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GWBASIC User's Manual

1. Examples vS DATES PRINT VS Ol Di1 1325 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DATES htm128 03 2004 21 29 21 GW BASIC User s Guide DEFINT SNG DBL STR Statements Purpose To declare variable types as integer single precision double precision or string Syntax DEFtype letters Comments type is INT integer SNG single precision number DBL double precision number or STR string of 0 255 characters letters are letters separated by commas or range of letters of the alphabet A DEF type statement declares that variable names beginning with the letter s specify that type of variable However a type declaration character always takes precedence over a DEF type statement in the typing of a variable If no type declaration statements are encountered BASIC assumes all variables are single precision Single precision is the default value Examples 10 DEPDEL L P All variables beginning with the letters L M N O and P will be double precision variables 10 DEFSTR A 20 A 120 All variables beginning with the letter A will be string variables The declaration is unnecessary in this example 10 DEFINT I N W Z 20 WS 120 All variables beginning with the letters I J K L M N W X Y Z will be integer variables W in Line 20 establishes a string variable beginning with the letter W However the variable W will remain an integer elsewhere in the progra
2. When an error trap takes place this automatically disables all trapping Trapping will never take place when BASIC is not executing a program The following are valid values for event specifier COM n nis the number of the COM channel 1 or 2 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ONCOMN html 1 of 5 28 03 2004 21 28 58 GW BASIC User s Guide KEY n PEN PLAY n SIRIG N TIMER n RETURN line number nis a function key number 1 20 1 through 10 are the function keys F1 through F10 11 through 14 are the cursor control keys as follows 11 CURSOR UP 13 CURSOR RIGHT 12 CURSOR LEFT 14 CURSOR DOWN 15 20 are user defined keys Since there is only one pen no number is given n 1s an integer expression in the range of 1 32 Values outside this range result in Illegal function call errors nis 0 2 4 or 6 O trigger Al 4 trigger A2 2 trigger B1 6 trigger B2 n is a numeric expression within the range of 1 to 86 400 A value outside of this range results in an Illegal function call error This optional form of RETURN is primarily intended for use with event trapping The event trapping routine may want to go back into the GW BASIC program at a fixed line number while still eliminating the GOSUB entry that the trap created Use of the nonlocal RETURN must be done with care Any other GOSUB WHILE or FOR that was active at the time of the trap remains active If the trap c
3. 47 48 49 50 51 179 181 183 185 186 1 N W e N RS Nr NW Mode FCB CURLOC ORNOFS NMLOFS KKK DEVICE WIDTH POS FLAGS OUTPOS BUFFER VRECL PHYREC LOGREC KKK OUTPOS The mode in which the file was opened 1 Input only 2 Output only 4 Random I O 16 Append only 32 Internal use 64 Future use 128 Internal use Diskette file control block Number of sectors read or written for sequential access The last record number 1 read or written for random files Number of bytes in sector when read or written Number of bytes left in INPUT buffer Reserved for future expansion Device Number 0 9 Disks A through J 255 KYBD 254 SCRN 253 LPT1 252 CASI 251 COM1 250 COM2 249 LPT2 248 LPT3 Device width Position in buffer for PRINT Internal use during BLOAD BSAVE Not used for data files Output position used during tab expansion Physical data buffer Used to transfer data between DOS and BASIC Use this offset to examine data in sequential I O mode Variable length record size Default is 128 Set by length option in OPEN statement Current physical record number Current logical record number Future use Disk files only Output position for PRINT INPUT and WRITE file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic VARPTR html 2 of 3 28 03 2004 21 29 51 GW BASIC User s Guide 188 n FIELD Actual FIELD data buffer Si
4. CURSOR LEFT or CTRL CURSOR RIGHT Or CTRL CURSOR UP Or CTRL 6 CTRL BACKSPACE or DEL CTRL END Or CTRL E CTRL N Or END CTRL RETURN or CTRL J CTRL M Or RETURN CTRL Or ESC Moves the cursor to the beginning of the next word The next word is defined as the next character to the right of the cursor in the set A to Z or in the set 0 to 9 In other words the cursor moves to the next number or letter after a blank or other special character Moves the cursor down one line on the screen Moves the cursor one position left When the cursor is advanced beyond the left edge of the screen it will wrap to the right side of the screen on the preceding line Moves the cursor one position right When the cursor is advanced beyond the right edge of the screen it will wrap to the left side of the screen on the following line Moves the cursor up one line on the screen Deletes the character positioned over the cursor All characters to the right of the one deleted are then moved one position left to fill in where the deletion was made If a logical line extends beyond one physical line characters on subsequent lines are moved left one position to fill in the previous space and the character in the first column of each subsequent line is moved up to the end of the preceding line DEL delete is the opposite of INS insert Deleting text reduces logical line length Erases from the cursor position to the end of the logical l
5. GW BASIC User s Guide SOUND Statement Purpose To generate sound through the speaker Syntax SOUND freq duration Comments freq is the desired frequency in Hertz cycles per second freq is a numeric expression within the range of 37 to 32767 duration is the desired duration in clock ticks Clock ticks occur 18 2 times per second duration must be a numeric expression within the range of 0 to 65535 Values below 022 produce an infinite sound until the next SOUND or PLAY statement is executed If duration is zero any active SOUND statement is turned off If no SOUND statement is running a duration of zero has no effect The sound is executed in foreground or background depending on the PLAY statement Examples The following example creates random sounds of short duration 2500 SOUND RND 1000 37 2 2600 GOTO 2500 The following table shows the relationship of notes and their frequencies in the two octaves adjacent to middle C Table 5 Relationships of Notes and Frequencies Note Frequency Note Frequency C 130 810 Ce 323 250 D 146 830 D 587 330 E 164 810 E 659 260 F 174 610 F 698 460 G 196 000 G 783 990 A 220 000 A 880 000 B 246 940 B 987 770 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SOUND html 1 of 2 28 03 2004 21 29 47 GW BASIC User s Guide Dratrmond 261 630 293 660 329 630 349 230 392 000 440 000 493 880 Middle C Dratrmond 1046 500 1174 700 1318 5
6. PE AS filenum LEN number Comments COM n is a valid communications device com1 or com speed is a literal integer specifying the transmit receive baud rate Valid speeds are as follows 75 110 150 300 600 1200 1800 2400 4800 and 9600 The default is 300 bps parity isa one character literal specifying the parity for transmitting and receiving Valid characters specifying parity are as follows S SPACE Parity bit always transmitted and received as space 0 bit M MARK Parity bit always transmitted and received as mark 1 bit O ODD Odd transmit parity odd receive parity checking Default is even E EVEN Even transmit parity even receive parity checking Even is default N NONE No transmit parity No receive parity checking data is a literal integer indicating number of transmit receive data bits Valid values for the number of data bits are 4 5 6 7 or 8 the default is 7 bits Note Four data bits with no parity is illegal eight data bits with any parity is illegal stop is a literal integer expression returning a valid file number Valid values for number of stop bits are 1 and 2 If omitted 75 and 110 bps transmit two stop bits All others transmit one stop bit filenumis a number between and the maximum number of files allowed A communications device may be opened to only one file number at a time The fi 1 enum is associated with the file for as long as the file is open and is used to refer
7. Unprintable error No error message is available for the existing error condition This is usually caused by an error with an undefined error code Direct statement in file A direct statement is encountered while loading a ASCII format file The LOAD is terminated Too many files An attempt is made to create a new file using SAVE or OPEN when all directory entries are full or the file specifications are invalid Device Unavailable An attempt is made to open a file to a nonexistent device It may be that hardware does not exist to support the device such as Ipt2 or Ipt3 or is disabled by the user This occurs if an OPEN COMI statement is executed but the user disables RS 232 support with the c switch directive on the command line file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20A html 5 of 7 28 03 2004 21 29 03 GW BASIC User s Guide 69 70 TI T2 73 74 Communication buffer overflow Occurs when a communications input statement is executed but the input queue is already full Use an ON ERROR GOTO statement to retry the input when this condition occurs Subsequent inputs attempt to clear this fault unless characters continue to be received faster than the program can process them In this case several options are available e Increase the size of the COM receive buffer with the c switch e Implement a hand shaking protocol with the host satellite such as XON XOFF as demo
8. EXP X XP X EXP X X EXP X EXP X 2 1 G X SQR X X 1 G X SQR X X 1 Gi lex 7 1 X 2 G SGN X Bo e G SQR X X 1 1 X G X4 1 7 X o file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20B htm128 03 2004 21 29 04 GW BASIC User s Guide Appendix C ASCH Character Codes Dec Oct Hex Chr Dec Oct Hex Chr 000 000 00 NUL 032 040 20 SP 001 001 Ol SOH 033 l 28 002 002 02 STX 034 042 22 i 003 003 03 ETX 035 043 23 004 004 04 EOT 036 044 24 005 005 05 ENQ 037 045 25 006 006 06 ACK 038 046 26 amp 007 007 07 BEL 039 047 27 i 008 010 08 BS 040 050 28 009 O11 09 HT 041 051 29 010 012 OA LF 042 052 2A 011 013 OB VT 043 053 2B 012 014 0C FF 044 054 20 013 015 0D CR 045 055 2D 014 016 OE SO 046 056 2E 015 07 OF SI 047 057 2F 016 020 10 DLE 048 060 30 0 017 021 11 DCI 049 061 31 1 018 022 12 DC2 050 062 32 2 019 023 13 DC3 051 063 33 3 020 024 14 DC4 052 064 34 4 021 025 15 NAK 053 065 35 5 022 026 16 SYN 054 066 36 6 023 027 17 ETB 055 067 37 7 024 030 18 CAN 056 070 38 8 025 031 19 EM 057 O71 39 9 026 032 1A SUB 058 072 3A 027 033 1B ESC 059 073 3B 028 034 1C FS 060 074 3C lt 029 035 1D GS 061 0755 3D 030 036 1E RS 062 076 3E gt 031 037 1F US 063 O77 3F Dec Oct Hex Chr Dec Oct Hex Chr 064 100 40 096 140 60 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Appendix 20C html 1 of 2 28 03 2004 21 29 04
9. The following line causes a carriage return after the 60th character is printed on a line 100 IF LPOS X gt 60 THEN LPRINT CHR 13 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LPOS htm128 03 2004 21 29 37 GW BASIC User s Guide MID Statement Purpose To replace a portion of one string with another string Syntax MIDS stringexpl n m stringexp2 Comments Both n and m are integer expressions stringexp1 and stringexp2 are string expressions The characters in st ringexp1 beginning at position n are replaced by the characters in stringexp2 The optional m refers to the number of characters from st ringexp2 that are used in the replacement If mis omitted all of st ringexp2 is used Whether m is omitted or included the replacement of characters never goes beyond the original length of st ringexpl Examples 10 AS KANSAS CITY MO 20 MIDS AS 14 KS 30 PRINT AS RUN KANSAS CITY Ks Line 20 overwrites MO in the A string with KS file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic MIDSS htm128 03 2004 21 29 38 GW BASIC User s Guide MKDIR Command Purpose To create a subdirectory Syntax MKDIR pathname Comments pathname is a string expression not exceeding 63 characters identifying the subdirectory to be created Examples MKDIR C SALES JOHN Creates the subdirectory JOHN within the directory of SALES file Cl Documents 20and 20Sett
10. binary digit A quantity which is expressed in the binary digits of 0 and 1 bit A contraction of binary digit A bit can either be 0 or 1 and is the smallest unit of information recognizable by a computer block An amount of storage space or data of arbitrary length usually contiguous and often composed of several similar records all of which are handled as a unit boolean logic A field of mathematical analysis in which comparisons are made A pro grammed instruction can cause a comparison of two fields of data and modify one of those fields or another field as a result of comparison This system was formulated by British mathematician George Boole 1815 1864 Some boolean operators are OR AND NOT XOR EQV and IMP boot A machine procedure that allows a system to begin operations at the desired level by means of its own initiation The first few instructions are loaded into a computer from an input device These instructions allow the rest of the system to be loaded The word boot is abbreviated from the word bootstrap bps Bits per second buffer A temporary storage area from which data is transferred to or from various devices built in clock A real time clock that lets your programs use the time of day and date Built into MS DOS it lets you set the timing of a program It can be used to keep a personal calendar and it automatically measures elapsed time byte An element of data which is composed of eight
11. 110 CIRCLE XY By Cry gp 1a 9 120 CIRCLE XY p RCs 9 SO 130 CIRCLE X Y R Croee Sat 140 IF VERT GOTO 60 150 RETURN 160 CLS SCREEN 1 COLOR 0 1 KEY OFF VERT 0 170 X 160 Y 100 C 1 R 50 GOSUB 50 180 X 30 Y 30 C 2 R 30 GOSUB 50 190 X 30 Y 169 GOSUB 50 200 X 289 Y 30 GOSUB 50 210 X 289 Y 169 GOSUB 50 220 LINE 30 30 289 169 1 230 LINE 30 169 2e9 20 1 240 LINE 30 169 259 30 1 8 250 ZS INKEYS IF ZS THEN 250 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CIRCLE html 2 of 2 28 03 2004 21 29 15 GW BASIC User s Guide COLOR Statement Purpose To select display colors Syntax COLOR foreground background border COLOR background palette COLOR foreground background Comments In general COLOR allows you to select the foreground and background colors for the display In SCREEN 0 a border color can also be selected In SCREEN 1 no foreground color can be selected but one of two four color palettes can be selected for use with graphics statements The different syntaxes and effects that apply to the various screen modes are described below Mode Effect SCREEN 0 Modifies the current default text foreground and background colors and the screen border The foreground color must be an integer expression in the range 0 31 It is used to determine the foreground color in text mode which is the default color of text Sixteen col
12. 2 Write data to the file using the PRINT or WRITE statement PRINT 1 A PRINT 1 B PRINT 1 C 3 To access the data in the file you must close the file and reopen it in input 1 mode CLOSE 1 OPEN I 1 filename 4 Use the INPUT or LINE INPUT statement to read data from the sequential file into the program INPUT 1 X Y Z file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 205 html 2 of 9 28 03 2004 21 29 02 GW BASIC User s Guide Example 1 is a short program that creates a sequential file data from information input at the terminal Example 1 10 OPEN O 1 DATA 20 INPUT NAME NS 30 IF NS DONE THEN END 40 INPUT DEPARTMENT DS 50 INPUT DATE HIRED HS 60 PRINT L NSs DS FHS 70 PRINT GOTO 20 RUN NAME MICKEY MOUSE DEPARTMENT AUDIO VISUAL AIDS DATE HIRED 01 12 72 NAME SHERLOCK HOLMES DEPARTMENT RESEARCH DATE HIRED 12 03 65 NAME EBENEEZER SCROOGE DEPARTMENT ACCOUNTING DATE HIRED 04 27 78 NAME SUPER MANN DEPARTMENT MAINTENANCE DATE HIRED 08 16 78 NAME DONE OK 5 2 2 Accessing a Sequential File The program in Example 2 accesses the file data created in the program in Example 1 and displays the name of everyone hired in 1978 Example 2 10 OPEN I 1 DATA 20 INPUT 1 NS DS HS 30 IF RIGHTS H 2 78 THEN PRINT NS 40 GOTO 20 50 CLOSE 1 RUN EBENEEZER SCROOGE SUPER MANN Input past end in 20 Ok file Cl Documents
13. 20Basic ONERROR html 2 of 2 28 03 2004 21 29 39 GW BASIC User s Guide ON GOSUB and ON GOTO Statements Purpose To branch to one of several specified line numbers depending on the value returned when an expression is evaluated Syntax ON expression GOTO line numbers ON expression GOSUB line numbers Comments In the ON GOTO statement the value of expression determines which line number in the list will be used for branching For example if the value is 3 the third line number in the list will be destination of the branch If the value is a non integer the fractional portion is rounded In the ON GOSUB statement each line number in the list must be the first line number of a subroutine If the value of expression is zero or greater than the number of items in the list but less than or equal to 255 GW BASIC continues with the next executable statement If the value of expression is negative or greater than 255 an Illegal function call error occurs Examples 100 IF R lt l or R gt 4 then print ERROR END If the integer value of R is less than 1 or greater than 4 program execution ends 200 ON R GOTO 150 300 520 390 If R 1 the program goes to line 150 If R 2 the program branches to line 300 and continues from there If R 3 the branch will be to line 320 and so on file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ONGOSUB htm128 03 2004 21 29 39 GW BASIC User s Guide OP
14. COM2 RS 232 Communications 2 For each device the following OPEN modes are allowed KYBD Input Only SCRN Output Only Leis Output Only LPT2 Output Only LPT3 Output Only COMI Input Output or Random Only file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic OPEN html 2 of 5 28 03 2004 21 29 39 GW BASIC User s Guide COM2 Input Output or Random Only Disk files allow all modes When a disk file is opened for APPEND the position is initially at the end of the file and the record number is set to the last record of the file LOF x 128 PRINT WRITE or PUT then extends the file The program may position elsewhere in the file with a GET statement If this is done the mode is changed to random and the position moves to the record indicated Once the position is moved from the end of the file additional records may be appended to the file by executing a GET x LOF x reclen statement This positions the file pointer at the end of the file in preparation for appending Any values entered outside of the ranges given result in Illegal function call errors The files are not opened If the file is opened as INPUT attempts to write to the file result in Bad file mode errors If the file is opened as OUTPUT attempts to read the file result in Bad file mode errors Opening a file for OUTPUT or APPEND fails if the file is already open in any mode Since it is possible to reference the same file in a
15. Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic FRE htm128 03 2004 21 29 28 GW BASIC User s Guide GET Statement Graphics Purpose To transfer graphics images from the screen Syntax GET x1 y1 x2 y2 array name Comments The PUT and GET statements are used to transfer graphics images to and from the screen PUT and GET make animation and high speed object motion possible in either graphics mode The GET statement transfers the screen image bounded by the rectangle described by the specified points into the array The rectangle is defined the same way as the rectangle drawn by the LINE statement using the B option The array is used simply as a place to hold the image and can be of any type except string It must be dimensioned large enough to hold the entire image The contents of the array after a GET will be meaningless when interpreted directly unless the array is of the type integer as shown below The storage format in the array is as follows e 2 bytes given x dimension in bits e 2 bytes given y dimension in bits e the array data itself The data for each row of pixels is left justified on a byte boundary If less than a multiple of eight bits is stored the rest of the byte will be filled out with zeros The required array size in bytes is as follows 4 INT x bitsperpixelt 7 8 y See the SCREEN statement for bits per pixel values for different screen modes The bytes per element of an a
16. If the current time and date are entered during system start up the correct time and date are given the internal clock in the computer keeps track 2 4 4 3 User Defined Functions Functions can be user defined by means of the DEF FN statement These functions can be either string or numeric 2 4 5 Variables Certain groups of alphanumeric characters are assigned values and are called variables When variables are built into the GW BASIC program they provide information as they are executed For example ERR defines the latest error which occurred in the program ERL gives the location of that error Variables can also be defined and or redefined by the user or by program content All GW BASIC commands statements functions and variables are individually described in the GW BASIC User s Reference 2 5 Line Format Each of the elements of GW BASIC can make up sections of a program that are called statements These statements are very similar to sentences in English Statements are then put file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 202 html 6 of 8 28 03 2004 21 28 57 GW BASIC User s Guide together in a logical manner to create programs The GW BASIC User s Reference describes all of the statements available for use in GW BASIC In a GW BASIC program lines have the following format nnnnn statement statements nnnnn is a line number statement is a GW BASIC statement A GW BASIC program line
