I O d indicates direction s station number i input O for broadcast o output own station for general listen input only default no default example OPEN 7 neti_32 OPEN 4 neto_0 COPY ser1 TO neto_ 21 MDVn_name Microdrive File Access n Microdrive number name Microdrive file name default no default example OPEN 9 mdv1_data_file OPEN 9 mdv1_test_program COPY mdv1_test_file TO scr_ Keyword Function OPEN initialise a device and activate it for use CLOSE deactivate a device COPY copy data between devices COPY_N copy data between devices but do not copy a file s header information EOF test for end of file WIDTH set width DIRECT COMMAND SuperBASIC makes a distinction between a statement typed in preceded bya line number and a statement typed in without a line nurnber Without a line number the statement is a direct command and is processed immediately by the SuperBASIC command interpreter For example RUN is typed in on the command line and is processed the effect being that the program starts to run If a statement is typed in with a line number then the syntax of the line is checked and any detectable syntax errors reported A correct line is entered into the SuperBASIC program and stored These statements constitute a SuperBASIC program and will only be executed when the program is started with the RUN or GOTO command Not all SuperBASIC s
69. DEFine 510 DEFine PROCedure layout 520 PAPER 6 4 CLS 6 530 BORDER 6 10 0 540 BLOCK 6 100 60 150 60 2 4 550 END DEFine 560 DEFine PROCedure printem 570 LET inc 12 INK 6 7 580 LET p 0 590 FOR seat 1 TO 4 600 READ ac dn 610 FOR row 1 TO4 620 getline 630 CURSOR 6 ac dn 640 PRINT 6 1in 650 LET dn dn inc 660 END FOR row 670 END FOR seat 680 END DEFine 690 DEFine PROCedure getline 700 IF row MOD 2 0 THEN STRIP 6 0 710 IF row MOD 2 1 THEN STRIP 6 2 720 LET lin tok row 730 LET max row 13 740 REPeat one_suit 750 LETp p 1 760 LET n card p 770 IF n gt max THEN p p 1 EXIT one_suit 780 LET n n MOD 13 790 IF n 0 THEN n 13 800 IF n 1 LET ch A 810 IF n gt 2 AND n lt 9 LET ch n 820 IF n 10 LET ch T 830 IF n 11 LET ch J 840 IF n 12 LET ch Q 850 IF n 13 LET ch K 860 LET lin ling amp amp ch 870 IF p 52 EXIT one_suit 880 IF card p gt card p 1 EXIT one_suit 890 END REPeat one_suit 900 END DEFine 910 DATA H C D S 920 DATA 150 10 260 60 150 130 30 60 COMMENT The program works in the 256 mode But the various lines of card symbols may overlap the table or overflow at the edge of the window A simple change in procedure getline from 860 LET lin ling amp amp ch to 860 LET lin lin amp ch will correct this The spaces between characters disappear but the larger sized characters
70. EEP duration pitch pitch_2 grad_x grad_y wrap fuzzy random III duration specifies the duration of the sound in units of 72 microseconds A duration of zero will run the sound until terminated by another BEEP command pitch specifies the pitch of the sound A pitch of 1 is high and 255 is low Pitch_2 specifies an second pitch level between which the sound will bounce grad_x defines the time interval between pitch steps grad_y defines the size of each step grad_x and grad_y control the rate at which the pitch bounces between levels wrap will force the sound to wrap around the specified number of times If wrap is equal to 15 the sound will wrap around forever fuzzy defines the amount of fuzziness to be added to the sound random defines the amount of randomness to be added to the sound BEEPING sound BEEPING is a function which will return zero false if the QL is currently not beeping and a value of one true if it is beeping syntax BEEPING example 100 DEFine PROCedure be quiet 110 BEEP 120 END DEFine 130 IF BEEPING THEN be quiet BLOCK windows BLOCK will fill a block of the specified size and shape at the specified position relative to the origin of the window attached to the specified or default channel BLOCK uses the pixel coordinate system syntax width numeric_expression height numeric_expression x numeric_expression y numeric_expression BLOCK channel wi
71. ENTER and the output 105 should appear The advantage of this arrangement is that you can edit or add to the program with minimal extra typing EDITING A PROGRAM Later you will see the full editing features of SuperBASIC but even at this early stage you can do three things easily replace a line insert a new line delete a line REPLACE A LINE Suppose you wish to alter the previous program because the price has changed to 20p for a pen Simply re type line 10 10 LET price 20 ENTER This line will replace the previous line 10 Assuming the other lines are still stored test the program by typing RUN ENTER and the new answer 140 should appear INSERT A NEW LINE Suppose you wish to insert a line just before the last one to print the words Total Cost This situation often arises so we usually choose line numbers 10 20 30 to allow space to insert extra lines To put in the extra line type 35 PRINT Total Cost ENTER and it will be inserted just before line 40 The system allows line numbers in the range 1 to 32768 to allow plenty of flexibility in choosing them It is difficult to be quite sure in advance what changes may be needed Now type RUN ENTER and the new output should be Total cost 140 DELETE LINE You can delete line 35 by typing 35 ENTER itis as though an empty line has replaced the previous one OUTPUT PRINT Note how useful the PRINT statement is You can PRINT text by using
72. ER 120 PRINT words would cause the six letter word LONGER to be printed The first line would cause space for four letters to be allocated but this allocation would be overruled by the second line which requires space for six characters It is however possible to dimension i e reserve space for a string variable in which case the maximum length becomes defined and the variable behaves as an array JOINING STRINGS You may wish to construct records in data processing from a number of sources Suppose for example that you are a teacher and you want to store a set of three marks for each student in Literature History and Geography The marks are held in variables as shown HIT lit 62 hist 56 geog 71 HIT As part of student record keeping you may wish to combine the three string values into one six character string called mark You simply write LET mark lit amp hist amp geog You have created a further variable as shown mark 625671 But remember that you are dealing with a character string which happens to contain number characters rather than an actual number Note that in SuperBASIC the amp symbol is used to join strings together whereas in some other BASICs the symbol is used for that purpose COPY A STRING SLICE A string slice is part of a string It may be anything from a single character to the
73. FT ALT Right Pan right 206 CE SHIFT CTRL Right Delete word under amp right of cursor 207 CF SHIFT CTRL ALT Right 208 DO Up Cursor right 209 D1 ALT Up Scroll up 210 D2 CTRL Up Search backward 211 D3 ALT CTRL Up 212 D4 SHIFT Up Top of screen 213 D5 SHIFT ALT Up 214 D6 SHIFT CTRL Up 215 D7 SHIFT CTRL ALT Up 216 D8 Down Cursor down 217 D9 ALT Down Scroll down 218 DA CTRL Down Search forwards 219 DB ALT CTRL Down 220 DC SHIFT Down Bottom of screen 221 DD SHIFT ALT Down 222 DE SHIFT CTRL Down 223 DF SHIFT CTRL ALT Down 224 EO CAPS LOCK Toggle CAPS LOCK function 225 E1 ALT CAPS LOCK 226 E2 CTRL CAPS LOCK 227 E3 ALT CTRL CAPS LOCK 228 E4 SHIFT CAPS LOCK 229 E5 SHIFT ALT CAPS LOCK 230 E6 SHIFT CTRL CAPS LOCK 231 E7 SHIFT CTRL ALT CAPS LOCK 232 E8 F1 233 E9 CTRL F1 234 EA SHIFT F1 235 EB CTRL SHIFT F1 236 EC F2 237 ED CTRL F2 238 EE SHIFT F2 239 EF CTRL SHIFT F2 240 FO F3 241 F1 CTRL F3 242 F2 SHIFT F3 243 F3 CTRL SHIFT F3 244 F4 F4 245 F5 CTRL F4 246 F6 SHIFT F4 247 F7 CTRL SHIFT F4 248 F8 F5 249 F9 CTRL F5 250 FA SHIFT F5 251 FB CTRL SHIFT F5 252 FC SHIFT space Special space 253 FD SHIFT TAB Back tab CTRL ignored 254 FE SHIFT ENTER Special newline CTRL ignored 255 FF See below Codes up to 20 hex are either control characters or non printing characters Alternative keyings are shown in brackets after the main keying Note that CTRL C is trapped by Qdos and cannot be detec
74. H character flash RECOL recolour a window
75. IC comparisons Note also that comparison of strings containing non printable characters may give unexpected results TYPES OF COMPARISON type 0 case dependent character by character comparison type 1 case independent character by character type 2 case dependent numbers are sorted in numerical order type 3 case independent numbers are sorted in numerical order type 0 not normally used by the SuperBASIC system USAGE type 1 File and variable comparison type 2 SuperBASIC lt lt gt gt INSTR and lt gt type 3 SuperBASIC equivalence SYNTAX DEFINITIONS SuperBASIC syntax is defined using a non rigorous meta language type notation Four types of construction are used Select one of Enclosed item s are optional Enclosed items are repeated Range Comment e g A B AorB A A is optional A Ais repeated A Z A B C etc this is a comment Consider a SuperBASIC identifier A sequence of numbers digits underscores starting with a letter and finishing with an optional or letter A Z a z a letter is one of ABCDEFGHIJKLMNOPQRSTUVWXYZ or abcdefghijklmnopqrstuvwxyz digit 0 1 2 3 4 5 6 7 8 9 a digit is 0 or 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9 underscore _ an underscore is _ identifier letter letter digit underscore pacientes enti ae it eet must start with a letter a sequence of letters digits an
76. IFT 442C 45 2D 46 2E 47 2F 48 3000 493111 50 3222 513333 52 3444 53 3555 54 3666 55 3777 56 38 8 8 57 3999 58 3A SHIFT 59 3B 60 3C SHIFT lt 62 3E SHIFT 7 gt 63 3F SHIFT 64 40 SHIFT 2 65 41 SHIFTAA 66 42 SHIFT B B 67 43 SHIFTC C 68 44 SHIFT D D 69 45 SHIFTEE 70 46 SHIFT FF 71 47 SHIFT GG 72 48 SHIFTHH 73 49 SHIFT II 74 4A SHIFT JJ 75 4B SHIFT K K 76 4C SHIFTLL 77 4D SHIFTMM 78 4E SHIFTNN 79 4F SHIFT OO 80 50 SHIFT P P 8151 SHIFTQQ 82 52 SHIFTRR 83 53 SHIFTS S 84 54 SHIFTTT 85 55 SHIFT U U 86 56 SHIFT V V 87 57 SHIFT W W 88 58 SHIFT X X 89 59 SHIFT YY 90 5A SHIFTZZ 91 5B 92 5C 93 5D 94 5E SHIFT 6 95 5F SHIFT _ 96 60 9761Aa 98 62B b 9963C c 10064 D d 10165Ee 102 66 F f 103 67 Gg 10468 Hh 105 69 li 106 6A Jj 107 6B Kk 108 6C LI 109 6D Mm 1106ENn 111 6F Oo 11270Pp 11371Qq 11472Rr 11573Ss 116 74Tt 11775 Uu 118 76 Vv 11977 Ww 120 78 X x 12179Yy 122 7AZz 123 7B SHIFT 124 7C SHIFT 125 7D SHIFT 126 7E SHIFT 127 7F SHIFT ESC 128 80 CTRL ESC 129 81 CTRL SHIFT 1 130 82 CTRL SHIFT 131 83 CTRL SHIFT 3 f 132 84 CTRL SHIFT 4 133 85 CTRL SHIFT 5 134 86 CTRL SHIFT 7 t 135 87 CTRL t 136 88 CTRL SHIFT 9 137 89 CTRL SHIFT 0 o 138 8A CTRL SHIFT 8 139 8B CTRL SHIFT lt 140 8C CTRL 141 8D CTRL _ 142 8E CTRL 143 8F CTRL 144 90 CTRLO 145 91 CTRL 1 146 92 CTRL 2 147 93 C
77. INK RND 5 ENTER 50 LINE 50 60 TO RND 100 RND 100 ENTER 60 END REPEAT star ENTER RUN ENTER We have give the repeat structure a name star The structure consists of the two lines REPeat star END REPeat star and what lies between them is called the content of the structure The use of upper case letters indicates that REP is a valid abbreviation of REPeat This program should produce coloured lines indefinitely to make a star diagram of random length lines emanating from a central point like a broken pane of glass Chapt3B_pic caption The STAR program You can stop it by pressing the break keys Hold down CTRL and then press SPACE SuperBASIC provides a consistent and versatile method of stopping repetitive processes Imagine running round and round inside the program activating statements How can you escape The answer is to use an EXIT statement But there must be some reason for escaping You might extend the choice of line colours by typing as an amendment to the program do not type NEW 40 INK RND 0 TO 6 ENTER so that if RND produces 6 the ink is the same colour as the paper and you will not see it This could be the reason for terminating the repetition We can re arrange the program as follows NEW ENTER 10 PAPER 6 CLS ENTER 20 BORDER 1 2 ENTER 30 REPeat star ENTER 40 LET colour RND 6 ENTER 50 IF colour 6 THEN EXIT star ENTER 60 INK colour ENTER 70 LINE 50 60 TO RND 100
78. INT Correct 160 ELSE 170 PRINT Not correct 180 END IF The operator INSTR returns zero if the guess is incorrect If the guess is correct INSTR returns the number which is the starting position of the string slice in this case 6 Because the expression an INSTR iumble can be treated as a logical expression the position of the string ina successful search can be regarded as true while in an unsuccessful search it can be regarded as false OTHER STRING FUNCTIONS You have already met LEN which returns the length number of characters of a string You may wish to repeat a particular string or character several times For example if you wish to output a row of asterisks rather than actually enter forty asterisks ina PRINT statement or organise a loop you can simply write PRINT FILL 40 Finally it is possible to use the function CHR to convert internal codes into string characters For example PRINT CHR 65 would output A COMPARING STRINGS A great deal of computing is concerned with organising data so that it can be searched quickly Sometimes it is necessary to sort it in to alphabetical order The basis of various sorting processes is the facility for comparing two strings to see which comes first Because the letters A B C are internally coded as 65 66 67 itis natural to regard as correct the following statements A is less than B B is less than C and because internal character by character compar
79. ND FOR name closing keyword END REPeat name In addition the REPeat loop must normally have an EXIT amongst the statements or it will never end Note also that the EXIT statement causes control to go to the statement which is immediately after the END of the loop A NEXT statement may be placed ina loop It causes control to go to the statement which is just after the opening keyword FOR or REPeat It should be considered as a kind of opposite to the EXIT statement By a curious coincidence the two words NEXT and EXIT both contain EXT Think of an EXTension to loops and N means Now start again I means It s ended EXAMPLE 3 The situation is the same as in example 1 The sheriff has a gun loaded with six bullets and he is to fire at the bandit but two more conditions apply 1 If he hits the bandit he stops firing and returns to Dodge City 2 fhe runs out of bullets before he hits the bandit he tells his partner to watch the bandit while he sheriff returns to Dodge City Program 1 100 REMark Western FOR with Epilogue 110 FOR bullets 1 TO 6 120 PRINT Take aim 130 PRINT FIRE A SHOT 140 LET hit RND 9 150 IF hit 7 THEN EXIT bullets 160 NEXT bullets 170 PRINT Watch Bandit 180 END FOR bullets 190 PRINT Return to Dodge City In this case the content between NEXT and END FOR is a kind of epilogue which is only executed if the FOR loop runs its full course If there is a premature EXIT the epilogue is not ex
80. Network and serial channel communication Keyboard input Memory management MEMORY MAP A full description of Qdos is beyond the scope of this guide but a brief description is included The system RAM has an organisation imposed by the QDOS operating system and is defined as follows SV_RAMT 1 QDOS MEMORY MAP II Resident Procedures SV_RESPR v fills II Transient Programs SV_TRNSP v fills SuperBASIC command interpreter data and SV_BASIC SuperBASIC programs v fills i Filing subsystem slave block SV_FREE A Channels and other heap items SV_HEAP fills System tables and System Variables 28000 Hex Display memory The terms SV_RAMT SV_RESPR SV_TRNSP SV_BASIC SV_FREE SV_HEAP are used to represent addresses inside the QL These terms are not recognised by SuperBASIC or the QDOS operating system Furthermore the addresses represented are liable to change as the system is running sv_ramt RAM Top This will vary according to the memory expansion boards attached to the system sv_respr Resident Procedures Resident procedures are loaded into the top of RAM Space can be allocated in the resident procedure area using the RESPR fu
81. O on the QL is to or from a logical file Various file types exist DATA SuperBASIC programs text files Created using PRINT SAVE accessed using INPUT INKEY LOAD etc EXEC An executable transient program Saved using SEXEC loaded using EXEC EXEC_W etc CODE Raw memory data screen images etc Saved using SBYTES loaded using LBYTES FUNCTIONS AND PROCEDURES SuperBASIC functions and procedures are defined with the DEFine FuNction and DEFine PROCedure statements A function is activated or called by typing its name at the appropriate point ina SuperBASIC expression The function must be included in an expression because it is returning a value and the value must be used A procedure is activated or called by typing its name as the first item ina SuperBASIC statement Data can be passed into a function or procedure by appending a list of actual parameters after the function or procedure name This list is compared to a similar list appended after te name of the function or procedure when it was defined This second list is called the formal parameters of the function or procedure The formal parameters must be SuperBASIC variables The actual parameters must be an array an array slice or a SuperBASIC expression of which a single variable or constant is the simplest form Since the actual parameters are actual expressions they must have an actual type associated with them The formal parameters are merely used to indicate
82. OARD SYMBOLS OF IMMEDIATE USE multiply add __ underscore becomes equal to used in LET quotes apostrophe comma exclamation semi colon amp ampersand colon decimal point or full stop backslash dollar left bracket right bracket UPPER AND LOWER CASE SuperBASIC recognises commands keywords whether they are in upper or lower case For example the SuperBASIC command to clear the screenis CLS and can be typed in as CLS ENTER cls ENTER clS ENTER These are all correct and have the same effect Some keywords are displayed partly In upper case to show allowed abbreviations Where a keyword cannot be abbreviated it is displayed completely in upper case USE OF QUOTES The usual use of quotes is to define a word or sentence a string of characters Try PRINT This works ENTER The computer will respond with This works The quotes are not printed but they indicate that some text is to be printed and they define exactly what it is everything between the opening and closing quote marks If you wish to use the quote symbol itself in a string of characters then the apostrophe symbol can be used instead For example PRINT The quote symbol is will work and will print The quote symbol is COMMON TYPING ERRORS The zero key is with the other numeric digits at the top of the keyboard and is slightly thinner The letter O key is amongst the other letters Be careful to use the right s
83. ODE 512 4 Colour Mode MODE 4 512 pixels across 256 down In both modes pixels are addressed by the range of numbers 0 511 across and 0 255 down Since mode 8 has only half the number of pixels across the screen as mode 4 mode 8 pixels are twice as wide as mode 4 pixels and so in mode 8 each pixel can be specified bv two coordinates For example Oor12or3 510 or 511 It also means that you use the same range of numbers for addressing pixels irrespective of the mode Always think 0 511 across and 0 255 down f you are using a television then not all the pixels may be visible COLOURS The colours available are black 0 black blue 1 red 2 red magenta 3 green 4 green cyan 5 yellow 6 white white 7 You may find the following mnemonic helpful in remembering the codes Bonny Babies Really Make Good Children You Wonder In the high resolution mode each colour can be selected by one of two codes You will see later how a startling range of colour and stipple texture effects can be produced if you have a good quality colour monitor Some of the screen presentation keywords are as follows INK colour foreground colour BORDER width colour draw border at edge of screen or window PAPER colour background colour BLOCK width height across down colour colour a rectangle which has its top left hand corner at position across down SCREEN ORGANISATION When you switch on your QL the screen display is split into three areas
84. OW command and a border added to a window with the BORDER command Output can be directed to a window by printing to the relevant channel Input can be directed to have come from a particular window by inputting from the relevant channel If more than one channel is ready for input then input can be switched between the ready channels by pressing CTRL C The cursor will flash in the selected window Windows can be used for graphics and non graphic output at the same time The non graphic output is relative to the current cursor position which can be positioned anywhere within the specified window with the CURSOR command and at any line column boundary with the AT command The graphics output is relative to a graphics cursor which can be positioned and manipulated with the graphics procedures PARTS Certain commands CLS PAN etc will accept an optional parameter to define part of the current window for their operation This parameter is as defined below 0 whole screen 1 above and excluding cursor line 2 bottom of screen excluding cursor line 3 whole of cursor line 4 line right of and including cursor WINDOW re define a window BORDER take a border from a window PAPER define the paper colour for a window INK define the ink colour for a window STRIP define a strip colour for a window PAN pan a window s contents SCROLL scroll a window s contents AT position the print position CLS clear a window CSIZE set character size FLAS
85. PAPER7 CLS 120 FOR pair 1 TO 20 130 INK RND 5 140 LET side RND 10 TO 20 150 LET ac RND 50 up RND 70 160 square side ac up 170 LET ac actside 5 up up side 5 180 square side ac up 190 END FOR pair The advantages of procedures are 1 You can use the same code more than once in the same program or in others 2 You can break down a task into sub tasks and write procedures for each sub task This helps the analysis and design 3 Procedures can be tested separately This helps the testing and debugging 4 Meaningful procedure names and clearly defined beginnings and ends help to make a program readable When you get used to properly named procedures with good parameter facilities you should find that your problem solving and programming powers are greatly enhanced SELF TESTON CHAPTER 7 You can score a maximum of 14 points from the following test Check your score with the Answers To Self Tests section at the back of this Beginner s Guide 1 How do we normally tackle the problem of great size and complexity in human affairs 2 How can this principle be applied in programming 3 What are the two most obvious features of a simple procedure definition two points 4 What are the two main effects of using a procedure name to call the procedure two points 5 What is the advantage of using procedure names in a main program before the procedure definitions are written 6 What is the advantage of
86. PROCEDURES We use three procedures to match the jobs identified store_data stores the three sets of thirteen words get_random gets three random numbers in range 1 to 13 make_phrase prints a phrase MAIN PROGRAM This is very simple because the main work is done by the procedures Declare DIM the arrays Store_data FOR ten phrases get_random make_phrase END Program 100 REMark KRKKRKKRKKRKKRKKEK 110 REMark Buzzword 120 RE Mark KRKKEKKEKKRKKEKEK 130 DIM adjec1 13 12 adjec2 13 16 noun 13 15 140 store_data 150 FOR phrase 1 TO 10 160 get_random 170 make_phrase 180 END FOR phrase 190 RE Mark KKRKEKEKEKEKEKEKREKREKREREKER 200 REMark Procedure Definitions 21 0 REMark KKRKEKREKEKRKRKERERERERERERE 220 DEFine PROCedure store_data 230 REMark procedureto store the buzzword data 240 RESTORE 420 250 FOR item 1 TO 13 260 READ adjec1 item adjec2 item noun item 270 END FOR item 280 END DEFine 290 DEFine PROCedure get_random 300 REMark procedure to seLect the phrase 310 LET ad1 RND 1 TO 13 320 LET ad2 RND 1 TO 13 330 LET n RND 1 TO 13 340 END DEFine 350 DEFine PROCedure make_phrase 360 REMark procedure to print out the phrase 370 PRINT adjec ad1 adjec2 ad2 noun n 380 END DEFine 390 RE Mark KRKRKEKEKERKRKEKEK 400 REMark Program Data 41 0 REMark KKRKEKRKRKRKERKERKE 420 DATA Full fifth generation systems 430 DATA Systematic
87. QL User Manual Paolo Proietti Libro 1 di Sinclair QL Tei THE SINCLAIR QL MANUAL In no circumstances will either Sinclair Research Limited or Psion Limited be liable for any direct indirect incidental or consequential damage or loss including but not limited to loss of use stored data profit or contracts which may arise from any error defect or failure of the QL hardware or the software supplied with it Sinclair Research has a policy of constant development and improvement of their products Therefore the right is reserved to change manuals hardware software and firmware at any time and without notice QL User Guide First Edition Published by Sinclair Research Limited 1984 25 Willis Road Cambridge Edited by Stephen Berry Sinclair Research Limited C Sinclair Research Limited C Psion Limited No part of this User Guide may be reproduced in any form whatsoever without the written permission of Sinclair Research Limited QL QLUB QLNet Qdos and QL Microdrive are trade marks of Sinclair Research Limited Quill Archive Easel and Abacus are trade marks of Psion Limited PLEASE READ THIS BEFORE UNPACKING THESE PAGES Your QL user Guide is supplied unbound to avoid damage in transit and to make rapid updating easy In addition to this packet containing the pages of the Guide itself you should also find a ring binder and then divider cards packed with your QL Insert the dividers into the binder first The recomm
88. R 20 PRINT die ENTER RUN ENTER f you run the program several times you will get different numbers You can get random whole numbers in any range you like For example RND O TO 100 will produce a number which can be used in scale graphics You can re write the line program so that it produces a random colour Where the range of random numbers starts from zero you can omit the first number and write RND 100 NEW ENTER 10 PAPER 7 CLS ENTER 20 INK RND 5 ENTER 30 LINE 50 60 TO RND 100 RND 100 ENTER RUN ENTER This produces a line starting somewhere near the centre of the screen and finishing at some random point The range of possible colours depends on which mode is selected You will find that a range of numbers something TO something occurs often in SuperBASIC BORDERS The part of the screen in which you have drawn lines and create other output is called a window Later you will see how you can change the size and position of a window or create other windows For the present we shall be content to draw a border round the current window The smallest area of light or colour you can plot on the screen is called a pixel In mode 8 called low resolution mode there are 256 possible pixel positions across the screen and 256 down In mode 4 called high resolution mode there are 512 pixels across the screen and 256 down Thus the size of a pixel depends on the mode You can make a border round the inside edge o
89. RR RRRR ICCCC ICCCC ICCCC ICCCC ICCCC ICCCC The possible effects are shown using red R and contrast C 0 Single pixel of contrast RC RR 1 Horizontal Stripes RR CC 2 Vertical Stripes CR CR 3 Chequerboard CC Stipple Patterns COLOUR PARAMETERS You can specify a colour stipple effect as described above by using three numbers For example INK colour contrast stipple could be used with colour in range 0 to 7 contrast in range 0 to 7 stipple in range 0 to 3 You could achieve the same effect with a single number if you wish though it is not so easy to construct See the Concept Reference Guide colour The following program will display all the possible colour effects 100 REMark Colour Effects 110 FOR num 0 TO 255 120 BLOCK 100 50 40 50 num 130 PAUSE 50 140 END FOR num PAPER PAPER followed by one two or three numbers specifies the background For example PAPER 2 red PAPER 2 4 red green chequerboard PAPER 2 4 1 red green horizontal stripes The colour will not be visible until something else is done for example the screen is cleared by typing CLS INK INK followed by one two or three numbers specifies the colour for printing characters lines or other graphics The colour and stipple effects are the same as for PAPER For example INK 2 red ink INK 2 4 red green chequerboard ink 3 INK 2 4 1 red green horizontal striped ink The ink will be chang
90. S A device is a piece of equipment on the QL to which data can be sent input and from which data can be output Since the system makes no assumptions about the ultimate IO input output device which will be used the O device can be easily changed and the data diverted between devices For example a program may have to output to a printer at some point during its run If the printer is not available then the output can be diverted to a Microdrive file and stored The file can then be printed at a later date VO on the QL can be thought of as being written to and read from a logical file which is in a standard device independent form All device specific operations are performed by individual device drivers specially written for each device on the QL The system can automatically find and include drivers for peripheral devices which are fitted These should be written in the standard QL device driver format see the concept peripheral expansion When a device is activated a channel is opened and linked to the device To correctly open a channel device basic information must sometimes be supplied This extra information is appended to the device name The file name should conform to the rules for a SuperBASIC type name though it is also possible to build up the file name device name as a SuperBASIC string expression In summary the general form of a file name is identifier information where the complete file name including the
91. TING The keyword PRINT can be followed by a sequence of print items A print item may be any of text such as This is text variables such as num word expressions such as 3 num day amp week Print items may be mixed in any print statement but there must be one or more print separators between each pair Print separators may be any of No effect it just separates print items Normally inserts a space between output items If an item will not fit on the current line it behaves as a new line symbol If the item is at the start of line a space is not generated A tabulator causes the output to be tabulated in columns of 8 characters A new line symbol will force a new line TO Allows tabbing The numbers 1 2 3 are legitimate print items and are convenient for illustrating the effects of print separators 100 PRINT 1 2 3123 100 print1 2 3 123 100 PRINT 1 2 3 1 2 3 100 PRINT 1 2 3 123 100 PRINT This is text This is text 100 LET word moves print position 110 PRINT word 100 LET num 13 13 110 PRINT num 100 LET an yes 110 PRINT I say an I say yes 110 PRINT Sum is 4 2 Sum is 6 You can position print output anywhere on the screen with the AT command For example AT 10 15 PRINT This is on row 10 at column 15 The CURSOR command can be used to position the print output anywhere on the screen s scale system For example CURSOR 100 150 PRINT this is 100 pixel grid uni
92. TING A MICRODRIVE FILE In order to sort the file phone into alphabetical order of names we must read it into an internal array sort it and then create a new file which will be in alphabetical order of names It is never good practice to delete a file before its replacement is clearly established and proven correct You should therefore copy the file first as security using a different name The required processes are as follows 1 Copy the file phone to phone_temp 2 Read the file phone into an array 3 Sort the array 4 Pause to check that everything is in order 5 Delete file phone 6 Create new file phone This is all the program needs to do but the new file should be immediately checked using COPY mdv1_phone TO scr Any further necessary checks should be carried out then DELETE mdv2 phone COPY mdv1_phone TO mdv2_phone COPY mdv1_phone TO scr DELETE mdv1_phone_temp The above operations complete the process of substituting a sorted file for the original unsorted one in both master and back up files ARRAY PARAMETERS In the following program we illustrate the passing of complete arrays between main program and procedure The data passes in both directions In line 40 the array row holding the numbers 1 2 3 is passed to the procedure addsix The parameter come receives the incoming data and the procedure adds six to each element The array parameter send at this point holds the numbers 7 8
93. TRL 3 148 94 CTRL 4 14995 CTRL 5 150 96 CTRL 6 151 97 CTRL 7 152 98 CTRL 87 153 99 CTRL 9 154 9A CTRL SHIFT 155 9B CTRL gt 156 9C CTRL SHIFT ce 157 9D CTRL 158 9E CTRL SHIFT 159 9F CTRL SHIFT Y 160 AO CTRL SHIFT 2 161 A1 CTRL SHIFTA j 162 A2 CTRL SHIFTB 163 A3 CTRL SHIFTCE 164 A4 CTRL SHIFT D 165 A5 CTRL SHIFT E 166 A6 CTRL SHIFT F 167 A7 CTRL SHIFT G 168 A8 CTRL SHIFT H 169 A9 CTRL SHIFT 1 170 AA CTRL SHIFT J 171 AB CTRL SHIFT K 172 AC CTRL SHIFT L 7 173 AD CTRL SHIFT M 174 AE CTRL SHIFT N 175 AF CTRL SHIFT O 176 BO CTRL SHIFT P 177 B1 CTRL SHIFT Q 178 B2 CTRL SHIFT R 179 B3 CTRL SHIFT S 180 B4 CTRL SHIFT T 181 B5 CTRL SHIFT Uu 182 B6 CTRL SHIFT V 183 B7 CTRL SHIFT W 184 B8 CTRL SHIFT X 185 B9 CTRL SHIFT Y 186 BA CTRL SHIFT Z 187 BB CTRL 188 BC CTRL 189 BD CTRL 190 BE CTRL SHIFT6 191 BF CTRL SHIFT _ 192 CO Left Cursor left one character 193 C1 ALT Left Cursor to start of line 194 C2 CTRL Left Delete left one character 195 C3 CTRL ALT Left Delete line 196 C4 SHIFT Left Cursor left one word 197 C5 SHIFT ALT Left Pan left 198 C6 SHIFT CTRL Left Delete left one word 199 C7 SHIFT CTRL ALT Left 200 C8 Right Cursor right one character 201 C9 ALT Right Cursor to end of line 202 CA CTRL Right Delete character under cursor 203 CB CTRL ALT Right Delete to end of line 204 CC SHIFT Right Cursor right one word 205 CD SHI
94. _R WIDTH DATE DATE INSTR POKE POKE_W WINDOW DAY INT POKE_L DEFine FuNction KEYROW PRINT END DEFine LBYTES RAD MATHS FUNCTIONS SuperBASIC has the standard trigonometrical and mathematical functions Function Name COS cosine SIN sin TAN tangent ATAN arctangent ACOT arcotangent ACOS arcosine ASIN arcsine COT cotangent EXP exponential LN natural logarithm LOG10 common logarithm INT integer ABS absolute value RAD convert to radians DEG convert to degrees Pl return the value of pi RND generate a random number RANDOMISE reseed the random number generator MEMORY MAP The QL contains a Motorola 68008 microprocessor which can address 1 Megabyte of memory i e from 00000 to FFFFF Hex The use of addresses within this range are defined by Sinclair Research to be as follows FFFFF RESERVED expansion O C0000 RESERVED add on RAM 40000 RAM 96 Kbytes main RAM 28000 RAM 32 Kbytes screen RAM 20000 t VO QL VO 18000 ROM 16 Kbytes plug in ROM O0C000 ROM 48 Kbytes system ROM Physical Memory Map The screen RAM is organised as a series of sixteen bit words starting at address Hex 20000 and progressing in the order of the raster scan i e from left to right with e
95. _boot press ENTER and loading will proceed as before In both cases the program will occasionally need to load extra information from the Microdrive so keep the program cartridge in the microdrive slot until the program has finished SCREEN LAYOUT The control area at the top of the screen will guide you through each program by displaying the options that you will need most often and prompting you further if necessary In many cases the program will suggest a suitable answer when it asks for information Press ENTER to accept this suggestion or simply type in your own answer and the computer s suggestion will disappear Pressing F2 will remove this area and will make the central area larger Pressing F2 again will restore the control area The central area of the screen shows the information that you are working on for example the text of a document the contents of a card index a graph or financial forecast It is shown in the style most suitable for the particular application The bottom of the screen shows the input line where for example commands that you type in are displayed Below this is the status area which reports on the current state of work It displays things like the name of the data or document on which you are working how much unused memory remains etc FUNCTION KEYS Three of the five function keys have the same meaning in all the QL programs These are Key Function F1 request help F2 remove or restore the