17. PRINT Statement PRINT USING Statement PUT Statement Files PUT Statement Graphics RANDOMIZE Statement READ Statement REM Statement RENUM Command RESET Command RESTORE Statement RESUME Statement RETURN Statement RIGHT Function RMDIR Command RND Function RSET Statement RUN Command SAVE Command SCREEN Function SCREEN Statement SGN Function SHELL Statement SIN Function SOUND Statement SPACE Function SPC Function SQR Function STICK Function STOP Statement STR Function STRIG Statement STRIG n Statement STRING Function SWAP Statement SYSTEM Command TAB Function file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic index html 5 of 6 28 03 2004 21 28 55 GWBASIC User s Manual TAN Function TIME Statement TIMER Function TROFEF Command TRON Command UNLOCK Statement USR Function VAL Function VARPTR Function VARPTR Function VIEW Statement VIEW PRINT Statement WAIT Statement WHILE WEND Statement WIDTH Statement WINDOW Statement WRITE Statement WRITE Statement file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic index html 6 of 6 28 03 2004 21 28 55 GW BASIC User s Guide Chapter 1 Welcome to GW BASIC Notational Conventions Microsoft GW BASIC is a simple easy to learn easy to use computer programming language with English like statements and mathematical notations With GW BASIC you will be a
18. Purpose To call an assembly or machine language subroutine Syntax CALL numvar variables Comments numvar Is the starting point in memory of the subroutine being called as an offset into the current segment variables are the variables or constants separated by commas and enclosed in parentheses that are to be passed to the routine The CALL statement is recommended for interfacing assembly language programs with GW BASIC Although the USR function may also be used CALL is compatible with more languages produces a more readable source code and can pass multiple arguments Invocation of the CALL statement causes the following to occur e Each parameter location in the variable is pushed onto the stack The parameter location is a 2 byte offset into GW BASIC s data segment e The return address code segment CS and the offset are pushed onto the stack e Control is transferred to the user routine by the segment address given in the last DEF SEG statement and the offset given in the variable name e The user routine now has control Parameters may be referenced by moving the stack pointer SP to the base pointer BP and adding a positive offset to BP e The called routine may destroy the contents of any registers e The called program must know how many parameters were passed Parameters are referenced by adding a positive offset to BP assuming the called routine moved the current stack pointer into BP that
19. SCREEN statements Animation of an object is usually performed as follows 1 Put the object s on the screen 2 Recalculate the new position of the object s file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PUTG html 1 of 2 28 03 2004 21 29 43 GW BASIC User s Guide 3 Put the object s on the screen a second time at the old location s to remove the old image s 4 Return to Step 1 this time putting the object s at the new location Movement done this way leaves the background unchanged Flicker can be cut down by minimizing the time between Steps 4 and 1 and by making sure that there is enough time delay between Steps and 3 If more than one object is being animated process every object at once one step at a time If it is not important to preserve the background animation can be performed using the PSET action verb Leave a border around the image when it is first gotten as large or larger than the maximum distance the object will move Thus when an object is moved this border effectively erases any points This method may be somewhat faster than the method using XOR described above since only one PUT is required to move an object However the image to be PUT must be larger than the existing image Examples 10 CLS SCREEN 1 20 PSET 130 120 30 DRAW U2Z57 E77 R207 Daz Lo Ul2 L14 40 DRAW Diz Lo PSET 137 102 50 DRAW U4 E4 R8 D8 L12 60 PSET 137 88 70 DRAW E4
20. 20Settings Lorenzo Desktop GW 20Basic FIX htm128 03 2004 21 29 01 GW BASIC User s Guide LET Statement Purpose To assign the value of an expression to a variable Syntax LET variable expression Comments The word LET is optional that is the equal sign is sufficient when assigning an expression to a variable name The LET statement is seldom used It is included here to ensure compatibility with previous versions of BASIC that require it When using LET remember that the type of the variable and the type of the expression must match If they don t a Type mismatch error occurs Example 1 The following example lets you have downward compatibility with an older system If this downward compatibility is not required use the second example as it requires less memory 110 LET D 12 120 LET H 12 2 130 LET F 12 4 140 LET SUM D E F Example 2 110 D 12 120 EH 12 2 130 F 12 4 140 SUM D E F file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LET htm128 03 2004 21 29 01 GW BASIC User s Guide DEF FN Statement Purpose To define and name a function written by the user Syntax DEF FNname arguments expression Comments name must be a legal variable name This name preceded by FN becomes the name of the function arguments consists of those variable names in the function definition that are to be replaced when the function is called The items in the list are separated by co
21. 3 12 3 98 4 24 120 DATA 3 06 5 35 4 00 3 lt 216 3 37 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DATA html 1 of 2 28 03 2004 21 29 21 GW BASIC User s Guide This program segment reads the values from the DATA statements into array A After execution the value of A 1 is 3 08 and so on The DATA statements lines 110 120 may be placed anywhere in the program they may even be placed ahead of the READ statement Example 2 5 PRINT LO PRINT CITY STATE ZIP 20 BEAD C97 S92 30 DATA DENVER COLORADO 80211 40 PRINT S 8s 2 RUN CITY STATE ZIP DENVER COLORADO 80211 This program reads string and numeric data from the DATA statement in line 30 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DATA html 2 of 2 28 03 2004 21 29 21 GW BASIC User s Guide RESTORE Statement Purpose To allow DATA statements to be reread from a specified line Syntax RESTORE Jine number Comments If line number is specified the next READ statement accesses the first item in the specified DATA statement If line number is omitted the next READ statement accesses the first item in the first DATA statement Examples 10 READ A B C 20 RESTORE 30 READ D E F 40 DATA 57 68 79 Assigns the value 57 to both A and D variables 68 to B and E and so on file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic RESTORE htm128 03 2004 21 29 21 GW BASIC Use
22. 3 2 Examples for the Indirect Mode The GW BASIC language can be used for functions other than simple algebraic calculations You can create a program that performs a series of operations and then displays the answer To begin programming you create lines of instructions called statements Remember that there can file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 203 html 1 of 5 28 03 2004 21 28 59 GW BASIC User s Guide be more than one statement on a line and that each line is preceded by a number For example to create the command PRINT 2 3 as a statement type the following 10 print 2 3 When you press the RETURN key the cursor shifts to the next line but nothing else happens To make the computer perform the calculation type the following and press the RETURN key run Your screen should look like this Ok LO print 243 run 5 Ok You have just written a program in GW BASIC The computer reserves its calculation until specifically commanded to continue with the RUN command This allows you to enter more lines of instruction When you type the RUN command the computer does the addition and displays the answer The following program has two lines of instructions Type it in 10 x 3 20 print 2 x Now use the RUN command to have the computer calculate the answer Your screen should look like this Ok 10 x 3 20 print 2 x CUIN 5 Ok The two features that distinguish a program from a calculati
23. BASIC User s Guide 1040 PRINT 1 CHRS 28 Z to make close file 1050 CLOSE 2 CLS LOCATE 25 10 PRINI Upload complete 1060 GOTO 200 9999 CLOSE KEY ON F 7 Notes on the TTY Sample Program Note Asynchronous implies character I O as opposed to line or block I O Therefore all prints either to the COM file or screen are terminated with a semicolon This retards the return line feed normally issued at the end of the PRINT statement Line Number Comments 10 Sets the SCREEN to black and white alpha mode and sets the width to 80 15 Turns off the soft key display clears the screen and makes sure that all files are closed 20 Defines all numeric variables as integer primarily for the benefit of the subroutine at 600 620 Any program looking for speed optimization should use integer counters in loops where possible 40 Defines Boolean true and false 50 Defines the ASCII ASC value of the MENU key 60 Defines the ASCII XON and XOFF characters 100 130 Prints program ID and asks for baud rate speed Opens communications to file number 1 even parity 7 data bits 200 280 This section performs full duplex I O between the video screen and the device connected to the RS 232 connector as follows 1 Read a character from the keyboard into A INKEY returns a null string if no character is waiting 2 If a keyboard character is available waiting then e If the character is the MENU key the operator is ready t
24. Comments EXTERR returns extended error information provided by versions of DOS 3 0 and greater For versions of DOS earlier than 3 0 EXTERR always returns zero The single integer argument must be in the range 0 3 as follows Value of nReturn Value 0 Extended error code 1 Extended error class 2 Extended error suggested action 3 Extended error locus The values returned are not defined by GW BASIC but by DOS Refer to the MS DOS Programmer s Reference version 3 0 or later for a description of the values returned by the DOS extended error function The extended error code is actually retrieved and saved by GW BASIC each time appropriate DOS functions are performed Thus when an EXTERR function call is made these saved values are returned file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic EXTERR htm128 03 2004 21 29 26 GW BASIC User s Guide FIELD Statement Purpose To allocate space for variables in a random file buffer Syntax FIELD filenum width AS stringvar width AS stringvar Comments filenum is the number under which the file was opened width 1s the number of characters to be allocated to the string variable string variable is a string variable which will be used for random file access A FIELD statement must have been executed before you can e Get data out of a random buffer after a GET statement e Enter data before a PUT statement For example the following line allocat
25. GET filenumber nbytes PUT filenumber nbytes Comments filenumber is an integer expression returning a valid file number nbytes is an integer expression returning the number of bytes to be transferred into or out of the file buffer nbytes cannot exceed the value set by the s switch when GW BASIC was invoked Because of the low performance associated with telephone line communications it is recommended that GET and PUT not be used in such applications Example The following TTY sample program is an exercise in communications I O It is designed to enable your computer to be used as a conventional terminal Besides full duplex communications with a host the TTY program allows data to be downloaded to a file Conversely a file may be uploaded transmitted to another machine In addition to demonstrating the elements of asynchronous communications this program is useful for transferring GW BASIC programs and data to and from a computer Note This program is set up to communicate with a DEC System 20 especially in the use of XON and XOFF It may require modification to communicate with other types of hardware F 6 The TTY Sample Program 10 SCREEN 0 0 WIDTH 80 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20F html 3 of 7 28 03 2004 21 28 59 GW BASIC User s Guide 15 KEY OFF CLS CLOSE 20 DEFINT A Z 25 LOCATE 25 1 30 P RINT STRINGS 60 T 40 FALSE 0 TRUE NOT FALSE 50 MENU 5 Va
26. GW 20Basic A ppendix H htm128 03 2004 21 28 58 GW BASIC User s Guide ON COM n ON KEY n ON PEN ON PLAY n ON STRIG n and ON TIMER n Statements Purpose To create an event trap line number for a specified event such as communications pressing function or cursor control keys using the light pen or using joysticks Syntax ON event specifier GOSUB line number Comments The syntax shown sets up an event trap line number for the specified event A line number of 0 disables trapping for this event Once trap line numbers have been set event trapping itself can be controlled with the following syntax lines event specifier ON When an event is ON and a nonzero line number is specified for the trap then every time BASIC starts a new statement it checks to see if the specified event has occurred If it has BASIC performs a GOSUB to the line specified in the ON statement event specifier OFF When an event is OFF no trapping occurs and the event is not remembered even if it occurs event specifier STOP When an event is stopped no trapping can occur but if the event happens it is remembered so an immediate trap occurs when an event specifier ON is executed When a trap is made for a particular event the trap automatically causes a stop on that event so recursive traps can never take place The return from the trap routine automatically does an ON unless an explicit OFF has been performed inside the trap routine
27. GW BASIC User s Guide 065 101 41 066 102 42 067 103 43 068 104 44 069 105 45 070 106 46 071 107 47 072 110 48 073 111 49 074 112 4A 075 113 4B 076 114 4C 077 115 4D 078 116 4E 079 117 4F 080 120 50 081 121 51 082 122 52 083 123 53 084 124 54 085 125 55 086 126 56 087 127 57 088 130 58 089 131 59 090 132 5A 091 133 5B 092 134 5C 093 135 5D 125 175 7D 094 136 5E 126 176 7E 095 137 5F 127 177 7F DEL Dec Decimal Oct 0ctal Hex Hexadecimal H Chr Character LF Line feed FF Form feed CR Carriage return DEL Rubout 097 141 6l 098 142 62 099 143 63 100 144 64 101 145 65 102 146 66 103 147 67 104 150 68 105 151 69 106 152 6A 107 153 6B 108 154 6C 109 155 6D 110 156 6E 111 157 6F 112 160 70 113 161 71 114 162 72 115 163 73 116 164 74 117 165 75 118 166 76 119 167 77 120 170 78 121 171 79 122 172 7A 123 173 7B 124 174 7C ans xg lt ac nTntann anano E el a e r e Oe E E o a gt T NK KR SK CHMANTVTO ZZMATTTATMAGUASS file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Appendix 20C html 2 of 2 28 03 2004 21 29 04 GW BASIC User s Guide Appendix D Assembly Language Machine Code Subroutines This appendix is written primarily for users experienced in assembly language programming GW BASIC lets you interface with assembly language subroutines by using the USR function and the CALL statement The USR function allows assembly language subroutines to be called in the s
28. If rounding causes the number to exceed the field a percent sign is printed in front of the rounded number For example PRINT USING 111 22 111 27 PRINT USING 4 7 7 999 61 00 If the number of digits specified exceeds 24 an Illegal function call error results file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PRINTUSING html 4 of 4 28 03 2004 21 29 32 GW BASIC User s Guide WIDTH Statement Purpose To set the printed line width in number of characters for the screen and line printer Syntax WIDTH size WIDTH file number size WIDTH dev size Comments size an integer within the range of 0 to 255 is the new width file number is the number of the file that is open dev is a valid string expression identifying the device Valid devices are SCRN LPT1 LPT2 LPT3 COM1 and COM2 Changing Screen Width The following statements are used to set the screen width Only a 40 or 80 column width is allowed WIDTH size WIDTH SCRN T size See the SCREEN statement for more information Changing SCREEN mode affects screen width only when moving between SCREEN 2 and SCREEN 1 or SCREEN 0 Note Changing the screen width clears the screen and sets the border screen color to black Changing Line printer Width The following WIDTH statement is used as a deferred width assignment for the line printer This statement stores the new width value without actually changing the current w
29. Open the file for random access R mode The following example specifies a record length of 32 bytes If the record length is omitted the default is 128 bytes OPEN R 1 filename 32 Use the FIELD statement to allocate space in the random buffer for the variables that will be written to the random file FIELD 1 20 AS N 4 AS AS 8 AS P In this example the first 20 positions bytes in the random file buffer are allocated to the string variable N The next 4 positions are allocated to A the next 8 to P Use LSET or RSET to move the data into the random buffer fields in left or right justified format L left SET R right SET Numeric values must be made into strings when placed in the buffer MKI converts an integer value into a string MKS converts a single precision value and MKDS converts a double precision value LSET N X LSET AS MKSS AMT LSET PS TELS 4 Write the data from the buffer to the diskette using the PUT statement file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 205 html 5 of 9 28 03 2004 21 29 02 GW BASIC User s Guide PUT 1 CODES The program in Example 4 takes information keyed as input at the terminal and writes it to a random access data file Each time the PUT statement is executed a record is written to the file In the example the 2 digit CODE input in line 30 becomes the record number Note Do not use a fielded string variable in an INPUT or
30. SOUND 1000 2 GOTO 20 1010 SOUND 2000 8 GOTO 20 1020 SOUND 400 4 GOTO 20 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic TIMES html 2 of 2 28 03 2004 21 29 50 GW BASIC User s Guide TIMER Function Purpose To return single precision floating point numbers representing the elapsed number of seconds since midnight or system reset Syntax v TIMER Comments Fractions of seconds are calculated to the nearest degree possible Timer is read only file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic TIMER htm128 03 2004 21 29 51 GW BASIC User s Guide TRON TROFF Commands Purpose To trace the execution of program statements Syntax TRON TROFF Comments As an aid in debugging the TRON trace on command enables a trace flag that prints each line number of the program as it is executed The numbers appear enclosed in square brackets TRON may be executed in either the direct or indirect mode The trace flag is disabled with the TROFF trace off command or when a NEW command is executed Examples TRON 10 K 10 20 FOR J 1 TO 2 30 L K 10 40 PRINT J K L 50 K K 10 60 NEXT 70 END RUN 10I T20 3S0 40 1 10 20 50 60 30 40 2 20 30 L50 T60 70 TROFF file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic TRON htm128 03 2004 21 29 51 GW BASIC User s Guide VARPTR Function Purpose To return the address in memory of the v
31. USING S 22 34 KKKS 2 34 A comma to the left of the decimal point in the format string causes a comma to be printed to the left of every third digit to the left of the decimal point A comma at the end of the format string is printed as part of the string PRINT USING 1234 5 1234 50 Four carets may be placed after the digit position characters to specify exponential format The four carets allow space for E xx to be printed Any decimal point position may be specified The significant digits are left justified and the exponent is adjusted Unless a leading or trailing or is specified one digit position is used to the left of the decimal point to print a space or a minus sign For example PRINT USING 234 56 44 258702 PRINT USING 888888 OK PRINT USING 4 48 7 7123 L ZE 05 Note that in the above examples the comma is not used as a delimiter with the exponential format file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PRINTUSING html 3 of 4 28 03 2004 21 29 32 oO GW BASIC User s Guide An underscore in the format string causes the next character to be output as a literal character For example PRINT USING _ _ 12 34 112 34 The literal character itself may be an underscore by placing in the format string A percent sign is printed in front of the number if the number to be printed is larger than the specified numeric field
32. User s Guide PALETTE PALETTE USING Statements Purpose Changes one or more of the colors in the palette Syntax PALETTE attribute color PALETTE USING integer array name arrayindex Comments The PALETTE statement works only for systems equipped with the IBM Enhanced Graphics Adapter EGA A GW BASIC palette contains a set of colors with each color specified by an attribute Each attribute is paired with an actual display color This color determines the actual visual color on the screen and is dependent on the setting of your screen mode and your actual physical hardware display PALETTE with no arguments sets the palette to a known initial setting This setting is the same as the setting when colors are first initialized If arguments are specified color will be displayed whenever attribute is specified in any statement that specifies a color Any color changes on the screen occur immediately Note that when graphics statements use color arguments they are actually referring to attributes and not actual colors PALETTE pairs attributes with actual colors For example assume that the current palette consists of colors 0 1 2 and 3 The following DRAW statement DRAW C3L100 selects attribute 3 and draws a line of 100 pixels using the color associated with the attribute 3 in this case also 3 If the statement PALETTE 3 2 is executed then the color associated with attribute 3 is changed to color 2 All t
33. X Y Z XY Z X Y 2 X Y Z X Y Z X2 Y 420 aY xY X n X Y X Y Two consecutive operators must be separated by parentheses 6 4 1 1 Integer Division and Modulus Arithmetic Two additional arithmetic operators are available integer division and modulus arithmetic Integer division is denoted by the backslash The operands are rounded to integers must be within the range of 32768 to 32767 before the division is performed and the quotient is truncated to an integer The following are examples of integer division 10 4 2 9468 6 99 3 In the order of occurrence within GW BASIC the integer division will be performed just after floating point division file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 6 html 7 of 12 28 03 2004 21 29 00 GW BASIC User s Guide Modulus arithmetic is denoted by the operator MOD It gives the integer value that is the remainder of an integer division The following are examples of modulus arithmetic 10 4 MOD 4 2 10 4 2 with a remainder 2 25 68 MOD 6 99 5 26 7 3 with a remainder 5 In the order of occurrence within GW BASIC modulus arithmetic follows integer division The INT and FIX functions described in the GW BASIC User s Reference are also useful in modulus arithmetic 6 4 1 2 Overflow and Division by Zero If during the evaluation of an expression a division by zero is encountered the Division by zero error message appears machine in
34. a diskette file Only the name of the file is changed The file is not modified and it remains in the same space and position on the disk This command can also be used with data files 5 2 Data Files GW BASIC programs can work with two types of data files file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 205 html 1 of 9 28 03 2004 21 29 02 GW BASIC User s Guide e Sequential files e Random access files Sequential files are easier to create than random access files but are limited in flexibility and speed when accessing data Data written to a sequential file is a series of ASCII characters Data is stored one item after another sequentially in the order sent Data is read back in the same way Creating and accessing random access files requires more program steps than sequential files but random files require less room on the disk because GW BASIC stores them in a compressed format in the form of a string The following sections discuss how to create and use these two types of data files 5 2 1 Creating a Sequential File The following statements and functions are used with sequential files CLOSE LOF BOF OPEN INPUT PRINT LINE INPUT PRINT USING LOC UNLOCK LOCK WRITE The following program steps are required to create a sequential file and access the data in the file 1 Open the file in output mode The current program will use this file first for output OPEN O 1 filename
35. a line number for branching or one or more statements to be executed GOTO 1s always followed by a line number If the statement does not contain the same number of ELSE s and THEN s line number each ELSE is matched with the closest unmatched THEN For example IF A B THEN IF B C THEN PRINT A C ELSE PRINT A lt gt C will not print a lt gt c whenA lt gt B If an IF THEN statement is followed by a line number in the direct mode an Undefined line number error results unless a statement with the specified line number was previously entered in the indirect mode Because IF THEN ELSE is all one statement the ELSE clause cannot be on a separate line It must be all on one line Nesting of IF Statements IF THEN ELSE statements may be nested Nesting is limited only by the length of the line For example the following is a legal statement 100 IF X gt Y THEN PRINT GREATER ELSE IF Y gt X THENG 110 PRINT LESS THAN 200 ELSE PRINT EQUAL file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic IF html 1 of 2 28 03 2004 21 29 29 GW BASIC User s Guide Testing Equality When using IF to test equality for a value that is the result of a floating point computation remember that the internal representation of the value may not be exact Therefore test against the range over which the accuracy of the value may vary For example to test a computed variable A against the value 1 0 use the foll
36. always begins with a line number and must contain at least one character but no more than 255 characters Line numbers indicate the order in which the program lines are stored in memory and are also used as references when branching and editing The program line ends when you press the RETURN key Depending on the logic of your program there may be more than one statement on a line If so each must be separated by a colon Each of the lines in a program should be preceded by a line number This number may be any whole integer from 0 to 65529 It is customary to use line numbers such as 10 20 30 and 40 in order to leave room for any additional lines that you may wish to include later Since the computer will run the statements in numerical order additional lines needn t appear in consecutive order on the screen for example if you entered line 35 after line 60 the computer would still run line 35 after line 30 and before line 40 This technique may save your reentering an entire program in order to include one line that you have forgotten The width of your screen is 80 characters If your statement exceeds this width the cursor will wrap to the next screen line automatically Only when you press the RETURN key will the computer acknowledge the end of the line Resist the temptation to press RETURN as you approach the edge of the screen or beyond The computer will automatically wrap the line for you You can also press CTRL RETURN which
37. be restated in the chained program When using the merge command place user defined functions before any CHAIN MERGE statements in the program Otherwise they will be undefined after the merge is complete file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CHAIN html 2 of 2 28 03 2004 21 29 15 GW BASIC User s Guide MERGE Command Purpose To merge the lines from an ASCII program file into the program already in memory Syntax MERGE filename Comments filename is a valid string expression containing the filename If no extension is specified then GW BASIC assumes an extension of BAS The diskette is searched for the named file If found the program lines on the diskette are merged with the lines in memory After the MERGE command the merged program resides in memory and GW BASIC returns to the direct mode If the program being merged was not saved in ASCII code with the a option to the SAVE command a Bad file mode error is issued The program in memory remains unchanged If any line numbers in the file have the same number as lines in the program in memory the lines from the file replace the corresponding lines in memory Examples MERGE SUBRTN Merges the file subrtn bas with the program currently in memory provided subrtn was previously saved with the a option If some of the program lines are the same as those in the subrtn bas file being merged then the original program lines are repl
38. be used as a last in first out stack to store retrieve the contents of the accumulator the flags or any of the data registers Many units contain a 16 bit stack pointer to control the addressing of this external stack One of the major advantages of the stack is that multiple level interrupts can be handled easily since complete system status can be saved when an interrupt occurs and then be restored after the interrupt Another major advantage is that almost unlimited subroutine nesting is possible statement A high level language instruction to the computer to perform some sequence of operations synchronous A type of computer operation in which the execution of each instruction or each event is controlled by a clock signal evenly spaced pulses that enable the logic gates for the execution of each logic step A synchronous operation can cause time delays by causing waiting for clock signals although all other signals at a particular logic gate were available See asynchronous switch An instruction added to a command that designates a course of action other than default for the command process to follow syntax Rules of statement structure in a programming language system file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 16 of 17 28 03 2004 21 29 08 GW BASIC User s Guide A collection of hardware software and firmware that is interconnected to operate as a unit task A machine run a progra
39. call a predetermined operation that is to be performed on an operand GW BASIC has intrinsic functions that reside in the system such as SOR square root or SIN sine GW BASIC also allows user defined functions written by the programmer See the DEF FN statement in the GW BASIC User s Reference 6 4 5 String Operators To compare strings use the same relational operators used with numbers OperatorMeaning Equal to lt gt Unequal Less than Greater than Less than or equal to a Greater than or equal to The GW BASIC Interpreter compares strings by taking one character at a time from each string and comparing their ASCII codes If the ASCII codes in each string are the same the strings are equal If the ASCII codes differ the lower code number will precede the higher code If the interpreter reaches the end of one string during string comparison the shorter string is said to be smaller providing that both strings are the same up to that point Leading and trailing blanks are significant For example AA lt AB FILENAME FILENAME XS S X W Vet 1 s NERY kg gt KG SMYTH lt SMYTHE B lt 9 12 78 where B 8 12 78 String comparisons can also be used to test string values or to alphabetize strings All string constants used in comparison expressions must be enclosed in quotation marks Strings can be concatenated by using the plus sign For example 10 AS FILE BS NAME 20 PRINT
40. causes the cursor to move to the beginning of the next screen line without actually entering the line When you press RETURN the entire logical line is passed to GW BASIC for storage in the program In GW BASIC any line of text that begins with a numeric character is considered a program line and is processed in one of three ways after the RETURN key is pressed e A new line is added to the program This occurs if the line number is legal within the range of 0 through 65529 and if at least one alpha or special character follows the line number in the line e An existing line is modified This occurs if the line number matches the line number of an existing line in the program The existing line is replaced with the text of the newly entered line This process is called editing file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 202 html 7 of 8 28 03 2004 21 28 57 GW BASIC User s Guide Note Reuse of an existing line number causes all of the information contained in the original line to be lost Be careful when entering numbers in the indirect mode You may erase some program lines by accident e An existing line is deleted This occurs if the line number matches the line number of an existing line and the entered line contains only a line number If an attempt is made to delete a nonexistent line an Undefined line number error message is displayed 2 6 Returning to MS DOS Before you return to MS DOS yo
41. command LINE or PSET The current position defaults to the center of the screen 160 100 in medium resolution 320 100 in high resolution when a program is run Movement commands move for a distance of scale factor n where the default for n is 1 thus they move one point if n is omitted and the default scale factor is used Command Moves Un up Dn down Ln left Rn right En diagonally up and right Fn diagonally down and right Gn diagonally down and left Hn diagonally up and left This command moves as specified by the following argument Mx y Move absolute or relative If x is preceded by a or x and y are added to the current graphics position and connected to the current position by a line Otherwise a line is drawn to point x y from the current position The following prefix commands may precede any of the above movement commands B Move but plot no points file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DRA W html 1 of 3 28 03 2004 21 29 17 GW BASIC User s Guide N Move but return to original position when done The following commands are also available An Set angle n n may range from 0 to 3 where 0 is 0 1 is 90 2 is 180 and 3 is 270 Figures rotated 90 or 270 are scaled so that they will appear the same size as with 0 or 180 on a monitor screen with the standard aspect ratio of 4 3 TAn Turn angle n n can be any value from negative 360 to positive 360 If the value
42. contains the latest value supplied by DEF SEG If no DEF SEG has been specified it then points to the same address as DS ES and SS the default DEF SEG Figure D 2 shows the condition of the stack during execution of the called subroutine Figure 2 Figure D 2 Stack Layout During Execution of a CALL Statement not shown The following seven rules must be observed when coding a subroutine 1 The called routine may destroy the contents of the AX BX CX DX SI DI and BP registers They do not require restoration upon return to GW BASIC However all segment registers and the stack pointer must be restored Good programming practice dictates that interrupts enabled or disabled be restored to the state observed upon entry 2 The called program must know the number and length of the parame ters passed References to parameters are positive offsets added to BP assuming the called routine file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20D html 2 of 8 28 03 2004 21 29 05 GW BASIC User s Guide moved the current stack pointer into BP that is MOV BP SP When 3 parameters are passed the location of PO is at BP 10 P1 is at BP 8 and P2 is at BP 6 3 The called routine must do a RETURN n n is two times the number of parameters in the argument list to adjust the stack to the start of the calling sequence Also programs must be defined by a PROC FAR statement 4 Values are returned to GW BASIC by inclu
43. current graphics coordinates POINT function returns the value of the current x or y graphics coordinates as follows Function Returns 0 the current physical x coordinate 1 the current physical y coordinate 2 the current logical x coordinate if WINDOW is active otherwise it returns the current physical x coordinate as in 0 above 3 the current logical y coordinate if WINDOW is active otherwise it returns the current physical y coordinate as in 1 above Example 1 10 SCREEN 1 20 FOR C 0 TO 3 30 PSET 10 10 40 IF POINT 10 10 lt gt C THEN PRINT BROKEN BASTC 90 NEXT C Example 2 The following inverts the current state of a point 10 SCREEN 2 20 IF POINT 1 I lt gt 0 THEN PRESET 1 I ELSE PSET 1 IJ Example 3 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic POINT html 1 of 2 28 03 2004 21 29 42 GW BASIC User s Guide The following is another way to invert a point 20 PSET I I 1 POINT I I file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic POINT html 2 of 2 28 03 2004 21 29 42 GW BASIC User s Guide PRINT and PRINT USING Statements Purpose To write data to a sequential disk file Syntax PRINT file number USINGstring expressions list of expressions Comments file number is the number used when the file was opened for output string expressions consists of the formatting characters described in the PRINT USING statement list of ex
44. defines the fields reads a record then displays it LO OPEN R 1 AsVENDOR F LL 20 FIELD 1 30 AS VENDNAMESS 20 AS ADDRS 15 AS CITYS 30 GET 1 40 PRINT VENDNAMESS ADDRS CITYS 50 CLOSE 1 This example opens the file vendor fil for random access with fields defined in line 20 In line 30 the GET statement reads a record into the file buffer Line 40 displays the information from the record just read Line 50 closes the file file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic GETF htm128 03 2004 21 29 27 GW BASIC User s Guide FILES Command Purpose To print the names of the files residing on the specified drive Syntax FILES pathname Comments If pathname is omitted the command lists all files in the current directory of the selected drive pathname may contain question marks to match any character in the filename or extension An asterisk as the first character of the filename or extension will match any file or any extension This syntax also displays the name of the directory and the number of bytes in the file When a tree structured directory is used two special symbols also appear Subdirectories are denoted by lt DIR gt following the directory name Examples FILES FILES BAS FILES Bp 1 FILES TEST BAS FILES now allows pathnames The directory for the specified path is displayed If an explicit path is not given the current directory is assumed
45. dummy argument and may be any value PLAY n returns 0 when in music foreground mode The maximum returned value of x is 32 Examples 10 when 4 notes are left in 20 queue play another tune 30 PLAY MBABCDABCDABCD 40 IF PLAY 0 4 then 200 200 PLAY MBCDEFCDEF file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PLA YN htm128 03 2004 21 29 42 GW BASIC User s Guide PMAP Function Graphics Purpose To map expressions to logical or physical coordinates Syntax X PMAP exp function Comments This function is valid for graphics modes only x is the physical coordinate of the point that is to be mapped exp is a numeric variable or expression Function Maps 0 logical expressions to physical x 1 logical expressions to physical y 2 physical expressions to logical x 3 physical expressions to logical y PMAP is used with WINDOW and VIEW to translate coordinates file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PMA P htm128 03 2004 21 29 42 GW BASIC User s Guide POINT Function Purpose To read the color or attribute value of a pixel from the screen Syntax POINT x y POINT function Comments In the first syntax x and y are coordinates of the point to be examined If the point given is out of range the value 1 is returned See the COLOR and PALETTE statements for valid color and attribute values POINT with one argument allows you to retrieve the
46. example in the next section illustrates how the file named picture is saved file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic BLOAD html 2 of 2 28 03 2004 21 29 13 GW BASIC User s Guide BSAVE Command Purpose To save portions of user memory on the specified device Syntax BSAVE filename offset length Comments filename is a valid string expression containing the filename offset is a valid numeric expression within the range of 0 to 65535 This is the offset into the segment declared by the last DEF SEG where saving is to start length is a valid numeric expression within the range of 0 to 65535 specifying the length of the memory image to be saved If filename is less than one character a Bad File Number error is issued and the load is aborted Execute a DEF SEG statement before the BSAVE The last known DEF SEG address is always used for the save The DEF SEG statement must be used to set up the segment address to the start of the screen buffer An offset of 0 and a length of 16384 specify that the entire 16K screen buffer is to be saved Examples 10 DEF SEG amp HB800 20 BSAVE PICTURE 0 16384 The DEF SEG statement in line 10 points the segment at the screen buffer The BSAVE command in line 20 saves the screen buffer in the file named picture file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic BSA VE htm128 03 2004 21 29 13 GW BASIC User s Guide CALL Statement