96. a 1 TO m will select from the beginning to the nth character inclusively a will select the entire contents of a a Some forms of BASIC have functions called LEFT MID RIGHTS These are not necessary in SuperBASIC Their equivalents are specified below SuperBASIC Other BASIC a n MID a n 1 a n TO m MID a n m 1 n a 1 TO n LEFT a n a n TO RIGHTS a LEN a 1 n WARNING Assigning data to a sliced string array or string variable may not have the desired effect Assignments made in this way will not update the length of the string The length of a string array or string variable is only updated when an assignment is made to the whole string START UP Immediately after switch on or reset the QL will perform a RAM test which will give a spurious pattern on the display If the RAM test is passed then the screen will be cleared and the copyright screen displayed F1 monitor F2 TV 1983 Sinclair Research Ltd After start up the QL displays the copyright message and asks whether it is being used ona television or a monitor The QL will set different initial screen modes and window sizes depending on the answer Press F1 if you are using a monitor and F2 if you are using a television set The QL has the ability to boot itself up from programs contained in either the ROM car
97. a NEW one SELF TEST ON CHAPTER 1 You can score a maximum of 16 points from the following test Check your score with the answers in the ANSWERS pages at the end of this Beginner s Guide 1 In what circumstances might you use the BREAK sequence 2 Where is the RESET button 3 What is the effect of the RESET button 4 Name two differences between a SHIFT key and the CAPS LOCK key 5 How can you delete a wrong character which you have just typed 6 What is the purpose of the ENTER key 7 What symbol do we use for the ENTER key What is the effect of the commands in questions 8 to 11 8 CLS ENTER 9 RUN ENTER 10 LIST ENTER 11 NEW ENTER 12 Do keywords have the proper effect if you type them in lower case 13 What is the significance of the parts of keywords which the QL displays in upper case CHAPTER 2 INSTRUCTING THE COMPUTER Computers need to store data such as numbers The storage can be imagined as pigeon holes Though you cannot see them you do need to give names to particular pigeon holes Suppose you want to do the following simple calculation A dog breeder has 9 dogs to feed for 28 days each at the rate of one tin of Beefo per day Make the computer print display on the screen the required number of tins One way of solving this problem would require three pigeon holes for number of dogs number of days total number of tins SuperBASIC allows y
98. a letter You will get a symbol in an upper position on the key Without a SHIFT key you get lower case small letters or a symbol in a lower position ona key CAPITALS LOCK This key works like a switch Just press it once and only the letter keys will be locked into a particular mode upper case or lower case Type some letter keys Type the CAPS LOCK key once Type some letter keys You will see that the mode changes and remains until you type the CAPS LOCK key again SPACE BAR The long key at the bottom of the keyboard gives spaces This is a very important key in SuperBASIC as you will see in chapter two RUBBING OUT The left cursor together with the CTRL key acts like a rubber You must hold down the CTRL key while you press the cursor key Each time you then press both together the previous character is deleted ENTER The system needs to know when you have typed a complete message or instruction When you have typed something complete such as RUN you type the ENTER key to enter it into the system for action Because this key is needed so often we have used a special symbol for it ENTER Where we use the ENTER symbol to represent a keystroke we mean press the key labelled ENTER not type in the letters e nter We shall use this for convenience better presentation and to save space Test the ENTER key by typing PRINT Correct ENTER If you made no mistakes the system will respond with Correct OTHER KEYB
99. ach display line and then from the top to the bottom of the picture The bits within eachbword are organised so that a pixel to the left is always more significant than a pixel to the right i e the pixel pattern on the screen looks the same as the binary pattern However the organisation of the colour information in the two screen modes is different high byte low byte mode AO 0 AO 1 HII GGGGGGGG RRRRRRRR 512 mode high res HII GFGFGFGF RBRBRBRB 256 mode low res G Green B Blue R Red F Flash Setting the Flash bit toggles the flash state and freezes the background colour for the flash to the value given by R G and B for that pixel Flashing is always reset at the beginning of each display line In high resolution mode red and green specified together is interpreted by the hardware as white WARNING Use of reserved areas in the memory map may cause incompatibility with future Sinclair products Spurious output to addresses defined to be peripheral VO addresses can cause unpredictable behaviour It is recommended that these areas are NOT written to and not used for any other purpose Poking areas in use as Microdrive buffers can corrupt Microdrive data and can result in a loss of information Pokng areas in u
100. again Under 6 You should work carefully through chapter three again and repeat the test ANSWERS TO SELF TEST ON CHAPTER 4 1 A character string is a sequence of characters such as letters digits or other symbols 2 The term character string is often abbreviated to string 3 A string variable name always ends with 4 Names such as word are sometimes pronounced worddollar 5 The keyword LEN will find the length or number of characters in a string For example if the variable meat has the value steak then the statement PRINT LEN meat will output 5 6 The symbol for joining two strings is amp 7 The limits of a string may be defined by quotes or apostrophes 8 The quotes are not part of the actual string and are not stored 9 The function is CHR You must use it with brackets as in CHR 66 or with brackets as in CHR RND 65 TO 67 10 You generate random letters with statements like lettercode RND 65 TO 90 PRINT CHR lettercode CHECK YOUR SCORE 9 or 10 is very good Carry on reading 7 or 8 is good but re read some parts of chapter four 5 or 6 is fair but re read some parts of chapter four and do the test again Under 5 You should work carefully through chapter four again and repeat the test ANSWERS TO SELF TEST ON CHAPTER 5 1 Lower case letters for variable names or loop names contrast with the keywords which are at least partly displayed in upper case 2 Indenting reve
101. als clearly what is the extent and content of loops and other structures 3 Identifiers names should normally be chosen so that they mean something for example count or word rather than C or W 4 You can edit a stored program by replacing a line inserting a line deleting a line three points 5 The ENTER key must be used to enter a command or program line 6 The word NEW will wipe out the previous SuperBASIC program in the QL and will ensure that a new program which you enter will not be merged with an old one 7 If you wish a line to be stored as part of a program then you must use a line number 8 The word RUN followed by ENTER will cause a program to execute 9 The word REMark enables you to put into a program information which is ignored at execution time 10 The keywords SAVE and LOAD enable programs to be stored on and retrieved from cartridges two points CHECK YOUR SCORE 12 to 14 is very good Carry on reading 10 or 11 is good but re read some parts of chapter five 8 or 9 is fair but re read some parts of chapter five and do the test again Under 8 You should re read chapter five carefully and do the test again ANSWERS TO SELF TEST ON CHAPTER 6 1 tis not easy to think of many different variable names for storing the data If you can think of enough names every one has to be written in a LET statement or a READ statement if you do not use arrays 2 A number called the subscript is part of an
102. alue of a pigeon hole with a PRINT statement 4 The technical name for a pigeon hole is variable because its values can vary as a program runs 5 A variable gets its first value when it is first used ina LET statement INPUT statement or READ statement 6 A change in the value of a variable is usually caused by the execution of a LET statement 7 The signin a LET statement represents an operation Evaluate whatever is on the right hand side and place it in the pigeon hole named on the left hand side that is Let the left hand side become equal to the right hand side 8 An un numbered statement is executed immediately 9 A numbered statement is not executed immediately It is stored 10 The quotes ina PRINT statement enclose text which is to be printed 11 When quotes are not used you are printing out the value of a variable 12 An INPUT statement makes the program pause so that you can type data at the keyboard 13 DATA statements are never executed 14 They are used to provide values for the variables in READ statements 15 The technical word for the name of a pigeon hole is identifier 16 Example answers i day ii day_23 iii day_of_week 3 points 17 The space bar is especially important for putting spaces after or before keywords so that they cannot be taken as identifiers names chosen by the user 18 Freely chosen identifiers are important because they help you to make programs easier t
103. ameter_2 where 1 will draw from the specified point to the next specified point turning through the specified angle 2 will draw from the the last point plotted to the specified point turning through the specified angle example i ARC 15 10 TO 40 40 PV 2 draw an are from 15 10 to 40 40 turning through PI 2 radians ii ARC TO 50 50 PV 2 draw an are from the last point plotted to 50 50 turning through PI 2 radians iii ARC_R 10 10 TO 55 45 0 5 draw an are starting 10 10 from the last point plotted to 55 45 from the start of the are turning through 0 5 radians AT windows AT allows the print position to be modified on an imaginary row column grid based on the current character size AT uses a modified form of the pixel coordinate system where row O column O is in the top left hand corner of the window AT affects the print position in the window attached to the specified or default channel syntax line numeric_expression column numeric_expression AT channel line column example AT 10 20 PRINT This is at line 10 column 20 AUTO AUTO allows line numbers to be generated automatically when entering programs directly into the computer AUTO will generate the next number in sequence and will then enter the SuperBASIC line editor while the line is typed in If the line already exists then a copy of the line is presented along with the line number Pressing ENTER at any point in the line will check the syntax
104. ams When line 10 is executed the system searches the program fora DATA statement It then uses the values in the DATA statement for the variables in the READ statement in exactly the same order We usually place DATA statements at the end of a program They are used by the program but they are not executed in the sense that every other line is executed in turn DATA statements can go anywhere in a program but they are best at the end out of the way Think of them as necessary to but not really part of the active program The rules about READ and DATA are as follows 1 All DATA statements are considered to be a single long sequence of items So far these items have been numbers but they could be words or letters 2 Every time a READ statement is executed the necessary items are copied from the DATA statement into the variables named in the READ statement The system keeps track of which items have been READ by means of an internal record Ifa program attempts to READ more items than exist in all the DATA statements an error will be signalled IDENTIFIERS NAMES You have used names for pigeon holes such as dogs bars You may choose words like these according to certain rules A name cannot include spaces A name must start with a letter A name must be made up from letters digits _ underscore The symbols have special purposes to be explained later but you can use the underscore to make names such as d
105. and so can display more text and is therefore more expensive A colour television or monitor will of course be required to make use of the QL s colour display but the computer will work perfectly well in black and white representing colours as shades of grey Most television sets in current use will be suitable for the QL provided they are able to receive 625 line UHF transmissions i e BBC2 and Channel 4 Locate the aerial socket at the back of your TV and remove the aerial cable that may be plugged into it If your set has more than one socket use the one labelled UHF or 625 Plug in the QL s aerial lead Use the end that looks similar to the original aerial plug and plug the other end into the socket marked UHF on the back of the computer Plug the power supply into a mains socket and switch on Remove any cartridges from the Microdrive slots and push the small power supply connector into the three pin plug marked POWER on the back of the QL The yellow power light below the F5 key should now be glowing and your set up should look like this TV SET POWER SUPPLY UHF When the computer has been on for a while the case above the Microdrives will feel warm this is quite normal The QL has no on off switch but can be turned off by unplugging the power supply connector Remember that any program or data in the machine will be lost when it is turned off and should first be saved ona Microdrive car
106. ariable name Functions and procedures in SuperBASIC can be used recursively That is a function or procedure can call itself either directly or indirectly Command Function DEFine FuNction define a function DEFine PROCedure define a procedure RETurn leave a function or procedure return data from a function LOCal define local data in a function or procedure GRAPHICS itis important to realise that the QL screen has non square pixels and that changing screen mode will change the shape of the pixels Thus if the grapics procedures were simply pixel based they would draw different shapes in the two modes For example in one mode we would have a circle while the same figure in the other mode would be an ellipse The graphics procedures ensure that whatever screen mode is in use consistent figures are produced Itis not possible to use a simple pixel count to indicate sizes of figures so instead the graphics procedures use an arbitrary scale and coordinate system to specify sizes and positions of figures The graphics procedures use the Graphics Co ordinate System i e draw relative to the Graphics Origin which is in the bottom left hand corner of the specified or default window Note that this is not the same as the Pixel Origin used to define the position of Windows and Blocks etc The graphics origin allows a standard Cartesian coordinate system to be used A graphics cursor is updated after each graphics operation subsequent operations
107. articular if three keys at the corner of a rectangle in the matrix are depressed simultaneously it will appear as if the key at the fourth corner has also been depressed The three special keys CTRL SHIFT and ALT are an exception to this rule and do not interact with other keys in this way syntax row numeric_expression range 0 7 KEYROW row example 100 REMark run this program and press a few keys 110 REPeat loop 120 CURSOR 0 0 130 FOR row 0 to 7 140 PRINT row KEYROW row 150 END FOR row 160 END REPeat Loop KEYBOARD MATRIX COLUMN ROW 1 2 4 8 16 32 64 128 7 ISHIFT CTRL IALTIXIVIN 8121610 EIOMU 41L5 WILITABIRElv 31HIIAIPIDIJ CAPS LOCK KISIFFIG ZI1 IC BfM ENTER It up ESC I IISPACE down F41F15F2F3F547 LBYTES devices microdrives LBYTES will load a data file into memory at the specified start address syntax start_address numeric_expression LBYTES device startaddress example i LBYTES mdvl_screen 131072 load a screen image ii LBYTES mdvl_program start_address load a program ata specified address LEN string arrays LEN is a function which will return the length of the specified string expression syntax LEN string_ expression example i PRINT LEN LEN will find the ength of this string ii PRINT LEN output_string LET LET starts a SuperBASIC assignment statement The use of the LET keyword is optional The assignment may be used for both string and numeric as
108. assumed stipple 3 iii Triple colour background contrast stipple Background and contrast colours and stipple are each defined separately COLOURS The codes for colour selection depend on the screen mode in use 0000 black black 1001 blue blue black 2 0 1 0 red red red 3011 red blue magenta red 4 1 0 0 green green green 510 1 green blue cyan green 6 1 1 0 green red yellow white 7 111 green red blue white white Colour Composition and Codes STIPPLES Stipples mix a background and a contrast colour in a fine stipple pattern Stipples can be used on the QL in the same manner as ordinary solid colours although stipples may not be reproduced correctly on an ordinary domestic television There are four stipple patterns XO XX OX OX XX OO OX XO Stipple O Stipple 1 Stipple 2 Stipple 3 Stipple 3 is the default example i PAPER 255 CLS ii PAPER 2 4 CLS iii PAPER 0 2 0 CLS warning Stipples may not reproduce correctly on a domestic television set which is fed via the UHF socket COMMUNICATIONS RS 232 C The QL has two serial ports called SER1 and SER2 for connecting it to equipment which uses serial communications obeying EIA standard RS 232 C ora compatible standard The RS 232 C standard was originally designed to enable computers to send and receive data via telephone lines using a modem However it is now frequently used to connect computers directly with each other and to various items of p
109. at numbers or character strings can become values of variables You can picture this as numbers or words going into internal pigeon holes or houses Suppose for example that four employees of a company are to be sent to a small village perhaps because oil has been discovered The village is one of the few places where the houses only have names and there are four available for rent All the house names end with a dollar symbol Westlea Lakeside Roselawn Oaktree The four employees are called VAL HAL MEL DEL They can be placed in the houses by one of two methods Program 1 100 LET westlea VAL 110 LET lakeside HAL 120 LET roselawn MEL 130 LET oaktree DEL 140 PRINT westlea lakeside roselawn oaktree Program 2 100 READ westlea lakeside roselawn oaktree 110 PRINT westlea lakeside roselawn oaktree 120 DATA VAL HAL MEL DEL westlea lakeside roselawn oaktree VVVV VAL HAL MEL DEL As the amount of data gets larger the advantages of READ and DATA over LET become greater But when the data gets really numerous the problem of finding names for houses gets as difficult as finding vacant houses ina small village The solution to this and many other problems of handling data lies in a new type of pigeon hole or variable in which many may share a single name However they must be distinct so ea
110. at you test all possibilities by entering data which forms eight three digit binary numbers 000 to 111 000 001 010 011 100 101 110 111 PROBLEMS ON CHAPTER 10 1 Place ten numbers ina DATA statement READ each number and if itis greater than 20 then print it 2 Test all the numbers from 1 to 100 and print only those which are perfect squares or divisible by 7 3 Toys are described as Safe S or Unsafe U Expensive E or Cheap C and either for Girls G Boys B or Anyone A A trio of letters encodes the qualities of each toy Place five such trios ina DATA statement and then search it printing only those which are safe and suitable for girls 4 Modify program 3 to print those which are expensive and not safe 5 Modify program 3 to print those which are safe not expensive and suitable for anyone CHAPTER 11 HANDLING TEXT STRINGS You have used string variables to store character strings and you know that the rules for manipulating string variables or string constants are not the same as those for numeric variables or numeric constants SuperBASIC offers a full range of facilities for manipulating character strings effectively In particular the concept of string slicing both extends and simplifies the business of handling substrings or slices of a string ASSIGNING STRINGS Storage for string variables is allocated as it is required by a program For example the lines 100 LET words LONG 110 LET words LONG
111. ause data can occur on its own for example 3 4 or Blue hat as the value of a variable But if you understand the different types of variables you must also understand the different types of data IDENTIFIERS AND VARIABLES 1 A SuperBASIC identifier must begin with a letter and is a sequence of upper or lower case letters digits or underscore 2 Anidentifier may be up to 255 characters in length so there is no effective limit in practice 3 An identifier cannot be the same as a keyword of SuperBASIC 4 An integer variable name is an identifier with on the end 5 A string variable name is an identifier with on the end 6 No other identifiers must use the symbols and 7 Anidentifier should usually be chosen so that it means something to a human reader but for SuperBASIC it does not have any particular meaning other than that it identifies certain things FLOATING POINT VARIABLES Examples of the use of floating point variables are 100 LET days 24 110 LET sales 3649 84 120 LET sales_per_day sales days 130 PRINT sales_per_day The value of a floating point variable may be anything in the range 615 615 or 10 to or 10 with 8 significant figures Suppose in the above program sales were exceptionally only 3p Change line 110 to 110 LET sales 0 03 This system will change this to 110 LET sales 3E 2 To interpret this start with 3 or 3 0 and move the decimal point 2 places i e two places
112. byte keyboard type ahead buffer v OPEN 8 mdv1_read_write_file OVER windows OVER selects the type of over printing required in the window attached to the specified or default channel The selected type remains in effect until the next use of OVER syntax switch numeric_expression range 1 i OVER channel switch where switch 0 print ink on strip switch 1 print in ink on transparent stnp switch 1 XORs the data on the screen example i OVER 1 set overprinting ii 10 REMark Shadow Writing 11 PAPER7 INK O OVER1 CLS 12 CSIZE 3 1 13 FORI 0 TO 10 14 CURSOR i i 15 IF i 10 THEN INK 2 16 PRINT Shadow 17 END FORi PAN windows PAN the entire current window the specified number of pixels to the left or the right PAPER is scrolled in to fill the clear area An optional second parameter can be specified which will allow only part of the screen to be panned syntax distance numeric_expression part numeric_expression PAN channel distance part where part 0 whole screen or no parameter part 3 whole of the cursor line part 4 right end of cursor line including the cursor position f the expression evaluates to a positive value then the contents of the screen will be shifted to the right example i PAN 2 50 pan left 50 pixels ii PAN 100 pan right 100 pixels iii PAN 50 3 pan the whole of the current cursor line 50 pixels to the right If stipples are bei
113. ch variable also has a number like numbered houses in the same street Suppose that you need four vacant houses in High Street numbered 1 to 4 In SuperBASIC we say there is an array of four houses The name of the array is high_st and the four houses are to be numbered 1 to 4 But you cannot just use these array variables as you can ordinary simple variables You have to declare the dimensions or size of the array first The computer allocates space internally and it needs to know how many string variables there are in the array and also the maximum length of each string variable You use a DIM statement thus DIM high_st 4 3 maximum length of string number of string variables After the DIM statement has been executed the variables are available for use It is as though the houses have been built but are still empty The four houses share a common name high_st but each has its own number and each can hold up to three characters FaH ee i manana ananem I 1 2 3 4 ha a et eth pt high_st gt 4 4 H tt tt tet tt tt tet tt t t HITTITE 4 There are five programs below which all do the same thing they cause the four houses to be occupied and they PRINT to show that the occupation has really worked The final method uses only four lines but the other four lead up to
114. choose and make a tally of the number of times each dish is chosen 3 Pass the three numbers to a procedure waiter which passes back the cost of the order to the main program using a parameter cost Procedure waiter calls two other procedures compute and cook which compute the cost and simulate cooking 4 The procedure cook simply prints the number required and the name of each dish The main program should call procedures as necessary get the total cost from procedure waiter add 10 for a tip and print the amount of the total bill Design This program illustrates parameter passing in a fairly complex way and we will explain the program step by step before putting it together 100 REMark Procedures 110 RESTORE 490 120 DIM item 3 7 price 3 dish 3 130 REMark PROGRAM 140 LET tip 0 1 150 set_up 210 DEFine PROCedure set_up 220 FORK 1TO3 230 READ item k 240 READ price k 250 END FOR k 260 END DEFine 490 DATA Prawns 3 5 Chicken 2 8 Special 3 3 The names of menu items and their prices are placed in the arrays item and price The next step is to choose a menu number for each of the six customers The tally of the number of each dish required will be kept in the array dish 160 choose dish 270 DEFine PROCedure choose dish 280 FOR pick 1 TO 6 290 LET number RND 1 TO 3 300 LET dish number dish number 1 310 END FOR pick 320 END DEFine Note that the for
115. context may be contrived and trivial but it offers a simple basis for discussion and it illustrates difficulties which arise across the whole range of programming applications EXAMPLE 1 A bandit is holed up in the Old School House The sheriff has six bullets in his gun Simulate the firing of the six shots Program 1 100 REMark Western FOR 110 FOR bullets 1 TO6 120 PRINT Take aim 130 PRINT Fire shot 140 END FOR bullets Program 2 100 REMark Western REPeat 110 LET bullets 6 120 REPeat bandit 130 PRINT Take aim 140 PRINT Fire shot 150 LET bullets bullets 1 160 IF bullets 0 THEN EXIT bandit 170 END REPeat bandit Both these programs produce the same output Take aim Fire a shot is printed six times If in each program the 6 is changed to any number down to 1 both programs still work as you would expect But what if the gun is empty before any shots have been fired EXAMPLE 2 Suppose that someone has secretly taken all the bullets out of the sheriffs gun What happens if you simply change the 6 to 0 ineach program Program 1 100 REMark Western FOR Zero Case 110 FOR bullets 1 to 0 120 PRINT Take aim 130 PRINT Fire a shot 140 END FOR bullets This works correctly There is no output The zero case behaves properly in SuperBASIC Program 2 100 REMark Western REPeat Fails 110 LET bullets 0 120 REPeat bandit 130 PRINT Take aim 140 PRINT Fire shot 150 LET bullets bul
116. control area F3 call up the commands for selection The remaining two function keys are used for actions particular to each program HELP The first option displayed at the top left of the control area indicates that help is available by pressing F1 When you ask for HELP there will be a short pause before the display changes to show the Help information Help will suggest other topics for which help is available Type the name of the topic and press ENTER You do not need to type in the whole name just enough characters for it to be distinguished from the other topics You can repeat this as many times as necessary Pressing ENTER without selecting a topic will take you out to the previous level ESC will take you right out of HELP and back into the program Help is always available provided that the program cartridge is in Microdrive 1 Press F1 and the most appropriate Help information will be displayed THE LINE EDITOR You can use the line editor to change or correct a line of text that you have typed in All the QL programs use the same line editor but each program uses itina way most suitable for that application In QL Quill you use the line editor for example for editing the text in commands and QL Archive uses the editor extensively for editing database programs The line editor uses the four cursor keys together with the CTRL and SHIFT keys In the table below lt and gt mean the cursor left and right arrow keys re
117. converted to string before assigning LOAD mdv1_ data the string mdv1_data is converted to type name by the LOAD procedure before it is used Statements can be written in SuperBASIC which would generate errors in most other computer languages In general it is possible to mix data types ina very flexible manner i PRINT 1 2 3 ii LETa 1 2 a 4 COLOUR Colours on the QL can be either a SOLID colour or a STIPPLE a mixture of two colours to some predefined pattern Colour specification on the QL can be up to three items a colour a contrast colour and a stipple pattern i Single The single argument specifies the three parts of the colour specification The main colour is contained in the bottom three bits of the colour byte The next three bits contain the exclusive or XOR of the main colour and the contrast colour The top two bits indicate the stipple pattern stipple contrast XOR main mix colour II fc XXXXXXXXXXXX ANH HHH foc XXXXXXXXXXXX AAEM fe PXKKKKKKKKKXKX AAEM bit76543210 By specifying only the bottom three bits i e the required colour no stipple will be requested and a single solid colour will be used for display ii Double colour background contrast The colour is a stipple of the two specified colours The default checkerboard stipple is
118. ctive limit to the size of the parameter syntax angle nunieric_expression in radians ACOS angle ACOT angle ASIN angle ATAN angle example i PRINT ATAN angle ii PRINT ASIN 1 iii PRINT ACOT 3 6574 iv PRINT ATAN a b ADATE clock ADATE allows the clock to be adjusted syntax seconds numeric_expression ADATE seconds example i ADATE 3600 will advance the clock 1 hour ii ADATE 60 will move the clock back 1 minute ARC ARC_R graphics ARC will draw an arc of a circle between two specified points in the window attached to the default or specified channel The end points of the arc are specified using the graphics co ordinate system Multiple arcs can be drawn with a single ARC command The end points of the are can be specified in absolute coordinates relative to the graphics origin or in relative coordinates relative to the graphics cursor If the first point is omitted then the are is drawn from the graphics cursor to the specified point through the specified angle ARC will always draw with absolute coordinates while ARC_R will always draw relative to the graphics cursor syntax x numeric_expression y numeric_expression angle numeric_expression in radians point xy parameter_2 TO point angle 1 point TO point angle 2 parameter_1 point TO point angle 1 TO point angle 2 ARC channel parameter_1 parameter_2 ARC_R channel parameter_1 par
119. d in radians to an angle expressed in degrees syntax DEG numeric_expression example PRINT DEG PI Z will print 90 DELETE micrdrives DELETE will remove a file from the directory of the cartridge in the specified Microdrive syntax DELETE device The device specification must be a Microdrive device example i DELETE mdv_old_data ii DELETE mdv1_letter_file DIM arrays Defines an array to SuperBASIC String integer and floating point arrays can be defined String arrays handle fixed length strings and the final index is taken to be the string length Array indices run from 0 up to the maximum index specified in the DIM statement thus DIM will generate an array with one more element in each dimension than is actually specified When an array is specified itis initialised to zero for a numeric array and zero length strings for a string array syntax index numeric_expression array indentifier index index DIM array x array example i DIM string_array 10 10 50 ii DIM matrix 100 100 DIMN arrays DIMN is a function which will return the maximum size of a specified dimension of a specified array If a dimension is not specified then the first dimension is assumed If the specified dimension does not exist or the identifier is not an array then zero is returned syntax array identifier index numeric_expression 1 for dimension 1 etc DIMN array dimension example consider the array defined by
120. d underscores i e repeat something which is optional TURTLE GRAPHICS SuperBASIC has a set of turtle graphics commands Command Function PENUP stop drawing PENDOWN start drawing MOVE move the turtle TURN turn the turtle TURNTO turn to a specific heading The set of commands is the minimum and normally would be used within another procedure to expand on the commands For example 100 DEFine PROCedure forward distance 110 MOVE distance 120 END DEFine 130 DEFine PROCedure backwards distance 140 MOVE distance 150 END DEFine 160 DEFine PROCedure left angle 170 TURN angle 180 END DEFine 190 DEFine PROCedure right angle 200 TURN angle 210 END DEFine These will define some of the more famous turtle graphic commands Initially the turtle s penis up and the turtle is pointing at 0 degrees which is to the right hand side of the window The FILL command will also work with figures drawn with turtle graphics Also ordinary graphics and turtle graphics can be mixed although the direction of the turtle is not modified by the ordinary graphics commands WINDOWS Windows are areas of the screen which behave in most respects as though each individual window was a screen in its own right i e the window will scroll when it has become filled by text it can be cleared with the CLS command etc Windows can be specified and linked to a channel when the channel is opened The current window shape can be changed with the WIND
121. dth height x y colour example i BLOCK 10 10 5 5 7 10x10 pixel white block at 5 5 ii 100 REMark bar chart 110 CSIZE 3 1 120 PRINT bar chart 130 LET bottom 100 size 20 left 10 140 FOR bar 1 to 10 150 LET colour RND O TO 255 160 LET height RND 2 TO 20 170 BLOCK size height Leftt bar size bottom height 0 180 BLOCK size 2 height 2 lefttbar sizetl bottom height l colour 190 END FOR bar BORDER windows BORDER will add a border to the window attached to the specified channel or default channel For all subsequent operations except BORDER the window size is reduced to allow space for the BORDER If another BORDER command is used then the full size of the original window is restored prior to the border being added thus multiple BORDER commands have the effect of changing the size and colour of a single border Multiple borders are not created unless specific action is taken f BORDER is used without specifying a colour then a transparent border of the specified width is created syntax width numeric_expression BORDER channel size colour example i BORDER 10 0 7 black and white stipple border ii 100 REMark Lurid Borders 110 FOR thickness 50 to 2 STEP 2 120 BORDER thickness RND O TO 255 130 END FOR thickness 140 BORDER 50 CALL Qdos Machine code can be accessed directly from SuperBASIC by using the CALL command CALL can accept up to 13 long word parameters which will b
122. e CTRL with gt CTRL and right arrow keys and the character to the right of the cursor will move up to close the gap USING MICRODRIVE CARTRIDGES Before using a new Microdrive cartridge it must be formatted Follow the instructions in the Introduction The choice of name for the cartridge follows the same rules as SuperBASIC identifers etc but limited to only 10 characters It is a good idea to write the name of the cartridge on the cartridge itself using one of the supplied sticky labels You should always keep at least one back up copy of any program or data Follow the instructions in the Information section of the User Guide kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk k k k WARNING k k k f you FORMAT a cartridge which holds programs and or data ALL the programs and or data will be lost k k k KRR kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk SAVING PROGRAMS The following program sets borders 8 pixels wide in red code 2 in three windows designated 0 1 2 100 REMark Border 110 FOR k 0 TO 2 BORDER k 8 2 You can save it on a microdrive by inserting a cartridge and typing SAVE mdv1_bord The program will be saved in a Microdrive file called bord CHECKING A CARTRIDGE f you want to know what programs or data files are on a particular cartridge place it in Microdrive 1 and type DIR mdv1 _ The directory will be displayed on the screen If
123. e forma_parameters LOCal identifier x identifier statements RETurn expression END DEFine RETurn can be at any position within the procedure body LOCal statements must preceed the first executable statement in the function example 10 DEFine FuNction mean a b c 20 LOCaL answer 30 LET answer a b c 3 40 RETurn answer 50 END DEFine 60 PRINT mean 1 2 3 Comment To improve legibility of programs the name of the function can be appended to the END DEFine statement However the name will not be checked by SuperBASIC DEFine PROCedure END DEFine functions and procedures DEFine PROCedure defines a SuperBASIC procedure The sequence of statements between the DEFine PROCedure statement and the END DEFine statement constitutes the procedure The procedure definition may also include a list of formal parameters which will supply data for the procedure The formal parameters must be enclosed in brackets for the procedure definition but the brackets are not necessary when the procedure is called If the procedure requires no parameters then there is no need to include an empty set of brackets in the procedure definition Formal parameters take their type and characteristics from the corresponding actual parameters Variables may be defined to be LOCal to a procedure Local variables have no effect on similarly named variables outside the procedure If required local arrays should be dimensioned within the LOCal s