47. filename a default file extension of BAS is assumed The BAS extension indicates that the file is a GW BASIC file The maximum number of characters a filename may contain is eight with a decimal and three extension characters lt stdin redirects GW BASIC s standard input to be read from the specified file When used it must appear before any switches This might be used when you have multiple files that might be used by your program and you wish to specify a particular input file gt stdout redirects GW BASIC s standard output to the specified file or device When used it must appear before any switches Using gt gt before stdout causes output to be appended GW BASIC can be redirected to read from standard input keyboard and write to standard output screen by providing the input and output filenames on the command line as follows gwbasic program name lt input file gt gt output file An explanation of file redirection follows this discussion of the GW BASIC command line Switches appear frequently in command lines they designate a specified course of action for the command as opposed to using the default for that setting A switch parameter is preceded by a file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 202 html 2 of 8 28 03 2004 21 28 57 GW BASIC User s Guide slash n sets the maximum number of files that may be opened simultaneously during the execution of a GW BASIC program Eac
48. hex 2000 7FA absolute address hex 207FA file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CALL html 3 of 3 28 03 2004 21 29 13 GW BASIC User s Guide CDBL Function Purpose To convert x to a double precision number Syntax CDBL x Comments x must be a numeric expression Example 10 A 454 67 20 PRINT A CDBL A RUN 454 67 454 6700134277344 Prints a double precision version of the single precision value stored in the variable named A The last 11 numbers in the double precision number have no meaning in this example since A was previously defined to only two decimal place accuracy Note See the CINT and CSNG functions for converting numbers to integer and single precision respectively file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CDBL htm128 03 2004 21 29 14 GW BASIC User s Guide CINT Function Purpose To round numbers with fractional portions to the next whole number or integer Syntax CINT x Comments If x is not within the range of 32768 to 32767 an Overflow error occurs See the FIX and INT functions both of which return integers Examples PRINT CINT 45 67 46 45 67 is rounded up to 46 Note See the CDBL and CSNG functions for converting numbers to the double precision and single precision data types respectively file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CINT htm128 03 2004 21 29 14 GW BASIC
49. i Message NEXT without FOR NEXT statement does not have a corresponding FOR statement Check variable at FOR statement for a match with the NEXT statement variable Syntax error A line is encountered that contains an incorrect sequence of characters such as unmatched parentheses a misspelled command or statement incorrect punctuation This error causes GW BASIC to display the incorrect line in edit mode RETURN without GOSUB A RETURN statement is encountered for which there is no previous GOSUB statement Out of DATA A READ statement is executed when there are no DATA statements with unread data remaining in the program Illegal function call An out of range parameter is passed to a math or string function An illegal function call error may also occur as the result of e anegative or unreasonably large subscript e anegative or zero argument with LOG e anegative argument to SOR e anegative mantissa with a noninteger power e acall to a USR function for which the starting address has not yet been given e an improper argument to MIDS LEFTS RIGHTS INP OUT WAIT PEEK POKE TAB SPC STRINGS SPACES INSTR or ON GOTO Overflow The result of a calculation is too large to be represented in GW BASIC s number format If underflow occurs the result is zero and execution continues without an error Out of memory A program is too large has too many FOR loops GOSUBs variables or expressions that are too comp
50. in a complete turn is 27 radix A number that is arbitrarily made the fundamental number of a system of numbers a base Thus file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 14 of 17 28 03 2004 21 29 08 GW BASIC User s Guide 10 is the radix or base of the common system of logarithms and also of the decimal system of enumeration random access memory The system s high speed work area that provides access to memory storage locations by using a system of vertical and horizontal coordinates The computer can write information into or read information from the random access memory Random access memory is often called RAM raster unit On a graphic display screen a raster unit is the horizontal or vertical distance between two adjacent addressable points on the screen read only memory A type of memory that contains permanent data or instructions The computer can read from but not write to the read only memory Read only memory is often called ROM real number An ordinary number either rational or irrational a number in which there is no imaginary part a number generated from the single unit 1 any point in a continuum of natural numbers filled in with all rationals and all irrationals and extended indefinitely both positive and negative real time 1 The actual time required to solve a problem 2 The process of solving a problem during the actual time that a related physical process takes p
51. is MOV BP SP e The called program must know the variable type for numeric parameters passed e The called routine must do a RET n where n is the number of parameters in the variable times 2 This is necessary in order to adjust the stack to the point at the start of the calling sequence file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CALL html 1 of 3 28 03 2004 21 29 13 GW BASIC User s Guide e Values are returned to GW BASIC by including in the argument list the name of the variable that is to receive the result e If the argument is a string the parameter offset points to three bytes called the string descriptor Byte 0 of the string descriptor contains the length of the string 0 to 255 Bytes 1 and 2 respectively are the lower and upper eight bits of the string starting address in the string space e If the argument is a string literal in the program the string descriptor points to program text Be careful not to alter or destroy a program this way To avoid unpredictable results add to the string literal in the program as in the following 20 AS BASIC This forces the string literal to be copied into the string space Now the string may be modified without affecting the program Note Strings may be altered by user routines but their length must not be changed GW BASIC cannot correctly erase strings if their lengths are modified by external routines For more information on the CALL s
52. line 9999 This line closes the COM file left open and restores the function key display file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20F html 7 of 7 28 03 2004 21 28 59 GW BASIC User s Guide Chapter 3 Reviewing and Practicing GW BASIC The practice sessions in this chapter will help you review what you have learned If you have not done so this is a good time to turn on your computer and load the GW BASIC Interpreter 3 1 Example for the Direct Mode You can use your computer in the direct mode to perform fundamental arithmetic operations GW BASIC recognizes the following symbols as arithmetic operators Operation GW BASIC Operator Addition a Subtraction Multiplication Division To enter a problem respond to the Ok prompt with a question mark followed by the statement of the problem you want to solve and press the RETURN key In GW BASIC the question mark can be used interchangeably with the keyword PRINT The answer is then displayed Type the following and press the RETURN key T2te GW BASIC will display the answer on your screen 2272 4 Ok To practice other arithmetic operations replace the sign with the desired operator The GW BASIC language is not restricted to arithmetic functions You can also enter complex algebraic and trigonometric functions The formats for these functions are provided in Chapter 6 Constants Variables Expressions and Operators
53. message Redo from start to be printed No assignment of input values is made until an acceptable response is given A comma may be used instead of a semicolon after prompt string to suppress the question mark For example the following line prints the prompt with no question mark INPUT ENTER BIRTHDATE BS If the prompt string is preceded by a semicolon the RETURN key pressed by the operator is suppressed During program execution data on that line is displayed and data from the next PRINT statement is added to the line When an INPUT statement is encountered during program execution the program halts the prompt string is displayed and the operator types in the requested data Strings that input to an INPUT statement need not be surrounded by quotation marks unless they contain commas or leading or trailing blanks When the operator presses the RETURN key program execution continues file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic INPUT html 1 of 2 28 03 2004 21 29 30 GW BASIC User s Guide INPUT and LINE INPUT statements have built in PRINT statements When an INPUT statement with a quoted string is encountered during program execution the quoted string is printed automatically see the PRINT statement The principal difference between the INPUT and LINE INPUT statements is that LINE INPUT accepts special characters such as commas within a string without requiring double quotation marks while the IN
54. not return the cursor to the next line It is as though the TAB function has an implied semicolon after it TAB may be used only in PRINT LPRINT or PRINT statements see the SPC function Examples 10 PRINT NAME TAB 25 AMOUNT PRINT 20 READ AS BS 30 PRINT AS TAB 25 BS 40 DATA G T JONES 525 00 RUN NAME AMOUNT G T JONES 2500 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic TAB htm128 03 2004 21 29 50 GW BASIC User s Guide TAN Function Purpose To calculate the trigonometric tangent of x in radians Syntax TAN x Comments TAN x is calculated in single precision unless the d switch is used when GW BASIC is executed If TAN overflows the Overflow error message is displayed machine infinity with the appropriate sign is supplied as the result and execution continues To obtain TAN x when x is in degrees use TAN x pi 180 Examples 10 Y TAN X When executed Y will contain the value of the tangent of X radians file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic TAN htm128 03 2004 21 29 50 GW BASIC User s Guide TIMES Statement and Variable Purpose To set or retrieve the current time Syntax As a statement TIMES string exp As a variable string exp TIMES Comments string exp is a valid string literal or variable that lets you set hours hh hours and minutes hh mm or hours minutes and seconds hh mm ss hh sets
55. of an OPEN statement which allows a process to specify an access to the successfully opened file The access determines a guaranteed exclusivity range on that file by the process while the OPEN statement is in effect lock can be one of the following SHARED deny none mode No restrictions are placed on the read write accessibility of the the file to another process except that the default mode is not allowed by any of the modes including SHARED LOCK READ deny read mode Once a file is opened with the LOCK READ access no other process is granted read access to that file An attempt to open a file with this access will be unsuccessful if the file is currently open in default mode or with a read access LOCK WRITE deny write mode A file successfully opened with LOCK WRITE access may not be opened for a write access by another process An attempt to open a file with this access will be unsuccessful if the file has been opened in default mode or with a write access by another process LOCK READ WRITE deny all or exclusive mode If a file is successfully opened with this access the process has exclusive access to the file A file that is currently open in this mode cannot be opened again in any mode by any process default compatibility mode in which the compatibility with other BASICs is understood No access is specified The file may be opened any number of times by a process provided that the file is not currently opened by ano
56. of the called program For example the following begins execution of PROG BAS at line 1000 10 CHAIN PROG1 1000 If 1 ine is omitted execution begins at the first line line is not affected by a RENUM command However the line numbers in the specified range are affected by a RENUM command ALL specifies that every variable in the current program is chained to the called program For example 20 CHAIN PROGI 1000 ALL If the ALL option is omitted the current program must contain a COMMON statement to list the variables that are passed CHAIN executes a RESTORE before it runs the program that it is to be chained to The READ statement then gets the first item in the DATA statement Reading will not resume where it left off in the program that is being chained file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CHAIN html 1 of 2 28 03 2004 21 29 15 GW BASIC User s Guide After an overlay is executed and used for a specific purpose it is usually desirable to delete it so that a new overlay may be brought in To do this use the DELETE command The CHAIN statement with the MERGE command leaves the files open and preserves the current option base setting If the MERGE command is omitted the OPTION BASE setting is preserved and CHAIN preserves no variable types or user defined functions for use by the chained program That is any DEFINT DEFSNG DEFDBL DEFSTR or DEF FN statement containing shared variables must
57. program when executed prior to the running of the GW BASIC program will remain in memory until the system power is turned off or the system is rebooted 0100 org 100H 0100 double segment assume cs double 0100 EB 17 90 start jmp starci 0103 usrprg proc far 0103 55 push bp 0104 8B EC mov bp sp 0106 8B 76 08 mov si bp 3 get address of parameter b 0109 8B 04 mov ax si get value of b O10B 8B 76 OA mov si bp 10 get address of parameter a 010E 03 04 add ax si add value of a to value of b 0110 8B 7E 06 mov di bp 6 get address of parameter c 0113 89 05 mov di ax store sum in parameter c 0115 5D pop bp O116 ca 00 06 ret 6 0119 usrprg endp Program to put procedure in memory and remain resident The offset and segment are stored lt in location LOO 10SH 0119 Start 0119 Be 00 00 mov ax 0 O11C 8E D8 mov ds ax data segment to 0000H 011E BB 01 00 mov bx 0OLO00H pointer to int vector 100H 0121 83 7F 02 0 cmp word ptr bx 0 0125 75 16 jne quit program already run exit 0127 83 3F 00 cmp word ptrz bx 0 012A 73 11 jne quit program already run exit 012C BS 01 03 R mov ax offset usrprg 0112F 89 07 mov bx pax program offset 0131 8C C8 mov ax cs 0133 89 47 02 mov bx 2 ax data segment 0136 OE push cs 0137 IF pop ds 0138 BA 0141 R mov dx offset veryend 013B CD 27 int 27h 013D q it 013D CD 20 int 20N O13F veryend OTF double ends end start file Cl Docume
58. searches the string ABCDFBXYZ and finds the first occurrence of the character B at position 2 in the string It then starts another search at position 4 D and finds the second match at position 6 B The last three characters are ignored since all conditions set out in line 30 were satisfied file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic INSTR htm128 03 2004 21 29 33 GW BASIC User s Guide IOCTL Statement Purpose To allow GW BASIC to send a control data string to a character device driver anytime after the driver has been opened Syntax IOCTL file number string Comments file number is the file number open to the device driver string is a valid string expression containing characters that control the device TOCTL commands are generally 2 to 3 characters followed by an optional alphanumeric argument An IOCTL string may be up to 255 bytes long with commands within the string separated by semicolons Examples If a user had installed a driver to replace Ipt1 and that driver was able to set page length the number of lines to print on a page before issuing a form feed then the following lines would open the new Ipt1 driver and set the page length to 66 lines OPEN LPT1 FOR OUTPUT AS 1 1OCTL 1 ELGO The following statements open Ipt1 with an initial page length of 56 lines OPEN DEV LPT1 FOR OUTPUT AS 1 IOCTL 1 PL56 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20B
59. separate and organize items of data detail file A data file composed of records having similar characteristics but containing data which is relatively changeable by nature such as employee weekly payroll data Compare to master file device A piece of hardware that can perform a specific function A printer is an example of a device diagnostic programs Special programs used to align equipment or isolate equipment malfunctions directory A table that gives the name location size and the creation or last revision date for each file on the storage media diskette A flat flexible platter coated with magnetic material enclosed in a protective envelope and used for storage of software and data Disk Operating System A collection of procedures and techniques that enable the computer to operate using a disk drive system for data entry and storage Disk Operating System is usually abbreviated to DOS DOS The acronym for Disk Operating System DOS rhymes with boss double density A type of diskette that has twice the storage capacity of standard single density diskettes file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 7 of 17 28 03 2004 21 29 08 GW BASIC User s Guide double precision The use of two computer words to represent each number This technique allows the use of twice as many digits as are normally available and is used when extra precision is needed in calculations double side
60. specified by n is positive it turns the angle counter clockwise If the value specified by n is negative it turns clockwise Cn Set color n See the COLOR PALETTE and SCREEN statements for discussions of valid colors numbers and attributes Sn Set scale factor n may range from to 255 n is divided by 4 to derive the scale factor The scale factor is multiplied by the distances given with U D L R E F G H or relative M commands to get the actual distance traveled The default for s is 4 xstring variableExecute substring This command executes a second substring from a string much like GOSUB One string executes another which executes a third and so on string is a variable assigned to a string of movement commands Ppaint boundary Specifies the colors for a graphics figure and creates a filled in figure paint specifies what color you want the figure filled in with boundary specifies the border color outline See the COLOR PALETTE and SCREEN statements for discussions of valid colors numbers and attributes You must specify values for both paint and boundary when used This command Ppaint boundary does not paint color tiling Numeric Arguments Numeric arguments can be constants like 123 or variable where variable is the name of a variable When you use the second syntax variable the semicolon must be used Otherwise the semicolon is optional between commands You can also specify var
61. starting address in the GW BASIC data segment If the argument is a string literal in the program the string descriptor points to program text Be careful not to alter or destroy programs this way see the preceding CALL statement Usually the value returned by a USR function call is the same type integer string single precision or double precision as the argument that was passed to it The registers that must be preserved are the same as in the CALL statement A far return is required to exit the USR subroutine The returned value must be stored in the FAC D 4 Programs That Call Assembly Language Programs This section contains two sample GW BASIC programs that e load an assembly language routine to add two numbers together e return the sum into memory e remain resident in memory The code segment and offset to the first routine is stored in interrupt vector at 0 100H Example 1 calls an assembly language subroutine Example 1 10 DEF SEG 0 100 CS PEEK amp H102 PHEK amp H103 256 200 OFFSET PEEK amp H100 PEEK amp H101 256 250 DEF SEG 300 C1ls 2 C23 3 C3s 400 TWOSUM OFFSET 900 DEF SEG CS 600 CALL TWOSUM C1 C2 C3 700 PRINT C3 800 END The assembly language subroutine called in the above program must be assembled linked and file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20D html 6 of 8 28 03 2004 21 29 05 GW BASIC User s Guide converted to a COM file The
62. statements and other statements functions commands and variables mentioned in this text refer to the GW BASIC User s Reference Some examples of redirection follow GWBASIC MYPROG gt DATA OUT Data read by the INPUT and LINE INPUT statements continues to come from the keyboard Data output by the PRINT statement goes into the data out file gwbhasic MYPROG lt DATA IN Data read by the INPUT and LINE INPUT statements comes from data in Data output by PRINT continues to go to the screen gwbasic MYPROG lt MYINPUT DAT gt MYOUTPUT DAT Data read by the INPUT and LINE INPUT statements now come from the file myinput dat and data output by the PRINT statements goes into myoutput dat gwbasic MYPROG lt SALES JOHN TRANS DAT gt gt SALES SALES DAT Data read by the INPUT and LINE INPUT statements now comes from the file sales john trans dat Data output by the PRINT statement is appended to the file sales sales dat 2 4 GW BASIC Statements Functions Commands and Variables A GW BASIC program is made up of several elements keywords commands statements functions and variables 2 4 1 Keywords GW BASIC keywords such as PRINT GOTO and RETURN have special significance for the GW BASIC Interpreter GW BASIC interprets keywords as part of statements or commands Keywords are also called reserved words They cannot be used as variable names or the system will interpret them as commands However keywords may be embedded wi