124. e FuNction ack m n 120 IF m 0 THEN RETurn n l 130 IF n 0 THEN RETurn ack m l 1 140 RETernack m l ack m n 150 END DEFine ii 10 LET warning_flag 1 11 LET error_number RND 0 TO 10 12 warning error_number 13 DEFine PROCedure warning n 14 IF warning_flag THEN 15 PRINT WARNING 16 SELect ON n 17 ONn 1 18 PRINT Microdrive full 19 ONn 2 20 PRINT Data space full 21 ON n REMAINDER 22 PRINT Program error 23 END SELect 24 ELSE 25 RETurn 26 END IF 27 END DEFine it is not compulsory to have a RETurnin a procedure If processing reaches the END DEFine of a procedure then the procedure will return automatically RETurn by itself is used to ieturn from a GOSUB RND maths function RND generates a random number Up to two parameters may be specified for RND If no parameters are specified then RND returns a pseudo random floating point number in the exclusive range 0 to 1 Ifa single parameter is specified then RND returns an integer in the inclusive range 0 to the specified parameter If two parameters are specified then RND returns an integer in the inclusive range specified by the two parameters syntax RND numeric_expression TO numeric_expression example i PRINT RND floating point number between 0 and 1 ii PRINT RND 10 TO 20 integer between 10 and 20 iii PRINT RND 1 TO 6 integer between 1 and 6 iv PRINT RND 10 integer between 0 and 10 RUN program RUN allows a SuperBASI
125. e IAS NAE NSELE ESAE TES ee time LEVEL4 Randomness can be added to the sound This is a deviation from the specified step or gradient Depending on the amount of randomness added in relation to the pitches and the gradient it will generate a very wide and unexpected range of sounds pitch pitch2 HITT Li ibe I 11 Trees HITT ooo pitch E AERE en CRES TEEDE A AE NI AOLE a eee ae time LEVEL 5 More variation can be added by specifying fuzziness Fuzziness adds a random factor to the pitch continuously Fuzziness tends to make the sound buzz Combining all of the above effects can make a very wide range of sounds many of them unexpected QL sound is best explored through experiment By specifying a time interval of zero the sound can be made to repeat forever and so a sequence of BEEP commands can be used until the sound generated is the sound which is required A word of warning slight changes in the value of a single parameter can have alarming results on the sound generated STATEMENT A SuperBASIC statement is an instruction to the QL to perform a specific operation for example LETa 2 will assign the value 2 to the variable identified by a More than one statement can be written on a single line by separating the individual statements from each other by a colon for example LETa a 2 PRINTa will add 2 to the value identified by the variable a and w
126. e following program and try to consider what two numbers will be output 100 REMark scope 110 LET number 1 120 test 130 DEFine PROCedure test 140 LOCal number 150 LET number 2 160 PRINT number 170 try 180 END DEFine 190 DEFine PROCedure try 200 PRINT number 210 END DEFine Obviously the first number to be printed will be 2 but is the variable number in line 200 global The answer is that the value of number in line 160 will be carried into the procedure try A variable which is local to a procedure will be the same variable in a second procedure called by the first Equally if the procedure try is called by the main program the variable number will be the same number in both the main program and procedure try The implications may seem strange at first but they are logical 1 The variable number in line 110 is global 2 The variable number in procedure test is definitely local to the procedure 3 The variable number in procedure try belongs to the part of the program which was the last call to it We have covered many concepts in this chapter because SuperBASIC functions and procedures are very powerful However you should not expect to use all these features immediately Use procedures and functions in simple ways at first They can be very effective and the power is there if you need it 1 Six employees are identified by their surnames only Each employee has a particular pension fund rate
127. e machine will be lost if reset is pressed and sometimes data already recorded on Microdrive cartridges can be corrupted Use reset with caution and always remove Microdrive cartridges before doing so SETTING UP THE POWER SUPPLY To make the computer operate various connections have to be made Your QL power supply has two leads One is fitted with a small rectangular connector with three holes in it The other is the mains lead and is supplied with bare ends to which a suitable mains plug must be fitted Please do not connect the power supply lead to the computer until all other leads and peripherals have been connected Always connect the power supply lead to the computer last of all Connect the mains plug as follows The blue wire goes to the terminal marked N or neutral or coloured blue or black The brown wire goes to the terminal marked L or live and coloured brown or red The power supply is double insulated and does not need an earth connection If you are using a fused plug it must be fitted with a three amp fuse Make sure all connections are sound If necessary get someone with electrical experience to help you THE DISPLAY Although the QL will work once the power supply is connected you will not be able to see what it is doing until you add a television set or a monitor A monitor has a screen like a television but it cannot receive television signals It usually has better resolution than a television set
128. e placed into the 68008 data and address registers D1 to D7 AO to A5 in sequence No data is returned from CALL syntax address numeric_expression data numeric_expression CALL address data 13 data parameters maximum example i CALL 262144 0 0 0 ii CALL 262500 12 3 4 1212 6 Warning Address register A6 should not be used in routines called using this command To return to SuperBASIC use the instructions MOVEQ 0 DO RTS CHR BASIC CHR is a function which will return the character whose value is specified as a parameter CHR is the inverse of CODE syntax CHR numeric_expressen example i PRINT CHRS 27 print ASCII escape character ii PRINT CHR 65 print A CIRCLE CIRCLE_R graphics CIRCLE will draw a circle or an ellipse at a specified angle on the screen at a specified position and size The circle will be drawn in the window attached to the specified or default channel CIRCLE uses the graphics coordinate system and can use absolute coordinates i e relative to the graphics origin and relative coordinates i e relative to the graphics cursor For relative coordinates use CIRCLE_R Multiple circles or ellipses can be plotted with a single call to CIRCLE Each set of parameters must be separated from each other with a semi colon The word ELLIPSE can be substituted for CIRCLE if required syntax x numeric_expression y numeric_expession radius numeric_expression eccentricity
129. e to mean an appropriate mixture of readability shortness and efficiency Different people andlor different circumstances will place different importance on these three qualities which sometimes work against each other CHAPTER 8 FROM BASIC TO SUPERBASIC If you are familiar with one of the earlier versions of BASIC you may find it possible to omit the first seven chapters and use this chapter instead as a bridge between what you know already and the remaining chapters If you do this and still find areas of difficulty it may be helpful to backtrack a little into some of the earlier chapters If you have worked through the earlier chapters this one should be easy reading You may find that as well as introducing some new ideas it gives an interesting slant on the way BASIC is developing Apart from its program structuring facilities SuperBASIC also pushes forward the frontiers of good screen presentation editing operating facilities and graphics In short it is a combination of user friendliness and computing power which has not existed before So when you make the transition from BASIC to SuperBASIC you are moving not only to a more powerful more helpful language you are also moving into a remarkably advanced computing environment We will now discuss some of the main features of SuperBASIC and some of the features which distinguish it from other BASICs ALPHABETIC COMPARISONS The usual simple arithmetic comparisons are possible You
130. ecuted The same effect can be achieved with a REPeat loop though it is not necessarily the best way to do it However it is worth looking at perhaps at a second reading if you want to understand structures which are simple enough to use in simple ways and powerful enough to cope with awkward situations when they arise Program 2 100 REMark Western REPeat with Epilogue 110 LET bullets 6 120 REPeat Bandit 130 PRINT Take aim 140 PRINT Fire shot 150 LET hit RND 9 160 IF hit 7 THEN EXIT Bandit 170 LET bullets bullets 1 180 IF bullets lt gt 0 THEN NEXT Bandit 190 PRINT Watch Bandit 200 END REPeat Bandit 210 PRINT Return to Dodge City The program works properly as long as the sheriff has at least one bullet at the start It fails if line 20 reads 110 LET bullets 0 You might think that the sheriff would be a fool to start an enterprise of this kind if he had no bullets at all and you would be right We are now discussing how to preserve good structure in the most complex type of situation We have at least kept the problem context simple we know what we are trying to do Complex structural problems usually arise in contexts more difficult than Wild West simulations But if you really want a solution to the problem which caters for a possible hit running out of bullets and an epilogue and also the zero case then add the following line to the above program 125 IF bullets 0 THEN PRINT Watch Bandit
131. ed for all subsequent output CLS CLS means clear the window to the current paper colour like a teacher cleaning a blackboard except that it is electronic and multi coloured FLASHING You can make the ink colour flash in mode 8 only To turn flash on you might type FLASH 1 and to turn it off FLASH 0 Allowing flashing characters to overlap can produce alarming results FILES You will have used Microdrives for storing programs and you will have used the commands LOAD and SAVE Cartridges can be used for storing data as well as programs The word file usually means a sequence of data records a record being some set of related information such as name address and telephone number Two of the most widely used types of file are serial and direct access files Items in a serial file are usually read in sequence starting with the first If you want the fiftieth record you have to read the first forty nine in order to find it On the other hand the fiftieth record ina direct access file can be found quickly because the system does not need to work through the earlier records to get it Pop music on a cassette is like a serial file but eight pieces on a long playing record form a direct access file You can move the pick up arm directly onto any of the eight tracks The simplest possible type of file is just a sequence of numbers To illustrate the idea we will place the numbers 1 to 100 ina file called numbers However the complete file
132. ee things PAPER background colour INK drawing colour LINE start and end points The following program will draw a line as shown in the above figure in red colour code 2 on a white colour code 7 background NEW ENTER 10 PAPER7 CLS ENTER 20 INK 2 ENTER 30 LINE 50 60 TO 70 80 ENTER RUN ENTER In line 10 the paper colour is selected first but it only comes into effect with a further command such as CLS meaning clear the screen to the current paper colour MODES AND COLOURS So far it does not matter which screen mode you are using but the range of colours is affected by the choice of mode MODE 8 allows eight basic colours MODE 4 allows four basic colours Colours have codes as described below Code Effect 8 colour 4 colour 0 black black 1 blue black 2 red red 3 magenta red 4 green green 5 cyan green 6 yellow white 7 white white RANDOM EFFECTS For example INK 3 would give magenta in MODE 8 and red in MODE 4 We will explain in a later chapter how the basic colours can be mixed in various ways to produce a startling range of colours shades and textures RANDOM EFFECTS You can get some interesting effects with random numbers which can be generated with the RND function For example PRINT RND 1 TO 6 ENTER will print a whole number in the range 1 to 6 like throwing an ordinary six sided dice The following program will illustrate this NEW ENTER 10 LET die RND I TO 6 ENTE
133. egant form It produces Illl rather than V 100 REMark Roman numbers 110 INPUT number 120 RESTORE 210 130 FOR type 1 TO 7 140 READ letter vaLue 150 REPeat output 160 IF number lt value EXIT output 170 PRINT letter 180 LET number number value 190 END REPeat output 200 END FOR type 210 DATA M 1000 D 500 C 100 L 50 X 10 V 5 1 1 You should study the above examples carefully using dry runs if necessary until you are sure that you understand them CONCLUSION In SuperBASIC full structuring features are provided so that program elements either follow in sequence or fit into one another neatly All structures must be identified to the system and named There are many unifying and simplifying features and many extra facilities Most of these are explained and illustrated in the remaining chapters of this manual which should be easier to read than the Keyword and Concept Reference sections However it is easier to read because it does not give every technical detail and exhaust every topic which it treats There may therefore be a few occasions when you need to consult the reference sections On the other hand some major advances are discussed in the following chapters Few readers will need to use all of them and you may find it helpful to omit certain parts at least on first reading CHAPTER 9 DATATYPES VARIABLES AND IDENTIFIERS You will have noticed that a program a sequence of statements usually g
134. el The standard size is 0 0 in512 mode and 2 0 in 256 mode Width defines the horizontal size of the character space Height defines the vertical size of the character space The character size is adjusted to fill the space available Figure A Character Square width size height size 6 pixels 8 pixels 12 pixels 16 pixels 10 pixels 20 pixels syntax width numeric_expression range 0 3 height numeric_expression range 0 11 CSIZE channel width height example i CSIZE 3 0 ii CSIZE 3 1 CURSOR windows CURSOR allows the screen cursor to be positioned anywhere in the window attached to the specified or default channel CURSOR uses the pixel coordinate system relative to the window origin and defines the position for the top left hand corner of the cursor The size of the cursor is dependent on the character size in use If CURSOR is used with four parameters then the first pair is interpreted as graphics coordinates using the graphics coordinate system and the second pair as the position of the cursor in the pixel coordinate system relative to the first point This allows diagrams to be annotated relatively easily syntax x numeric_expression y numeric_expression CURSOR channel x y Lx y example i CURSOR 0 0 ii CURSOR 20 30 iii CURSOR 50 50 10 10 RESTORE BASIC READ DATA and RESTORE allow embedded data contained ina SuperBASIC program to be assigned to variables at run time DATA
135. em 150 END FOR num 160 CLOSE 6 f you wish you can alter the program to get the output in a different form Character file In a similar fashion the following programs will set up a file of one hundred randomly selected letters and read them back 100 REMark Letter File 110 OPEN NEW 6 mdv1_chfile 120 FOR num 1 TO 100 130 LET ch CHR RND 65 TO 90 140 PRINT 6 ch 150 END FOR num 160 CLOSE 6 100 REMark Get Letters 110 OPEN IN 6 mdv1_chfile 120 FOR num 1 TO 100 130 INPUT 6 item 140 PRINT item 150 END FOR num 160 CLOSE 6 SETTING UP A DATA FILE Suppose that you wish to set up a simple file of names and telephone numbers RON 678462 GEOFF 896487 ZOE 249386 BEN 584621 MEG 482349 CATH 438975 WENDY 982387 The following program will do it 100 REMark Phone numbers 110 OPEN NEW 6 mdv1_phone 120 FOR record 1 TO7 130 INPUT name num 140 PRINT 6 name num 150 END FOR record 160 CLOSE 6 Type RUN and enter a name followed by the ENTER key and a number followed by the ENTER key Repeat this seven times Notice that the data is buffered It is stored internally until the system is ready to transfer a batch to the Microdrive The Microdrive is only accessed once as you can tell from looking and listening COPY A FILE Once a file is established it should be copied immediately as a back up To do this type COPY mdv1_phone TO mdv2_phone READ A FILE You need to be certain
136. en changed The value of variables may be set or changed COPY COPY_N devices COPY will copy a file from an input device to an output device until an end of file marker is detected COPY_N will not copy the header if it exists associated with a file and will allow Microdrive files to be correctly copied to another type of device Headers are associated with directory type devices and should be removed using COPY_N when copying to non directory devices e g mdvl is a directory device serl is a non directory device syntax COPY device TO device COPY_N device TO device It must be possible to input from the source device and it must be possible to output to the destination device example i COPY mdvi_data_file TO con_ copy to default window ii COPY neti_3 TO mdvi_data copy data from network station to mdv_data iii COPY_N mdvil_test_data TO ser1_ copy mdvi_test_data to serial port 1 removing header information COT COS math functions COS will compute the cosine of the specified argument syntax angle numeric_expression range 10000 10000 in radians COS angle example i PRINT COS theta ii PRINT COS 3 141592654 2 COT will compute the cotangent of the specified argument syntax angle numeric_expression range 30000 30000 in radians COT angle example i PRINT COT 3 ii PRINT COT 3 141592654 2 CSIZE window Sets a new character size for the window attached to the specified or default chann
137. ended order is as follows Position Tab Label Front Introduction Beginniner s Guide Keywords Concepts QL Quill QL Abacus QL Archive QL Easel Back Information This will put the divider tabs in a logical order If you wish you may put the sections ina different order perhaps to put often used sections near the front or even miss out sections you do not expect to use Now look through the pages to identify the various sections each begins with a title page with the Sinclair logo at the top The pages within each section will be packed in the correct order so be careful not to mix them up the individual sections however may be in a different order to that shown above if a section or sections have recently been reprinted Once each section is placed in the binder as you like it this sheet may be discarded it does not form part of the Guide SINCLAIR QL USER GUIDE INTRODUCTION BEGINNER S GUIDE REFERENCE GUIDE KEYWORDS CONCEPTS APPLICATIONS SOFTWARE QL QUILL QL ABACUS QL ARCHIVE QL EASEL INFORMATION Sinclair Research has a policy of constant development and improvement of their products Therefore the right is reserved to change manuals hardware software and firmware at any time and without notice OL User Guide Second Edition Published by Sinclair Research Limited 1984 25 Willis Road Cambridge Edited by Stephen Berry Sinclair Research Limited C Sinclair Research Limited C Psion Limited P
138. erBASIC has the usual LET INPUT READ and DATA statements for input The PRINT statement handles most text output in the usual way with the separators tabulates output just separates no formatting effect forces new line normally provides a space but not at the start of line If an item will not fit at the end of a line it performs a new line operation TO Allows tabulation to a designated column position LOOPS You will be familiar with two types of repetitive loop exemplified as follows a Simulate 6 throws of an ordinary six sided die 100 FOR throw 1 TO6 110 PRINT RND 1 TO 6 120 NEXT throw b Simulate throws of a die until a six appears 100 die RND 1 TO 6 110 PRINT die 120 IF die lt gt 6 THEN GOTO 10 Both of these programs will work in SuperBASIC but we recommend the following instead They do exactly the same jobs Although program b is a little more complex there are good reasons for preferring it a 100 FOR throw 1 TO6 110 PRINT RND 1 TO 6 120 END FOR throw b 100 REPeat throws 110 die RND 1 TO 6 120 PRINT die 130 IF die 6 THEN EXIT throws 140 END REPeat throws it is logical to provide a structure for a loop which terminates ona condition REPeat loops as well as those which are controlled by a count The fundamental REPeat structure is REPeat identifier statements END REPeat identifier The EXIT statement can be placed anywhere in the structure but it must be follo
139. eripheral equipment e g printers plotters etc As the RS 232 C standard manifests itself in many different forms on different pieces of equipment it can be an extremely difficult job even for an expert to connect together for the first time two pieces of supposedly standard RS 232 C equipment This section will attempt to cover most of the basic problems that you may encounter The RS 232 C standard refers to two types of equipment 1 Data Terminal Equipment DTE 2 Data Communication Equipment DCE The standard envisaged that the terminal usually the DTE and the modem usually the DCE would both have the same type of connector TI HII 2 TxD output gt 2 HII HII 3 lt RxD input 3 ITI HII 7 lt GND ground gt 7 HII DTE DCE The diagram above illustrates how the DTE transmits data on pin 2 whilst the DCE must receive data on its pin 2 which is still called transmit data Likewise the DTE receives data on pin 3 whilst the DCE must transmit data on its pin 3 which is still called receive data Although this is confusing in itself it can lead to far greater problems when there is disagreement as to whether a certain device should be configured as DCE or DTE Unfortunately some people decide that their computers should be configured as DCE devices whilst others configure equivalent co
140. erly named and properly isolated into a self contained unit The power and simplifying effects of procedures are more obvious as programs get larger What procedures do as programs get larger is not so much make programming easier as prevent it from getting harder with increasing program size The above example just illustrates the way they work in a simple context Examples The following examples indicate the range of vocabulary and syntax of SuperBASIC which has been covered in this and earlier chapters and will form a foundation on which the second part of this manual will build The letters of a palindrome are given as single items in DATA statements The terminating item is an asterisk and you assume no knowledge of the number of letters in the palindrome READ the letters into an array and print them backwards Some palindromes such as MADAM I M ADAM only work if spaces and punctuation are ignored The one used here works properly 100 REMark Palindromes 110 DIM text 30 120 LET text FILL 30 130 LET count 30 140 REPeat get_letters 150 READ character 160 IF character THEN EXIT get_letters 170 LET count count 1 180 LET text count character 190 END REPeat get_letters 200 PRINT text 210 DATA A BY LYE WAS TER 220 DATA E T SAS W Y ES LBA The following program accepts as input numbers in the range 1 to 3999 and converts them into the equivalent In Roman numerals It does not generate the most el
141. ertain number of times is well known A special structure called a FOR loop has been invented for it In such a loop the count from 1 to 4 is handled automatically So is the exit when all four items have been handled Program 4 100 RESTORE 160 110 DIM high_st 4 3 120 FOR number 1 TO 4 130 READ high_st number 140 PRINT high_st number 150 END FOR number 160 DATA VAL HAL MEL DEL The output from all four programs is the same VAL HAL MEL DEL Which proves that the data is properly stored internally in the four array variables high_st 1 2 3 4 Method 4 is clearly the best so far because it can deal equally well with 4 or 40 or 400 items by just changing the number 4 and adding more DATA items You can use as many DATA statements as you need In its simplest form the FOR loop is rather like the simplest form of REPeat loop The two can be compared 100 REPeat greeting 100 FOR greeting 1 TO 40 110 PRINT Hello 110 PRINT Hello 120 END REPeat greeting 120 END FOR greeting Both these loops would work The REPeat loop would print Hello endlessly stop it with the BREAK sequence and the FOR loop would print Hello just forty times Notice that the name of the FOR loop is also a variable greeting whose value varies from 1 to 40 in the course of running the program This variable is sometimes called the loop variable or the control var
142. es are used for storing programs and data on the QL Next to each slot there is a small light When the light is on the Microdrive is in use and the cartridge should not be removed The yellow light on the front lefthand side indicates whether the QL is switched on On the right hand end of the QL there is a slot covered by a plastic strip This slot is for attaching up to six more QL microdrives ZX microdrives are not suitable for use with the QL but blank microdrive cartridges can be used on either machine The connectors at the back of the computer are for attaching the following NET connector for the QL Network NET connector for the QL Network POWER power supply for the computer RGB connection to a monochrome or colour monitor UHF connection to the aerial socket of a television set SERI RS232C serial port SER2 RS232C serial port CTLI control port for joystick CTL2 control port for joystick ROM QL ROM cartridge software use reversed one to 10 N B ZX ROM cartridges are not compatible with QL ROM cartridges and cannot be used with the QL The slot on the left hand side of the QL is used for adding peripherals equipment to expand the computer s capabilities to the QL One peripheral can be plugged directly into the expansion slot The reset button is on the right hand end of the computer near the Microdrive expansion slot It is used to reset the QL to its original switch on state Any programs in th
143. ets some data to work on input and produces some kind of results output You will also have understood that there are internal arrangements for storing this data In order to avoid unnecessary technical explanations we have suggested that you imagine pigeon holes and that you choose meaningful names for the pigeon holes For example if it is necessary to store a number which represents the score from simulated dice throws you imagine a pigeon hole named score which might contain a number such as 8 Internally the pigeon holes are numbered and the system maintains a dictionary which connects particular names with particular numbered pigeon holes We say that the name score points to its particular pigeon hole by means of the internal dictionary III score gt 8 IIT The whole arrangement is called a variable What you see is the word score We say that this word score is an identifier It is what we see and it identifies the concept we need in this case the result 8 of throwing a pair of dice Because the identifier is what we see it becomes the thing we talk or write or think about We write about score and its value at any particular moment There are four simple data types called floating point integer string and logical and these are explained below We talk about data types rather than variable types bec
144. ew one Now type 10 LET price 15 ENTER 20 PRINT How many pens ENTER 30 INPUT pens ENTER 40 LET cost price pens ENTER 50 PRINT cost ENTER RUN ENTER The program pauses at line 30 and you should type the number of pens you want say 4 ENTER Do not forget the ENTER key The output will be 60 The INPUT statement needs a variable name so that the system knows where to put the data which comes in from your typing at the keyboard The effect of line 30 with your typing is the same as a LET statement s effect It is more convenient for some purposes when interaction between computer and user is desirable However the LET statement and the INPUT statement are useful only for modest amounts of data We need something else to handle larger amounts of data without pauses in the execution of the program SuperBASIC like most BASICs provides another method of input known as READing from DATA statements We can retype the above program in a new form to give the same effects without any pauses Try this NEW ENTER 10 READ price pens 20 LET cost price pens ENTER 30 PRINT cost ENTER 40 DATA 15 4 ENTER RUN ENTER The output should be 60 as before Each time the program is run SuperBASIC needs to be told where to start reading DATA from This can either be done by typing RESTORE followed by the DATA line number or by typing CLEAR Both these commands can also be inserted at the start of the progr
145. expressed as a percentage The following data represent the total salaries and pension fund rates of the six employees Benson 13 800 6 25 Hanson 8 700 6 00 Johnson 10 300 6 25 Robson 15 000 7 00 Thomson 6 200 6 00 Watson 5 100 5 75 Write procedures to input the data into arrays compute the actual pension fund contributions output the lists of names and computed contributions Link the procedures with a main program calling them in sequence 2 Write a function select with two arguments range and miss The function should return a random whole number in the given range but it should not be the value of miss Use the function in a program which chooses a random PAPER colour and then draws random circles in random INK colours so that none is inthe colour of PAPER 3 Re write the solution to exercise 1 so that a function pension takes salary and contribution rate as arguments and returns the computed pension contribution Use two procedures one to input the data and one to output the required information using the function pension 4 Write the following a procedure which sets up a pack of cards a procedure which shuffles the cards a function which takes a number as an argument and returns a string value describing the card a procedure which deals and displays four poker hands of five cards each a main program which calls the above procedures see chapter 16 for discussion of a similar
146. extra information conforms to the rules for a SuperBASIC identifier Each logical device on the system requires its own particular extra information although default parameters will be assumed in each case where possible DEFINE device name where the form of the device name is outlined below EXAMPLE for console device Select Console Device III Separator read as AT III Window X coordinate III Separator IlllIl Window Y coordinate Int IIlIIl Separator TIMI IIIIIIII length of keyboard type ahead buffer MININ III con_wXhaxXy_k CON wXhaxXy_k Console O wXh window width height AxXy window X Y coordinate of upper left hand corner k Keyboard type ahead buffer length bytes default con_448x180a32x16_128 example OPEN 4 con_20x50a0x0_ 32 OPEN 8 con_20x50 OPEN 7 con_20x50a10x10 SCR_wxXhaxXy Screen Output wXh window width height AxXy window X Y coordinate default scr_448x180a32x16 xample PEN 4 scr _0x10a20x50 OPEN 5 scr_10x10 SERnphz Serial RS 232 C n port number 1 or 2 p parity h handshaking z protocol e eveni ignore r raw data no EOF o odd h handshake z control Z is EOF m mark c as z but converts s space ASCII 10 Qdos newline character to ASCII 13 lt CR gt default ser1rh 8 bit no parity with handshake example OPEN 3 serle OPEN 4 serc
147. f standard devices supplied with the QL can be expanded DEVICES The standard devices included in the system are discussed in this guide in the section DEVICES Further devices may be added to the system given a name e g SER1 NET and then accessed in the same way as any other QL device MULTITASKING Jobs will be allowed a share of the CPU in line with their priority and competition with other jobs in the system Jobs running under the control of Qdos can be in one of three states active Capable of running and sharing system resources A job in this state may not be runnign continuously but will obtain a share of the CPU in line with its priority suspended The job is capable of running but is waiting for another job or VO A job may be suspended indefinitely or for a specific period of time inactive The job is incapable of running its priority is O and so it can never obtain a share of the CPU Qdos will reschedule the system automatically at a rate related to the 50 Hz frame rate The system will also be rescheduled after certain system calls Example This program generates an on screen readout of the rel time clock running as an independent job First RUN this program with a formatted cartridge in microdrive 2 This generates a machine code title called clock Wait for the microdrive to stop Next set the clock using the SDATE command Then type EXEC mdv2_clock and a continuous time display will appear at the
148. f a circle POINT plot a point CIRCLE_R draw an ellipse or a circle LINE_R draw a line ARC_R draw an arc of a circle relative POINT_R plot a point SCALE set scale and move origin FILL fill in a shape CURSOR position text GRAPHICS FILL Figures drawn with the graphics and turtle graphics procedures can be optionally filled with a specified stipple or colour If FILL is selected then the figure is filled as it is drawn The FILL algorithm stores a list of points to plot rather than actually plotting them When the figure closes there are two points on the same horizontal line These two points are connected by a line in the current INK colour and the process repeats Fill must always be reselected before drawing a new figure to ensure that the buffer used to store the list of points is reset The following diagram illustrates FILL 50 80 1 a 10 20 FILL 1 LINE 10 20 TO 75 50 TO 50 80 WARNING There is an implementation restriction on FILL FILL must not be used for re entrant shapes i e a shape which is concave Re entrant shapes must be split into smaller shapes which are not re entrant and each sub shape filled independently IDENTIFIER A SuperBASIC identifier is a sequence of letters numbers and underscores define letter a Z A Z number 1 2 3 4 5 6 7 8
149. f a window by typing for example BORDER 4 2 ENTER This will create a border 4 pixels wide in colour red code 2 The effective size of the window is reduced by the border This means that any subsequent printing or graphics will automatically fit within the new window size The only exception to this is a further border which will overwrite the existing one A SIMPLE LOOP Computers can do things very quickly but it would not be possible to exploit this great power if every action had to be written as an instruction A building foreman has a similar problem If he wants a workman to lay a hundred paving stones that is roughly what he says He does not give a hundred separate instructions A traditional way of achieving looping or repetition in BASIC is to use a GO TO or GOTO they are the same statement as follows NEW ENTER 10 PAPER 6 CLS ENTER 20 BORDER 1 2 ENTER 30 INK RND 5 ENTER 40 LINE 50 60 TO RND 100 RND 100 ENTER 50 GOTO 0 ENTER RUN ENTER You may prefer not to type in this program because SuperBASIC allows a better way of doing repetition Note certain things about each line 10 Fixed part not repeated 20 30 Changeable part repeated 40 50 Controls program You can re write the above program by omitting the GOTO statement and instead putting REPeat and END REPeat around the part to be repeated NEW ENTER 10 PAPER 6 CLS ENTER 20 BORDER 1 2 ENTER 30 REPEAT star ENTER 40
150. from a specified device LRUN will perform NEW before loading another program and so any previously stored SuperBASIC program will be cleared by LRUN If a line input during a loading has incorrect SuperBASIC syntax the word MISTAKE is inserted between the line number and the body of the line Upon execution a line of this sort will generate an error syntax LRUN device example i LRUN mdv2_TEST ii LRUN mdv1_game MERGE devices microdrives MERGE will load a file from the specified device and interpret it as a SuperBASIC program If the new file contains a line number which doesn t appear in the program already in the QL then the line will be added If the new file contains a replacement line for one that already exists then the line will be replaced All other old program lines are left undisturbed If a line input during a MERGE has incorrect SuperBASIC syntax the word MISTAKE is inserted between the line number and the body of the line Upon execution a line of this sort will generate an error syntax MERGE device example i MERGE mdv1_overlay_program ii MERGE mdv1_new_data MOD operators MOD is an operator which gives the modulus or remainder when one integer is divided by another syntax numeric_expression MOD numeric_expression example i PRINT 5 MOD 2 will print 1 ii PRINT 5 MOD 3 will print 2 MODE screen MODE sets the resolution of the screen and the number of solid colours which it can display MODE wi