63. values and CVD for double precision values PRINT NS PRINT CVS AS The program in Example 5 accesses the random file infofile that was created in Example 4 By inputting the 3 digit code the information associated with that code is read from the file and displayed Example 5 10 20 30 40 50 60 70 80 OPEN FIELD INPUT GET PRINT PRINT PRINT GOTO R 1 INFOFILE 32 tly 20 AS Ne 4 AS Aas B AS PS 2 DIGIT CODE CODES I CODES NS USING SS CVS AS PS PRINT 30 With random files the Loc function returns the current record number The current record number is the last record number used in a GET or PUT statement For example the following line ends program execution if the current record number in file 1 is higher than 99 IF LOC 1 gt 99 THEN END Example 6 is an inventory program that illustrates random file access In this program the record number is used as the part number and it is assumed that the inventory will contain no more than 100 different part numbers Lines 900 960 initialize the data file by writing CHR 255 as the first character of each record This is used later line 270 and line 500 to determine whether an entry already exists for that part file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 205 html 7 of 9 28 03 2004 21 29 02 GW BASIC User s Guide number Lines 130 220 display the different inventory functions that the p
64. 0 464660 596326 119426 709225 RUN 903506 1162462 9293604 292443 322921 Example 2 The internal clock can be used for random number seed file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic RANDOMIZE html 1 of 2 28 03 2004 21 29 43 GW BASIC User s Guide 5 N VAL MIDS TIMES 7 2 get seconds for seed 10 RANDOMIZE N install number 20 PRINT N print seconds 30 PRINT RND print random number generated RUN 36 2466638 RUN Sgi 6530511 RUN 38 5 943847E 02 RUN 40 sBigz2lsi file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic RANDOMIZE html 2 of 2 28 03 2004 21 29 43 GW BASIC User s Guide RND Function Purpose To return a random number between 0 and 1 Syntax RND x Comments The same sequence of random numbers is generated each time the program is run unless the random number generator is reseeded see RANDOMIZE statement If x is equal to zero then the last number is repeated If x is greater than 0 or if x is omitted the next random number in the sequence is generated To get a random number within the range of zero through n use the following formula INT RND n 1 The random number generator may be seeded by using a negative value for x Examples 10 FOR I 1 TO 5 20 PRINT INT RND 101 30 NEXT RUN 93 30 31 5L 5 Generates five pseudo random numbers within the range of 0 100 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic R
65. 00 1396 900 1568 000 1760 000 1975 500 By doubling or halving the frequency the coinciding note values can be estimated for the preceding and following octaves To produce periods of silence use the following statement SOUND 32767 duration To calculate the duration of one beat divide beats per minute into the number of clock ticks in a minute 1092 The following table illustrates tempos requested by clock ticks Table 6 Tempos Requested by Clock Ticks Tempo very slow slow medium fast very fast Notation Larghissimo Largo Larghetto Grave Lento Adagio Adagietto Andante Andantino Moderato Allegretto Allegro Vivace Veloce Presto Prestissimo Beats Minute 40 66 60 66 66 76 76 108 108 120 120 168 168 208 Ticks Beat 27 3 18 2 18 2 16 55 16 55 14 37 14 37 10 11 10 11 9 1 9 1 6 5 6 5 5 25 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SOUND html 2 of 2 28 03 2004 21 29 47 GW BASIC User s Guide SPACE Function Purpose To return a string of x spaces Syntax SPACES x Comments x is rounded to an integer and must be within the range of 0 to 255 see SPC function Examples 10 FOR N 1 TO 5 20 XS SPACES N 30 PRINT XS N 40 NEXT N RUN Line 20 adds one space for each loop execution file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SPACES htm128 03 2004 21 29 47 GW BAS
66. 000 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic END htm128 03 2004 21 29 23 GW BASIC User s Guide ENVIRON Statement Purpose To allow the user to modify parameters in GW BASIC s environment string table This may be to change the path parameter for a child process see ENVIRONS SHELL and the MS DOS utilities PATH command or to pass parameters to a child by inventing a new environment parameter Syntax ENVIRON string Comments string isa valid string expression containing the new environment string parameter string must be of the following form parmid text where parmid is the name of the parameter such as PATH parmid must be separated from text by an equal sign or a blank ENVIRON takes everything to the left of the first blank or equal sign as the parmid everything following is taken as text text is the new parameter text If text is a null string or consists only of a single semicolon then the parameter including parmid is removed from the environment string table and the table is compressed text must not contain any embedded blanks If parmid does not exist then st ring is added at the end of the environment string table If parmid does exist it is deleted the environment string table is compressed and the new string is added at the end Examples Assuming the environment string table is empty the following statement will create a default path to the root directory on Disk A E
67. 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 205 html 3 of 9 28 03 2004 21 29 02 GW BASIC User s Guide The program in Example 2 reads sequentially every item in the file When all the data has been read line 20 causes an Input past end error To avoid this error insert line 15 which uses the EOF function to test for end of file 15 IF EOF 1 THEN END and change line 40 to GOTO 15 A program that creates a sequential file can also write formatted data to the diskette with the PRINT USING statement For example the following statement could be used to write numeric data to diskette without explicit delimiters PRINT 1 USING A B C D The comma at the end of the format string serves to separate the items in the disk file The Loc function when used with a sequential file returns the number of 128 byte records that have been written to or read from the file since it was opened 5 2 3 Adding Data to a Sequential File When a sequential file is opened in O mode the current contents are destroyed To add data to an existing file without destroying its contents open the file in append A mode The program in Example 3 can be used to create or to add onto a file called names This program illustrates the use of LINE INPUT LINE INPUT will read in characters until it sees a carriage return indicator or until it has read 255 characters It does not stop at quotation marks or commas Example 3 10 ON ER
68. 28 58 GW BASIC User s Guide STRIG Trapping Using STRIG n ON activates the interrupt routine that checks the trigger status Down strokes that cause trapping will not set STRIG 0 STRIG 2 STRIG 4 or STRIG 6 functions TIMER Trapping An ON TIMER n event trapping statement is used with applications needing an internal timer The trap occurs when n seconds have elapsed since the TIMER ON statement Example 1 This is a very simple terminal program 10 20 30 40 50 60 70 80 90 REM ON COM n EXAMPLE OPEN COM1 9600 O 7 AS 1 ON COM 1 GOSUB 80 COM 1 ON REM TRANSMIT CHARACTERS FROM KEYBOARD AS INKEYS IF AS THEN 50 PRINT 1 AS GOTO 50 REM DISPLAY RECEIVE CHARACTERS ALL LOC 1 IF ALL lt 1 THEN RETURN 100 BS INPUTS ALL 1 PRINT BS RETURN Example 2 Prevents a CTRL BREAK or system reset during a program 10 20 30 40 50 60 KEY 15 CHRS 4 CHRS 70 REM Trap BREAK KEY 16 CHRS 12 CHRS 83 REM Trap system reset ON REY 15 GOSUB 1000 ON KEY 16 GOSUB 2000 KEY 13 ON KEY 16 ON 1000 PRINT I m sorry I can t let you do that 1010 RETURN 2000 ATTEMPS ATTEMPS 1 2010 ON ATTEMPS GOTO 2100 2200 2300 2400 2500 2100 PRINT Mary had a little lamb RETURN 2200 PRINT Its fleece was white as snow RETURN 2300 PRINT And everywhere that Mary went RETURN 2400 PRINT The lamb was sure to go RETURN file Cl Documents 20and 20Settings Lorenzo Desktop GW 20
69. 7 R20 D327 G4 PAINT 131 119 80 DIM A 500 oO GET 125 130 170 60 A 100 FOR I 1 TO 1000 NEXT I 110 PUT 20 20 A PSET 120 FOR 1 TO 1000 NEXT i 140 FOR I 1 TO 1000 NEXT I 150 PUT 220 130 A PRESET t30 GEL 125 130 170 20 A file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PUTG html 2 of 2 28 03 2004 21 29 43 GW BASIC User s Guide RANDOMIZE Statement Purpose To reseed the random number generator Syntax RANDOMIZE expression RANDOMIZE TIMER Comments If expression is omitted GW BASIC suspends program execution and asks for a value by displaying the following line Random number seed 32768 to 32767 If the random number generator is not reseeded the RND function returns the same sequence of random numbers each time the program is run To change the sequence of random numbers every time the program is run place a RANDOMIZE statement at the beginning of the program and change the argument with each run see RND function RANDOMIZE with no arguments will prompt you for a new seed RANDOMIZE expression will not force floating point values to integer expression may be any numeric formula To get a new random seed without prompting use the new numeric TIMER function as follows RANDOMIZE TIMER Example 1 The internal clock can be set at intervals 10 RANDOMIZE TIMER 20 FOR I 1 to 5 30 PRINT RND 40 NEXT I RUN sOG07
70. 9 48 GW BASIC User s Guide VAL Function Purpose Returns the numerical value of string x Syntax VAL x Comments The VAL function also strips leading blanks tabs and line feeds from the argument string For example the following line returns 3 VAL t 3 The STRS function for numeric to string conversion is the complement to the VAL x function If the first character of x is not numeric the VAL x will return zero Examples 10 READ NAMES CITYS STATES ZIPS 20 IF VAL ZIPS lt 90000 OR VAL ZIP gt 96699 THEN PRINT NAMES TAB 25 OUT OF STATE 30 IF VAL ZIPS gt 90801 AND VAL ZIPS lt 90815 THEN PRINT NAMES TAB 25 LONG BEACH file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic V AL htm128 03 2004 21 29 48 GW BASIC User s Guide STRIG Statement and Function Purpose To return the status of the joystick triggers Syntax As a Statement STRIG ON STRIG OFF As a function X STRIG n Comments STRIG ON must be executed before any STRIG n function calls may be made Once STRIG ON is executed GW BASIC will check to see if a button has been pressed before every statement is executed STRIG OFF disables the checking x is a numeric variable for storing the result n is a numeric expression within the range of 0 to 7 that returns the following values Value of n Returns 1 if trigger Al is currently pressed returns 1 if trigger B1 is currently pr
71. AS BS 30 PRINT NEW AS BS5 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 6 html 11 of 12 28 03 2004 21 29 00 GW BASIC User s Guide RUN FILENAME NEW FILENAME file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 6 html 12 of 12 28 03 2004 21 29 00 GW BASIC User s Guide DIM Statement Purpose To specify the maximum values for array variable subscripts and allocate storage accordingly Syntax DIM variable subscripts variable subscripts Comments If an array variable name is used without a DIM statement the maximum value of its subscript s is assumed to be 10 If a subscript greater than the maximum specified is used a Subscript out of range error occurs The maximum number of dimensions for an array is 255 The minimum value for a subscript is always 0 unless otherwise specified with the OPTION BASE statement An array once dimensioned cannot be re dimensioned within the program without first executing a CLEAR or ERASE statement The DIM statement sets all the elements of the specified arrays to an initial value of zero Examples 10 DIM A 20 20 FOR I 0 TO 20 30 READ A T 40 NEXT I This example reads 21 DATA statements elsewhere in the program and assigns their values to A 0 through A 20 sequentially and inclusively If the A array is single precision default accuracy then line 10 will allocate 84 bytes of memory to this array 4 b
72. Adapter CGA and Color Display are typically paired with each other This hardware configuration permits the running of text mode programs and both medium resolution and high resolution graphics programs EGA with Color Display Modes 0 1 2 7 and 8 The five screen modes 0 1 2 7 and 8 allow you to interface to the IBM Color Display when it is connected to an IBM Enhanced Graphics Adapter EGA If EGA switches are set for CGA compatibility programs written for modes 1 and 2 will run just as they would with the CGA Modes 7 and 8 are similar to modes 1 and 2 except that a wider range of colors is available in modes 7 and 8 EGA with Enhanced Color Display Modes 0 1 2 7 and 8 With the EGA IBM Enhanced Display configuration modes 0 1 2 7 and 8 are virtually identical to their EGA Color Display counterparts Two possible differences are as follows e In mode 0 the border color cannot be the same as for the EGA Color Display because the border cannot be set on an Enhanced Color Display when it is in 640 x 350 text mode e The quality of the text is better on the Enhanced Color Display an 8 x 14 character box for Enhanced Color Display versus an 8 x 8 character box for color display file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SCREENS html 1 of 7 28 03 2004 21 29 16 GW BASIC User s Guide EGA with Enhanced Color Display Mode 9 The full capability of the Enhanced Color Display is taken advantage o
73. An area on a fixed disk set aside for a specific purpose such as a location for an operating system peripheral An external input output or storage device pixel The acronym for picture element A pixel is a single dot on a monitor that can be addressed by a single bit port The entry channel to and from the central computer for connection of a communications line or other peripheral device power The functional area of a system that transforms an external power source into internal DC supply voltage program A series of instructions or statements in a form acceptable to a computer designed to cause the computer to execute a series of operations Computer programs include software such as operating systems assemblers compilers interpreters data management systems utility programs sort merge programs and maintenance diagnostic programs as well as application programs such as payroll inventory control and engineering analysis programs prompt A character or series of characters that appear on the screen to request input from the user RAM Acronym for random access memory radian The natural unit of measure of the angle between two intersecting half lines on the angles from one half line to another intersecting half line It is the angle subtended by an arc of a circle equal in length to the radius of the circle As the circumference of a circle is equal to 27 times its radius the number of radians in an angle of 360 or
74. B X Y X 3 Y 2 420 T FNAB R S Line 410 defines the user defined function FNAB The function is called in line 420 When executed the variable T will contain the value R3 divided by S2 or 25 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DEFFN html 2 of 2 28 03 2004 21 29 01 GW BASIC User s Guide Chapter 5 Creating and Using Files There are two types of files in MS DOS systems e Program files which contain the program or instructions for the computer e Data files which contain information used or created by program files 5 1 Program File Commands The following are the commands and statements most frequently used with program files The GW BASIC User s Reference contains more information on each of them SAVE filename a p Writes to diskette the program currently residing in memory LOAD filename r Loads the program from a diskette into memory LOAD deletes the current contents of memory and closes all files before loading the program RUN filename r Loads the program from a diskette into memory and runs it immediately RUN deletes the current contents of memory and closes all files before loading the program MERGE filename Loads the program from a diskette into memory but does not delete the current program already in memory KILL filename Deletes the file from a diskette This command can also be used with data files NAME old filename AS new filename Changes the name of
75. BX will point at the fifth byte of the FAC Figure D 3 shows the representation of all the GW BASIC number types in the FAC Figure 3 Figure D 3 Number Types in the Floating Point Accumulator not shown If the argument is a single precision floating point number e BX 3 is the exponent minus 128 The binary point is to the left of the most significant bit of the mantissa e BX 2 contains the highest seven bits of mantissa with leading 1 suppressed implied Bit 7 is the sign of the number O positive 1 negative e BX 1 contains the middle 8 bits of the mantissa e BX 0 contains the lowest 8 bits of the mantissa If the argument is an integer e BX 1 contains the upper eight bits of the argument e BX 0 contains the lower eight bits of the argument If the argument is a double precision floating point number e BX 0 through BX 3 are the same as for single precision floating point file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20D html 5 of 8 28 03 2004 21 29 05 GW BASIC User s Guide e BX 1 to BX 4 contain four more bytes of mantissa BX 4 contains the lowest eight bits of the mantissa If the argument is a string indicated by the value 3 stored in the AL register the DX register pair points to three bytes called the string descriptor Byte 0 of the string descriptor contains the length of the string 0 to 255 Bytes 1 and 2 respectively are the lower and upper eight bits of the string
76. Basic ONCOMN html 4 of 5 28 03 2004 21 28 58 GW BASIC User s Guide 2500 KEY 16 OFF REM If they hit us once more 2510 RETURN REM then BASIC dies Example 3 Displays the time of day on line 1 every minute 10 ON TIMER 60 GOSUB 10000 20 TIMER ON 10000 10010 10020 10030 10040 OLDROW CSRLIN REM Saves the current row OLDCOL POS 0 REM Saves the current column LOCATE 1 1 PRINT TIMES LOCATE OLDROW OLDCOL REM Restores row and column RETURN file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ONCOMN html 5 of 5 28 03 2004 21 28 58 GW BASIC User s Guide KEY n Statement Purpose To initiate and terminate key capture in a GW BASIC program Syntax KEY n ON KEY n OFF KEY n STOP Comments nis anumber from to 20 that indicates which key is to be captured Keys are numbered as follows Key NumberKey 1 10 Function keys F1 through F10 11 CURSOR UP 12 CURSOR LEFT 13 CURSOR RIGHT 14 CURSOR DOWN 15 20 Keys defined in the following format see KEY statement KEY n CHR hex code CHRS scan code Execution of the KEY n ON statement is required to activate keystroke capture from the function keys or cursor control keys When the KEY n ON statement is activated and enabled GW BASIC checks each new statement to see if the specified key is pressed If so GW BASIC performs a GOSUB to the line number specified in the ON KEY n statement An ON KEY n statement must preced
77. C function for ASCII to numeric conversion ASCII Codes are listed in Appendix C of the GW BASIC User s Guide Examples PRINT CHRS 66 B This prints the ASCII character code 66 which is the uppercase letter B PRINT CHR 13 This command prints a carriage return file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CHRS htm128 03 2004 21 29 12 GW BASIC User s Guide ATN Function Purpose To return the arctangent of x when x is expressed in radians Syntax ATN x Comments The result is within the range of 7 2 to 7 2 The expression x may be any numeric type The evaluation of ATN is performed in single precision unless the d switch is used when GW BASIC is executed To convert from degrees to radians multiply by 7 180 Examples 10 INPUT X 20 PRINT ATN X RUN 2 2 1 249046 Prints the arctangent of 3 radians 1 249046 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ATN htm128 03 2004 21 29 12 GW BASIC User s Guide AUTO Command Purpose To generate and increment line numbers automatically each time you press the RETURN key Syntax AUTO line number increment AUTO increment Comments AUTO is useful for program entry because it makes typing line numbers unnecessary AUTO begins numbering at line number and increments each subsequent line number by increment The default for both values is 10 The period can be used as a sub
78. CCC Draws a vertical dotted line down the center of the screen in SCREEN 1 220 SCREEN 2 230 LINE 300 100 400 50 B amp HAAAA Draws a rectangle with a dotted line in SCREEN 2 LINE 0 0 160 100 3 eHePr00 Draws a dotted line from the upper left corner to the screen center file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LINE html 3 of 3 28 03 2004 21 29 17 GW BASIC User s Guide PAINT Statement Purpose To fill in a graphics figure with the selected attribute Syntax PAINT x start yv start paint actribute border attribute bckornd attribute Comments The PAINT statement fills in an arbitrary graphics figure of the specified border attribute with the specified paint attribute If paint attribute is not given it will default to the foreground attribute 3 or 1 border attribute defaults to paint attribute See the COLOR and PALETTE statements for more information PAINT must start on a non border point otherwise PAINT will have no effect PAINT can fill any figure but painting jagged edges or very complex figures may result in an Out of memory error The CLEAR statement may be used to increase the amount of stack space available Points that are specified outside the limits of the screen will not be plotted and no error will occur See the SCREEN statement for a description of the different screen modes Paint Tiling PAINT tiling is similar to LINE styling Like
79. Comments action verb may be PSET PRESET AND OR XOR The x y are the coordinates of the top left corner of the image to be transferred The PUT and GET statements transfer graphics images to and from the screen PUT and GET make possible animation and high speed object motion in either graphics mode The PUT statement transfers the image stored in the array onto the screen The specified point is the coordinate of the upper left corner of the image An Illegal function call error results if the image to be transferred is too large to fit onto the screen The action verb is used to interact the transferred image with the image already on the screen P SET transfers the data onto the screen verbatim PRESET is the same as PSET except that an inverse image black on white is produced AND transfers the image only if an image already exists under the transferred image OR superimposes the image onto the existing image XOR is a special mode often used for animation XOR causes the points on the screen to be inverted where a point exists in the array image This behavior is exactly like the cursor on the screen XOR is especially useful for animation When an image is put against a complex background twice the background is restored unchanged An object can be moved around the screen without obliterating the background The default action mode is XOR For more information about effects within the different modes see the COLOR PALETTE and
80. E INPUT file number string variable Comments file number is the number under which the file was opened string variable is the variable name to which the line will be assigned LINE INPUT reads all characters in the sequential file up to a carriage return If a line feed carriage return sequence this order only is encountered it is input LINE INPUT is especially useful if each line of a data file has been broken into fields or if a BASIC program saved in ASCII mode is being read as data by another program Examples 10 OPEN 6 1 INFO 20 LINE INPUT CUSTOMER INFORMATION CS 30 PRINT 1 C 40 CLOSE 1 50 OPEN TI 1 INFO 60 LINE INPUT 1 C 70 PRINT C 80 CLOSE 1 RUN CUSTOMER INFORMATION If the operator enters LINDA JONES 234 4 MEMPHIS then the program continues with the following LINDA JONES 234 4 MEMPHIS file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LINEINPUTF htm128 03 2004 21 29 35 GW BASIC User s Guide LIST Command Purpose To list all or part of a program to the screen line printer or file Syntax LIST line number line number filename LIST line number filename Comments linenumber is a valid line number within the range of 0 to 65529 If filename is omitted the specified lines are listed to the screen Use the hyphen to specify a line range If the line range is omitted the entire program is listed linenumber lists that line and all hi
81. ELETE htm128 03 2004 21 29 23 GW BASIC User s Guide EDIT Command Purpose To display a specified line and to position the cursor under the first digit of the line number so that the line may be edited Syntax EDIT line number EDIT Comments line number is the number of a line existing in the program A period refers to the current line The following command enters EDIT at the current line EDIT When a line is entered it becomes the current line The current line is always the last line referenced by an EDIT statement LIST command or error message If line number refers to a line which does not exist in the program an Undefined Line Number error occurs Examples EDIT 150 Displays program line number 150 for editing file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic EDIT htm128 03 2004 21 29 23 GW BASIC User s Guide END Statement Purpose To terminate program execution close all files and return to command level Syntax END Comments END statements may be placed anywhere in the program to terminate execution Unlike the STOP statement END does not cause a Break in line xxxx message to be printed An END statement at the end of a program is optional GW BASIC always returns to command level after an END is executed END closes all files Examples 520 IF K gt 1000 THEN END ELSE GOTO 20 Ends the program and returns to command level whenever the value of K exceeds 1
82. EN Statement Purpose To establish input output I O to a file or device Syntax OPEN mode file number filename reclen OPEN filename FOR mode ACCESS access lock AS file number LEN reclen Comments filename is the name of the file mode first syntax is a string expression with one of the following characters Expression Specifies O Sequential output mode I Sequential input mode R Random input output mode A Position to end of file mode second syntax determines the initial positioning within the file and the action to be taken if the file does not exist If the FOR mode clause is omitted the initial position is at the beginning of the file If the file is not found one is created This is the random I O mode That is records may be read or written at any position within the file The valid modes and actions taken are as follows INPUT Position to the beginning of the file A File not found error is given if the file does not exist OUTPUT Position to the beginning of the file If the file does not exist one is created APPEND Position to the end of the file If the file does not exist one is created RANDOM Specifies random input or output mode mode must be a string constant Do not enclose mode in double quotation marks access can be one of the following READ WRITE READ WRITE file number is a number between 1 and the maximum number of files allowed The number associates an I O buf
83. FILES ACCTS Lists all files in the directory named accts FILES B ACCTS PAY Lists all files in the directory named accts that are on the diskette in drive B and have the extension of PAY file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic FILES htm128 03 2004 21 29 27 GW BASIC User s Guide FOR NEXT Statements Purpose To execute a series of instructions a specified number of times in a loop Syntax FOR variable x TO y STEP z NEXT variable variable Comments variable is used as a counter x y and z are numeric expressions STEP z specifies the counter increment for each loop The first numeric expression x is the initial value of the counter The second numeric expression y is the final value of the counter Program lines following the FOR statement are executed until the NEXT statement is encountered Then the counter is incremented by the amount specified by STEP If STEP is not specified the increment is assumed to be 1 A check is performed to see if the value of the counter is now greater than the final value y If it is not greater GW BASIC branches back to the statement after the FOR statement and the process is repeated If it is greater execution continues with the statement following the NEXT statement This is a FOR NEXT loop The body of the loop is skipped if the initial value of the loop times the sign of the step exceeds the final value times th
84. FOR S 1 TO R 30 PRINT S 40 NEXT S In the next example the loop executes 10 times The final value for the loop variable is always set before the initial value is set 10 S 5 20 FOR S 1 TO S 5 30 PRINT S 40 NEXT RUN 12345 6 7 8 9 10 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic FORNEXT html 2 of 2 28 03 2004 21 29 27 GW BASIC User s Guide FRE Function Purpose To return the number of available bytes in allocated string memory Syntax FRE x FRE x Comments Arguments x and x are dummy arguments Before FRE x returns the amount of space available in allocated string memory GW BASIC initiates a garbage collection activity Data in string memory space is collected and reorganized and unused portions of fragmented strings are discarded to make room for new input If FRE is not used GW BASIC initiates an automatic garbage collection activity when all string memory space is used up GW BASIC will not initiate garbage collection until all free memory has been used Garbage collection may take 1 to 1 5 minutes FRE or any string forces a garbage collection before returning the number of free bytes Therefore using FRE periodically will result in shorter delays for each garbage collection It should be noted that the ctrl break function cannot be used during this housecleaning process Examples PRINT FRE 0 14542 Your computer may return a different value file
85. GWBASIC User s Manual User s Guide Chapters 1 Welcome 2 Getting Started 3 Reviewing and Practicing 4 The Screen Editor 5 Creating and Using Files 6 Constants Variables Expressions and Operators Appendicies A Error Codes and Messages B Mathematical Functions C ASCII Character Codes D Assembly Language E Converting Programs F Communications G Hexadecimal Equivalents H Key Scan Codes I Characters Recognized Glossary User s Reference ABS Function ASC Function ATN Function AUTO Command BEEP Statement BLOAD Command BSAVE Command CALL Statement CDBL Function CHAIN Statement CHDIR Command CHR Function CINT Function GW BASIC User s Guide Microsoft Corporation Information in this document is subject to change without notice and does not represent a commitment on the part of Microsoft Corporation The software described in this document is furnished under a license agreement or nondisclosure agreement It is against the law to copy this software on magnetic tape disk or any other medium for any purpose other than the purchaser s personal use Copyright Microsoft Corporation 1986 1987 All rights reserved Portions copyright COMPAQ Computer Corporation 1985 Simultaneously published in the United States and Canada Microsoft MS DOS GW BASIC and the Microsoft logo are registered trademarks of Microsoft Corporation Compaq is
86. IC User s Guide SPC Function Purpose To skip a specified number of spaces in a PRINT or an LPRINT statement Syntax SPC n Comments n must be within the range of 0 to 255 If n is greater than the defined width of the printer or the screen the value used will be n MOD width A semicolon is assumed to follow the SPC n command SPC may only be used with PRINT LPRINT and PRINT statements see the SPACES function Examples PRINT OVER SPC 15 THERE OVER THERE file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SPC htm128 03 2004 21 29 47 GW BASIC User s Guide SQR Function Purpose Returns the square root of x Syntax SOR x Comments x must be greater than or equal to 0 SQR x is computed in single precision unless the d switch is used when GW BASIC is executed Examples 10 FOR X 10 TO 25 STEP 5 20 PRINT X SOR X 30 NEXT RUN LO 3162218 15 3 872984 20 4 472136 29 5 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SQR htm128 03 2004 21 29 47 GW BASIC User s Guide STICK Function Purpose To return the x and y coordinates of two joysticks Syntax X STICK n Comments x is anumeric variable for storing the result n is a valid numeric expression within the range of 0 to 3 Value of n Coordinate Returned x coordinate of joystick A Stores the x and y values for both joysticks for the following three function calls 1
87. LET statement This causes the pointer for that variable to point into string space instead of the random file buffer Example 4 10 OPEN R 1 YINFOFILE 32 20 FIELD 1 20 AS NS 4 AS AS 8 AS PS 30 INPUT 2 DIGIT CODE CODES 40 INPUT NAME XS 50 INPUT AMOUNT AMT 60 INPUT PHONE TELS PRINT 70 LSET N X9 80 LSET AS MKSS AMT 90 LSET PS TELS 100 PUT 1 CODES 110 GOTO 30 5 3 2 Accessing a Random Access File The following program steps are required to access a random file 1 Open the file in R mode OPEN R 1 filename 32 2 Use the FIELD statement to allocate space in the random buffer for the variables that will be read from the file FIELD 1 20 AS NS 4 AS AS 8 AS PS In this example the first 20 positions bytes in the random file buffer are allocated to the string variable N The next 4 positions are allocated to A the next 8 to P Note file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 205 html 6 of 9 28 03 2004 21 29 02 GW BASIC User s Guide In a program that performs both INPUT and OUTPUT on the same random file you can often use just one OPEN statement and one FIELD statement 3 Use the GET statement to move the desired record into the random buffer GET 1 CODE The data in the buffer can now be accessed by the program 4 Convert numeric values back to numbers using the convert functions CVI for integers CVS for single precision
88. LINE PAINT looks at a tiling mask each time a point is put down on the screen If paint attribute is omitted the standard foreground attribute is used If paint attribute is a numeric formula then the number must be a valid color and it is used to paint the area as before If paint attribute isa string formula then tiling is performed as follows The tile mask is always eight bits wide and may be from 1 to 64 bytes long Each byte in the tile string masks eight bits along the x axis when putting down points Each byte of the tile string is rotated as required to align along the y axis such that tile_byte_mask y MOD tile_length where y is the position of the graphics cursor on the y axis file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PAINT html 1 of 3 28 03 2004 21 29 17 GW BASIC User s Guide tile length is the length in bytes of the tile string defined by the user 1 to 64 bytes This is done so that the tile pattern is replicated uniformly over the entire screen as if a PAINT 0 0 a4 x Increases gt X Y 00 yt 072 were used 87 65432 1 Ixixixix ixix ix x IXIXIXIXIXIXIXIX xe x x Bit of Tile Byte Tile byte 1 Tile byte 2 Tile byte 3 0 63 Ixixixix ixixixix Tile byte 64 maximum allowed In high resolution mode SCREEN 2 the screen can be painted with Xs by the following statement PAINT 320 100 CHRS H81 CHRS amp H42 CHRS amp H24 CH
89. MENU key was struck instead of RETURN When no more characters are being received LOC x returns 0 then performs a timeout routine If more than 128 characters are waiting signal a pause and send XOFF to the host Read all characters in COM queue LOC x and write them to diskette PRINT 2 until reception is caught up to transmission If a pause is issued restart host by sending XON and clearing the pause flag Continue the process until no characters are received for a predetermined time Time out subroutine The FOR loop count was determined by experimentation If no character is received from the host for 17 20 seconds transmission is assumed complete If any character is received during this time line 610 then set n well above the FOR loop range to exit loop and return to caller If host transmission is complete close the disk file and resume regular activities Transmit routine Until end of disk file read one character into AS with INPUT statement Send character to COM device in 1020 Send a Z at end of file in 1040 in case receiving device needs one to close its file Lines 1050 and 1060 close disk file print completion message and go back to conversation mode in line 200 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20F html 6 of 7 28 03 2004 21 28 59 GW BASIC User s Guide 9999 Presently not executed As an exercise add some lines to the routine 400 420 to exit the program via
90. ND htm128 03 2004 21 29 44 GW BASIC User s Guide REM Statement Purpose To allow explanatory remarks to be inserted in a program Syntax REM comment comment Comments REM statements are not executed but are output exactly as entered when the program is listed Once a REM or its abbreviation an apostrophe is encountered the program ignores everything else until the next line number or program end is encountered REM statements may be branched into from a GOTO or GOSUB statement and execution continues with the first executable statement after the REM statement However the program runs faster if the branch is made to the first statement Remarks may be added to the end of a line by preceding the remark with an apostrophe instead of REM Note Do not use REM in a DATA statement because it will be considered to be legal data Examples 120 REM CALCULATE AVERAGE VELOCITY 130 FOR I 1 TO 20 440 SUM SUM V I 450 NEXT I or file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic REM html 1 of 2 28 03 2004 21 29 44 GW BASIC User s Guide 129 FOR I 1 TO 20 CALCULATED AVERAGE VELOCITY 130 SUM SUM V I 140 NEXT I file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic REM html 2 of 2 28 03 2004 21 29 44 GW BASIC User s Guide RENUM Command Purpose To renumber program lines Syntax RENUM new number old number incrementR Comments new number
91. NVIRON PATH A If your work subdirectory were john you would be able to get DEBUG from the root A new parameter may be added ENVIRON COMSPEC A COMMAND COM The environment string table now contains file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic EN VIRON html 1 of 2 28 03 2004 21 29 23 GW BASIC User s Guide PATH A COMSPEC A COMMAND COM The path may be changed to a new value ENVIRON PATH A SALES A ACCOUNTING The path parameter may be appended by using the ENVIRONS function with the ENVIRON statement ENVIRON PATH ENVIRONS PATH B SAMPLES Finally delete the parameter COMSPEC ENVIRON COMSPEC The environment string table now contains PATH A SALES A ACCOUNTING B SAMPLES file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic EN VIRON html 2 of 2 28 03 2004 21 29 23 GW BASIC User s Guide ENVIRONS Function Purpose To allow the user to retrieve the specified environment string from the environment table Syntax vS ENVIRONS parmid VS ENVIRONS nt hparm Comments parmidis a valid string expression containing the parameter to search for nthparm is an integer expression in the range of 1 to 255 If a string argument is used ENVIRONS returns a string containing the text following parmid from the environment string table If parmid is not found then a null string is returned If a numeric argument is used ENVIRONS returns a string containi
92. OCTLS Function KEY Statement KEY n Statement KILL Command LEFT Function LEN Function LET Statement LINE Statement LINE INPUT Statement LINE INPUT Statement LIST Command LLIST Command LOAD Command LOC Function LOCATE Statement LOCK Statement LOF Function LOG Function LPOS Function LPRINT Statement file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic index html 3 of 6 28 03 2004 21 28 55 GWBASIC User s Manual LPRINT USING Statement LSET Statement MERGE Command MID Function MID Statement MKDIR Command MKD Function MKIS Function MKS Function NAME Command NEXT Statement NEW Command OCT Function N COM n Statement KEY n Statement PEN Statement PLAY n Statement N STRIG n Statement N TIMER n Statement T ERROR GOTO Statement N GOSUB Statement N GOTO Statement OPEN Statement OPEN COM n Statement OPTION BASE Statement OUT Statement zZ O IO JO O O O Z Z O O O PAINT Statement PALETTE Statement PALETTE USING Statement PCOPY Command PEEK Function PEN Statement and Function PLAY Statement PLAY n Function PMAP Function POINT Function POKE Statement POS Function PRESET Statement file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic index html 4 of 6 28 03 2004 21 28 55 GWBASIC User s Manual PSET Statement PRINT Statement PRINT USING Statement
93. PEN I 1 DATA 20 C 0 30 IF EOF 1 THEN 100 40 INPUT 1 M C 50 C C 1 GOTO 30 100 END The file named DATA is read into the M array until the end of the file is reached then the program branches to line 100 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic EOF htm128 03 2004 21 29 24 GW BASIC User s Guide ERASE Statement Purpose To eliminate arrays from a program Syntax ERASE list of array variables Comments Arrays may be re dimensioned after they are erased or the memory space previously allocated to the array may be used for other purposes If an attempt is made to re dimension an array without first erasing it an error occurs Examples 200 DIM B 250 450 ERASE A B 460 DIM B 3 4 Arrays A and B are eliminated from the program The B array is re dimensioned to a 3 column by 4 row array 12 elements all of which are set to a zero value file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ERASE htm128 03 2004 21 29 24 GW BASIC User s Guide ERDEV and ERDEVS Variables Purpose To return the actual value ERDEV of a device error and the name of the device ERDEVS causing the error Syntax ERDEV ERDEVS Comments ERDEV will contain the error code from interrupt 24H in the lower 8 bits Bits 8 to 15 from the attribute word in the Device Header Block are mapped directly into the upper 8 bits ERDEVS will contain the 8 byte character device name