151. gram at the keyboard 7 What must be at the beginning of every line to be stored as part of a program 8 What must you remember to type to make a program execute 9 What keyword enables you to put into a program information which has no effect on the execution 10 Which two keywords help you to store programs on and retrieve from cartridges two points PROBLEMS ON CHAPTER 5 1 Re write the following program using lower case letters to give a better presentation Add the words NEW and RUN Use line numbers and the ENTER symbol just as you would to enter and run a program Use REMark to give the program a name LET TWO TWO LET FOUR FOUR LET SIX TWO amp FOUR PRINT LEN six Explain how two and four can produce 7 2 Use indenting lower case letters NEW RUN line numbers and the ENTER symbol to show how you would actually enter and run the following program REPEAT LOOP LETTER_CODE RND 65 TO 90 LET LETTERS CHR LETTER_CODE PRINT LETTER IF LETTERS Z THEN EXIT LOOP END REPEAT LOOP 3 Re write the following program in better style using meaningful variable names and good presentation Write the program as you would enter it LETS O0O REPeat TOTAL LET N RND 1 TO 6 PRINT N LETS S N IF n 6 THEN EXIT TOTAL END REPeat TOTAL PRINTS Decide what the program does and then enter and run it to check your decision CHAPTER 6 ARRAYS AND FOR LOOPS WHAT IS AN ARRAY You know th
152. guishes the name of a string variable 4 How do some people pronounce a word such as word 5 What keyword is used to find the number of characters in a string 6 What symbol is used to join two strings 7 Spaces can be part of a string How are the limits of a string defined 8 When a statement such as LET meat steak is executed are the quotes stored 9 What function will turn a suitable code number into a letter 10 How can you generate random upper case letters PROBLEMS ON CHAPTER 4 1 Store the words Good and day in two separate variables Use a LET statement to join the values of the two variables in a third variable Print the result 2 Store the following words in four separate pigeon holes light let be there Join the words to make a sentence adding spaces and a full stop Store the whole sentence ina variable sent and print the sentence and the total number of characters it contains 3 Write a program which uses the keywords CHR RND 65 TO 90 to generate one hundred random three letter words See if you have accidentally generated any real English words Test the effects of a at the end of a PRINT statement b on either side of item printed CHAPTER 5 KNOWN GOOD PRACTICE You have already begun to work effectively with short programs You may have found the following practices are helpful 1 Use of lower case for identifiers names of variables pigeon holes or repeat str
153. h 150 DATA January February March 160 DATA April May June 170 DATA July August September 180 DATA October November December Warning An implicit RESTORE is not performed before running a program This allows a single program to run with different sets of data Either include a RESTORE in the program or perform an explicit RESTORE or CLEAR before running the program DATE DATE clock DATES is a function which will return the date and time contained in the QLIs clock The format of the string returned by DATES is yyyy mmm dd hh mm ss where yyyy is the year 1984 1985 etc mmm is the month Jan Feb etc dd is the day 01 to 28 29 30 31 hh is the hour 00 to 23 mm are the minutes 00 to 59 ss are the seconds 00 to 59 DATE will return the date as a floating point number which can be used to store dates and times in a compact form f DATE is used with a numeric parameter then the parameter will be interpreted as a date in floating point form and will be converted to a date string syntax DATE get the time from the clock DATE numeric_expression get time from supplied parameter example i PRINT DATE output the date and time ii PRINT DATE 234567 convert 234567 to a date DAY clock DAY is a function which will return the current day of the week If a parameter is specified then DAY will interpret the parameter as a date and will return the corresponding day of the week syntax DAY
154. have to be a bit more careful of expressions involving words such as OR AND NOT but they are well worth investigating indeed they are essential to good programming They will become even more important with the trend towards other kinds of languages based more on precise descriptions of what you require rather than what the computer must do AND The word AND in SuperBASIC is like the word and in ordinary English Consider the following program 100 REMark AND 110 PRINT Enter two values 1 for TRUE or 0 for FALSE 120 INPUT raining hole_in_roof 130 IF raining AND hole_in_roof THEN PRINT Get wet As in real life you will only get wet if it is raining and there is a hole in the roof If one or both of the simple logical variables raining hole_in_roof is false then the compound logical expression raining AND hole in_roof is also false It takes two true values to make the whole expression true This can be seen from the rules below Only when the compound expression is true do you get wet raining hole_in_roof raining AND hole_in_roof effect FALSE FALSE FALSE DRY FALSE TRUE FALSE DRY TRUE FALSE FALSE DRY TRUE TRUE TRUE WET Rules for AND OR In everyday life the word or is used in two ways We can illustrate the inclusive use of OR by thinking of a cricket captain looking for players He might ask Can you bat or bowl He would be pleased if a player could do just one thing well but he would also be pleased
155. he WINDOW command SLICING Under certain circumstances it is possible to refer to more than one element in an array i e slice the array The array slice can be thought of as defining a subarray or a series of subarrays to SuperBASIC Each slice can define a continuous sequence of elements belonging to a particular dimension of the original array The term array in this context can include a numeric array a string array or a simple string tis not necessary to specify an index for the full number of dimensions of an array If a dimension is omitted then slices are added which will select the full range of elements for that particular dimension i e the slice 0 TO SuperBASIC can only add slices to the end of a list of array indices syntax index numeric_exp single element numeric_exp TO numeric_exp range of elements numeric_exp TO range to end TO numeric_expression range from beginning array_reference variable variable index index An array slice can be used to specify a source or a destination subarray for an assignment statement example i PRINT data array ii PRINT letters 1 TO 15 iii PRINT two_d_array 3 2 TO 4 String slicing is performed in the same way as slicing numeric or string arrays Thus a n will select the nth character a n TO m will select all characters from the nth to the mth inclusively a n TO will select from a character n to the end inclusively
156. he required form and if the data cannot be converted an error is reported The type of a function or procedure parameter can also be converted to the correct type For example the SuperBASIC LOAD command requires a parameter of type NAME but can accept a parameter of type STRING and which will be converted to the correct type by the procedure itself Coercion of this form is always dependent on the way the function or procedure was implemented There is a natural ordering of data types on the QL see figure below String is the most general type since it can represent integer data almost exactly The figure below shows the ordering diagramatically Data can always be converted moving up the diagram but it is not always possible moving down not always string possible A IANI LIANI LIANI name IZI floating point HHI HII always possible integer lv EXAMPLE a b c no conversion is necessary before performing the addition Conversion is not necessary before assigning the result to a a b c no conversion is necessary before performing the addition but the result is converted to integer before assigning a b c b and c are converted to floating point if possible before being added together The result is
157. he string is not found then INSTR returns zero Zero can be interpreted as false i e the substring was not contained in the given string A non zero value the substrings position can be intepreted as true i e the substring was contained in the specified string syntax string_expression INSTR string expression example i PRINT a INSTR cat will print 2 ii PRINT CAT INSTR concatenate will print 4 iii PRINT x INSTR eggs will print 0 INT maths functions INT will return the integer part of the specified floating point expression syntax INT numeric_expression example i PRINT INT X ii PRINT INT 3 141592654 2 KEYROW KEYROW is a function which looks at the instantaneous state of a row of keys the table below shows how the keys are mapped onto a matrix of 8 rows by 8 columns KEYROW takes one parameter which must be an integer in the range 0 to 7 this number selects which row is to be looked at The value returned by KEYROW is an integer between 0 and 255 which gives a binary representation indicating which keys have been depressed in the selected row Since KEYROW is used as an alternative to the normal keyboard input mechanism using INKEY or INPUT any character in the keyboard type ahead buffer are cleared by KEYROW thus key depressions which have been made before a call to KEYROW will not be read bya subsequent INKEY or INPUT Note that multiple key depressions can cause surprising results In p
158. hen we type 130 LET mark 3 TO 4 num 140 PRINT mark The output from the whole program is 626371 which shows the history mark increased to 63 Strictly speaking it is illegal to mix data types ina LET statement It would be silly to write LET num LION and you would get an error message if you tried but if you write LET num 65 the system will conclude that you want the number 65 to become the value of num and do that The complete program is 100 LET mark 625671 110 LET hist mark 3 TO 4 120 LET num 1 125 hist 130 LET mark 3 TO 4 num 140 PRINT mark Again the output is the same In line 120 a string value was converted into numeric form so that it could be multiplied In line 130 a number was converted into string form This converting of data types is known as type coercion You can write the program more economically if you understand both string slicing and coercion now 100 LET mark 625671 110 LET mark 3 TO 4 1 125 mark 3 TO 4 120 PRINT mark If you have worked with other BASICs you will appreciate the simplicity and power of string slicing and coercion SEARCHING A STRING You can search a string for a given substring The following program displays a jumble of letters and invites you to spot the animal 100 REM Animal Spotting 110 LET jumble SYNDICATE 120 PRINT jumble 130 INPUT What is the animal an 140 IF an INSTR jumble AND an 1 C 150 PR
159. iable of the loop Note the structure of both loops takes the form Opening statement Content Closing statement However certain structures have allowable short forms for use when there are only one or a few statements in the content of the loop Short forms of the FOR loop are allowed so we could write the program in the most economical form of all Program 5 100 RESTORE 140 CLS 110 DIM high st 4 3 120 FOR number 1 TO 4 READ high_st number 130 FOR number 1 TO 4 PRINT high_st number 140 DATA VAL HAL MEL DEL Colons serve as end of statement symbols instead of ENTER and the ENTER symbols of lines 120 and 130 serve as END FOR statements There is an even shorter way of writing the above program To print out the contents of the array high_st we can replace line 130 by 130 PRINT high_st This uses an array slicer which we will discuss later in chapter 13 We have introduced the concept of an array of string variables so that the only numbers involved would be the subscripts in each variable name Arrays may be string or numeric and the following examples illustrate the numeric array Program 1 Simulate the throwing of a pair of dice four hundred times Keep a record of the number of occurrences of each possible score from 2 to 12 100 REMark DICE1 110 LET two 0 three 0 four 0 five 0 six 0 120 LET seven 0 eight 0 nine 0 ten 0 eleven 0 twelve 0 130 FOR throw 1
160. iables which share its name 5 Can you think of two ideas in ordinary life which correspond to the concept of an array in programming two points 6 Ina REPeat loop the process ends when some condition causes an EXIT statement to be executed What causes the process ina FOR loop to terminate 7 A REPeat loop needs a name so that you can EXIT to its END properly A FOR loop also has a name but what other function does a FOR loop name have 8 What are the two phrases which are used to describe the variable which is also the name of a FOR loop two points 9 The values of a loop variable change automatically as a FOR loop is executed Name one possible important use of these values 10 Which of the following do the long form of REPeat loops and the long form of FOR loops have in common For each of the four items either say that both have it or which type of loop has it a An opening keyword or statement b A closing keyword or statement c A loop name d A loop variable or control variable PROBLEMS ON CHAPTER 6 1 Use a FOR loop to place one of four numbers 1 2 3 4 randomly in five array variables card 1 card 2 card 3 card 4 card 5 It does not matter if some of the four numbers are repeated Use a second FOR loop to output the values of the five card variables 2 Imagine that the four numbers 1 2 3 4 represent Hearts Clubs Diamonds Spades What extra program lines would need to be in
161. ice was also used in the main program meaning something else say the price of a glass of lager 70p The following program fails to give the desired result Program 100 REMark Global price 110 LET price 70 120 item 3 130 item 4 140 PRINT price 150 DEFine PROCedure item num 160 IF num lt 3 THEN LET price 300 10 num 170 IF num gt 4 THEN LET price 12 num 180 PRINT price 190 END DEFine Output 330 48 48 The price of the lager has been altered by the procedure We say that the variable price is global because it can be used anywhere in the program EXAMPLE Make the procedure variable price LOCAL to the procedure This means that SuperBASIC will treat it as a special variable accessible only within the procedure The variable price in the main program will be a different thing even though it has the same name Program 100 REMark LOCAL price 110 LET price 70 120 item 3 130 item 4 140 PRINT price 150 DEFine PROCedure item num 160 LOCaL price 170 IF num lt 3 THEN LET price 300 10 num 180 IF num gt 4 THEN LET price 12 num 190 PRINT price 200 END DEFine Output 330 48 70 This time everything works properly Line 70 causes the procedure variable price to be internally marked as belonging only to the procedure item The other variable price is not affected You can see that local variables are useful things EXAMPLE Local variables are so useful that
162. ice name and passed to the OPEN command as a parameter See concepts DEVICE and PERIPHERAL EXPANSION Data can be output to a channel by PRINTing to that channel this is the same mechanism by which output appears on the QL screen PRINT without a parameter outputs to the default channel 1 For example 10 OPEN 5 mdv1_test_file 20 PRINT 5 this text is in file test_file 30 CLOSE 5 will output the text this text is in file test_file to the file test_file It is important to close the file after all the accesses have been completed to ensure that all the data is written Data can be input from a file in an analogous way using INPUT Data can be input from a channel a character at a time using INKEY A channel can be opened as a console channel output is directed to a specified window on the QL screen and input is taken from the QL keyboard When a console channel is opened the size and shape of the initial window is specified If more than one console channel is active then it is possible for more than one channel to be requesting input at the same time In this case the required channel can be selected by pressing CTRL C to cycle round the waiting channels The cursor in the window of the selected channel will flash The QL has three default channels which are opened automatically Each of these channels is linked to a window on the QL screen channel 0 command and error channel channel 1 output and graphics channel channel
163. if someone could do both So it is in programming a compound expression using OR is true if either or both of the simple statements or variables are true Try the following program 100 REMark OR test 110 PRINT Enter two values 1 for TRUE or 0 for FALSE 120 INPUT Can you bat batsman 130 INPUT Can you bowl bowler 140 IF batsman OR bowler THEN PRINT In the team You can see the effects of different combinations of answers in the rules below batsman bowler batsman OR bowler effect FALSE FALSE FALSE notin team FALSE TRUE TRUE in the team TRUE FALSE TRUE in the team TRUE TRUE TRUE in the team Rules for OR When the inclusive OR is used a true value in either of the simple statements will produce a true value in the compound expression If lan Botham the England all rounder were to answer the questions both as a bowler and as a batsman both simple statements would be true and so would the compound expression He would be in the team If you write O for false and 1 for true you will get all the possible combinations by counting in binary numbers NOT The word NOT has the obvious meaning NOT true is the same as false NOT false is the same as true However you need to be careful Suppose you hold a red triangle and say that it is NOT red AND square In English this may be ambiguous If you mean NOT red AND square then for a red triangle the expression is false If you mean NOT red AND square
164. igeon hole is as shown II dogs 10 A good way to understand what is happening to the pigeon holes or variables is to do what is called a dry run You simply examine each instruction in turn and write down the values which result from each instruction to show how the pigeon holes are set up and given values and how they retain their values as the program is executed LET dogs 9 ENTER LET days 28 ENTER LET tins dogs days ENTER PRINT tins ENTER The output should be 252 You may notice that so far a variable name has always been used first on the left hand side of a LET statement Once the pigeon hole is set up and has a value the corresponding variable name can be used on the right hand side of a LET statement Now suppose you wish to encourage a small child to save money You might give two bars of chocolate for every pound saved Suppose you try to compute this as follows LET bars pounds 2 ENTER PRINT bars ENTER You cannot do a dry run as the program stands because you do not know how many pounds have been saved We have made a deliberate error here in using pounds on the right of a LET statement without it having been set up and given some value Your QL will search internally for the variable pounds It will not find it so it concludes that there is an error in the program and gives an error message f we had tried to print out the value of pounds the QL would have p
165. ile condition has been reached on a specified channel If EOF is used without a channel specification then EOF will determine if the end of a program s embedded data statements has been reached syntax EOF channel example i IF EOF 6 THEN STOP ii IF EOF THEN PRINT Out of data EXEC EXEC_W Qdos EXEC and EXEC_W will load a sequence of programs and execute them in parallel EXEC will return to the command processor after all processes have started execution EXEC_W will wait until all the processes have terminated before returning syntax program device used to specify a Microdrive file containing the program EXEC program example i EXEC mdv1_communcations ii EXEC_W mdv1_printer_process EXIT repetition EXIT will continue processing after the END of the named FOR or REPeat structure syntax EXIT identifier example i 100 REM start Looping 110 LET count O 120 REPeat Loop 130 LET count count 1 140 PRINT count 150 IF count 20 THEN EXIT Loop 160 END REPeat loop the loop will be exited when count becomes equal to 20 ii 100 FOR n 1 TO 1000 110 REM program statements 120 REM program statements 130 IF RND gt 5 THEN EXIT n 140 END FORn the loop will be exited when a random number greater than 0 5 is generated EXP maths functions EXP will return the value of e raised to the power of the specified parameter syntax EXP numeric_expression range 500 500 example i PRINT EXP 3
166. ill store the result back in a The answer will then be printed out If a line is not preceded by a line number then the line is a direct command and SuperBASIC processes the statement immediately If the statement is preceded by a line number then the statement becomes part of a SuperBASIC program and is added into the SuperBASIC program area for later execution Certain SuperBASIC statements can have an effect on the other statements over the rest of the logical line in which they appear i e IF FOR REPeat REM etc Itis meaningless to use certain SuperBASIC statements as direct commands STRING ARRAYS STRING VARIABLES String arrays and numeric arrays are essentially the same however there are slight differences in treatment by SuperBASIC The last dimension of a string array defines the maximum length of the strings within the array String variables can be any length up to 32766 Both string arrays and string variables can be sliced String lengths on either side of a string assignment need not be equal If the sizes are not the same then either the right hand string is truncated to fit or the length of the left hand string is reduced to match If an assignment is made to a sliced string then if necessary the hole defined by the slice will be padded with spaces tis not necessary to specify the final dimension of a string array Not specifying the dimension selects the whole string while specifying a single element will pick out a si
167. internal effects I weekday FIRST length 15 II word OF l month FEBRUARY phrase FIRSTOFFEBRUARY There is one more reasonable simplification which is to use READ and DATA instead of the first three LET statements Type NEW ENTER 10 READ weekday word month ENTER 20 LET phrase weekday amp word amp month ENTER 30 LET length LEN phrase ENTER 40 PRINT length 3 ENTER 50 DATA FIRST OF FEBRUARY ENTER RUN ENTER The internal effects of this version are exactly the same as those of the previous one READ causes the setting up of internal pigeon holes with values in them in a similar way to LET IDENTIFIERS AND STRING VARIABLES Names of pigeon holes such as weekday word month phrase are called string identifiers The dollar signs imply that the pigeon holes are for character strings The dollar must always be at the end Pigeon holes of this kind are called string variables because they contain only character strings which may vary as a program runs The contents of such pigeon holes are called values Thus words like FIRST and OF may be values of string variables named weekday and word RANDOM CHARACTERS You can use character codes see C
168. is used to mark and define the data READ accesses the data and assigns it to variables and RESTORE allows specific data to be selected DATA allows data to be defined within a program The data can be read by a READ statement and the data assigned to variables A DATA statement is ignored by SuperBASIC when it is encountered during normal processing syntax DATA expression READ reads data contained in DATA statements and assigns it to a list of variables Initially the data pointer is set to the first DATA statement in the program and is incremented after each READ Re running the program will not reset the data pointer and so in general a program should contain an explicit RESTORE An error is reported if a READ is attempted for which there is no DATA syntax READ identifier RESTORE restores the data pointer i e the position from which subsequent READs will read their data If RESTORE is followed by a line number then the data pointer is set to that line If no parameter is specified then the data pointer is reset to the start of the program syntax RESTORE line_number example i 100 REMark Data statement example 110 DIM weekdays 7 4 120 RESTORE 130 FOR count 1 TO7 READ weekdays count 140 PRINT weekday 150 DATA MON TUE WED THUR FRI 160 DATA SAT SUN ii 100 DIM month I2 9 110 RESTORE 120 REMark Data statement example 130 FOR count TO 12 READ month count 140 PRINT mont
169. ision If your screen does not look like this read the section entitled Introduction This should enable you to solve any difficulties THE KEYBOARD The QL is a versatile and powerful computer so there are features of the keyboard which you do not need yet For the present we will explain just those items which you need for this and the next six chapters BREAK This enables you to break out of situations you do not like For example a line which you have decided to abandon something wrong which you do not understand a running program which has ceased to be of interest any other problem Because BREAK is so powerful it has been made difficult to type accidentally Hold down CTRL and then press SPACE If nothing was added or removed from a program while it was halted with BREAK then it can be restarted by typing CONTINUE RESET This is not a key but a small push button on the right hand side of the QL tis placed here deliberately out of the way because its effects are more dramatic than the break keys If you cannot achieve what you need with the break keys then press the RESET Button This is almost the same as switching the computer off and on again You get a clean re start SHIFT There are two SHIFT keys because they are used frequently and need to be available to either hand Hold down one SHIFT key and type some letter keys You will get upper case capital letters Hold down one SHIFT key and type some other key not
170. ision of a unique facility referred to as coercion The VAL and STR functions are therefore not provided BREAK if at any time the computer fails to respond or you wish to stop a SuperBASIC program or command then hold down CTRL and then press SPACE keys A program broken into in this way can be restarted by using the CONTINUE command CHANNELS A channel is a means by which data can be output to or input from a QL device Before a channel can be used it must first be activated or opened with the OPEN command Certain channels should always be kept open these are the default channels and allow simple communication with the QL via the keyboard and screen When a channel is no longer in use it can be deactivated closed with the CLOSE command A channel is identified by a channel number A channel number is a numeric expression preceded by a When the channel is opened a device is linked to a channel number and the channel is initialised Thereafter the channel is identified only by its channel number For example OPEN 5 SER1 Will link serial port 1 to the channel number 5 When a channel is closed only the channel number need be specified For example CLOSE 5 Opening a channel requires that the device driver for that channel be activated Usually there is more than one way in which the device driver can be activated for example the network requires a station number This extra information is appended to the dev
171. ison is automatically provided CAT is less than DOG CAN is less than CAT You can write for example IF CAT lt DOG THEN PRINT MEOW and the output would be MEOW Similarly IF DOG gt CAT THEN PRINT WOOF would give the output WOOF We use the comparison symbols of mathematics for string comparisons All the following logical statements expressions are both permissible and true ALF lt BEN KIT gt BEN KIT lt LEN KIT gt KIT PAT gt LEN LEN lt LEN PAT lt gt PET So far comparisons based simply on internal codes make sense but data is not always conveniently restricted to upper case letters We would like for example Cat to be less than COT and K2N to be less than K27N A simple character by character comparison based on internal codes would not give these results so SuperBASIC behaves in a more intelligent way The following program with suggested input and the output that will result illustrates the rules for comparison of strings 100 REMark comparisons 110 REPeat comp 120 INPUT input a string first 130 INPUT input another string second 140 IF first lt second THEN PRINT Less 150 IF first gt second THEN PRINT Greater 160 IF first second THEN PRINT Equal 170 END REPeat comp CAT COT Greater CAT CAT Equal PET PETE Less K6 K7 Less K66 K7 Greater K12N K6N Greater gt Greater than Case dependent comparision
172. ission of a byte or character The QL will receive data with one one and a half or two stop bits and will always transmit data with at least two stop bits Note that if the QL is set up to 9600 baud it will not receive data with only one stop bit at least one and a half stop bits are required The may be necessary to connect the handshake lines between the QL and a piece of equipment connected to it This allows the QL and its peripheral to monitor and control their rate of communication They may need to do this if one of them cannot cope with the speed at which data is being transmitted The QL uses two handshaking lines CTS Clear to Send DTR Data Terminal Ready f DTE cannot cope with the rate of transmission of data then it can negate the DTR line which tells the DCE to stop sending data Obviously when the DTE has caught up it tells the DCE via the DTR line to start transmitting again In the same way the DCE can stop the DTE sending data by negating the CTS line If additional control signals are required they can be wired up using the 12V supply available on both serial ports ALTHOUGH TRANSMISSION FROMT HE QL IS OFTEN POSSIBLE WITHOUT ANY HANDSHAKING AT ALL THE QL WILL NOT RECEIVE CORRECTLY UNDER ANY CIRCUMSTANCES WITHOUT THE USE OF CTS ON SER1 AND DTR ON SER2 Communications on the QL are full duplex that is both receive and transmit can operate concurrently The parity and handshaking are selected when the seria
173. its or other symbols which may or may not be words That is why the term character string has been invented It is usually abbreviated to string Strings are handled in ways similar to number handling but of course we do not do the same operations on them We do not multiply or subtract strings We join them separate them search them and generally manipulate them as we need NAMES AND PIGEON HOLES FOR STRINGS You can create pigeon holes for strings You can put character strings into pigeon holes and use the information just as you do with numbers If you intend to store not all at once words such as FIRST SECOND THIRD and JANUARY FEBRUARY MARCH you may choose to name two pigeon holes ui weekday month Notice the dollar sign Pigeon holes for strings are internally different from those for numbers and SuperBASIC needs to know which is which All names of string pigeon holes must end with Otherwise the rules for choosing names are the same as the rules for the names of numeric pigeon holes You may pronounce weekday as weekdaydollar month as monthdollar The LET statement works in the same way as for numbers If you type LET weekday FIRST ENTER an internal pigeon hole named weekday will be set up with the value FIRST in it thus weekday FIRST The quote marks are not stored They are used in the LET statement to make it abso
174. ive cartridges eventually suffer from wear Hence it is strongly recommended that all important programs and data should be stored on at least two cartridges that is backed up This means that if a cartridge is damaged and the data lost then at least part of the data can be recovered from the relevant back up cartridge If you are continually adding data to a cartridge it must be backed up often unless you do so you will lose everything that was added since the last backup if the main cartridge is damaged Instructions for backing up cartridges are contained in the Information section STARTING WORK There are several ways of using your computer and the User Guide You can use ready made programs such as those supplied with the QL or you can write your own programs in SuperBASIC To use the QL programs first read the Introduction To The QL Programs later in this introduction and then the relevant section for each program concerned If you are a newcomer to computing and wish to write your own programs you should read the Beginner s Guide If you are familiar with BASIC programming you may prefer to read from Chapter 8 in the Beginner s Guide From BASIC to SuperBASIC This chapter describes the major differences between BASICs you may already be familiar with and QL SuperBASIC Alternatively if you are feeling confident the Keywords and Concepts sections should be useful IF YOU HAVE A PROBLEM If you have a problem using your QL o
175. ixels XXXXXXXXXxX XXXXXXXxX XXXXXXXXxX XXXXXXXxX III XXXXXXxX XXXXXXXXXxX XXXXXXXXX XXXXXX XXXXXXxX XXXXXXXXxX XXXXXXXxX XXXXXXX XXXXXXXXXXX XXXXXXxX XXXXXXXxX XXXXXXXXXxX it is useful to recall that the possible character heights are 10 pixels or 20 pixels It is obvious that the 10 pixel height must be used to allow space for a proper layout The number of character positions across the screen must be estimated If we adopt the convention of T for ten instead of 10 all card values can be represented as a single character Suppose that we also allow a maximum of eight cards of the same suit as a first approach We can reconsider the problem again if necessary That would require a total of 10 characters for each hand The across requirement is therefore west hand table width east hand Allowing a space between characters that would be 20 table width 20 The decision now depends on which screen mode you choose The 256 mode will cope with the problem as you will see later but first we will work in 512 pixel mode The smallest character width is six pixels which would give a total of 240 pixels table width The diagram will have some balance if we have a table width of about half of 240 We should therefore ex
176. knowledge based machines 440 DATA Intelligent compatible computers 450 DATA Controlled cybernetic feedback 460 DATA Automated user friendly transputers 470 DATA Synchronised parallel micro chips 480 DATA Functional Learning capability 490 DATA Optional adaptable programming 500 DATA Positive modular packages 510 DATA Balanced structured databases 520 DATA Integrated logic oriented spreadsheets 530 DATA Coordinated file oriented word processors 540 DATA Sophisticated standardised objectives Automated fifth generation capability FunctionaL learning packages Full parallel objectives Positive user friendly spreadsheets Intelligent file oriented capability Synchronised cybernetic transputers FunctionaL logic oriented micro chips Positive parallel feedback Balanced learning databases Controlled cybernetic objectives PASSING INFORMATION TO PROCEDURES Suppose we wish to draw squares of various sizes and various colours in various positions on the scale graphics screen If we define a procedure square to do this it will require four items of information length of one side colour colour code position across and up The square s position is determined by giving two values across and up which fix the bottom left hand corner of the square as shown below ac up side actside uptside act
177. l channel is opened BAUD set transmission speed OPEN open serial channels CLOSE close serial channels see concept DEVICE for a full specification DATA TYPES VARIABLES INTEGER Integers are whole numbers in the range 32768 to 32767 Variables are assumed to be integer if the variable identifier is suffixed with a percent There are no integer constants in SuperBASIC so all constants are stored as floating point numbers syntax identifier example i counter ii size_limit iii this_is_an_integer_variable FLOATING POINT Floating point numbers are in the range 10 615 to 10615 with 8 significant digits Floating point is the default data type in SuperBASIC All constants are held in floating point form and can be entered using exponent notation syntax identifier constant example i current accumuLation ii 76 2356 iii 354E25 STRING A string is a sequence of characters up to 32766 characters long Variables are assumed to be type string if the variable name is suffixed bya String data is represented by enclosing the required characters in either single or double quotation marks syntax identifier text example i string_variables ii this is string data iii this is another string Type name has the same form as a standard SuperBASIC identifier and is used by the name system to name Microdrive files etc syntax identifier example i mdv1_data_file ii ser1e DEVICE
178. l resume normal processing at the next logical line syntax REPeat identifier statements example REPeat wait IF INKEY THEN EXIT wait LONG The REPEAT keyword and the loop identifier are the only statements on the logical line Subsequent lines contain a series of SuperBASIC statements terminated by an END REPeat statement The statements between the REPeat and the END REPeat are repeatedly processed by SuperBASIC syntax REPeat identifier statements END REPeat identifier example 10 LET number RND 1 TO 50 11 REPeat guess 12 INPUT What is your guess guess 13 IF guess number THEN 14 PRINT You have guessed correctly 15 EXIT guess 16 ELSE 17 PRINT You have guessed incorrectly 18 END IF 19 END REPeat guess Comment Normally at least one statement in a REPeat loop will be an EXIT statement RESPR Qdos RESPR is a function which will reserve some of the resident procedure space For example to expand the SuperBASIC procedure list syntax space numeric_expression RESPR space example PRINT RESPR 1024 will print the base address of a 1024 byte block RETurn functions and procedures RETurn is used to force a function or procedure to terminate and resume processing at the statement after the procedure or function call When used within a function definition them RETurn statement is used to return the function s value syntax RETern expression example i 100 PRINT ack 3 3 110 DEFin
179. led even if not in operation NEVER touch the cartridge while the Microdrive is in operation DO NOT repeatedly insert and remove the cartridge without running the Microdrive TAPE LOOPS ff a tape loop appears at either of the two places shown in figure 1 then gently ease it back into the cartridge Use a non fibrous instrument for this e g the side of a pen or pencil NEVER tocuh the tape with your fingers for this or any reason lt write protect lug gt V FESSssssSSsSSSS 5 FeSSsssssssSSsSS 5 A Microdrive Cartridge A label Command Function FORMAT prepare a new cartridge for use DELETE delete a file from a cartridge DIR list the files on a cartridge SAVE SBYTES saves data from a cartridge SEXEC LOAD LBYTES EXEC loads data from a cartridge MERGE OPEN_IN OPEN_NEW OPEN opens and closes files CLOSE PRINT INPUT SuperBASIC file VO INKEY WARNING If you attempt to write to a cartridge which is write protected then the QL will repeatedly attempt to write the data but will eventually give up and give a bad medium error MONITOR A monitor may be connected to the QL via the RGB socket on the back of the computer Connection is via an 8 way DIN plug plus cable for colour monitors or a 3 way DIN plug plus cable for monochrome The RGB socket connections are as in the following table and the column indicating wire
180. left This shows that 3E 2 is the same as 0 03 After running the program the average daily sales are 1 25E 3 which is the same as 0 00125 Numbers with an E are said to be in exponent form mantissa E exponent mantissa x 10 to the power exponent INTEGER VARIABLES Integer variables can have only whole number values in the range 32678 to 32768 The following are examples of valid integer variable names which must end with LET count 10 LET six_tally RND 10 LET number_3 3 The only disadvantage of integer variables when whole numbers are required is the slightly misleading symbol on the end of the identifier It has nothing to do with the concept of percentage Itis just a convenient symbol tagged on to show that the variable is an integer NUMERIC FUNCTIONS Using a function is a bit like making an omelette You put in an egg which is processed according to certain rules the recipe and get out an omelette For example the function INT takes any number as input and outputs the whole number part Anything which is input to a function is called a parameter or argument INT is a function which gives the integer part of an expression You may write PRINT INT 5 6 and 5 would be the output We say that 5 6 is the parameter and the function returns the value 5 A function may have more than one parameter You have already met RND 1 TO 6 which is a function with two parameters But functions always return exac
181. lets 1 160 IF bullets 0 THEN EXIT bandit 170 END REPeat bandit The program fails in two ways 1 Take aim Fire a shot is printed though there were never any bullets 2 By the time the variable bullets is tested in line 160 it has the value 1 and it never becomes zero afterwards The program loops indefinitely You can cure the infinite looping by re writing line 160 160 IF bullets lt 1 THEN EXIT bandit There is an inherent fault in the programming which does not allow for the possible zero case This can be corrected by placing the conditional EXIT before the PRINT statements Program 3 100 REMark Western REPeat Zero Case 110 LET bullets 0 120 REPeat Bandit 130 IF bullets 0 THEN EXIT Bandit 140 PRINT Take aim 150 PRINT Fire shot 160 LET bullets bullets 1 170 END REPeat Bandit This program now works properly whatever the initial value of bullets as long as itis a positive whole number or zero Method 2 corresponds to the REPEAT UNTIL loop of some languages Method 3 corresponds to the WHLLE ENDWHILE loop of some languages However the REPeat END REPeat with EXIT is more flexible than either or the combination of both If you have used other BASICs you may wonder what has happened to the NEXT statement We will re introduce it soon but you will see that both loops have a similar structure and both are named FOR name opening keyword REPeat name statements content statements E
182. ll clear all windows currently on the screen but will preserve their position and shape Changing to low resolution mode 8 colour will set the minimum character size to 2 0 syntax MODE numeric_expression where 8 or 256 will select low resolution mode 4 or 512 will select high resolution mode example i MODE 256 ii MODE 4 MOVE turtle graphics MOVE will move the graphics turtle in the window attached to the default or specified channel a specified distance in the current direction The direction can be specified using the TURN and TURNTO commands The graphics scale factor is used in determining how far the turtle actually moves Specifying a negative distance will move the turtle backwards The turtle is moved in the window attached to the specified or default channel syntax distance numeric_expression MOVE channel distance example i MOVE 2 20 move the turtle in channel 2 20 units forwards ii MOVE 50 move the turtle in the default channel 50 units backwards MRUN devices microdrives MRUN will interpret a file as a SuperBASIC program and merge it with the currently loaded program If used as direct command MRUN will run the new program from the start If used as a program statement MRUN will continue processing on the line following MRUN ff a line input during a merge has incorrect SuperBASIC syntax the word MISTAKE is inserted between the line number and the body of the line Upon execution a line of this
183. ll reach its correct position Another eight runs will guarantee eight more correct positions leaving only the lowest number which must be in the only correct position left The simplest form of bubble sort of ten numbers requires nine runs of nine comparisons 2 Consider ways of speeding up bubblesort but do not expect that it will ever be very efficient 3 An auctioneer wishes to sell an old clock and he has instructions to invite a first bid of 50 If no one bids he can come down to 40 30 20 but no lower in an effort to start the bidding If no one bids the clock is withdrawn from the sale When the bidding starts he takes only 5 increases until the final bid is made If the final bid is 35 the reserve price or more the clock is sold Otherwise it is withdrawn Simulate the auction using the equivalent of a six sided die throw to start the bidding A six at any of the starting prices will start it off When the bidding has started there should be a three out of four chance of a higher bid at each invitation 4 Ina wild west shoot out the Sheriff has no ammunition and wishes to arrest a gunman camped in a forest He rides amongst the trees tempting the gunman to fire He hopes that when six shots have been fired he can rush in and overpower the gunman as he tries to re load Simulate the encounter giving the gunman a one twentieth chance of hitting the Sheriff with each shot If the Sheriff has not been hit af
184. lotted to the specified point 3 will move to the specified point no line will be drawn example i LINE 0 0 TO 0 50 TO 50 0 TO 50 0 TO 0 0 a square ii LINE TO 0 75 0 5 a line iii LINE 25 25 move the graphics cursor LIST LIST allows a SuperBASIC line or group of lines to be listed ona specific or default channel LIST is terminated by CTRL SPACE syntax line line_number TO line_number 1 line_number TO 2 TO line_number 3 line_number 4 5 LIST channel line line where 1 will list from the specified line to the specified line 2 will list from the specified line to the end 3 will list from the start to the specified line 4 will list the specified line 5 will list the whole program example i LIST list all lines ii LIST 10 TO 300 list lines 10 to 300 iii LIST 12 20 50 list lines 12 20 and 50 only f LIST output is directed to a channel opened as a printer channel then LIST will provide hard copy LOAD devices microdrives LOAD will load a SuperBASIC program from any QL device LOAD automatically performs a NEW before loading another program and so any previously loaded program will be cleared by LOAD If a line input during a load has incorrect SuperBASIC syntax the word MISTAKE is inserted between the line number and the body of the line Upon execution a line of this sort will generate an error syntax LOAD device example i LOAD mdvl_test_program ii LOAD
185. lue If the FOR loop is exhausted then processing will continue at the statement following the NEXT otherwise processing will continue at the statement after the FOR ON GOTO ON GOSUB To provide compatibility with other BASICs SuperBASIC supports the ON GOTO and ON GOSUB statements These statements allow a variable to select from a list of possible line numbers a line to process ina GOTO or GOSUB statement If too few line numbers are specified in the list then an error is generated syntax ON variable GOTO expression expression ON variable GOSUB expression expression example i ON x GOTO 10 20 30 40 ii ON select_variable GOSUB 1000 2000 3000 4000 comment SELect can be used to replace these two BASIC commands OPEN OPEN_IN OPEN_NEW devices Microdrives OPEN allows the user to link a logical channel to a physical QL device for O purposes If the channel is to a Microdrive then the Microdrive file can be an existing file or a new file In which case OPEN_IN will open an already existing Microdrive file for input and OPEN_NEW will create a new Microdrive file for output syntax channel numeric_expressicn OPEN channel device example i OPEN 5 f_name ii OPEN_IN 9 mdv1_ filename open file mdvi_file__ name iii OPEN NEW 7 mdv1_ datafile open file mdvi_datafile iv OPEN 6 con_10x20a20x2032 Open channel 6 to the console device creating a window size 10x20 pixels at position 20 20 with a 32
186. lustrating the use of logical variables and procedures CHAPTER 12 SCREEN OUTPUT SuperBASIC has so extended the scope and variety of facilities for screen presentation that we describe the features in two sections Simple Printing and Screen The first section describes the output of ordinary text Here we explain the minimal well established methods of displaying messages text or numerical output Even in this mundane section there is innovation in the concept of the intelligent space an example of combining ease of use with very useful effects The second section is much bigger because it has a great deal to say The wide range of features actually makes things easier For example you can draw a circle by simply writing the word CIRCLE followed by a few details to define such things as its position and size Many other systems require you to understand some geometry and trigonometry in order to do what is in concept simple Each keyword has been carefully chosen to relect the effect it causes WINDOW defines an area of the screen BORDER puts a border round it PAPER defines the background colour INK determines the colour of what you put on the paper If you work through this chapter and get a little practice you will easily remember which keyword causes which effect You will add that extra quality to your programming fairly easily With experience you may see why computer graphics is becoming a new art form SIMPLE PRIN
187. lutely clear what is to be stored in the pigeon hole You can check by typing PRINT weekday ENTER and the screen should display what is in the pigeon hole FIRST You can use a pair of apostrophes instead of a pair of quote marks LENGTHS OF STRINGS SuperBASIC makes it easy to find the length or number of characters of any string You simply write for example PRINT LEN weekday ENTER lf the pigeon hole weekday contains FIRST the number 5 will be displayed You can see the effect in a simple program NEW ENTER 10 LET weekday FIRST ENTER 20 PRINT LEN weekday ENTER RUN ENTER The screen should display 5 LEN is a keyword of SuperBASIC An alternative method of achieving the same result uses both a string pigeon hole and a numeric pigeon hole NEW ENTER 10 LET weekday FIRST ENTER 20 LET length LEN weekday ENTER 30 PRINT length ENTER RUN ENTER The screen should display 5 as before and two internal pigeon holes contain the values shown ui weekday FIRST length 5 ui Let us return to the problem of average lengths of words Write a program to find the average length of the three words FIRST OF FEBRUARY PROGRAM DESIGN When problems get beyond what you regard as very trivial itis a good idea to construct a program design before writing the program itself 1 Store the three words in pigeon holes 2 Compute the lengths and st
188. mal parameter dish is both local to procedure choose an array in main program The three values are passed back to the global array also called dish These values are then passed to the procedure waiter 170 waiter dish bill 330 DEFine PROCedure waiter dish cost 340 compute dish cost 350 cook dish 360 END DEFine The waiter passes the information about the number of each dish required to the procedure compute which computes the cost and returns it 370 DEFine PROCedure compute dish total 380 LET total 0 390 FOR k 1 to 3 400 LET total total dish k price k 410 END FORk 420 END DEFine The waiter also passes information to the cook who simply prints the number required for each menu item 430 DEFine PROCedure cook dish 440 FORc 1TO3 450 PRINT dish c item c 460 END FORc 470 END DEFine Again the array dish in the procedure cook is local It receives the information which the procedure uses in its PRINT statement The complete program is listed below Program 100 REMark Procedures 110 RESTORE 490 120 DIM item 3 7 price 3 dish 3 130 REMark PROGRAM 140 LET tip 0 1 150 set_up 160 choose dish 170 waiter dish bill 180 LET bill bill tip bill 190 PRINT Total cost is bill 200 REMark PROCEDURE DEFINITIONS 210 DEFine PROCedure set_up 220 FORK 1TO3 230 READ item k 240 READ price k 250 END FOR k 260 END DEFine 270 DEFine PROCedure choose dish
189. mode the QL will not allow you to select a character size smaller than default size STRIP You can provide a special background for characters to make them stand out For example STRIP 7 will give a white strip while STRIP 2 4 2 will give a red green vertical striped strip All the normal colour combinations are possible OVER Normally printing occurs on the current paper colour You can alter this by using strip You can make further effects by using OVER 1 1 prints inink ona transparent strip OVER 1 1 prints in ink over existing display on screen To revert to normal printing on current strip use OVERO UNDER You can underline characters UNDER 1 underlines all subsequent output in the current ink UNDER 0 switches off underling SCALE GRAPHICS If you wish to draw reasonably true geometric figures on a TV or video screen you cannot easily use a pixel based system If you use scale graphics then the system will do the necessary work to ensure that you can fairly easily draw reasonable circles squares and other shapes The default scale of the graphics coordinate system is 100 in the vertical direction and whatever is needed in the across direction to ensure that shapes drawn with the special graphics keywords PLOT DRAW CIRCLE are true The graphics origin is not the same as the pixel origin which is used to define the position of windows and blocks The graphics origin is at the bottom left hand corner of the c
190. mputers as DTE devices This obviously leads to difficulties in the configuration of the serial ports on each piece of equipment SER1 on the QL is configured as DCE while SER2 is configurd as DTE Therefore it should be possible to connect at least one of the serial ports to a given device simply by using whichever port is wired the correct way The pin out for the serial ports is given below A cable for connecting the QL to a standard 25 way D type connector is available from Sinclair Research Limited 1 GND signal ground 1 GND signal ground 2 TxD input 2 TxD output 3 RxD output 3 RxD input 4 DTR ready input 4 DTR ready output 5 CTS ready output 5 CTS ready input 6 12V 6 12V TxD Transmit Data DTR Data Terminal Ready RxD Receive Data CTS Clear To Send Once the equipment has been connected to the correct port the baud rate the speed of transmission of data must be set so that the baud rates for both the QL and the connected equipment are the same The QL can be set to operate at 19200 transmit only baud The QL baud rate is set by the BAUD command and is set for both channels The baud rates cannot be set independently The parity to be used by the QL must also be set to match that expected by the peripheral equipment Parity is usually used to detect simple transmission errors and may be set to be even odd mark space or no parity i e all 8 bits of the byte are used for data Stop bits mark the end of transm
191. n a snake or the digits 1 2 3 etc to denote a particular player s position Set up six snakes and six ladders by placing numbers in the array and simulate one solo run by a single player to test the game 3 CROSSWORD BLANKS 12345 columns TTT 2 Xxx row 3 II 4XXXI SHIT II The squares represented by XXX above are black squares the file Chapt13a_pic contains a better diagram Crosswords usually have an odd number of rows or columns in which the black squares have a symmetrical pattern The pattern is said to have rotational symmetry because rotation through 180 degrees would not change it Note that after rotation through 180 degrees the square in row 4 column 1 could become the square in row 2 column 5 That is row 4 column 1 becomes row 2 column 5 ina 5 x5 grid Write a program to generate and display a symmetrical pattern of this kind 4 Modify the crossword pattern so that there are no sequences across or down of less than four white squares 5 CARD SHUFFLE Cards are denoted by the numbers 1 52 stored in an array They can be converted easily to actual card values when necessary The cards should be shuffled as follows Choose any position in range 1 51 e g 17 Place the card in this position in a temporary store Shunt all the cards in positions 52
192. n can be an expression syntax GOSUB line_number example i GOSUB 100 ii GOSUB 4 select_variable Comment The control structures available in SuperBASIC make the GOSUB statement redundant GOTO For compatibility with other BASICs SuperBASIC supports the GOTO statement GOTO will unconditionally transfer processing to the statement number specified The statement number specification can be an expression syntax GOTO line_number example i GOTO program start ii GOTO 9999 comment The control structures available in SuperBASIC make the GOTO statement redundant END IF The IF statement allows conditions to be tested and the outcome of that test to control subsequent program flow The IF statement can be used in both a long and a short form SHORT The THEN keyword is followed on the same logical line by a sequence of SuperBASIC keyword This sequence of SuperBASIC statements may contain an ELSE keyword If the expression in the IF statement is true evaluates to be non zero then the statements between the THEN and the ELSE keywords are processed If the condition is false evaluates to be zero then the statements between the ELSE and the end of the line are processed If the sequence of SuperBASIC statements does not contain an ELSE keyword and if the expression in the IF statement is true then the statements between the THEN keyword and the end of the line are processed If the expression is false then processing continue
193. n contain i Software to be used instead of or with the SuperBASIC system For example assemblers compilers debuggers application software etc ii Software to expand the SuperBASIC system FOr example special procedures etc tis not possible to use ZX ROM Cartridges on the QL PIN OUT _ a1b VDD A12 a2b A14 A7 a3b A13 A6 a4b A8 A5 a5b A9 SLOT a6b SLOT A4 a7b A11 A3 a 8 b ROMOEH A2 a9b A10 A1 a10b A15 AO a 11 b D7 DO a 12 b D6 D1 a13b D5 D2 a 14b D4 GND a 15b D3 Side b is the upper side of the connector side a is the lower Signal Function A0 A15 Address lines DO D7 Data lines ROMOEH ROM Output Enable VDD 5V GND Ground WARNING Never plug or unplug a ROM cartridge while the QL power is on SCREEN 512 MODE The screen is 512 pixels across and 256 pixels deep Only the solid colours black red green and white can be displayed in this mode 256 MODE Low resolution mode also has a hardware flash The screen is 256 pixels across and 256 pixels deep The full set of solid colours is available in this mode black blue red magenta green cyan yellow and white WARNING A domestic television is not capable of displaying the complete QL screen Portions of the screen at the top and the sides will not be reproduced The default initial window will take account of this and will reduce the effective picture size The full size can be restored with t
194. name is made up of two parts device name appended information Suppose that we wish to create the file numbers on a cartridge in Microdrive 1 The device name is mdv1 _ and the appended information is just the name of the file numbers So the complete file name is mdv1_numbers CHANNELS t is possible for a program to use several files at once but it is more convenient to refer to a file by an associated channel number This can be any integer in the range 0 to 15 A file is associated with a channel number by using the OPEN statement or if it is a new file OPEN NEW For example you may choose channel 7 for the numbers file and write OPEN_NEW 7 mdv1_numbers AANA HII file device channel number keyword You can now refer to the file just by quoting the number 7 The complete program is 100 REMark Simple file 110 OPEN NEW 7 mdv1_numbers 120 FOR number 1 to 100 130 PRINT 7 number 140 END FOR number 150 CLOSE 7 The PRINT statement causes the numbers to be printed on the cartridge file because 7 has been associated with it The CLOSE 7 statement is necessary because the system has some internal work to do when the file has been used It also releases channel 7 for other possible uses After the program has executed type DIR mdv1 _ and the directory should show that the file numbers exists on the cartridge in Mic
195. nction but this space cannot be released except by resetting the QL Resident Procedures written in machine code can be added to the SuperBASIC name list and so become extensions to the SuperBASIC system sv_trnsp Transient Programs Transient programs are loaded immediately below the resident procedures Each program must be self contained i e it must contain space for its own data and its own stack It must be position independent or must be loaded by a specially written linking loader A transient program is executed from BASIC by using the EXEC command or from QDOS by activating it as a job The transient program area may be used for storing data only but this data will still be treated by QDOS as a job and therefore must not be activated sv_basic SuperBASIC Area This area contains all loaded SuperBASIC programs and related data This area expands and contracts using up the free space as required sv_free Free Space Free space is used by the Qdos file subsystem to create Microdrive Slave Blocks i e copies of Microdrive blocks which can be held in RAM sv_heap System Heap This is used by the system to store data channel definitions and also provides working storage for the O subsystem Transient programs may allocate working space for themselves on the heap via Qdos system calls System Tables System Variables This area is directly above the screen memory The System Tables and supervisor stack are resident abo
196. nd i e deviations on every cycle of the sound Fuzziness tends to result in buzzy sounds while randomness depending on the other parameters will result in melodic sounds or noise The complexity of the sound can be built up stage by stage gradually building more complex sounds This is in fact the best way to master sound on the QL Specify a duration and a single pitch The specified pitch will be beeped for the specified time LEVEL 1 a Se time This is the simplest sound command other than the command to stop the sound on the QL LEVEL 2 A second pitch and a gradient can be added to the command The sound will then pounce between the two pitches at the rate specified by the gradient The sounds produced at this level can vary between semi musical beeps growls zaps and moans It is best to experiment pitch BPS eee aE ERS Pe SONY Pane eRe ne Pe Se oe ee eee Ree Pate ee Pa EE ASE time LEVEL3 A parameter can be added which controls how the sound behaves when it becomes equal to one of the specified pitches The sound can be made to bounce or wrap The number of wraps can be specified including wrap forever It is even more important to experiment pitch i S aa E aa pitch2 HITT HITT HITT EE ooo pitch he ne ee time pitch nae nae pitch2 HIT sex HIT eer HIT nnn wan Pitch F
197. ndows 1 and 2 so that more character positions per line are available for program listings KEYWORD EFFECT DEFAULT AT Character position 1 BLOCK Draws block 1 BORDER Draw border 1 CLS Clear screen 1 CSIZE Character size 1 CURSOR Position cursor 1 FLASH Causes cancels flashing 1 INK Foreground colour 1 OVER Effect of printing and graphics 1 PAN Moves screen sideways 1 PAPER Background colour 1 RECOL Changes colour 1 SCROLL Moves screen vertically 1 STRIP Background for printing 1 UNDER Underlines 1 WINDOW Changes existing window 1 LIST Lists program 2 DIR Lists directory 1 PRINT Prints characters 1 INPUT Takes keyboard input 1 Statements or direct commands appear in window 0 For more details about the syntax or use of these keywords see other parts of the manual RECTANGLES AND LINES The program below draws a green rectangle in 256 mode on red paper witha yellow border one pixel wide The rectangle has its top left corner at pixel co ordinates 100 100 see QL Concepts Its width is 80 units across 40 pixels and its height is 20 units down 20 pixels 100 REMark Rectangle 110 MODE 256 120 BORDER 1 6 130 PAPER 2 CLS 140 BLOCK 80 20 100 100 4 You have to be a bit careful in mode 256 because across values range from 0 to 511 even though there are only 256 pixels We cannot say that the block produced by the above program is 80 pixels wide so we say 80 units INPUT AND OUTPUT Sup
198. ne FuNction compute dish LET total 0 FORk 1TO3 LET total total dish k price k END FORk RETurn total END DEFine The function call to waiter also takes a different form LET bill waiter dish This program works as before Notice that there are fewer parameters though the program structure is similar That is because the function names are also serving as parameters retuning information to the source of the function call EXAMPLE All the variables used as formal parameters in procedures or functions are safe because they are automatically local Which variables used in the procedures or functions are not local What additional statements would be needed to make them local Program Changes The variables k pick and num are not local The necessary changes to make them so are LOCAL k LOCAL pick num TYPELESS PARAMETERS Formal parameters do not have any type You may prefer that a variable which handles numbers has the appearance of a numeric variable and which handles strings looks like a string variable but however you write your parameters they are typeless To prove it try the following program Program 100 REMark Number or word 110 waiter 2 120 waiter Chicken 130 DEFine PROCedure waiter item 140 PRINT item 150 END DEFine Output 2 Chicken The type of the parameter is determined only when the procedure is called and an actual parameter arrives SCOPE OF VARIABLES Consider th
199. ng the program the program can be restarted at the statement which triggered the error Type RETRY EXPRESSIONS SuperBASIC expressions can be string numeric logical or a mixture unsuitable data types are automatically converted to a suitable form by the system wherever this is possible monop NOT expression monop expression operator expression expression atom atom variable constant function expression expression array_element variable identifier identifier identifier function identifier identifier identifier constant digit digit digit digit digit digit E digit The final value returned by the evaluation of the expression can be integer giving an integer_expression string giving a string_expression or floating point giving a floating expression Often floating point and integer expressions are equivalent and the term numeric_expression is then used Logical operators can be included in an expression If the specified operation is true then a one is returned as the value of the operation If the operation is false then a zero is returned Though logical operators can be used in any expression they are usually used in the expression part of an IF statement example i test_data 23 3 5 ii abcdefghijkimnopqrstuwwxyz 2 TO 4 iii 32 1 colour 1 iv count limit FILE TYPES FILES All V
200. ng used or the screen is in low resolution mode then to maintain the stipple pattern the screen must be panned in multiples of two pixels PAPER windows PAPER sets a new paper colour tie the colour which will be used by CLS PAN SCROLL etc The selected paper colour remains in effect until the next use of PAPER PAPER will also set the STRIP colour PAPER will change the paper colour in the window attached to the specified or default channel syntax PAPER channel colour example i PAPER 3 7 White paper on channel 3 ii PAPER 7 2 White and red stipple iii PAPER 255 Black and white stipple iv 10 REMark Show colours and stipples 11 FOR colour 0 TO 7 12 FOR contrast 0 TO 7 13 FOR stipple 0 TO 3 14 PAPER colour contrast stipple 15 SCROLL 6 16 END FOR stipple 17 END FOR cent rest 18 END FOR colour PAUSE PAUSE will cause a program to wait a specified period of time delays are specified in units of 20ms in the UK only otherwise 16 67ms If no delay is specified then the program will pause indefinitely Keyboard input will terminate the PAUSE and restart program execution syntax delay numeric_expression PAUSE delay example i PAUSE 50 wait 1 second ii PAUSE 500 wait 10 seconds PEEK PEEICW PEEK_L BASIC PEEK is a function which returns the contents of the specified memory location PEEK has three forms which will access a byte 8 bits a word 16 bits or a long word 32 bits syntax
201. nge is tested exactly and is inclusive The ON REMAINDER statement allows a catch all which will respond if no other select conditions are satisfied syntax SELect ON select_variable ON select_variable select_list statements ON selectvariable REMAINDER statements END SELect example 100 LET error number RND 1 TO 10 110 SELect ON error_number 120 ON error_number 1 130 PRINT Divide by zero 140 LET error_number 0 150 ON error_number 2 160 PRINT File not found 170 LET error_number 0 180 ON error_number 3 TO 5 190 PRINT Microdrive file not found 200 LET error_number 0 210 ON error_number REMAINDER 220 PRINT Unknown error 230 END SELect If the select variable is used in the body of the SELect statement then it must match the select variable given in the select header SHORT The short form of the SELect statement allows simple single line selections to be made A sequence of SuperBASIC statements follows on the same logical line as the SELect statement If the condition defined in the select statement is satisfied then the sequence of SuperBASIC statements is processed syntax SELect ON select_variable select_list statement statement example i SELect ON test data 1 TO 10 PRINT Answer within range ii SELect ON answer 0 00001 TO 0 00005 PRINT Accuracy OK iii SELect ON a 1 TO 10 PRINT a in range Comment The short form of the SELect statement all
202. ngle character and specifying a slice will define a sub string COMMENT Unlike many BASICs SuperBASIC does not treat string arrays as fixed length strings If the data stored ina string array is less than the maximum size of the string array then the length of the string is reduced WARNING Assigning data to a sliced string array Or string variable may not have the desired effect Assignments made in this way will not update the length of the string and so it is possible that the system will not recognise the assignment The length of a string array or a string variable is only updated when an assignment is made to the whole string FILL generate a string LEN find the length of a string STRING COMPARISON ORDER decimal point full stop digits or numbers in numerical order AaBbCcDdEeFfGgHhliJjKkKLIMmNnOoPpQqRrSs TtUuV WwxxYyZz space amp lt gt 7 4_ other non printing characters The relationship of one string to another may be equal All characters or numbers are the same or equivalent lesser The first part of the string which is different from the corresponding character in the second string is before it in the defined order greater The first part of the first string which is different from the corresponding character in the second string is after it in the defined order Note that a may be treated as a decimal point in the case of string comparison which sorts numbers such as SuperBAS
203. ns that the correct array subscript is automatically chosen for an increase in the tally after each throw You can think of the array tally as a set of pigeon holes numbered 2 to 12 Each time a particular score occurs the tally of that score is increased by throwing a stone into the corresponding pigeon hole In the second short form FOR loop the subscript is number As the value of number changes from 2 to 12 all the values of the tallies are printed Notice that in the DIM statement for a numeric array you need only declare the number of variables required There is no question of maximum length as there is ina string array If you have used other versions of BASIC you may wonder what has happened to the NEXT statement All SuperBASIC structures end with END something That is consistent and sensible but the NEXT statement has a part to play as you will see in later chapters SELF TEST ON CHAPTER 6 You can score a maximum of 16 points from the following test Check your score with the answers on page 109 1 Mention two difficulties which arise when the data needed for a program becomes numerous and you try to handle it without arrays two points 2 If in an array ten variables have the same name then how do you know which is which 3 What must you do normally in a program before you can use an array variable 4 What is another word for the number which distinguishes a particular variable of an array from the other var
204. nt the THEN is optional In the short form it must comment be replaced by a colon to distinguish the end of the IF and the start of the next statement In the long form it can be removed completely IF statements may be nested as deeply as the user requires subject to available memory However confusion may arise as to which ELSE END IF etc matches which IF SuperBASIC will match nested ELSE statements etc to the closest IF statement for example 100 IF a b THEN 110 IF c d THEN 120 PRINT error 130 ELSE 140 PRINT no error 150 END IF 160 ELSE 170 PRINT not checked 180 END IF The ELSE at line 130 is matched to the second IF The ELSE at line 160 is matched with the first IF at line 100 INK windows This sets the current ink colour i e the colour in which the output is written INK will windows be effective for the window attached to the specified or default channel syntax INK channel colour example i INK 5 ii INK 6 2 iii INK 2 255 INKEY INKEY is a function which returns a single character input from either the specified or default channel An optional timeout can be specified which can wait for a specified time before returning can return immediately or can wait forever If no parameter is specified then INKEY will return immediately syntax INKEY channel channel time time where time 1 32767 wait for specified number of frames time 1 wait forever time 0