94. PUT statement requires double quotation marks Example 1 To find the square of a number 10 INPUT X 20 PRINT X SQUARED IS X 2 30 END RUN The operator types a number 5 in response to the question mark 5 SQUARED IS 25 Example 2 To find the area of a circle when the radius is known 10 PI 3 14 20 INPUT WHAT IS THE RADIUS R 30 A PI R 2 40 PRINT THE AREA OF THE CIRCLE IS A 50 PRINT 60 GOTO 20 RUN WHAT IS THE RADIUS 7 4 THE AREA OF THE CIRCLE IS 171 9464 Note that line 20 in the above example makes use of the built in PRINT statement contained within INPUT file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic INPUT html 2 of 2 28 03 2004 21 29 30 GW BASIC User s Guide PRINT Statement Purpose To output a display to the screen Syntax PRINT list of expressions list of expressions Comments If list of expressions 1s omitted a blank line is displayed If list of expressions is included the values of the expressions are displayed Expressions in the list may be numeric and or string expressions separated by commas spaces or semicolons String constants in the list must be enclosed in double quotation marks For more information about strings see the STRING function A question mark may be used in place of the word PRINT when using the GW BASIC program editor Print Positions GW BASIC divides the line into print zones of 14 spaces The posit
95. R amp H18 CHR S amp H18 CHRS amp H24 CHRS amp H81 This appears on the screen as follows x increases gt OO ise Oy dL X 02 X O3 XIX 0 4 x x O75 De 056 X QT X x CHRS amp H81 Tile byte 1 CHRS amp H42 Tile byte 2 CHRS amp H24 Tile byte 3 CHRS amp H18 Tile byte 4 CHRS amp H18 Tile byte 5 CHRS amp H24 Tile byte 6 CHRS amp H42 Tile byte 7 CHRS amp H81 Tile byte 8 Since there are two bits per pixel in medium resolution mode SCREEN 1 each byte of the tile pattern only describes four pixels In this case every two bits of the tile byte describes one of the four possible colors associated with each of the four pixels to be put down bckgrnd attribute specifies the background tile pattern or color byte to skip when checking for boundary termination bckgrnd attribute is a string formula returning one character When omitted the default is CHRS 0 Occasionally you may want to paint tile over an already painted area that is the same color as two consecutive lines in the tile pattern PAINT quits when it encounters two consecutive lines of the same color as the point being set the point is surrounded It is not possible to draw alternating blue and red lines on a red background without bckgrnd attribute PAINT stops file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PAINT html 2 of 3 28 03 2004 21 29 17 GW BASIC User s Guide as soo
96. RIGHTS functions Examples 10 AS GOoD 20 BS MORNING EVENING AFTERNOON 30 PRINT AS MIDS BS 8 8 RUN GOOD EVENING Line 30 concatenates joins the A string to another string with a length of eight characters beginning at position 8 within the B string file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic MIDSF htm128 03 2004 21 29 34 GW BASIC User s Guide RIGHTS Function Purpose To return the rightmost n characters of string x Syntax RIGHTS xS n Comments If n is equal to or greater than LEN x RIGHTS returns x If n equals zero the null string length zero is returned see the MID and LEFT functions Examples 10 AS DISK BASIC 20 PRINT RIGHTS AS 5 RUN BASIC Prints the rightmost five characters in the A string file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic RIGHTS htm128 03 2004 21 29 34 GW BASIC User s Guide LEN FUNCTION Purpose To return the number of characters in xS Syntax LEN x Comments Nonprinting characters and blanks are counted Example x is any string expression 10 XS PORTLAND OREGON 20 PRINT LEN XS RUN 16 Note that the comma and space are included in the character count of 16 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LEN htm128 03 2004 21 29 34 GW BASIC User s Guide LINE INPUT Statement Purpose To input an entire line up to 255 characters from the keyboard
97. ROR GOTO 2000 20 OPEN A 1 NAMES 110 REM ADD NEW ENTRIES TO FILE 120 INPUT NAME NS 130 IF N THEN 200 CARRIAGE RETURN EXITS INPUT LOOP 140 LINE INPUT ADDRESS AS 150 LINE INPUT BIRTHDAY BS 160 PRINT 1 NS 170 PRINT 1 AS 180 PRINT 1 BS 190 PRINT GOTO 120 200 CLOSE 1 2000 ON ERROR GOTO 0 In lines 10 and 2000 the ON ERROR GOTO statement is being used This statement enables error trapping and specifies the first line 2000 of the error handling subroutine Line 10 enables the file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 205 html 4 of 9 28 03 2004 21 29 02 GW BASIC User s Guide error handling routine Line 2000 disables the error handling routine and is the point where GW BASIC branches to print the error messages 5 3 Random Access Files Information in random access files is stored and accessed in distinct numbered units called records Since the information is called by number the data can be called from any disk location the program needn t read the entire disk as when seeking sequential files to locate data GW BASIC supports large random files The maximum logical record number is 232 1 The following statements and functions are used with random files CLOSEPIELD MKIS CVD LOC MKSS CVI LOCK OPEN CVS LOF Pur EOF LSET RSETUNLOCK ET MKDS 5 3 1 Creating a Random Access File The following program steps are required to create a random data file 1
98. S HEXADECIMAL RUN INPUT DECIMAL NUMBER 32 32 DECIMAL IS 20 HEXADECIMAL file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic HEXS htm128 03 2004 21 29 29 GW BASIC User s Guide OCTS Function Purpose To convert a decimal value to an octal value Syntax OCTS x Comments x is rounded to an integer before OCTS x is evaluated This statement converts a decimal value within the range of 32768 to 65535 to an octal string expression Octal numbers are numbers to the base 8 rather than base 10 decimal numbers See the HEX function for hexadecimal conversion Examples 10 PRINT OCTS 13 RUN 22 Decimal 18 equals octal 22 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic OCTS htm128 03 2004 21 29 29 GW BASIC User s Guide IF THEN ELSE Statement Purpose To make a decision regarding program flow based on the result returned by an expression Syntax ELSE statement s IF expression THEN statement s IF expression GOTO line number ELSE statement s Comments If the result of expression is nonzero logical true the THEN or GOTO line number is executed If the result of expression is zero false the THEN or GOTO line number is ignored and the ELSE line number if present is executed Otherwise execution continues with the next executable statement A comma is allowed before THEN and ELSE THEN and ELSE may be followed by either
99. S htm128 03 2004 21 29 20 GW BASIC User s Guide DATA Statement Purpose To store the numeric and string constants that are accessed by the program READ statement s Syntax DATA constants Comments constants are numeric constants in any format fixed point floating point or integer separated by commas No expressions are allowed in the list String constants in DATA statements must be surrounded by double quotation marks only if they contain commas colons or significant leading or trailing spaces Otherwise quotation marks are not needed DATA statements are not executable and may be placed anywhere in the program A DATA statement can contain as many constants that will fit on a line separated by commas and any number of DATA statements may be used in a program READ statements access the DATA statements in order by line number The data contained therein may be thought of as one continuous list of items regardless of how many items are on a line or where the lines are placed in the program The variable type numeric or string given in the READ statement must agree with the corresponding constant in the DATA statement or a Type Mismatch error occurs DATA statements may be reread from the beginning by use of the RESTORE statement For further information and examples see the RESTORE statement and the READ statement Example 1 80 FOR I 1 TO 10 90 READ A T 100 NEXT I 110 DATA 3 06 5 19
100. SIC be sure all elements on a line are separated by a colon E 4 MAT Functions Programs using the MAT functions available in some GW BASIC languages must be rewritten using FOR NEXT loops to execute properly E 5 FOR NEXT Loops Some GW BASIC languages will always execute a FOR NEXT loop once regardless of the limits GW BASIC checks the limits first and does not execute the loop if past limits file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20E html 2 of 2 28 03 2004 21 29 06 GW BASIC User s Guide Appendix G Hexadecimal Equivalents Table G 1 lists decimal and binary equivalents to hexadecimal values Table G 1 Decimal and Binary Equivalents to Hexadecimal Values Hex Dec Bin 0 0 0000 1 1 0001 2 2 0010 3 3 0011 4 4 0100 5 5 0101 6 6 0110 7 7 0111 8 8 1000 9 9 1001 A 10 1010 B 11 1011 C 12 1100 D 13 1101 E 14 1110 F 15 1111 Table G 2 lists decimal equivalents to hexadecimal values Table G 2 Decimal Equivalents to Hexadecimal Values Hex Dec Hex Dec Hex Dec Hex Dec Hex Dec 0 0 10 16 100 256 1000 4096 1 1 11 17 20 32 200 512 2000 8192 2 2 12 18 30 48 300 768 3000 12288 3 3 13 19 40 64 400 1024 4000 16384 4 4 14 20 50 80 500 1280 5000 20480 5 5 15 21 60 96 600 1536 6000 24576 6 6 16 22 70 112 700 1792 7000 28672 7 7 17 23 80 128 800 2048 8000 32768 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Appendix 20G html 1 of 2 28 03 2004 21 29 06 GW BASIC Use
101. SWAP variablel variable2 Comments Any type variable may be swapped integer single precision double precision string but the two variables must be of the same type or a Type mismatch error results Examples List 10 A 0ONE s BS ALL z Ce FoR 20 PRINT AS CS BS 30 SWAP AS BS 40 PRINT AS CS BS RUN ONE FOR ALL ALL FOR ONE Line 30 swaps the values in the A and B strings file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic S W AP htm128 03 2004 21 29 49 GW BASIC User s Guide SYSTEM Command Purpose To return to MS DOS Syntax SYSTEM Comments Save your program before pressing return or the program will be lost The SYSTEM command closes all the files before it returns to MS DOS If you entered GW BASIC through a batch file from MS DOS the SYSTEM command returns you to the batch file which continues executing at the point it left off Examples SYSTEM A gt file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic S YSTEM htm128 03 2004 21 29 49 GW BASIC User s Guide TAB Function Purpose Spaces to position n on the screen Syntax TAB n Comments If the current print position is already beyond space n TAB goes to that position on the next line Space is the leftmost position The rightmost position is the screen width n must be within the range of 1 to 255 If the TAB function is at the end of a list of data items GW BASIC will
102. T htm128 03 2004 21 29 19 GW BASIC User s Guide COS Function Purpose To return the cosine of the range of x Syntax COS x Comments x must be the radians COS is the trigonometric cosine function To convert from degrees to radians multiply by 7 180 COS x is calculated in single precision unless the d switch is used when GW BASIC is executed Example 1 10 X 2 COS 4 20 PRINT X RUN 1 842122 Example 2 10 PI 3 141593 20 PRINT COS PI 30 DEGREES 180 40 RADIANS DEGREES PI 180 50 PRINT COS RADIANS RUN 1 1 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic COS htm128 03 2004 21 29 19 GW BASIC User s Guide CSRLIN Variable Purpose To return the current line row position of the cursor Syntax y CSRLIN Comments y is anumeric variable receiving the value returned The value returned is within the range of 1 to 25 The CSRLIN variable returns the vertical coordinate of the cursor on the active page see the SCREEN statement x POS 0 returns the column location of the cursor The value returned is within the range of 1 to 40 or 1 to 80 depending on the current screen width see the POS function Examples 10 Y CSRLIN 20 X POS 0 30 LOCATE 24 1 40 PRINT HELLO 50 LOCATE Y X RUN HELLO The CSRLIN variable in line 10 records the current line The POS function in line 20 records the current column In line 40 the PRINT statement displays the c
103. TRS Y file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic V ARPTRS htm128 03 2004 21 29 51 GW BASIC User s Guide VIEW Statement Purpose To define a physical viewport limit from x1 y1 upper left x y coordinates to x2 y2 lower right x y coordinates Syntax VIEW SCREEN xi y1 x2 y2 fi111 border Comments RUN or VIEW with no arguments define the entire screen as the viewport x1 y1 are the upper left coordinates x2 y2 are the lower right coordinates The fi 11 attribute lets you fill the view area with color The border attribute lets you draw a line surrounding the viewport if space for a border is available If border is omitted no border is drawn The x and y coordinates must be within the physical bounds of the screen and define the rectangle within the screen that graphics map into The x and y coordinate pairs will be sorted with the smallest values placed first Points are plotted relative to the viewpoint if the screen argument is omitted that is x1 and y1 are added to the x and y coordinates before the point is plotted It is possible to have a varied number of pairs of x and y The only restriction is that x1 cannot equal x2 and y1 cannot equal y2 Points are plotted absolutely if the SCREEN argument is present Only points within the current viewpoint will be plotted When using VIEW the CLS statement clears only the current viewport To clear the entire sc
104. The degree of freedom from error Accuracy is often confused with precision which refers to the degree of preciseness of a measurement acronym A word formed by the initial letters of words or by initial letters plus parts of several words Acronyms are widely used in computer technology For example COBOL is an acronym for COmmon Business Oriented Language active partition A section of the computer s memory that houses the operating system being used address A name label or number identifying a register location or unit where information is stored algebraic language A language whose statements are structured to resemble the structure of algebraic expression Fortran is a good example of an algebraic language algorithm A set of well defined rules or procedures to be followed in order to obtain the solution of a problem in a finite number of steps An algorithm can involve arithmetic algebraic logical and other types of procedures and instructions An algorithm can be simple or complex However all algorithms must produce a solution within a finite number of steps Algorithms are fundamental when using a computer to solve problems because the computer must be supplied with a specific set of instructions that yields a solution in a reasonable length of time alphabetic file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 1 of 17 28 03 2004 21 29 08 GW BASIC User s Guide Data representation by alph
105. User s Guide INT Function Purpose To truncate an expression to a whole number Syntax INT x Comments Negative numbers return the next lowest number The FIX and CINT functions also return integer values Examples PRINT INT 9 e 89 93 PRINT INT l12 11 I file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic INT htm128 03 2004 21 29 14 GW BASIC User s Guide CSNG Function Purpose To convert x to a single precision number Syntax CSNG x Comments x must be a numeric expression see the CINT and CDBL functions Examples 10 A 975 3421222 20 PRINT A CSNG A RUN Vio oA L222 Biacst2al file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CSNG htm128 03 2004 21 29 14 GW BASIC User s Guide CHAIN Statement Purpose To transfer control to the specified program and pass chain variables to it from the current program Syntax CHAIN MERGE filename line ALL DELETE range Comments MERGE overlays the current program with the called program Note The called program must be an ASCII file previously saved with the a option if it is to be merged see the MERGE command filename is the name of the program that is called to be chained to The BAS extension is assumed unless another is specified line is a line number or an expression that corresponds to a line number in the called program It is the starting point for execution
106. W 20Basic Chapter 6 html 1 of 12 28 03 2004 21 29 00 GW BASIC User s Guide Hexadecimal Hexadecimal numbers with prefix H For example amp H76 amp H32F Octal Octal numbers with the prefix lt 0 or amp For example amp 0347 amp 1234 6 1 1 Single and Double Precision Form for Numeric Constants Numeric constants can be integers single precision or double precision numbers Integer constants are stored as whole numbers only Single precision numeric constants are stored with 7 digits although only 6 may be accurate Double precision numeric constants are stored with 17 digits of precision and printed with as many as 16 digits A single precision constant is any numeric constant with either e Seven or fewer digits e Exponential form using E e A trailing exclamation point A double precision constant is any numeric constant with either e Eight or more digits e Exponential form using D e A trailing number sign The following are examples of single and double precision numeric constants Single Precision ConstantsDouble Precision Constants 46 8 345692811 1 09F 06 09432006 3489 0 3490 04 22 5 7654321 1234 6 2 Variables file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 6 html 2 of 12 28 03 2004 21 29 00 GW BASIC User s Guide Variables are the names that you have chosen to represent values used in a GW BASIC program The value of a variable may be assigned specifical
107. a S MW EW FH file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 205 html 8 of 9 28 03 2004 21 29 02 GW BASIC User s Guide 480 REM ADD TO STOCK 490 GOSUB 840 500 IF ASC FS 255 THEN PRINT NULL ENTRY RETURN 510 PRINT DS INPUT QUANTITY TO ADD A 520 Q CVI OS A 530 LSET QOS MKIS 03 540 PUT 1 PART 550 RETURN 560 REM REMOVE FROM STOCK 570 GOSUB 840 580 IF ASC FS 255 THEN PRINT NULL ENTRY RETURN 590 PRINT D 600 INPUT QUANTITY TO SUBTRACT S3 610 Q CVI Q 620 IF Q S lt 0 THEN PRINT ONLY Q IN STOCK GOTO 600 630 Q 0 S 640 IF Q lt CVI RS THEN PRINT QUANTITY NOW Q REORDER LEVEL CVI RS 650 LSET QS MKIS Q 660 PUT 1 PART 670 RETURN 680 REM DISPLAY ITEMS BELOW REORDER LEVEL4 690 FOR I 1 TO 100 710 GET 1 I1 720 IF CVI O lt CVI RS THEN PRINT DS OQUANTITY CVI Q TAB 50 REORDER LEVEL CVI RS 730 NEXT I 740 RETURN 840 INPUT PART NUMBER PARTS 850 IF PART S lt 1 OR PART S gt 100 THEN PRINT BAD PART NUMBER GOTO 840 ELSE GET 1 PART RETURN 890 END 900 REM INITIALIZE FILE 910 INPUT ARE YOU SURE BS IF BS lt gt Y THEN RETURN 920 LSET FS CHRS 255 930 FOR I 1 TO 100 940 PUT 1 I1 950 NEXT I 960 RETURN file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 205 html 9 of 9 28 03 2004 21 29 02 GW BASIC User s Guide Appendix A Error Codes and Messages Code
108. a registered trademark of COMPAQ Computer Corporation DEC is a registered trademark of Digital Equipment Corporation Document Number 410130001 330 RO02 078 GW BASIC User s Reference Microsoft Corporation Information in this document is subject to change without notice and does not represent a commitment on the part of Microsoft Corporation The software described in this document is furnished under a license agreement or nondisclosure agreement The software may be used or copied only in accordance with the terms of the agreement It is against the law to copy this software on magnetic tape disk or any other medium for any purpose other than the purchaser s personal use file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic index html 1 of 6 28 03 2004 21 28 55 GWBASIC User s Manual CIRCLE Statement CLEAR Command CLOSE Statement CLS Statement COLOR Statement COM n Statement COMMON Statement CONT Command COS Function CSNG Function CSRLIN Variable CVD Function CVI Function CVS Function DATA Statement DATES Statement DEF FN Statement DEFINT Statement DEFDBL Statement DEFSNG Statement DEFSTR Statement DEF SEG Statement DEF USR Statement DELETE Command DIM Statement DRAW Statement EDIT Command END Statement ENVIRON Statement ENVIRON Function EOF Function ERASE Statement ERDEV Variables ERL Variable ERR Variable ERROR Statement EXP Function EXTERR Funct