205. ntified as follows 100 REM Card identification 110 LET card 23 120 LET suit card 1 DM 13 130 LET value card MOD 13 140 IF value 0 THEN LET value 13 150 IF value 1 THEN PRINT Ace of 160 IF value gt 2 AND value lt 10 THEN PRINT value of 170 IF value 11 THEN PRINT Jack of 180 IF value 12 THEN PRINT Queen of 190 IF value 13 THEN PRINT King of 200 IF suit 0 THEN PRINT hearts 210 IF suit 1 THEN PRINT clubs 220 IF suit 2 THEN PRINT diamonds 230 IF suit 3 THEN PRINT spades There are new ideas in this program They are in line 160 The meaning is clearly that the number is actually printed only if two logical statements are true These are value is greater than or equal to 2 AND value is less than or equal to 10 Cards outside this range are either aces or court cards and must be treated differently Note also the use of in the PRINT statement to provide a space and to ensure that output continues on the same line There are two groups of mathematical functions which we have not discussed here They are the trigonometric and logarithmic You may need the former in organising screen displays Types of functions are also fully defined in the reference section LOGICAL VARIABLES Strictly speaking SuperBASIC does not allow logical variables but it allows you to use other variables as logical ones For example you can run the following program 100 REMark Logical Va
206. numbers compared in numerical order lt Less than Case dependent numbers compared in numerical order Equals Case dependent strings must be the same Equivalent String must be almost the same Case independent numbers compared in numerical order gt Greater than or equal to Case dependent numbers compared in numerical order lt Less than or equal to Case dependent numbers compared in numerical order PROBLEMS ON CHAPTER 11 1 Place 12 letters all different ina string variable and another six letters ina second string variable Search the first string for each of the six letters in turn saying in each case whether it is found or not found 2 Repeat using single character arrays instead of strings Place twenty random upper case letters in a string and list those which are repeated 3 Write a program to read a sample of text all in upper case letters Count the frequency of each letter and print the results GOVERNMENT IS A TRUST AND THE OFFICERS OF THE GOVERNMENT ARE TRUSTEES AND BOTH THE TRUST AND THE TRUSTEES ARE CREATED FOR THE BENEFIT OF THE PEOPLE HENRY CLAY 1829 4 Write a program to count the number of words in the following text A word is recognised because it starts with a letter and is followed by a space full stop or other punctuation character THE REPORTS OF MY DEATH ARE GREATLY EXAGGERATED CABLE FROM MARK TWAIN TO THE ASSOCIATED PRESS LONDON 1896 5 Rewrite the last program il
207. o understand Such programs are less prone to errors and more adaptable CHECK YOUR SCORE 18 to 21 is very good Carry on reading 16 or 17 good but re read some parts of chapter two 14 or 15 fair but re read some parts of chapter two and do the test again Under 14 you should work carefuly through chapter two again and repeat the test ANSWERS TO SELF TEST ON CHAPTER 3 1 A pixel is the smallest area of light that can be displayed on the screen 2 There are 256 pixel positions across the low resolution mode 3 There are 256 pixel positions from top to bottom in the low resolution mode 4 An address is determined by the up value 0 to 100 the across value 0 to a number computed by the system 5 There are eight colours available in the low resolution mode including black and white 6 i LINE draws a line e g LINE a b TO x y ii INK selects a colour for drawing e g INK 5 iii PAPER selects a background colour e g PAPER 7 iv BORDER draws a border e g BORDER 1 5 7 REPeat name END REPeat name 8 A REPeat loop terminates when an EXIT name statement is executed 9 Loops in SuperBASIC have names so that it is possible to EXIT from them in a straightforward way It is not necessary to work out line numbers in advance CHECK YOUR SCORE 11 to 13 is very good Carry on reading 8 to 10 is good but re read some parts of chapter three 6 or 7 is fair but re read some parts of chapter three and do the test
208. oe F t You can refer to the variables in the usual way but remember to use the right subscript Suppose that Tom and Sevvy wished to exchange flats In computing terms one of them Tom say would have to move into a temporary flat to allow Sevvy time to move You can write LET temp flat 1 REMark Tom into temporary LET flat 1 flat 3 REMark Sevwy into flat 1 LET flat 3 temp REMark Tom into flat 3 The following program places the ten golfers in an array named flat and prints the names of the occupants with their flat numbers array subscripts to prove that they are in residence The occupants of flats 1 and 3 then change places The list of occupants is then printed again to show that the exchange has occurred 100 REMark Golfers Flats 110 DIM flat 10 8 120 FOR number 1 TO 10 READ flat number 130 printlist 140 exchange 150 printlist 160 REMark End of main program 170 DEFine PROCedure printlist 180 FOR num 1 TO 10 PRINT num flat num 190 END DEFine 200 DEFine PROCedure exchange 210 LET temp ftat 1 220 LET flat 1 f1at 3 230 LET flat 3 temp 240 END DEFine 250 DATA Tom Graham Sewy Jack Lee 260 DATA Nick Bernard Ben Greg HaL output line 130 output line 150 1 Tom 1 Sewy 2 Graham 2 Graham 3 Sewy 3 Tom 4 Jack 4 Jack 5 Lee 5 Lee 6 Nick 6 Nick 7 Bernard 7 Bernard 8 Ben 8 Ben 9 Gregg 9 Gregg 10 Hal 10 Hal TWO DIMENSION
209. of the whole line and will enter it into the program AUTO is terminated by pressing CTRL SPACE syntax first_line line_number gap numeric_expression AUTO ffirst_line gap example i AUTO start at line 100 with intervals of 10 ii AUTO 10 5 start at line 10 with intervals of 5 iii AUTO 7 start at line 100 with intervals of 7 BAUD communications BAUD sets the baud rate for communication via both serial channels The speed of the channels cannot be set independently syntax rate numeric_expression BAUD rate The value of the numeric expression must be one of the supported baud rates on the QL 75 300 600 1200 2400 4800 9600 19200 transmit only If the selected baud rate is not supported then an error will be generated Example i BAUD 9600 ii BAUD print_speed BEEP sound BEEP activates the inbuilt sound functions on the QL BEEP can accept a variable number of parameters to give various levels of control over the sound produced The minimum specification requires only a duration and pitch to be specified BEEP used with no parameters will kill any sound being generated syntax duration numeric_expression range 32768 32767 pitch numeric_expression range 0 255 grad_x numeric_expression range 32768 32767 grad_y numeric_expression range 8 7 wrap numeric_expression range 0 15 fuzzy numeric_expression range 0 15 random numeric_expressian range 0 15 B
210. og_food month_wage_total more readable SuperBASIC does not distinguish between upper and lower case letters so names like TINS and tins are the same The maximum number of characters ina name is 255 Names which are constructed according to these rules are called identifiers Identifiers are used for other purposes in SuperBASIC and you need to understand them The rules allow great freedom in choice of names so you can make your programs easier to understand Names like total count pens are more helpful than names like Z P Q SELF TEST ON CHAPTER 2 You can score a maximum of 21 points from this test Check your score with the answers in Answers To Self Test section at the end of this Beginner s Guide 1 How should you imagine an internal number store 2 State two ways of storing a value in an internal pigeon hole to be created two points 3 How can you find out the value of an internal pigeon hole 4 What is the usual technical name for a pigeon hole 5 When does a pigeon hole get its first value 6 A variable is so called because its value can vary as a program is executed What is the usual way of causing such a change 7 The signin a LET statement does not mean equals as in mathematics What does it mean 8 What happens when you ENTER an un numbered statement 9 What happens when you ENTER a numbered statement 10 What is the purpose of quotes ina PRINT statement 11 What happens
211. ol to the statement after the END FOR or END REPeat selected by the EXIT statement EXIT can be used to exit through many levels of nested repeat structures EXIT should always be used in REPeat loops to terminate the loop on some condition A combination of NEXT EXIT and END statements allows FOR and REPeat loops to have a loop EPILOGUE added A loop epilogue is a series of SuperBASIC statements which are executed on some special condition arising within the loop FOR identifier for_list statements lt exit NEXT identifier next epilogue END FOR identifier lt The loop epilogue is only processed if the FOR loop terminates normally If the loop terminates via an EXIT statement then processing will continue at the END FOR and the epilogue will not be processed itis possible to have a similar construction ina REPeat loop REPeat identifier lt statements IF condition THEN NEXT identifier epilogue END REPeat identifier This time entry into the loop epilogue is controlled by the IF statement The epilogue will or will not be processed depending on the condition in the IF statement A SELect statement can also be used to control entry into the epilogue ROM CARTRIDGE SLOT Allows software to be used in the QL system from a Sinclair QL ROM Cartridge The ROM Cartrdge can contain software to directly change the behaviour of the SuperBASIC system The cartridge ca
212. ommand Function NET assign a network station number OPEN open a network channel CLOSE close a network channel PRINT INPUT network O INKEY LOAD SAVE LBYTES SBYTES EXEC load and save via network If you are planning to connect several QLs on the network or use a long piece of cable then you should wire it up with low capacitance twin core cable such as 3 amp light flex or bell wire Take care to connect the centres of each jack to each other and the outsides to each other You will find that although the software can handle 63 stations the hardware will not drive more than about 100m of cable depending on what type itis If you are only connecting a few machines with the lads supplied you need not worry OPERATORS Operator Type Function floating string logical type 2 comparison numeric string almost equal type 3 comparison numeric addition numeric subtraction numeric division numeric multiplication lt numeric string less than type 2 comparison gt numeric string greater than type 2 comparison lt numeric string less than or equal to type 2 comparison gt numeric string greater than or equal type 2 comparison lt gt numeric string not equal to type 3 comparison amp string concatenation amp amp bitwise AND bitwise OR M bitwise XOR bitwise NOT OR logical OR AND logical AND XOR logical XOR NOT logical NOT MOD integer modulus DM integer divide INSTR
213. oncept Reference Guide to generate random letters The upper case letters A to Z have the codes 65 to 90 The function CHR converts these codes into letters The following program will print a letter B NEW ENTER 10 LET lettercode 66 ENTER 20 PRINT CHR lettercode ENTER RUN ENTER The following program will generate trios of letters A B or C until the word CAB is spelled accidentally NEW ENTER 10 REPeat taxi ENTER 20 LET first CHR RND 65 TO 67 ENTER 30 LET second CHR RND 65 TO 67 ENTER 40 LET third CHR RND 65 TO 67 ENTER 50 LET word first amp second amp third ENTER 60 PRINT word ENTER 70 IF word CAB THEN EXIT taxi ENTER 80 END REPeat taxi ENTER Random characters like random numbers or random points are useful for learning to program You can easily get interesting effects for program examples and exercises Note the effect the have on the spacing of the output From now on we shall omit the ENTER key symbol at the end of each line of a program to be entered on the assumption that you are by now familiar with the use of the ENTER key SELF TEST ON CHAPTER 4 You can score a maximum of 10 points from the following test Check your score with the answers in the Answers To Self Tests section at the end of this Beginner s Guide 1 What is a character string 2 What is the usual abbreviation of the term character string 3 What distin
214. ontrol of the FOR statement syntax FOR variable for_list statements END FOR variable example 100 INPUT data please x 110 LET factorial 1 120 FOR value x TO 1 STEP 1 130 LET factorial factorial value 140 PRINT x factorial 150 IF factorial gt IE20 THEN 160 PRINT Very Large number 170 EXIT value 180 END IF 190 END FOR value Warning A floating point variable must be used to control a FOR loop FORMAT microdrives FORMAT will format and make ready for use the cartridge contained in the specified Microdrive syntax FORMAT channel device Device specifies the Microdrive to be used for formatting and the identifier part of the specification is used as the medium or volume name for that cartridge FORMAT will write the number of good sectors and the total number of sectors available on the cartridge on the default or on the specified channel it is helpful to format a new cartridge several times before use This conditions the surface of the tape and gives greater capacity example i FORMAT mdv1_data_cartridge ii FORMAT mdv2_wp_letters FORMAT can be used to reinitialise a used cartridge However all data contained on that cartridge will be lost GOSUB For compatibility with other BASICs SuperBASIC supports the GOSUB statement GOSUB transfers processing to the specified line number a RETurn statement will transfer processing back to the statement following GOSUB The line number specificatio
215. oop and place green in position 3 We are then ready to focus on the sixth item cyan 12345 678 black blue green magenta red cyan yellow white AN PROBLEM ANALYSIS 1 We will first store the colour in an array colour 8 and use comp the current colour being compared p to point at the position where we think the colour in comp might go 2 A FOR loop will focus attention on positions 2 to 8 in turn a single item is already sorted 3 A REPeat loop will allow comparisons until we find where the comp value actually goes REPeat compare IF comp need go no further left EXIT copy a colour into the position on its right and decrease p END REPeat compare 4 After EXIT from the REPeat loop the colour in comp is placed in position p and the FOR loop continues Program Design 1 Declare array colour 2 Read colours into the array 3 FOR item 2 TO 8 LET p item LET comp colour p REPEAT compare IF comp gt colour p 1 EXIT compare LET colour p colour p 1 LETp p 1 END REPeat compare LET colour p comp END FOR item 4 PRINT sorted array colour 5 DATA Further testing reveals a fault It arises very easily if we have data in which the first item is notin its correct position at the start A simple change of initial data to red black blue magenta green cyan yellow white reveals the problem We compare black with red and decrease p to the value 1 We come round again and t
216. ore them 3 Compute the average 4 Print the result NEW ENTER 10 LET weekday FIRST ENTER 20 LET word OF ENTER 30 LET month FEBRUARY ENTER 40 LET length1 LEN weekday ENTER 50 LET length2 LEN word ENTER 60 LET length3 LEN month ENTER 70 LET sum lengthl length2 length3 ENTER 80 LET average sum 3 ENTER 90 PRINT average ENTER RUN ENTER The symbol means divided by The output or result of running the program is simply 5 and there are eight internal pigeon holes involved I weekday FIRST length1 5 1i word OF length2 2 HII HII month FEBRUARY length3 8 HIT sum 15 average 5 If you think that is a lot of fuss for a fairly simple problem you can certainly shorten it The shortest version would be a single line but it would be less easy to read A reasonable compromise uses the symbol amp which stands for the operation Join two strings Now type NEW ENTER 10 LET weekday FIRST ENTER 20 LET word OF ENTER 30 LET month FEBRUARY ENTER 40 LET phrase weekday amp word amp month ENTER 50 LET length LEN phrase ENTER 60 PRINT length 3 ENTER RUN ENTER The output is 5 as before but there are some different
217. orth the effort When you are ready take the test again QL Keywords The Keyword Reference Guide lists all SuperBASIC keywords in alphabetical order A brief explanation of the keywords function is given followed by loose definition of the syntax and examples of usage An explanation of the syntax definition is given in the Concept Reference Guide under the entry syntax Each keyword entry indicates to which if any group of operations it relates i e DRAW is a graphics operation and further information can be obtained from the graphics section of the Concept Reference Guide Sometimes it is necessary to deal with more than one keyword ata time i e IF ELSE THEN END IF these are all listed under IF An index is provided which attempts to cover all possible ways you might describe a SuperBASIC keyword For example the clear screen command CLS is also listed under clear screen and screen clear 01984 SINCLAIR RESEARCH LIMITED ABS maths functions ABS returns the absolute value of the parameter It will return the value of the parameter if the parameter is positive and will return zero minus the value of the parameter if the parameter is negative syntax ABS numeric_expression example i PRINT ABS 0 5 ii PRINT ABS a b ACOS ASIN ACOT ATAN maths functions ACOS and ASIN will compute the arc cosine and the arc sine respectively ACOT will calculate the arc cotangent and ATAN will calculate the arc tangent There is no effe
218. other than itself or 1 100 REMark Divisible numbers 110 FOR num 4 6 8 TO 10 12 14 TO 16 18 20 120 PRINT num 130 END FOR num More will be said about handling repetition in a later chapter but the features described above will handle all but a few uncommon or advanced situations DECISION MAKING You will have noticed the simple type of decision IF die 6 THEN EXIT throws This is available in most BASICs but SuperBASIC offers extensions of this structure and a completely new one for handling situations with more than two alternative courses of action However you may find the following long forms of IF THEN useful They should explain themselves i 100 REMark Long form IF END IF 110 LET sunny RND 0 TO 1 120 IF sunny THEN 130 PRINT Wear sunglasses 140 PRINT Go for walk 150 END IF ii 100 REMark Long form IF ELSE END IF 110 LET sunny RND 0 TO 1 120 IF sunny THEN 130 PRINT Wear sunglasses 140 PRINT Go for walk 150 ELSE 160 PRINT Wear coat 170 PRINT Go to cinema 180 END IF The separator THEN is optional in long forms or it can be replaced bya colon in short forms The long decision structures have the same status as loops You can nest them or put other structures into them When a single variable appears where you expect a condition the value zero will be taken as false and other values as true SUBROUTINES AND PROCEDURES Most BASICs have a GOSUB statement which may be
219. ou to choose sensible names for pigeon holes and you may choose as shown HIT dogs days tins HIT You can make the computer set up a pigeon hole name it and store a number in it with a single instruction or statement such as LET dogs 9 ENTER This will set up an internal pigeon hole named dogs and place in it the number 9 thus Dogs 9 The word LET has a special meaning to SuperBASIC It is called a keyword SuperBASIC has many other keywords which you will see later You must be careful about the space after LET and other keywords Because SuperBASIC allows you to choose pigeon hole names with great freedom LETdogs would be a valid pigeon hole name The LET keyword is optional In SuperBASIC and because of this statements like LETdogs 9 ENTER are valid This would refer to a pigeon hole called LETdogs Just as in English names numbers and keywords should be separated from each other by spaces If they are not separated by special characters Even if it were not necessary a program line without proper spacing is bad style Machines with small memory size may force programmers into it but that is not a problem with the QL You can check that a pigeon hole exists internally by typing PRINT dogs ENTER The screen should displav what is in the pigeon hole 9 Again be careful to put a space after PRINT To solve the problem we can wri
220. ours when they are used with PAPER and IM etc black 0 black blue 1 black red 2 red magenta 3 red green 4 green cyan 5 green yellow 6 white white 7 white Colour Codes For example INK 3 would give magenta in MODE 8 STIPPLES You can if you wish specify two colours in a suitable statement For example 2 4 would give a chequerboard stipple as shown In each group of four pixels two would be red code 2 corresponding to the colour selected first The other two pixels would be a contrast It is not really possible to display this effect on a domestic television set ICCCC RRRR CCCC RRRR CCCC RRRR IRRRR CCCC red gt RRRR CCCC lt contrast IRRRR CCCC If you write INK 2 4 the mix colour is formed from the two codes 2 and 4 We will call these choices colour and contrast INK colour contrast You can find out what the stipple effects are by trying them but we give more technical details below 100 REMark Colour Contrast 110 FOR colour 0 TO 7 STEP 2 120 PAPER colour CLS 140 FOR contrast 0 TO 7 STEP 2 150 BLOCK 100 50 40 50 colour contrast 160 PAUSE 50 170 END FOR contrast 180 END FOR colour If you wish to try different stipples you can add a third code number to the colour specification For example INK 2 4 1 would specify a red and green horizontal stripe effect A block of four pixels would be IRRRR RRRR IRRRR RRRR IRR
221. ows ranges to be tested more easily than with an IF statement Compare example ii above with the corresponding IF statement SEXEC Qdos Will save an area of memory in a form which is suitable for loading and executing with the EXEC command The data saved should constitute a machine code program Syntax start_address numeric_expression start of area length numeric_expression length of area data_space numeric_expression length of data area which will be required by the program SEXEC device start_address length data_space example SEXEC mdv1_program 262144 3000 500 The Qdos system documentation should be read before attempting to use this command SIN maths function SIN will compute the sine of the specified parameter syntax angle numeric_expression range 10000 10000 in radians SIN angle example i PRINT SIN 3 ii PRINT SIN 3 141592654 2 SQRT maths function will compute the square root of the specified argument The argument must be greater maths functions than or equal to zero syntax SORT numeric_expression range gt 0 example i PRINT SQRT 3 print square root of 3 ii LET C SQRT a 2 b 2 let c become equal to the square root of a42 b 2 STOP BASIC STOP will terminate execution of a program and will return SuperBASIC to the command BASIC interpreter syntax STOP example i STOP ii IF n 100 THEN STOP You may CONTINUE after STOP The last executable line of a program will
222. periment with a table width of about 120 pixels which may be adjusted A little testing produced the layout shown I H 68TQ JK C 24568 89K D 7TQ 57JK S 6 panp el O0 02 gt 3 gt O000f gt 7F O00 WINDOW 440 x 220 at 35 15 Green with black border of 10 units TABLE 100 x 60 at 150 60 Chequerboard stipple of red and green HANDS Room for at least eight card symbols Initial cursor positions are north 150 10 east 260 60 south 150 130 west 30 60 CHARACTER SIZE Standard for 512 mode NUMBER OF PIXELS between lines is 12 CHARACTER COLOUR White CHARACTER STRIP Red for Hearts and Diamonds Black for Clubs and Spades VARIABLES card 52 stores card numbers sort 13 used to sort each hand tok 4 2 stores tokens H C D S kmemh working loop variables ran random position for card exchange temp used in card exchange item card to be inserted in sort dart pointer to find position in sort comp hold card number in sort inc pixel increment in card rows seat current deal position ac dn cursor position for characters row current row for characters lin builds up row of characters max highest card number p points to card position n current number of card PROCEDURES shuffle shuffles 52 cards split splits cards into four hands and calls sortem to sort each hand so
223. quotes or apostrophes PRINT Chocolate bars ENTER You can print the values of variables contents of pigeon holes by typing statements such as PRINT bars ENTER without using quotes You will see later how very versatile the PRINT statement can be in SuperBASIC It will enable you to place text or other output on the screen exactly where you want it But for the present these two facilities are useful enough printing of text printing values of variables contents of pigeon holes INPUT INPUT READ AND DATA A carpet making machine needs wool as input It then makes carpets according to the current design design program VV Carpet gt Machine gt gt Computer gt wool carpets input data output data If the wool is changed you may get a different carpet The same sort of relations exist ina computer However if the data is input into pigeon holes by means of LET there are two disadvantages when you get beyond very trivial programs writing LET statements is laborious changing such input is also laborious You can arrange for data to be given to a program as it runs The INPUT statement will cause the program to pause and wait for you to type in something at the keyboard First type NEW ENTER so that the previous stored program if it is still there will be erased ready for this n
224. r QL programs then 1 Refer to the appropriate sections in the QL User Guide 2 Consider joining the QL Users Bureau for assistance on the QL programs Full details of the services offered by QLUB and instructions for joining are contained in the Information section of the QL User Guide under the heading QLUB 3 Refer to books published about the QL If your problems persist and you think they may be caused by a fault in either your QL or in the QL program cartridges then refer to the Guarantee details in the Information section of the QL User Guide INTRODUCTION TO THE QL PROGRAMS This introduction outlines the four programs supplied with the OL and describes their common features The four programs are QL Ouill a wordprocessor QL Abacus a spreadsheet QL Archive a database QL Easel a graphics program Individual sections in this guide describe each of the four programs in detail Don t just read them try out the examples and experiment with each new idea MICRODRIVES Before you use any of the OL programs you should make at least one backup on a blank cartridge and use this copy only Keep the original program cartridge in a safe place and use it only for making copies Any accidents will not then cause permanent loss of your programs Each QL program has a built in duplicating routine which is used as follows Place the master cartridge in Microdrive 2 Place the blank cartridge or one containing nothing
225. racter can produce spurious results and should be avoided FOR END FOR repetition The FOR statement allows a group of SuperBASIC statements to be repeated a controlled number of times The FOR statement can be used in both a long and a short form NEXT and END FOR can be used together within the same FOR loop to provide a loop epilogue ie a group of SuperBASIC statements which will not be executed if a loop is exited via an EXIT statement but which will be executed if the FOR loop terminated normally define for_item numeric_expression numeric_exp TO numeric_exp numeric_exp TO numeric_exp STEP numeric_exp for_list for_item for_item SHORT The FOR statement is followed on the same logical line by a sequence of SuperBASIC statements The sequence of statements is then repeatedly executed under the control of the FOR statement When the FOR statement is exhausted processing continues on the next line The FOR statement does not require its terminating NEXT or END FOR Single line FOR loops must not be nested syntax FOR variable for_list statement x statement example i FOR i 1 2 3 4 TO 7 STEP 2 PRINT i ii FOR element first TO last LET buffer element 0 LONG The FOR statement is the last statement on the line Subsequent lines contain a series of SuperBASIC statements terminated by an END FOR statement The statements enclosed between the FOR statement and the END FOR are processed under the c
226. riable 110 LET hungry 1 120 IF hungry THEN PRINT Have a bun You expect a logical expression in line 120 but the numeric variable hungry is there on its own The system interprets the value 1 of hungry as true and the output is Have a bun f line 110 read LET hungry 0 there would be no output The system interprets zero as false and all other values as true That is useful but you can disguise the numeric quality of hungry by writing 100 REMark Logical Variable 110 LET true 1 false 0 120 LET hungry true 130 IF hungry THEN PRINT Have a bun STRING VARIABLES There is much to be said about handling strings and string variables and this is left to a separate chapter PROBLEMS ON CHAPTER 9 1 A rich oil dealer gambles by tossing a coin in the following way If it comes down heads he gets 1 If it comes down tails he throws again but the possible reward is doubled This is repeated so that the rewards are as shown THROW 1234567 REWARDS 1 2 4 8 16 32 64 By simulating the game try to decide what would be a fair initial payment for each such game a if the player is limited to a maximum of seven throws per game b if there is no maximum number of throws 2 Billand Ben agree to gamble as follows At a given signal each divides his money into two halves and passes one half to the other player Each then divides his new total and passes half to the other Show what happens as the game proceeds if Bill sta
227. rinted a to indicate that pounds was undefined We say that the variable pounds has not been initialised given an initial value The program works properly if you do this first bars pounds LET pounds 7 ENTER 7 LET bars pounds 2 ENTER 7 14 The program works properly and gives the output 14 A STORED PROGRAM Typing statements without line numbers may produce the desired result but there are two reasons why this method as used so far is not satisfactory except as a first introduction 1 The program can only execute as fast as you can type This is not very impressive for a machine that can do millions of operations per second 2 The individual instructions are not stored after execution so you cannot run the program again or correct an error without re typing the whole thing Charles Babbage a nineteenth century computer pioneer knew that a successful computer needed to store instructions as well as data in internal pigeon holes These instructions would then be executed rapidly in sequence without further human intervention The program instructions will be stored but not executed if you use line numbers Try this 10 LET price 15 ENTER 20 LET pens 7 ENTER 30 LET cost price pens ENTER 40 PRINT cost ENTER Nothing happens externally yet but the whole program is stored internally You make it work by typing RUN
228. rinted and bound in Great Britain by William Clowes Limited Beccles and London Designed and typeset by Keywords Manchester No part of this User Guide may be reproduced in any form whatsoever without the written permission of Sinclair Research Limited QL QLUB QL Net Qdos and QL Microdrive are trade marks of Sinclair Research Limited Quill Archive Easel and Abacus are trade marks of Psion Limited INTRODUCTION An Introduction To The QL When you unpack your QL computer you will find The QL computer The QL User Guide A Power Supply Two Wallets One of which contains QL Abacus QL Archive QL Easel QL Quill And the other contains 4 Blank QL Microdrive Cartridges Three Plastic Feet These can be fitted under the QL to tilt the keyboard for more comfortable typing The pips in the top of the legs should be fitted into the holes in the rubber feet twisting them to make them fit securely An Aerial Lead About two metres long with different connectors at either end It is used for connecting your QL to your television s aerial socket A Network Lead Also about two metres long with identical connectors at either end It is used to connect your QL to other QLs so that data and messages can be sent between them A GUIDED TOUR On the back and sides of the computer there are a series of connectors There are two slots on the right hand side of the computer the two QL Microdrives The cartridges for these Microdriv
229. rodrive mdv1_ You also need to know that the file is correct and you can only be certain of this if the file is read and checked The necessary keyword is OPEN_IN otherwise the program for reading data from a file is similar to the previous one 100 REMark Reading a file 110 OPEN IN 6 mdv1_numbers 120 FOR item 1 TO 100 130 INPUT 6 number 140 PRINT number 150 END FOR item 160 CLOSE 6 The program should output the numbers 1 to 100 but only if the cartridge containing the file numbers is still in Microdrive mdv1_ DEVICES AND CHANNELS You have seen one example of a device a file of data on a Microdrive We may say loosely that a file has been opened but strictly we mean that a device has been associated with a particular channel Any further necessary information has also been provided Certain devices have channels permanently associated with them by the system 0 OUTPUT command window INPUT keyboard 1 OUTPUT print window 2 LIST list output WINDOWS You can create a window of any size anywhere on the screen The device name for a window is scr and the appended information is for example scr_360x50a80x40 III down value across value height width The following program creates a window with the channel number 5 and fills it with green code 4 and then closes it 100 REMark Create a window 110 OPEN 5 scr_400x200a20x50 120
230. rograms well and handle procedures then you have the capability to write three hundred line programs You can produce ready made buzz phrases for politicians or others who wish to give an impression of technological fluency without actually knowing anything Store the following words in three arrays and then produce ten random buzz phrases adjec1 adjec2 noun Full fifth generation systems Systematic knowledge based machines Intelligent compatible computers Controlled cybernetic feedback Automated user friendly transputers Synchronised parallel micro chips Functional learning capability Optional adaptable programming Positive modular packages Balanced structured databases Integrated logic oriented spreadsheets Coordinated file oriented word processors Sophisticated standardised objectives ANALYSIS We will write a program to produce ten buzzword phrases The stages of the program are 1 Store the words in three string arrays 2 Choose three random numbers which will be the subscripts of the array variables 3 Print the phrase 4 Repeat 2 and 3 ten times DESIGN VARIABLES We identify three arrays of which the first two will contain adjectives or words used as adjectives describing words The third array will hold the nouns There are 13 words in each section and the longest word has 16 characters including a hyphen adjec1 13 12 first adjectives adjec2 13 16 second adjectives noun 13 15 nouns
231. rowth RND 2 TO 20 160 INK colour 170 FOR unit 1 TO growth 180 SELect ON direction 190 ON direction 1 200 LET up up 1 210 ON direction 2 220 LET across across 1 230 ON direction 3 240 LET up up 1 250 ON direction 4 260 LET across across 1 270 END SELect 280 IF across lt 1 OR across gt 99 OR up lt 1 OR up gt 99 EXIT snake 290 POINT across up 300 END FOR unit 310 END REPeat snake 320 PRINT Snake off edge The syntax of the SELect ON structure also allows for the possibility of selecting ona list of values such as 5 6 8 10 TO 13 tis also possible to allow for an action to be executed if none of the stated values is found The full structure is of the form given below LONG FORM SELect ON num ON num list of values statements ON num list of values statements ON num REMAINDER statements END SELect where num is any numeric variable and the REMAINDER clause is optional SHORT FORM There is a short form of the SELect structure For example 100 INPUT num 110 SELect ON num 0 TO 9 PRINT digit will perform as you would expect PROBLEMS ON CHAPTER 14 1 Store 10 numbers in an array and perform a bubble sort This is done by comparing the first pair and exchanging if necessary the second pair second and third numbers up to the ninth pair ninth and tenth numbers The first run of nine comparisons and possible exchanges guarantees that the highest number wi
232. rsor 4 the right hand side of the line occupied by the cursor The area of the cursor is also included f you are using stipples or are in 8 colour mode then windows must be panned or scrolled in multiples of 2 pixels PROBLEMS ON CHAPTER 12 1 Write a program which draws a Snakes and Ladders grid of ten rows of ten squares 2 Place the numbers 1 to 100 in the squares starting at the bottom left and place F for finish in the last square 3 Draw a dartboard on the screen It should consist of an outer ring which could hold numbers A doubles ring and triples ring as shown and a centre consisting of a bull s eye and a ring around it CHAPTER 13 ARRAYS Suppose you are a prison governor and you have a new prison block which is called the West Block It is ready to receive 50 new prisoners You need to know which prisoner known by his number is in which cell You could give each cell a name but it is simpler to give them numbers 1 to 50 In a computing simulation we will imagine just 5 prisoners with numbers which we can put ina DATA statement DATA 50 37 86 41 32 We set up an array of variables which share the name west and are distinguished by a number appended in brackets west 1 west 2 west 3 west 4 west 5 It is necessary to declare an array and give its dimensions with a DIM statement DIM we
233. rtem sorts 13 cards in ascending order layout provides background colour border and table printem prints each line of card symbols getline gets one row of cards and converts numbers into the symbols A 2 3 4 5 6 7 8 9 T J Q K PROGRAM DESIGN OUTLINE 1 Declare arrays pick up tokens and place 52 numbers in array card 2 Shuffle cards 3 Split into 4 hands and sort each 4 OPEN screen window 5 Fix the screen layout 6 Print the four hands 7 CLOSE the screen window 100 DIM card 52 sort 13 tok 4 2 110 FOR k 1 TO 4 READ tok k 120 FOR k 1 TO 52 LET card k k 130 shuffle 140 split 150 OPEN 6 scr_440x220a35x15 160 layout 170 printem 180 CLOSE 6 190 DEFine PROCedure shuffle 200 FOR c 52 TO 3 STEP 1 210 LET ran RND 1 to c 1 220 LET temp card c 230 LET card c card ran 240 LET card ran temp 250 END FORc 260 END DEFine 270 DEFine PROCedure split 280 FORh 1 TO4 290 FORc 1 TO 13 300 LET sort c card h 1 13 c 310 END FOR c 320 sortem 330 FOR c 1 TO 13 340 LET card h 1 13 c sort c 350 END FOR c 360 END FOR h 370 END DEFine 380 DEFine PROCedure sortem 390 FOR item 2 TO 13 400 LET dart item 410 LET comp sort dart 420 LET sort 0 comp 430 REPeat compare 440 IF comp gt sort dart 1 EXIT compare 450 LET sort dart sort dart 1 460 LET dart dart 1 470 END REPeat compare 480 LET sort dart comp 490 END FOR item 500 END
234. rts with 16p and Ben starts with 64p 3 What happens if the game is changed so that each hands over an amount equal to half of what the other possesses 4 Write a program which forms random three letter words chosen from A B C D and prints them until BAD appears 5 Modify the last program so that it terminates when any real three letter word appears CHAPTER 10 LOGIC If you have read previous chapters you will probably agree that repetition decision making and breaking tasks into sub tasks are major concepts in problem analysis program design and encoding programs Two of these concepts repetition and decision making need logical expressions such as those in the following program lines IF score 7 THEN EXIT throws IF suit 3 THEN PRINT spades The first enables EXIT from a REPeat loop The second is simply a decision to do something or not A mathematical expression evaluates to one of millions of possible numeric values Similarly a string expression can evaluate to millions of possible strings of characters You may find it strange that logical expressions for which great importance is claimed can evaluate to one of only two possible values true or false In the case of score 7 this is obviously correct Either score equals 7 or it doesn t The expression must be true or false assuming that it s not meaningless It may be that you do not know the value at some time but that will be put right in due course You
235. ry good but think a bit more about some of the ideas Look at programs to see how they work 11 or 12 is good but re read some parts of chapter six 8 to 10 is fair but re read some parts of chapter six and do the test again Under 8 You should re read chapter six carefully and do the test again ANSWERS TO SELF TEST ON CHAPTER 7 1 We normally break down large or complex jobs into smaller tasks until they are small enough to be completed 2 This principle can be applied in programming by breaking the total job down and writing a procedure for each task 3 A simple procedure is a separate block of code properly named two points 4 A procedure call ensures that the procedure is activated control returns to just after the calling point two points 5 Procedure names can be used ina main program before the procedures have been written This enables you to think about the whole job and get an overview without worrying about the detail 6 If you write a procedure definition before using its name you can test it and then when it works properly forget the details You need only remember its name and roughly what it does 7 A programmer who can write up to thirty line programs can break down a complex task into procedures in such a way that none is more than thirty lines and most are much less In this way he need only worry about one bit of the job at a time 8 The use of a procedure would save memory space if it is necessary
236. ry to compare black with a variable colour p 1 which is colour 0 which does not exist This is a well known problem in computing and the solution is to posta sentinel on the end of the array Just before entering the REPeat loop we need LET colour 0 comp Fortunately SuperBASIC allows zero subscripts otherwise the problem would have to be solved at the expense of readability MODIFIED PROGRAM 100 REM Insertion Sort 110 DIM colour 8 7 120 FOR item 1 TO 8 READ colour item 130 FOR item 2 TO 8 140 LET p item 150 LET comp colour p 160 LET colour 0 comp 170 REPeat compare 180 IF comp gt colour p 1 EXIT compare 190 LET colour p colour p 1 200 LET p p 1 210 END REPeat compare 220 LET colour p comp 230 END FOR item 240 PRINT Sorted colour 250 DATA black blue magenta red 260 DATA green cyan yellow white COMMENT 1 The program works well It has been tested with awkward data AAAAAAA BABABAB ABABABA BCDEFGH GFEDCBA 2 Aninsertion sort is not particularly fast but it can be useful for adding a few items to an already sorted list It is sometimes convenient to allow modest amounts of time frequently to keep items in order rather than a substantial amount of time less frequently to do a complete re sorting You now have enough background knowledge to follow a development of the handling of the file of seven names and telephone numbers SOR
237. s at the next line syntax statements statement statement IF expression THEN statements ELSE statements example i IF a 32 THEN PRINT Limit ELSE PRINT OK ii IF test gt maximum THEN LET maximum test iii IF 1 1 2 THEN PRINT coercion OK LONG 1 The THEN keyword is the last entry on the logical line A sequence of SuperBASIC statements is written following the IF statements The sequence is terminated by the END IF statement The sequence of SuperBASIC statements is executed if the expression contained in the IF statement evaluates to be non zero The ELSE keyword and second sequence of SuperBASIC statements are optional LONG 2 The THEN keyword is the last entry on the logical line A sequence of SuperBASIC statements follows on subsequent lines terminated by the ELSE keyword IF the expression contained in the IF statement evaluates to be non zero then this first sequence of SuperBASIC statements is processed After the ELSE keyword a second sequence of SuperBASIC statements is entered terminated by the END IF keyword If the expression evaluated by the IF statement is zero then this second sequence of SuperBASIC statements is processed syntax IF expression THEN statements ELSE statements END IF example 100 LET Limit 10 110 INPUT Type ina number number 120 IF number gt limit THEN 130 PRINT Range error 140 ELSE 150 PRINT Inside Limit 160 END IF In all three forms of the IF stateme
238. s must be plugged into the QL Expansion Module which in turn is plugged into the QL Expansion Slot via a buffer card In this context the term device also includes expansion memory Although the areas of the QL memory map allocated to expansion memory are different from those allocate to expansion devices the basic mechanism is the same Only one expansion memory peripheral can be plugged into the QL at any one time The address space allocated for peripheral expansion in the QL Physical memory map allows 16 Kbytes per peripheral This area must contain the memory mapped I O required for the driver and the code for the driver itself QDOS includes facilities for queue management and simple serial O which may be of use when writing device drivers The position of each peripheral device in the overall memory map of the QL is determined by the select peripheral lines SPO SP1 SP2 and SP3 These select lines generate a signal corresponding to the slot position in the QL expansion module thus for a device to be selected the address input from address lines A14 A15 A16 and A17 must be the same as the signals from SPO SP1 SP2 and SP3 respectively PIXEL COORDINATE SYSTEM The pixel coordinate system is used to defien the positions and sizes of windows blocks and cursor positions on the QL screen The coordinate system has its origin in the top left hand corner of the default window or screen and always assumes that positions are specified a
239. s on the cartridge Use a file name of not more than eight characters long without spaces It is a good idea to use a name which describes the contents of a file for instance sales is obviously a better name for a file of sales figures than fred File saving and loading will use a data cartridge which is assumed to be in Microdrive 2 unless a different drive number is given The simplest way of replying to a file name request is just to type in the name by itself for example sales which automatically accesses Microdrive 2 If you wanted to access Microdrive 1 you would type mdvl_sales There is a third component of a file name which you do not usually see because it is automatically added by the program This is an extension three letters long which identifies which program saved the file The extensions used are QL Quill _doc QL Abacus _aba QL Easel _grf QL Archive data file _dbf QL Archive program file _prg or _pro QL Archive screen layout _scn If you want to transfer information between programs a special file is generated with the extension _ exp for export All the programs will recognise this extension More information on this process is contained in the _Information_ section under the heading _QL Program Import and Export_ You can direct printer output to a file instead of to a printer so that you can print the text later This file has the extension _lis LISTING FILES In all the programs except Archi
240. s though the screen were in 512 mode high resolution mode The system will use the nearest pixel available for the particular mode set making the coordinate system independent of the screen mode in use Some commands are always relative to the default window origin e g WINDOW while some are always relative to the current window origin e g BLOCK Re a OIIE en ESTE 0 0 0 512 II II II II lly II II 256 0 II The Pixel Coordinate System PROGRAM A SuperBASIC program consists of a sequence of SuperBASIC statements where each statement is preceded by a line number Line numbers are in the range of 1 to 32767 RUN start a loaded program LRUN load a program from a device and start it CTRL SPACE force a program to stop syntax line_number digit range 1 32767 line_number statement statement example i 100 PRINT This is a valid line number RUN ii 100 REMark a small program 110 FOR foreground 0 TO 7 120 FOR contrast 0 TO 7 130 FOR stipple 0 TO 3 140 PAPER foreground contrast stipple 150 CURSOR 0 70 160 FORn 0TO2 170 SCROLL 2 1 180 SCROLL 2 2 190 END FORn 200 END FOR stipple 210 END FOR contrast 220 END FOR foreground RUN QDOS Qdos is the QL Operating System and supervises Task Scheduling and resource allocation Screen VO including windowing Microdrive O
241. se such as system tables can cause the system to crash and can result in the loss of data and programs All VO should be performed using either the relevant SuperBASIC commands or the QDOS Operating System traps MICRODRIVES Microdrives provide the main permanent storage on the QL Each Microdrive cartridge has a capacity of at least 100Kbytes Available free memory space is allocated by QDOS as Microdrive buffers when necessary to improve performance Each blank cartridge must be formatted before use and can hold up to 255 sectors of 512 bytes per sector QDOS keeps a directory of files stored on the cartridge Each microdrive file is identified using a standard SuperBASIC file or device name A cartridge can be write protected be removing the small lug on the right hand sie On receiving new blank microdrive cartridges format them a few times to condition the tape GENERAL CARE Physically each Microdrive cartridge contains a 200 inch loop of high quality video tape which is moved at 28 inches per second The tape completes one circuit every 7 5 seconds NEVER touch the tape with your fingers or insert anything into the cartridge NEVER turn the computer on or off with cartridges in place ALWAYS store cartridges in their sleeves when not in use ALWAYS insert or remove cartridges from the Microdrive slowly and carefully ALWAYS ensure the cartridge is firmly installed before starting the microdrive NEVER move the QL with cartridges instal
242. serted to get output in the form of these words instead of numbers 3 Use a FOR loop to place five random numbers in the range 1 to 13 in an array of five variables card 1 card 2 card 3 card 4 and card 5 Use a second FOR loop to output the values of the five card variables 4 Imagine that the random numbers generated in problem 1 represent cards Write down the extra statements that would cause the following output 1 the word Ace 2 to 10 the actual number 11 the word Jack 12 the word Queen 13 the word King CHAPTER 7 SIMPLE PROCEDURES If you were to try to write computer programs to solve complex problems you might find it difficult to keep track of things A methodical problem solver therefore divides a large or complex job into smaller sections or tasks and then divides these tasks again into smaller tasks and so on until each can be be easily tackled This is similar to the arrangement of complex human affairs Successful government depends on a delegation of responsibility The Prime Minister divides the work amongst ministers who divide it further through the Civil Service until tasks can be done by individuals without further division There are complicating features such as common services and interplay between the same and different levels but the hierarchical structure is the dominant one A good programmer will also work in this way and a modern language like SuperBASIC which allows properly named
243. signments SuperBASIC will automatically convert unsuitable data types to a suitable form wherever possible syntax LET variable expression example i LETa 1 2 ii LET a 12345 iii LET a 6789 iv b test_data LINE LINE_R LINE allows a straight line to be drawn between two points in the window attached to the default or specified channel The ends of the line are specified using the graphics coordinate system Multiple lines can be drawn with a single LINE command The normal specification requires specifying the two end points for a line These end points can be specified either in absolute coordinates relative to the graphics origin or in relative coordinates relative to the graphics cursor If the first point is omitted then a line is drawn from the graphics cursor to the specified point If the second point is omitted then the graphics cursor is moved but no line is drawn LINE will always draw with absolute coordinates i e relative to the graphics origin while LINE_R will always draw relative to the graphics cursor syntax x numeric_expression y numeric_expression point x y parameter_2 TO point 1 point XO point 2 parameter_1 TO point angle 1 TO point 2 point 3 LINE channel parameter_1 parameter_2 LINE_R channel parameter_1 parameter_2 where 1 will draw from the specified point to the next specified point 2 will draw from the the last point p
244. sort will generate an error syntax MRUN device example i MRUN mdv1_chain_program ii MRUN mdv1_new_data NET network NET allows the network station number to be set If a station number is not explicitly set then the QL assumes station number 1 syntax station numeric_expression range 1 127 NET station example i NET 63 ii NET 1 Confusion may arise if more than one station on the network has the same station number NEW NEW will clear out the old program variables and channels other than 0 1 and 2 syntax NEW example NEW NEXT repetition NEXT is used to terminate or create a loop epilogue in REPeat and FOR loops syntax NEXT identifier The identifier must match that of the loop which the NEXT is to control example i 10 REMark this loop must repeat forever 11 REPeat infinite loop 12 PRINT sti LI looping 13 NEXT infinite loop ii 10 REMark this loop will repeat 20 times 11 LET limit 20 12 FOR index 1 TO Limit 13 PRINT index 14 NEXT index iii 10 REMark this Loop will tell you when a 30 is found 11 REPeat Loop 12 LET number RND 1 TO 100 13 IF number 30 THEN NEXT Loop 14 PRINT number is 30 15 EXIT LOOP 16 END REPeat loop If NEXT is used inside a REPeat END REPeat construct it will force processing to continue at the statement following the matching REPeat statement The NEXT statement can be used to repeat the FOR loop with the control variable set at its next va
245. spectively while the cursor up and down arrow keys are represented by lt cursor up gt and lt cursor down gt respectively Keys Action lt Move the cursor one character to the left gt Move the cursor one character to the right SHIFT amp lt Move the cursor one word to the left SHIFT amp gt Move the cursor one word to the right CTRL amp lt Delete the character to the left of the cursor CTRL amp gt Delete the character under the cursor CTRL amp lt cursor up gt Delete the line to the left of the cursor CTRL amp lt cursor down gt Delete the line to the right of the cursor SHIFT amp CTRL amp lt Delete the word to the left of the cursor SHIFT amp CTRL amp gt Delete the word to the right of the cursor The amp symbol indicates that the first key should be held down while the second is pressed When SHIFT and CTRL are used together then hold them both down before pressing the cursor key MICRODRIVE USE The program is loaded from the cartridge in Microdrive You must always make sure that before using Help or using a print command that this cartridge is in Microdrive 1 Otherwise you can remove the cartridge at any time Use a cartridge in Microdrive 2 and in additional Microdrives for storing information for example Ouill documents Archive data files etc FILE NAMES Information can be stored ona cartridge in a file The file must be given a file name to distinguish it from other
246. st 5 This enables SuperBASIC to allocate space which might be a large amount After the DIM statement has been executed the five variables can be used The convicts can be READ from the DATA statement into the five array variables FOR cell 1 TO 5 READ west cell We can add another FOR loop with a PRINT statement to prove that the convicts are in the cells HITTITE ISIOIISIZII8 161141111312 HITTITE west 1 west 2 west 3 west 4 west 5 The complete program is shown below 100 REMark Prisoners 110 DIM west 5 120 FOR cell 1 1 TO 5 READ west cell 130 FOR cell 1 TO 5 PRINT cell west cell 140 DATA 50 37 86 41 32 The output from the program is 5 32 The numbers 1 to 5 are called subscripts of the array name west The array west is a numeric array consisting of five numeric array elements You can replace line 130 by 130 PRINT west This will output the values only The zero at the top of the list appears because subscripts range from zero to the declared number We will show later how useful the zero elements in arrays can be Note also that when a numeric array is DIMensioned its elements are all given the value zero STRING ARRAYS String arrays are similar to numeric arrays but an extra dimension in the DIM statement specifies the length of each string variable in the array Suppose tha
247. string type 1 string comparison floating raise to the power floating unary minus floating unary plus almost equal equal to 1 part in 10 7 If the specified logical operation is true then a value not equal to zero will be returned If the operation is false then a value of zero will be returned The precedence of SuperBASIC operators is defined in the table above If the order of evaluation in an expression cannot be deduced from this table then the relevant operations are performed from left to right The inbuilt precedence of SuperBASIC operators can be overriden by enclosing the relevant sections of the expression in parentheses HIGHEST unary plus and minus string concatenation INSTR exponentiation multiply divide modulus and integer divide add and subtract logical comparison NOT bitwise or logical AND bitwise or logical LOWEST OR and XOR bitwise or logical PERIPHERAL EXPANSION The expansion connector allows extra peripherals to be plugged into the QL The connections available at the connector are GND a 1 b GND D3 a 2b D2 D4 a3b D1 D5 a4b DO D6 a 5b ASL D7 a 6b DSL A19 a 7 b RDWL A18 a 8 b DTACKL A17 a 9 b BGL A16 a 10 b BRL CLKCPU a 11 b A15 RED a 12 b RESEYCPUL A14 a 13 b CSYNCL A13 al4b E A12 a15b VSYNCH A11 a 16 b VPAL A10 a 17 b GREEN A9 a 18 b BLUE A8 a 19 b FC2 A7 a 20b FC1 A6 a 21 b FCO A5 a 22 b AO A4 a
248. t ENTER symbols But you must use these keys as usual You must also remember to use NEW and RUN as necessary AUTOMATIC LINE NUMBERING It is tedious to enter line numbers manually Instead you can type AUTO before you start programming and the QL will reply with a line number 100 Continue typing lines until you have finished your program when the screen will show 100 PRINT First 110 PRINT Second 120 PRINT End To finish the automatic production of line numbers use the BREAK sequence Hold down the CTRL and press the SPACE bar This will produce the message 130 not compLete and line 130 will not be included in your program If you make a mistake which does not cause a break from automatic numbering you can continue and EDIT the line later If you want to start at some particular line number say 600 and use an increment other than 10 you can type for an increment of 5 AUTO 600 5 Lines will then be numbered 600 605 610 etc To cancel AUTO press CTRL and the SPACE bar at the same time EDITING A LINE To edit a line simply type EDIT followed by the line number for example EDIT 110 The line will then be displayed with the cursor at the end thus 110 PRINT Second You can move the cursor using lt left arrow key one place left gt right arrow key one place right To delete a character to the left use CTRL with lt CTRL and left arrow keys To delete the character in the cursor position typ
249. t allows you to do the simpler things in simple ways and then offers you more if you want it Extra facilities and some technical matters are explained in the second part of this chapter but you could omit these certainly at a first reading and still be in a stronger position than most users of older types of BASIC VALUE PARAMETERS You have seen in previous chapters how a value can be passed to a procedure Here is another example EXAMPLE In Chan s Chinese Take Away there are just six items on the menu 1 prawns 4 ice 2 chicken 5 fritter 3 special 6 lychees Chan has a simple way of computing prices He works in pence and the prices are for a rice dish 300 10 times menu number for a sweet 12 times menu number Thus a customer who ate special rice and an ice would pay 300 10 3 12 4 378 pence A procedure item accepts a menu number as a value parameter and prints the cost Program 100 REMark Cost of Dish 110 item 3 120 item 4 130 DEFine PROCedure item num 140 IF num lt 3 THEN LET price 300 10 num 150 IF num gt 4 THEN LET price 12 num 160 PRINT price 170 END DEFine Output 330 48 In the main program actual parameters 3 and 4 are used The procedure definition has a formal parameter num which takes the value passed to it from the main program Note that the formal parameters must be in brackets but that actual parameters need not be EXAMPLE Now suppose the working variable pr
250. t device channel 1 ii PRINT 5 data 1 2 3 4 will output the supplied data to channel 5 which must have been previously opened iii PRINT TO 20 This is in column 20 Normal action is to insert a space between items output on the screen If the item will not fit on the current line a line feed will be generated If the current print position is at the start of a line then a space will not be output affects the next item to be printed and therefore must be placed in front of the print item being printed Also a ora must be placed at the end of a print list if the spacing is to be continued over a series of PRINT statements Normal separator SuperBASIC will tabulate output every 8 columns Will force a new line Will leave the print position immediately after the last item to be printed Output will be printed in one continuous stream TO Will perform a tabbing operation TO followed by a numeric_expression will advance the print position to the column specified by the numeric_expression If the requested column is meaningless or the current print position is beyond the specified position then no action will be taken RAD maths functions RAD is a function which will convert an angle specified in degrees to an angle specified in radians syntax RAD numeric_expressio example PRINT RAD 180 will print 3 141593 RANDOMISE maths functions RANDOMISE allows the random number generator to be reseeded Ifa
251. t fear that such an able assistant would try to take over He would accept a good golfer who could not run the shop He would also accept a poor golfer who could run the shop This is an exclusive OR situation either is acceptable but not both The following program would test applicants 100 REMark XOR test 110 PRINT Enter 1 for yes or 0 for no 120 INPUT Can you run a shop shop 130 INPUT Can you teach golf golf 140 IF shop XOR golf THEN PRINT Suitable The only combinations of answers that will cause the output Suitable are 0 and 1 or 1 and 0 The rules for XOR are given below Able to run shop Able to teach Shop XOR teach effect FALSE FALSE FALSE no job FALSE TRUE TRUE gets the job TRUE FALSE TRUE gets the job TRUE TRUE FALSE no job rules for XOR PRIORITIES The order of priority for the logical operators is highest first NOT AND OR XOR For example the expression rich OR tall AND fair means the same as rich OR tall AND fair The AND operation is performed first To prove that the two logical expressions have identical effects run the following program 100 REMark Priorities 110 PRINT Enter three values Type 1 for Yes and 0 for No 120 INPUT rich tall fair 130 IF rich OR tall AND fair THEN PRINT YES 140 IF rich OR tall AND fair THEN PRINT AYE Whatever combination of three zeroes or ones you input at line 120 the output will be either nothing or YES AYE You can make sure th
252. t ten of the top players at Royal Birkdale for the 1982 British Golf Championship were denoted by their first names and placed in DATA statements DATA Tom Graham Sewy Jack Lee DATA Nick Bernard Ben Gregg Hal You would need ten different variable names but if there were a hundred or a thousand players the job would become impossibly tedious An array is a set of variables designed to cope with problems of this kind Each variable name consists of two parts a name according to the usual rules a numeric part called a subscript Write the variable names as flat 1 flat 2 flat 3 etc Before you can use the array variables you must tell the system about the array and its dimensions DIM flat 10 8 This causes eleven 0 to 10 variables to be reserved for use in the program Each string variable in the array may have up to eight characters DIM statements should usually be placed all together near the beginning of the program Once the array has been declared ina DIM statement all the elements of the array can be used One important advantage is that you can give the numeric part the subscript as a numeric variable You can write FOR number 1 TO 10 READ flat number This would place the golfers in their flats flat 1 flat 2 flat 3 flat 10 We Tom Graham Sewy Hal Hamnnmwmnnn tt pammnnnnnnnt fannnnnnnnn tt
253. tatement The procedure is called by entering its name as the first item ina SuperBASIC statement together with a list of actual parameters Procedure calls in SuperBASIC are recursive that is a procedure may call itself directly or indirectly via a sequence of other calls tis possible to regard a procedure definition as a command definition in SuperBASIC many of the system commands are themselves defined as procedures syntax formal_parameter expression expression actual_parameters expression expression DEFine PROCedure identifier forma_parameters LOCal identifier identifier statements RE Turn END DEFine RETURN can appear at any position within the procedure body If present the LOCal statement must be before the first executable statement in the procedure The END DEFine statement will act as an automatic return example i 100 DEFine PROCedure start_screen 110 WINDOW 100 100 10 10 120 PAPER7 INK O CLS 130 BORDER 4 255 140 PRINT Hello Everybody 150 END DEFine 160 start_screen ii 100 DEFine PROCedure slow_scroll scroll_limit 110 LOCal count 120 FOR count 1 TO scroll 130 SCROLL 2 140 END FOR count 150 END DEFine 160 slow_scroll 20 Comment To improve legibility of programs the name of the procedure can be appended to the END DEFine statement However the name will not be checked by SuperBASIC DEG math functions DEG is a function which will convert an angle expresse
254. tatements make sense when entered as a direct command for example END FOR END DEFine etc ERROR HANDLING Errors are reported by SuperBASIC ina standard form At line line_number error_text Where the line number is the number of the line where the error was detected and the error text is listed below 1 Not complete An operation has been prematurely terminated or break has been pressed 2 Invalid job An error return from Qdos relating to system calls controlling multitasking or VO 3 Out of memory Qdos and or SuperBASIC has insufficient free memory 4 Out of range Usually results from attempts to write outside a window or an incorrect array index 5 Buffer full An VO operation to fetch a buffer full of characters filled the buffer before a record terminator was found 6 Channel not open Attempt to read write or close a channel which has not been opened Can also occur if an attempt to open a channel fails 7 Not found File system device medium or file cannot be found SuperBASIC cannot find an identifier This can result from incorrectly nested structures 8 Already exists The file system has found an already existing file with the same name as a new file to be opened for writing 9 In use The file system has found that a file or device is already exclusively used 10 End of file End of file detected during input 11 Drive full A device has been filled usually Microdrive 12
255. te a program which is a sequence of instructions or statements You can now understand the first two LET dogs 9 ENTER LET days 28 ENTER These cause two pigeon holes to be set up named and given numbers or values The next instruction must perform a multiplication for which the computer s symbol is and place the result in a new pigeon hole called tins thus LET tins dogs days ENTER 1 The computer gets the values 9 and 28 from the two pigeon holes named dogs and days 2 The number 9 is multiplied by 28 3 A new pigeon hole is set up and named tins 4 The result of the multiplication becomes the value in the pigeon hole named tins All this may seem elaborate but you need to understand the ideas which are very Important The only remaining task is to make the computer print the result which can be done by typing PRINT tins ENTER which will cause the output 252 to be displayed on the screen In summary the program LET dogs 9 ENTER LET days 28 ENTER LET tins dogs days ENTER PRINT tins ENTER causes the internal effects best imagined as three named pigeon holes containing numbers HIT dogs 9 x days 28 tins 252 HIT and the output on the screen 252 Of course you could achieve this result more easily with a calculator or a pencil and paper You could do it quickly with the QL by typing PRINT 9 28 ENTER
256. ted without changes to the system variables Note that codes CO DF are cursor control commands The ALT key depressed with any key combination other than cursor keys or CAPS LOCK generates the code FF followed by a byte indicating what the keycode would have been if ALT had not been depressed Note that CAPS LOCK and CTRL F5 are trapped by Qdos and cannot be detected without special software CLOCK The QL contains a real time clock which runs when the computer is switched on The format used for the date and time is standard ISO format 1983 JAN 01 12 09 10 Individual year month day and time can all be obtained by assigning the string returned by DATE to a string variable and slicing it The clock will run from 1961 JAN 01 00 00 00 For a description of the format see BS5249 Part 1 1976 and as modified in Appendix D 2 1 Table 5 Serial 5 and Appendix E 2 Table 6 Serials 1 and 2 Command Function SDATE set the clock ADATE adjust the clock DATE return the date as a number DATE return the date as a string DAY return day of the week COERCION If necessary SuperBASIC will convert the type of unsuitable data to a type which will allow the specified operation to proceed The operators used determine the conversion required For example if an operation requires a string parameter and a numeric parameter is supplied then SuperBASIC will first convert the parameter to type string It is not always possible to convert data to t
257. ter six shots he will arrest the gunman 5 The Sheriffs instructions to his Deputy are If the gun is empty then re load it and if it ain t then keep on firing until you hit the bandit or he surrenders If Mexico Pete turns up get out fast Write a program which caters properly for all these situations Whatever happens return to Dodge City If Mexico Pete turns up return immediately If the gun is empty reload it If the gun is not empty ask the bandit to surrender If the bandit surrenders arrest him If he doesn t surrender fire a shot If the bandit is hit arrest him and fix his wound Assume an unlimited supply of ammunition Use a simulated twenty sided die and let a seven mean surrender and a thirteen mean the bandit is hit CHAPTER 15 PROCEDURES AND FUNCTIONS In the first part of this chapter we explain the more straightforward features of SuperBASIC s procedures and functions We do this with very simple examples so that you can understand the working of each feature as it is described Though the examples are simple and contrived you will appreciate that once understood the ideas can be applied in more complex situations where they really matter After the first part there is a discussion which attempts to explain Why procedures If you understand more or less up to that point you will be doing well and you should be able to use procedures and functions with increasing effectiveness SuperBASIC firs
258. that the file exists in a correct form so you should read it back from a Microdrive and display it on the screen You can do this easily using COPY mdv2_phone TO scr The output to the screen will not provide spaces automatically between the name and the number but it will provide a newline at the end of each record The output will be RON678462 GEOFF896487 ZOE249386 BEN584621 MEG482349 CATH438975 WENDY982387 You can get a more controlled presentation of the data with the following program 100 REMark Read Phone Numbers 110 OPEN_IN 5 mdv1_ phone 120 FOR record 1 TO7 130 INPUT 5 rec 140 PRINT rec 150 END FOR record 160 CLOSE 5 The data is printed as before but this time each pair of fields is held in the variable rec before being printed on the screen You have the opportunity to manipulate it into any desired form Note that more than one string variable may be used at the file creation stage with INPUT and PRINT but the whole record so created may be retrieved from the Microdrive file with a single string variable rec in the above example AN INSERTION SORT The following colours are available in the low resolution screen mode in code number order 0 7 black blue red magenta green cyan yellow white EXAMPLE Write a program to sort the colours into alphabetical order using an insertion sort We place the eight colours in an array colour which we divide into two parts
259. the cartridge is in Microdrive 2 then type instead DIR mdv2_ COPYING PROGRAMS AND FILES Once a program is stored as a file on a Microdrive cartridge it can be copied to other files This is one way of making a backup copy of a Microdrive cartridge You might copy all the previous programs and similar commands for other programs onto another cartridge in Microdrive 2 by typing COPY mdv1_bord TO mdv2_bord DELETING A CARTRIDGE FILE A file is anything such as a program or data stored ona cartridge To delete a program called prog you type DELETE mdv1_prog LOADING PROGRAMS A program can be loaded from a Microdrive cartridge by typing LOAD mdv2_bord lf the program loads correctly it will prove that both copies are good You can test the program by using LIST to list it RUN to run it Instead of using LOAD followed by RUN you can combine the two operations in one command LRUN mdv2_bord The program will load and execute immediately MERGING PROGRAMS Suppose that you have two programs saved on Microdrive 1 as prog1 and prog2 100 PRINT First 110 PRINT Second If you type LOAD mdv1_prog1 followed by MERGE mdv1_prog2 The two programs will be merged into one To verify this type LIST and you should see 100 PRINT First 110 PRINT Second f you MERGE a program make sure that all its line numbers are different from the program already in main memory Otherwise it will overwrite some of the lines of
260. the correct socket on your television set if it has more than one If you wish to use a monitor instead of a television set the connections will depend on whether it is colour or monochrome details can be found in the Concepts section under the heading Monitor A monitor lead with a plug to fit the QL s RGB socket is available from Sinclair Research The order form is in the Information section of this guide The QL needs to know if you are using a monitor or a television set Press F1 for a monitor or F2 for a television Microdrive 1 will run briefly and the red Microdrive light will glow the QL is looking for programs to load and run this can be ignored for now The computer will start up and display its cursor a flashing coloured square and the computer is now ready to accept commands USING THE QL KEYBOARD Unlike previous Sinclair computers there is no single keyword entry on the QL However various keys and groups of keys have special meanings ENTER The ENTER key is used to indicate to the computer that you want it to do something Perhaps you have typed ina command and want the computer to execute it or you may want to tell the computer that you have finished typing in data SHIFT The keyboard has two SHIFT keys which perform the same function Pressing SHIFT and an alphabetic key together will generate capital letters upper case characters On non alphabetic keys SHIFT will cause the upper engraved character
261. the longer ones are more helpful in conveying to the human reader what a program should do But they have to be typed and as in ordinary English spade is more sensible than horticultural earth turning implement Shorter words are preferred if they convey the meaning but very short words or single letters should be used sparingly Variable names like X Z P3 Q2 introduce a level of abstraction which most people find unhelpful INTEGER VARIABLES SuperBASIC allows integer variables which take only whole number values We distinguish these with a percentage sign thus count number nearest_pound There are now two kinds of numeric variable We call the other type which can take whole or fractional values floating point Thus you can write LET price 9 LET cost 7 31 LET count 13 But if you write LET count 5 43 the value of count will become 5 On the other hand LET count 5 73 will cause the value of count to be 6 You can see that SuperBASIC does the best it can rounding off to the nearest whole number COERCION The principle of always trying to be intelligently helpful rather than give an error message or do something obviously unwanted is carried further For example if a string variable mark has the value 64 then LET score mark will produce a numeric value of 64 for score Other versions of BASIC would be likely to halt and say something like Type mis match or Nonsense in BASIC
262. then for a red triangle the whole expression is true There must be a rule in programming to make it clear what is meant The rule is that NOT takes precedence over AND so the interpretation NOT red AND square is the correct one This is the same as NOT red AND square To get the other interpretation you must use brackets If you need to use a complex logical expression it is best to use brackets and NOT if their usage naturally reflects what you want But you can if you wish always remove brackets by using the following laws attributed to Augustus De Morgan NOT a AND b is the same as NOT a OR NOT b NOT a OR b is the same as NOT a AND NOT b For example NOT tall AND fair is the same as NOT tall OR NOT fair NOT hungry OR thirsty is the same as NOT hungry AND NOT thirsty Test this by entering 100 REMark NOT and brackets 110 PRINT Enter two values 1 for TRUE or 0 for FALSE 120 INPUT tall tall 130 INPUT fair fair 140 IF NOT tall AND fair THEN PRINT FIRST 150 IF NOT tall OR NOT fair THEN PRINT SECOND Whatever combination of numbers you give as input the output will always be either two words or none never one This will suggest that the two compound logical expressions are equivalent XOR Exclusive OR Suppose a golf professional wanted an assistant who could either run the shop or give golf lessons If an applicant turned up with both abilities he might not get the job because the golf professional migh
263. tly one value This must be so because you can put functions into expressions For example PRINT 2 INT 5 6 would produce the output 10 It is an important property of functions that you can use them in expressions It follows that they must return a single value which is then used in the expression INT and RND are system functions they come with the system but later you will see how to write your own The following examples show common uses of the INT function 100 REMark Rounding 110 INPUT decimal 120 PRINT INT decimal 0 5 In the example you input a decimal fraction and the output is rounded Thus 4 7 would become 5 but 4 3 would become 4 You can achieve the same result using an integer variable and coercion Trigonometrical functions will be dealt with in a later section but other common numeric functions are given in the list below FUNCTION EFFECT EXAMPLES RETURNED VALUES ABS Absolute or ABS 7 7 unsigned value ABS 4 3 4 3 Integer part of a INT 2 4 2 INT floating point INT 0 4 0 number INT 2 7 3 SQRT 2 1 414214 SQRT Square root SQRT 16 4 SQRT 2 6 1 612452 There is a way of computing square roots which is easy to understand To compute the square root of 8 first make a guess It doesn t matter how bad the guess may be Suppose you simply take half of 8 as the first guess which is 4 Because 4 is greater than the square root of 8 then 8 4 must be less than it The reverse is also true If you had guessed
264. to be generated For example SHIFT amp 5 will give CAPS LOCK Pressing the CAPS LOCK key once will force alphabetic keys to generate capital letters regardless of whether the SHIFT key is pressed This will remain in effect until CAPS LOCK is pressed again DELETE Hold down the CTRL key and then press the lt left arrow key The character to the left of the cursor will disappear and the cursor will move to the left Hold down CTRL and press the gt right arrow key The cursor will not move the character it was on will disappear and text to the right will move to fill the gap THE SCREEN The QL screen may be divided into different areas or windows at will Once you have switched on or reset and pressd FI or F2 the screen will look like this 0 to 511 gt 0 to 511 gt 2 1 0 1 amp 2 256 HT O O V The long thin window at the bottom is used to display commands typed into the computer and initially will display the flashing cursor When the cursor is visible the QL is ready to accept commands or data it disappears when the computer is busy As you type the cursor will move along the line showing where the next character to be typed will appear If the machine ever fails to respond correctly or you want to force a Super
265. to call it more than once from different parts of a program The definition of a procedure only occurs once but it can be called as often as necessary 9 A main program can place information in pigeon holes by means of LET or READ statements These pigeon holes can be accessed by the procedure Thus the procedure uses information originally set up by the main program A second method is to use parameters in the procedure call These values are passed to variables in the procedure definition which then uses them as necessary 10 An actual parameter is the actual value passed from a procedure callin a main program to a procedure 11 A formal parameter is a variable in a procedure definition which receives the value passed to the procedure by the main program CHECK YOUR SCORE This is a searching test You may need more experience of using procedures before the ideas can be fully appreciated But they are very powerful and when understood extremely helpful ideas They are worth whatever effort is necessary 12 to 14 excellent Read on with confidence 10 or 11 very good Just check again on certain points 8 or 9 good but re read some parts of chapter seven 6 or 7 fair but re read some parts of chapter seven Work carefully through the programs writing down all changes in variable values Then do the test again Under 6 read chapter seven again Take it slowly working all the programs These ideas may not be easy but they are w
266. to heading 0 degrees UNDER windows Turns underline either on or off for subsequent output lines Underlining is in the current INK colour in the window attached to the specified oi default channel syntax switch numeric_expression range 0 1 UNDER channel switch example i UNDER 1 underlining on ii UNDER 0 underlining off WIDTH WINDOW windows WIDTH allows the default width for non console based devices to be specified for example printers syntax line_width numeric_expression WIDTH channel line_ width example i WIDTH 80 set the device width to 80 ii WIDTH 6 72 set the width of the device attached to channel 6 to 72 WINDOW windows Allows the user to change the position and size of the window attached to the specified or default channel Any borders are removed when the window is redefined Coordinates are specified using the pixel system relative to the screen origin syntax width numeric_expression depth numeric_expression x numeric_expression y numeric_expression WINDOW channel width depth x y example WINDOW 30 40 10 10 window 30x40 pixels at 10 10 QL CONCEPTS MANUAL Arrays must be DIMensioned before they are used When an array is dimensioned the value of each of its elements is set to zero or a zero length string if it is a string array An array dimension runs from zero up to the specified value There is no limits to the number of dimensions which can be defined
267. tridge for details of how to do this see the Beginner s Guide and Concept sections If the QL is not going to be used for a while you should also switch the power supply off at the mains TUNING IN The display signal to the television set is near channel 36 If your set has continuous tuning tune to channel 36 If your television has push buttons choose an unused button and tune this to the computer s signal You may need to consult your dealer or the TV instruction manual to find out how to do this Once you are correctly tuned in you should see the copyright screen MONITOR C 1983 Sinclair Research Ltd The QL doesn t use television sound because it has its own internal loudspeaker You can turn the television volume down if you wish A coloured pattern will appear after you switch on or reset the computer this is the QL testing its memory The pattern will disappear after a few seconds to be replaced by the copyright screen f you cannot get a picture at all first check that your television can receive the normal broadcast stations If it can then try the computer with another television set If you get a fuzzy or indistinct picture check that you are tuned in correctly it may be possible to pick up the computer s signal in more than one place in the tuning range Also check that the aerial lead is firmly plugged in and that you are using
268. tridge slot or in Microdrive 1 If the ROM cartridge slot contains a self starting program then start up will continue under the control of the program in the ROM cartridge If nothing suitable is found then the QL will check Microdrive 1 for a cartridge If a cartridge is found and if it contains a file called BOOT it is loaded and run DEFAULT SCREEN The QL has three default channels which are linked to three default windows HIT HIT I KIRI Channel 0 is used for listing commands and error messages channel 1 for program and graphics output and channel 2 for program listings The default channel can be modified using the optional channel specifier in the relevant command it is important NOT to switch on the QL with a Microdrive cartridge in position If booting from a Microdrive cartridge is required then the cartridge must be inserted between switching on and pressing either F1 or F2 SOUND Sound on the QL is generated by the QL s second processor an 8049 and is controlled by specifying up to two pitches the rate at which the sound must move between the pitches the ramp how the sound is to behave after it has reached one of the specified pitches the wrap if any randomness should be built into the sound i e deviations from the ramp if any fuzziness should be built into the sou
269. ts 7 What are the statements which open and close the REPeat loop 8 When does an executing REPeat loop terminate 9 Why do loops in SuperBASIC have names PROBLEMS ON CHAPTER 3 1 Write a program to draw straight lines all over the screen The lines should be of random length and direction Each should start where the previous one finished and each should have a randomly chosen colour 2 Write a program to draw lines randomly with the restriction that each line has a random start on the left hand edge of the screen 3 Write a program to draw lines randomly with the restriction that the lines start at the same point on the bottom edge of the screen 4 Write a program to produce lines of random length starting points and colour All lines must be horizontal 5 As problem 4 but make the lines vertical 6 Write a program to produce a square spiral in such a way that each line makes a random colour HINT First find the co ordinates of some of the corners then put them in groups of four You should discover a pattern CHAPTER 4 CHARACTERS AND STRINGS Teachers sometimes wish to assess the reading ability needed for particular books or classroom materials Various tests are used and some of these compute the average lengths of words and sentences We will introduce ideas about handling words or character strings by examining simple approaches to finding average word lengths We are talking about sequences of letters dig
270. ts across and 150 down If you read the Keyword Reference Guide you may find it difficult to reconcile the section on PRINT with the above description Two of the difficulties disappear if you understand that Text in quotes variables and numbers are all strictly speaking expressions they are the simplest degenerate forms of expressions Print separators are strictly classified as print items SCREEN This section introduces general effects which apply whether you wish to output text or graphics The statement MODE 8 or MODE 256 will select MODE 8 in which there are 256 pixels across numbered 0 511 two numbers per pixel 256 pixels down numbered 0 255 8 colours A pixel is the smallest area of colour which can be displayed We use the term solid colour because these start with ordinary solid looking colours of which there are only eight However by using various effects a variety of shades and textures can be achieved If you are using your QL with an ordinary television set then the television set will not be able to reproduce any of these extra effects The statement MODE 4 or MODE 512 will select MODE 4 in which there are 512 pixels across numbered 0 to 511 256 pixels down numbered 0 to 255 4 colours COLOUR You can select a colour by using the following code in combination with suitable keywords such as PAPER INK etc Note that the numbers by themselves mean nothing The numbers are only interpreted as col
271. ttern of ellipses with the program 100 FOR rot 0 TO 2 PI STEP P6 110 CIRCLE 50 50 40 0 5 rot 120 END FOR rot The order of the parameters for a circle or ellipse is centre across centre_up height eccentricity angle The last two parameters are optional and this is indicated by putting them inside square brackets Example Write a program which does the following 1 Open a window 100x100 at 100 50 2 Scale 100 in mode 8 3 Select black paper and clear window 4 Make green border 2 units wide 5 Draw a pattern of six coloured circles 6 Close the window 100 REMark pattern 110 MODE 8 120 OPEN 7 scr_100x100a100x50 130 SCALE 7 100 0 0 140 PAPER 7 0 CLS 7 150 BORDER 7 2 4 160 FOR colour 1 TO6 170 INK 7 colour 180 LET rot 2 Pl colour 190 CIRCLE 7 50 50 30 0 5 rot 200 END FOR colour 210 CLOSE 7 You can get some interesting effects by altering the program For example try the amendments 160 FOR colour 1 TO 100 180 LET rot colour PV 50 ARCS If you want to draw an arc you need to decide starting point end point amount of curvature The first two items are straightforward but the amount of curvature is not so easy You can do it by drawing accurately or by trial and error but you must decide what angle the arc subtends and then specify the angle in radians An angle of 1 5 radians would give a sharp bend and a small angle would give a very gentle curvature Try for example
272. uctures etc 2 Indenting of statements to show the content of a repeat structure 3 Well chosen identifiers reflecting what a variable or repeat structure is used for 4 Editing a program by replacing a line inserting a line deleting a line PROGRAMS AS EXAMPLES You have reached the stage where it is helpful to be able to study programs to learn from them and to try to understand what they do The mechanics of actually running them should now be well understood and in the following chapters we will dispense with the constant repetition of NEW before each program ENTER at the end of each line RUN to start each program You will understand that you should use all these features when you wish to enter and run a program But their omission in the text will enable you to see the other details more clearly as you try to imagine what the program will do when it runs If we dispense with the above details we may use and understand programs more easily without the technical clutter For example the following program generates random upper case letters until a Z appears It does not show the words NEW or RUN or the ENTER symbol but you still need to use these 10 REPeat letters 20 LET lettercode RND 65 TO 90 30 cap CHR lettercode 40 PRINT cap 50 IF cap Z THEN EXIT letters 60 END REPeat letters In this and subsequent chapters programs will be shown without ENTER symbols Direct commands will also be shown withou
273. udent 120 LET student 9 TO 13 subject 9 TO 13 We say that BULL is a slice of the string APQOLBULLATSUZ The defining phrase 6 TO 9 is called a slicer It has other uses Notice how the same notation may be used on both sides of the LET statement If you want to refer to a single character it would be clumsy to write jumble 6 TO 6 just to pick out the B possibly as a clue so you can write instead jumble 6 to refer to a single character COERCION Suppose you have a variable mark holding a record of examination marks The slice giving the history mark may be extracted and scaled up perhaps because the history teacher has been too strict in the marking The following lines will extract the history mark 100 LET mark 625671 110 LET hist mark 3 TO 4 The problem now is that the value 56 of the variable hist is a string of characters not numeric data If you want to scale it up by multiplying by say 1 125 the value of hist must be converted to numeric data first SuperBASIC will do this conversion automatically when we type 120 LET num 1 125 hist Line 120 converts the string 56 to the number 56 and multiplies it by 1 125 giving 63 Now we should replace the old mark by the new mark but now the new mark is still the number 63 and before it can be inserted back into the original string it must be converted back to the string 63 Again SuperBASIC will convert the number automatically w
274. underscore _ See the devices entry in the Concept Reference Guide For example to load and save via the network Before loading a QL program each computer on the network must be givena station number Switch the computer on but do not insert a program cartridge press Fl or F2 when prompted To set the station number type the command NET followed by the station number of your choice For example to set the QL to station 5 type the command NET 5 ENTER Place the program cartridge In Microdrive 1 and load the program by typing Irun mdvi_boot ENTER Once the program is running you can receive data sent along the network by typing the LOAD command in the normal way If the data was being sent by station 12 you would enter LOAD _ neti_12 This must be done before station 12 starts sending To send data type in the SAVE command Assuming you were sending to station 23 you would enter SAVE _neto_23 Station 23 must be ready to receive before you press ENTER THE QL BEGINNER S GUIDE CHAPTER 1 STARTING COMPUTING THE SCREEN Your QL should be connected to a monitor screen or TV set and switched on Press a few keys say abc and the screen should appear as shown below The small flashing light is called the cursor Itti HITT HITT HITT HITT labc abc I Monitor Telev
275. uperBASIC standard identifier The case of the keyword is not significant Keywords are echoed as a mixture of upper and lower case letters and are always reproduced in full The upper case portion indicates the minimum required to be typed in for SuperBASIC to recognise the keyword The set of SuperBASIC keywords may be extended by adding PROCEDURES to the QL itis a good idea to define these with their names in upper case and this will indicate their special function in the SuperBASIC system Conversely ordinary procedures should be defined with their names in lower case WARNING Existing keywords cannot be used as ordinary identifiers within a SuperBASIC program SuperBASIC keywords are ABS DEFine PROCedure LEN RANDOMISE ACOS ASIN END DEFine LET RND ACOT ATAN DEG LIST RECOL ADATE DELETE LOAD REMark ARC ARC_R DIM LOCal RENUM AT DIMN LN LOG10 REPeat AUTO DIR LRUN END REPeat BAUD DIV MERGE RESPR BEEP DLINE MOD RETurn BEEPING EDIT MODE RETRY BLOCK ELLIPSE MOVE RUN BORDER ELLIPSE_RMRUN SAVE CALL EOF NET SIN CHR EXEC EXEC_W NEW SCALE CIRCLE EXIT NEXT SCROLL CIRCLE_R EXP ON GO TO SDATE CLEAR FILL ON GO SUB SELect CLOSE FILL OPEN OPEN_IN END SELect CLS FLASH OPEN_NEW SEXEC CODE FOR OVER SQRT CONTINUE END FOR PAN STOP RETRY FORMAT PAPER STRIP COPY COPY_N GO SUB PAUSE TAN COS GO TO PEEK PEEK_W TO COT IF THEN ELSE PEEK_L TURN CSIZE END IF PENUP TURN TO CURSOR INK PENDOWN UNDER DATA READ INKEY PI VER RESTORE INPUT POINT POINT
276. urn statement as shown Program 100 REMark FuNction with RETurn 110 LET num 70 120 LET bill num price 3 price 4 130 PRINT bill 140 DEFine FuNction price num 150 IF num lt 3 THEN RETurn 300 10 num 160 IF num gt 4 THEN RETurn 12 num 170 END DEFine Output 448 Notice the simplification in the calling of functions as compared with procedure calls WHY PROCEDURES The ultimate concept of a procedure is that it should be a black box which receives specific information from outside and performs certain operations which may include sending specific information back to the outside The outside may be the main program or another procedure The term black box implies that its internal workings are not important you only think about what goes in and what comes out If for example a procedure uses a variable count and changes its value that might affect a variable of the same name in the main program Think of a mail order company You send them an order and cash they send you goods Information is sent to a procedure and it sends back action and or new information Order by cash Order Goods Company Information Action and or Procedure new information You do not want the mail order company to use your name and address or other information for other purposes That would be an
277. urrent screen or window POINTS AND LINES tis easy to draw points and lines using scale graphics Using a vertical scale of 100 a point near the centre of the window can be plotted with POINT 60 50 The point 60 units across and 50 units up will be plotted in the current ink colour Similarly a line may be drawn with the statement LINE 60 50 TO 80 90 Further elements can be added For example the following will draw a square LINE 60 50 TO 70 50 TO 70 60 TO 60 60 TO 60 50 60 across Dette ected 50 up Foa RELATIVE MODE Pair of coordinates such as across up normally define a point relative to the origin 0 0 in the bottom left hand corner of a window or elsewhere if you choose It is sometimes more convenient to define points relative to the current cursor position For example the square above may be plotted in another way using the LINE _R statement which means Make all pairs of coordinates relative to the current cursor position POINT 60 50 LINE_R 0 0 TO 10 0 TO 0 10 TO 10 0 TO 0 10 First the point 60 50 becomes the origin then as lines are drawn the end of a line becomes the origin for the next one The following program will plot a pattern of randomly placed coloured squares 100 REMark Coloured Squares 110 PAPER7 CLS 120 FOR sq 1 TO 100 130 INK RND 1 TO 6 140 POINT RND 90 RND 90 150 LINE R 0 0 TO 10 0 TO 0 10 TO 10 0 TO 0 10 160 END FOR sq
278. ut channel CLS windows Will clear the window attached to the specified or default channel to current PAPER colour excluding the border if one has been specified CLS will accept an optional parameter which specifies if only a part of the window must be cleared syntax part numeric_expression CLS channel part where part O whole screen default if no parameter part 1 top excluding the cursor line part 2 bottom excluding the cursor line part 3 whole of the cursor line part 4 right end of cursor line including the cursor position example i CLS the whole window ii CLS 3 clear the cursor line iii CLS 2 2 clear the bottom of the window on channel 2 CODE CODE is a function which returns the internal code used to represent the specified character If a string is specified then CODE will return the internal representation of the first character of the string CODE is the inverse of CHR syntax CODE string_ expression example i PRINT CODE A prints 65 ii PRINT CODE SuperBASIC prints 83 CONTINUE RETRY error handling CONTINUE allows a program which has been halted to be continued RETRY allows a program statement which has reported an error to be re executed syntax CONTINUE RETRY example CONTINUE RETRY warning A program can only continue if 1 No new lines have been added to the program 2 No new variables have been added to the program 3 No lines have be
279. ve the system variables SYSTEM CALLS System calls are processed by Qdos in supervisor mode When in supervisor mode Qdos will not allow any other job to take over the processor System calls processed in this way are said to be atomic i e the system call will process to completion before relinquishing the processor Some system calls are only partially atomic i e once they have completed their primary function they will relinquish the processor if necessary Unless specifically requested all the system calls are partially atomic The standard mechanism for making a system call is by making a trap to one of the Qdos system vectors with appropriate parameters in the processor registers The action taken by Qdos following a system call is dependent on the particular call and the overall state of the system at the time the call was made INPUT OUTPUT Qdos supports a multitasking environemtn and therefore a file can be accessed by more than one process at a time The Qdos filing sub system can handle files which have been opened as EXCLUSIVE files or as SHARED files A shared file cannot be written to QL devices are processed by the SERIAL O SYSTEM As its name suggests any data output by this system can be redirected to any other device also supported by the redirectable O system The device names required by Qdos are the same as the device names required by SuperBASIC and are discussed in the concept section DEVICES The collection o
280. ve you can request a list of the file names ona cartridge whenever a command needs a file name This is useful if you cannot remember the exact name that you gave to the file when you first saved it Every time the program is waiting for you to type ina file name you have the following options Press ENTER to accept the name the program suggests Type in the file name followed by ENTER Press followed by ENTER for a list of the files on Microdrive 2 If you type in a question mark and ENTER instead of the file name the program displays mdv2_ suggesting that it should list the files on Microdrive 2 You can accept this suggestion or you can edit the drive specifier to refer to a different Microdrive mdv1_ and then press ENTER to list the files When the list is complete the program asks you to type in the file name Archive does not use this method Instead there is a command dir which lists the files It allows you to type in mdvl_ mdv2_ and so on to specify the drive for which the list of files is needed ESCAPE In general ESC cancels the current action and will restore you to a sensible point in the program You can also use ESC to cancel any numbers or text that you have typed into the input line or abort a partially completed command OTHER DEVICES Data can be loaded and saved on other devices besides a Microdrive The device is specified in the standard SuperBASIC way except that the device name is preceded by an
281. wed by an identifier to tell SuperBASIC which loop to exit for example EXIT throws would transfer control to the statement after END REPeat throws This may seem like a using a sledgehammer to crack the nut of the simple problem illustrated However the REPeat structure is very powerful It will take you a long way If you know other languages you may see that it will do the jobs of both REPEAT and WHILE structures and also cope with other more awkward situations The SuperBASIC REPeat loop is named so that a correct clear exit is made The FOR loop like all SuperBASIC structures ends with END and its name is given for reasons which will become clear later You will also see later how these loop structures can be used in simple or complex situations to match exactly what you need to do We will mention only three more features of loops at this stage They will be familiar if you are an experienced user of BASIC The increment of the control variable of a FOR loop is normally 1 but you can make it other values by using the STEP keyword As the examples show i 100 FOR even 2 TO 10 STEP 2 110 PRINT even 120 END FOR even output is 2 4 6 8 10 ii 100 FOR backwards 9 TO 1 STEP 1 110 PRINT backwards 120 END FOR backwards outputis98 7654321 The second feature is that loops can be nested You may be familiar with nested FOR loops For example the following program outputs four rows of ten crosses 100 REMark Crosses
282. well defined procedures will be much more helpful than older versions which do not have such features The idea is that a separately named block of code should be written for a particular task It doesn t matter where the block of code is in the program If it is there somewhere the use of its name will activate the code return control to the point in the program immediately after that use If a procedure square draws a square the scheme is as shown below procedure definition procedure call DEFine PROCedure square REMark code to draw square lt square END DEFine v draws a square In practice the separate tasks within a job can be identified and named before the definition code is written The name is all that is needed in calling the procedure so the main outline of the program can be written before all the tasks are defined Alternatively if it is preferred the tasks can be written first and tested If it works you can then forget the details and just remember the name and what the procedure does Example The following example could quite easily be written without procedures but it shows how they can be used in a reasonably simple context Almost any task can be broken down ina similar fashion which means that you never have to worry about more than say five to thirty lines at any one time If you can write thirty line p
283. when you do not use quotes ina PRINT statement 12 What does an INPUT statement do which a LET statement does not 13 What type of program statement is never executed 14 What is the purpose of a DATA statement 15 What is another word for the name of a pigeon hole or variable 16 Write down three valid identifiers which use letters letters and digits letters and underscore three points 17 Why is the space bar especially important in SuperBASIC 18 Why are freely chosen identifiers important in programming PROBLEMS ON CHAPTER 2 1 Carry out a dry run to show the values of all variables as each line of the following program is executed 10 LET hours 40 ENTER 20 LET rate 31 ENTER 30 LET wage hours rate ENTER 40 PRINT hours rate wage ENTER 2 Write and test a program similar to that of problem 1 which computes the area of a carpet which is 3 metres in width and 4 metres in length Use the variable names width length area 3 Re write the program of problem 1 so that it uses two INPUT statements instead of LET statements 4 Re write the program of problem 1 so that the input data 40 and 3 appears ina DATA statement instead of a LET statement 5 Re write the program of problem 2 using a different method of data input Use READ and DATA if you originally used LET and vice versa 6 Bill and Ben agree to have a gamble Each will take out of his wallet all the pound notes and give them to the
284. whole string In order to identify the string slice you need to know the positions of the required characters Suppose you are constructing a children s game in which they have to recognise a word hidden in a jumble of letters Each letter has an internal number an index corresponding to its position in the string Suppose the whole string is stored in the variable jumble and the clue is Big cat string slice jumble A P QJO LILIIJO N JA T S U Z 1234567891011 121314 You can see that the answer is defined by the numbers 6 to 9 which indicate where it is You can abstract the answer as shown 100 jumble APQOLLIONATSUZ 110 LET an jumble 6 TO 9 120 PRINT an REPLACE A STRING SLICE Now suppose that you wish to change the hidden animal into a bull You can write two extra lines 130 LET jumble 6 TO 9 BULL 140 PRINT jumble The output from the whole five line program is LION APQOLBULLATSUZ All string variables are initially empty they have length zero If you attempt to copy a string into a string slice which has insufficient length then the assignment may not be recognised by SuperBASIC If you wish to copy a string into a string slice then it is best to ensure the destination string is long enough by padding it first with spaces 100 LET subject ENGLISH MATHS COMPUTING 110 LET st
285. ymbol Similarly avoid confusion between one amongst the digits and the letter amongst the letters When using a SHIFT key hold it down while you type the other key so that the SHIFT key makes contact before the other key and also remains in contact until after the other key has lifted The same rule applies to the control CTRL and alternate ALT keys which are used in conjunction with others but you do not need those at present Type the two simple instructions CLS ENTER PRINT Hello ENTER Strictly speaking these constitute a computer program however it is the stored program that is important in computing The above instructions are executed instantly as you type ENTER Now type the program with line numbers 10 CLS ENTER 20 PRINT HELLO ENTER This time nothing happens externally except that the program appears in the upper part of the screen This means that it is accepted as correct grammar or syntax It conforms to the rules of SuperBASIC but it has not yet been executed merely stored To make it work type RUN ENTER The distinction between direct commands for immediate action and a stored sequence of instructions is discussed in the next chapter For the present you can experiment with the above ideas and two more LIST ENTER causes an internally stored program to be displayed listed on the screen or elsewhere NEW ENTER causes an internally stored program to be deleted so that you can type in
286. yntax x numeric_expression y numeric_expression parameters x y POINT channel parameters parameters example i POINT 256 128 plot a point at 256 128 ii POINT x x x plot a point at x x x iii 10 REPeat example 20 INK RND 255 30 POINT RND 100 RND 100 40 END REPeat example POKE POKL_W POKE_L BASIC POKE allows a memory location to be changed For word and long word accesses the specified address must be an even address POKE has three forms which will access a byte 8 bits a word 16 bits a long word 32 bits syntax address numeric_expression data numeric_expression POKE address data byte access POKE_W address data word access POKE_L address data long word access example i POKE 12235 0 set byte at 12235 to O ii POKE_L 131072 12345 set long word at 131072 to 12345 Warning Poking data into areas of memory used by Qdos can cause the system to crash and data to be lost Poking into such areas is not recommended PRINT devices microdrives Allows output to be sent to the specified or default channel The normal use of PRINT is to send data to the QL screen Syntax separator TO numeric_expression item expression channel separator PRINT item Multiple print separators are allowed At least one separator must separate channel specifications and expressions Example i PRINT Hello World will output Hello World on the default outpu

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