109. abetical characters in contrast to numerical the letters of the alphabet alphanumeric A contraction of the words alphabetic and numeric a set of characters including letters numerals and special symbols application The system or problem to which a computer is applied Reference is often made to an application as being either of the computational type in which arithmetic computations predominate or of the data processing type in which data handling operations predominate application program A computer program designed to meet specific user needs argument 1 A type of variable whose value is not a direct function of another variable It can represent the location of a number in a mathematical operation or the number with which a function works to produce its results 2 A known reference factor that is required to find a desired item function in a table For example in the square root function SORT X X is the argument The value of x determines the square root value returned by this function array 1 An organized collection of data in which the argument is positioned before the function 2 A group of items or elements in which the position of each item or element is significant A multiplication table is a good example of an array ASCII Acronym for American Standard Code for Information Interchange ASCII is a standardized 8 bit code used by most computers for interfacing ASCII was developed by the American Natio
110. aced by the lines from subrtn bas file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic MERGE htm128 03 2004 21 29 15 GW BASIC User s Guide CHDIR Command Purpose To change from one working directory to another Syntax CHDIR pathname Comments pathname is a string expression of up to 63 characters To make sales the working directory on Drive A and inventory the working directory on Drive B assume A is the default drive type the following commands CHDIR SALES CHDIR B INVENTORY file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CHDIR htm128 03 2004 21 29 15 GW BASIC User s Guide CIRCLE Statement Purpose To draw a circle ellipse and angles on the screen during use of the Graphics mode Syntax CIRCLE xcenter ycenter radius color start end aspect Comments xcenterand ycenter are the x and y coordinates of the center of the ellipse and radius is the radius measured along the major axis of the ellipse The quantities xcenter and ycenter can be expressions The center attributes can use either absolute or relative coordinates color specifies the color of the ellipse Its value depends on the current screen mode See the COLOR and SCREEN statements for more information on using colors in different screen modes In the high resolution mode 0 indicates black and 1 indicates white The default for the high resolution mode is 1 The start and en
111. ame way GW BASIC intrinsic functions are called However the CALL statement is recommended for interfacing machine language programs with GW BASIC The CALL statement is compatible with more languages than the USR function call produces more readable source code and can pass multiple arguments D 1 Memory Allocation Memory space must be set aside for an assembly language or machine code subroutine before it can be loaded There are three recommended ways to set aside space for assembly language routines e Specify an array and use VARPTR to locate the start of the array before every access e Use the m switch in the command line Get GW BASIC s Data segment DS and add the size of DS to reference the reserved space above the data segment e Execute a COM file that stays resident and store a pointer to it in an unused interrupt vector location e There are three recommended ways to load assembly language routines e BLOAD the file Use DEBUG to load in an EXE file that is in high memory run GW BASIC and BSAVE the EXE file e Execute a COM file that contains the routines Save the pointer to these routines in unused interrupt vector locations so that your application in GW BASIC can get the pointer and use the routine s e Place the routine into the specified area If when an assembly language subroutine is called more stack space is needed GW BASIC stack space can be saved and a new stack set up for use by the as
112. an 2 magenta 3 white With the EGA the default color settings for the palette parameter are equivalent to the following COLOR 0 Same as the next three PALETTE statements PALETTE 1 2 Attribute 1 color 3 green PALETTE 2 4 Attribute 2 color 5 red PALETTE 3 6 Attribute 3 color 6 brown COLOR 1 Same as the next three PALETTE statements PALETTE 1 3 Attribute 1 color 3 cyan PALETTE 2 5 Attribute 2 color 5 magenta PALETTE 3 7 Attribute 3 color 15 white Note that a COLOR statement will override previous PALETTE statements No effect An Illegal function call error message occurs if COLOR is used in this mode In these modes no border color can be specified The graphics background is given by the background color number which must be in the valid range of color numbers appropriate to the screen mode See the SCREEN statement reference pages for more details The foreground color argument is the default line drawing color Arguments outside valid numeric ranges result in Illegal function call errors The foreground color may be the same as the background color making displayed characters invisible The default background color is black or color number 0 for all display hardware configurations and all screen modes With the Enhanced Graphics Adapter EGA installed the PALETTE statement gives you flexibility in assigning different display colors to the actual color number ranges fo
113. ange an error results If both operands are supplied as 0 or 1 logical operators return 0 or 1 The given operation is performed on these integers in bits that is each bit of the result is determined by the corresponding bits in the two operands Thus it is possible to use logical operators to test bytes for a particular bit pattern For instance the AND operator may be used to mask all but one of the bits of a status byte at a machine I O port The OR operator may be used to merge two bytes to create a particular binary value The following examples demonstrate how the logical operators work Example Explanation 63 AND 16 16 63 binary 111111 and 16 binary 10000 so 63 AND 16 16 15 AND 14 14 15 binary 1111 and 14 binary 1110 so 15 AND 14 14 binary 1110 1 AND 8 8 1 binary 1111111111111111 and 8 binary 1000 so 1 AND 8 8 4 OR 2 6 4 binary 100 and 2 binary 10 so 4 OR 2 6 binary 110 10 OR 10 10 10 binary 1010 so 1010 OR 1010 1010 10 1 binary 1111111111111111 and 2 binary 1111111111111110 so 1 OR 1 OR 2 1 2 1 The bit complement of 16 zeros is 16 ones which is the two s complement representation of 1 NOT X X 1 The two s complement of any integer is the bit complement plus one 6 4 4 Functional Operators file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 6 html 10 of 12 28 03 2004 21 29 00 GW BASIC User s Guide A function is used in an expression to
114. any valid line number within the program If line number is an executable statement that statement and those following are executed If it is a non executable statement execution proceeds at the first executable statement encountered after line number Examples 10 READ R 20 PRINT R R 30 A 3 14 R 2 40 PRINT AREA A 50 GOTO 10 60 DATA 5 7 12 RUN R 5 AREA 78 5 R 7 AREA 153 86 R 12 AREA 452 16 Out of data in 10 The out of data advisory is generated when the program attempts to read a fourth DATA statement which does not exist in line 60 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic GOTO htm128 03 2004 21 29 29 GW BASIC User s Guide HEX Function Purpose To return a string which represents the hexadecimal value of the numeric argument Syntax v S HEXS x Comments HEXS converts decimal values within the range of 32768 to 65535 into a hexadecimal string expression within the range of 0 to FFFF Hexadecimal numbers are numbers to the base 16 rather than base 10 decimal numbers Appendix C and Appendix G in the GW BASIC User s Guide contain more information on hexadecimals and their equivalents x is rounded to an integer before HEXS x is evaluated See the OCT function for octal conversions If x is negative 2 s binary complement form is used Examples 10 CLS INPUT INPUT DECIMAL NUMBER xX 20 AS HEXS X 30 PRINT X DECIMAL IS A
115. apshot of the screen CTRL I or TAB Moves the cursor to the next tab stop Tab stops occur every eight columns 4 4 Function Keys Certain keys or combinations of keys let you perform frequently used commands or functions with a minimum number of keystrokes These keys are called function keys The special function keys that appear on the left side of your keyboard can be temporarily redefined to meet the programming requirements and specific functions that your program may require Function keys allow rapid entry of as many as 15 characters into a program with one keystroke These keys are located on the left side of your keyboard and are labeled F1 through F10 GW BASIC has already assigned special functions to each of these keys You will notice that after you load GW BASIC these special key functions appear on the bottom line of your screen These key assignments have been selected for you as some of the most frequently used commands Initially the function keys are assigned the following special functions Table 4 1 GW BASIC Function Key Assignments KeyFunction KeyFunction Fl LIST F6 p EE Tiss F2 RUNA F7 TRON F3 LOAD F8 TROFFJ F4 SAVE F9 KEY F5 CONTA F10 SCREEN 0 0 04 Note The following a function indicates that you needn t press the RETURN key after the function key The selected command will be immediately executed If you choose you may change the assignments of these keys Any one or all of the 10 funct
116. arate these strings properly write successive double quotation marks using CHR 34 For example 40 PRINT 1 CHRS 34 AS CHRS 34 CHRS 34 BS CHR 34 CAMERA AUTOMATIC 93604 1 The PRINT statement may also be used with the USING option to control the format of the disk file For example PRINT 1 USING SSti t t 7 J K L PRINT does not compress data on the diskette An image of the data is written to the diskette just as it would be displayed on the terminal screen with a PRINT statement For this reason be sure to delimit the data on the diskette so that it is input correctly from the diskette In list of expressions numeric expressions must be delimited by semicolons For example PRINT Ag Bo Cy XP Ye Z If commas are used as delimiters the extra blanks inserted between print fields will also be written to the diskette Commas have no effect however if used with the exponential format String expressions must be separated by semicolons in the list To format the string expressions correctly on the diskette use explicit delimiters in list of expressions For example the following 10 A CAMERA BS 93604 1 20 PRINT 1 AS BS gives a diskette image of CAMERA93604 1 Because there are no delimiters this would not be input as two separate strings To correct the problem insert explicit delimiters into the PRINT statement as follows 30 PRINT 1 Ase B This gives the following diskette image which ca
117. ariable or file control block FCB Syntax VARPTR variable name VARPTR file number Comments VARP TR is usually used to obtain the address of a variable or array so it can be passed to an assembly language subroutine A function call of the following form VARPTR A 0 is usually specified when passing an array so that the lowest addressed element of the array is returned All simple variables should be assigned before calling VARPTR for an array because the addresses of the arrays change whenever a new simple variable is assigned VARPTR file number returns the starting address of the GW BASIC File Control Block assigned to file number VARPTR variable name returns the address of the first byte of data identified with the variable name A value must be assigned to variable name prior to execution of VARPTR otherwise an Tllegal function call error results Any type variable name may be used numeric string or array and the address returned will be an integer within the range of 32767 to 32768 If a negative address is returned it is added to 65536 to obtain the actual address Offsets to information in the FCB from the address returned by VARPTR are shown in the following table Table 7 Offsets to FCB Information Offset Length Name Description file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic VARPTR html 1 of 3 28 03 2004 21 29 51 GW BASIC User s Guide 0 39 4 42 43 46
118. asic IOCTL htm128 03 2004 21 29 33 GW BASIC User s Guide IOCTLS Function Purpose To allow GW BASIC to read a control data string from an open character device driver Syntax IOCTLS file number Comments file number is the file number open to the device The IOCTLS function is generally used to get acknowledgement that an IOCTL statement succeeded or failed It is also used to get device information such as device width after an IOCTL statement requests it Examples 10 GW is a possible command 20 for get device width 30 OPEN DEV MYLPT AS 1 40 IOCTYL 1 GW 50 Save it in WID 60 WID VAL IOCTLS 1 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic IOCTLS htm128 03 2004 21 29 33 GW BASIC User s Guide KILL Command Purpose To delete a file from a disk Syntax KILL filename Comments filename can be a program file sequential file or random access data file KILL 1s used for all types of disk files including program random data and sequential data files Note You must specify the filename s extension when using the KILL command Remember that files saved in GW BASIC are given the default extension BAS If a KILL command is given for a file that is currently open a File already open error occurs Examples The following command deletes the GW BASIC file DATA and makes the space available for reallocation to another file 200 KILL DATA1 BAS Th
119. asic PCOPY htm128 03 2004 21 29 41 GW BASIC User s Guide PEN Statement and Function Purpose To read the light pen Syntax As a Statement PEN ON PEN OFF PEN STOP As a function x PEN n Comments PEN ON enables the PEN read function PEN OFF disables the PEN read function PEN STOP disables trapping It remembers the event so immediate trapping occurs when PEN ON is executed The PEN function is initially off A PEN ON statement must be executed before any PEN read function calls can be made or a PEN read function call results in an Illegal function call error xXx PEN n reads the light pen coordinates x is the numeric variable receiving the PEN value n 1s an integer within the range of 0 to 9 Light pen coordinates 0 il If PEN was down since last poll returns 1 if not returns 0 Returns the x pixel coordinate when PEN was last activated The range is within 0 to 319 for medium resolution 0 to 639 for high resolution Returns the y pixel coordinate when PEN was last activated The range is within 0 to 199 Returns the current PEN switch value Returns 1 if down 0 if up Returns the last known valid x pixel coordinate The range is within 0 to 319 for medium resolution or 0 to 639 for high resolution file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PEN html 1 of 2 28 03 2004 21 29 41 GW BASIC User s Guide Returns the last known valid y pix
120. ator it cannot be renumbered by RENUM Because ERL and ERR are reserved variables neither may appear to the left of the equal sign in a LET assignment statement file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ERRERL htm128 03 2004 21 29 25 GW BASIC User s Guide ERROR Statement Purpose To simulate the occurrence of an error or to allow the user to define error codes Syntax ERROR integer expression Comments The value of integer expression must be greater than 0 and less than 255 If the value of integer expression equals an error code already in use by GW BASIC the ERROR statement simulates the occurrence of that error and the corresponding error message is printed A user defined error code must use a value greater than any used by the GW BASIC error codes There are 76 GW BASIC error codes at present It is preferable to use a code number high enough to remain valid when more error codes are added to GW BASIC User defined error codes may be used in an error trapping routine If an ERROR statement specifies a code for which no error message has been defined GW BASIC responds with the message Unprintable Error Execution of an ERROR statement for which there is no error trapping routine causes an error message to be printed and execution to halt For a complete list of the error codes and messages already defined in GW BASIC refer to Appendix A in the GW BASIC User s Guide Exampl
121. ber system uses eight digits 0 1 2 3 4 5 6 and 7 with each position in an octal numeral representing a power of 8 The octal system is used in computing as a simple means of expressing binary quantities operand A quantity or data item involved in an operation An operand is usually designated by the address portion of an instruction but it may also be a result a parameter or an indication of the name or location of the next instruction to be executed operating system An organized group of computer instructions that manage the overall operation of the computer operator A symbol indicating an operation and itself the subject of the operation It indicates the process that is being performed For example is addition is subtraction x is multiplication and is division option An add on device that expands a system s capabilities output Computer results or data that has been processed parallel output The method by which all bits of a binary word are transmitted simultaneously parameter A variable that is given a value for a specific program or run A definable characteristic of an item device or system parity file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 13 of 17 28 03 2004 21 29 08 GW BASIC User s Guide An extra bit of code that is used to detect data errors in memory by mak ing the sum of the active bit in a data word either an odd or an even number partition
122. ble to write both simple and complex programs to run on your computer You will also be able to modify existing software that is written in GW BASIC This guide is designed to help you use the GW BASIC Interpreter with the MS DOS operating system Section 1 5 lists resources that will teach you how to program 1 1 System Requirements This version of GW BASIC requires MS DOS version 3 2 or later 1 2 Preliminaries Your GW BASIC files will be on the MS DOS diskette located at the back of the MS DOS User s Reference Be sure to make a working copy of the diskette before you proceed Note This manual is written for the user familiar with the MS DOS operating system For more information on MS DOS refer to the Microsoft MS DOS 3 2 User s Guide and User s Reference 1 3 Notational Conventions Throughout this manual the following conventions are used to distinguish elements of text bold Used for commands options switches and literal portions of syntax that must appear exactly as shown italic Used for filenames variables and placeholders that represent the type of text to be entered by the user monospaceUsed for sample command lines program code and examples and sample sessions SMALL CAPS Used for keys key sequences and acronyms Brackets surround optional command line elements file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 1 html 1 of 3 28 03 2004 21 28 56 GW BASIC User s Guide 1 4 Organ
123. can use The maximum block size is in multiples of 16 It is used to reserve space for user programs assembly language subroutines beyond GW BASIC s workspace The default for maximum block size is the highest memory location The default for the highest memory location is 64K bytes unless maximum block size is specified in which case the default is the maximum block size in multiples of 16 d allows certain functions to return double precision results When the d switch is specified approximately 3000 bytes of additional code space are used The functions affected are ATN COS EXP LOG SIN SOR and TAN Note All switch numbers may be specified as decimal octal preceded by 0 or hexadecimal preceded by H file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 202 html 3 of 8 28 03 2004 21 28 57 GW BASIC User s Guide Sample GW BASIC command lines are as follows The following uses 64K bytes of memory and three files loads and executes the program file payroll bas A gt gwbasic PAYROLL The following uses 64K bytes of memory and six files loads and executes the program file invent bas A gt gwbasic INVENT F 6 The following disables RS 232 support and uses only the first 32K bytes of memory 32K bytes above that are reserved for user programs A gt gwbasic C 0 M 32768 4096 The following uses four files and allows a maximum record length of 512 bytes A gt gwbasic F 4 S 512 The
124. cation Optionally the LOCATE statement may be used to start the cursor blinking on or off or change the size of the blinking cursor Any values entered outside of these ranges results in Illegal function call errors Previous values are retained As you set up the parameters for the LOCATE statement you may find that you do not wish to change one or more of the existing specifications To omit a parameter from this LOCATE statement insert a comma for the parameter that is being skipped If the omitted parameter s occurs at the end of the statement you do not have to type the comma If the start scan line parameter is given and the stop scan line parameter is omitted stop assumes the start value Examples 10 LOCATE 1 1 Moves cursor to the home position in the upper left corner 20 LOCATE 1 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LOCATE html 1 of 2 28 03 2004 21 29 36 GW BASIC User s Guide Makes the cursor visible Its position remains unchanged Notice that the first two parameters are not used A comma has been inserted for each omitted parameter 30 LOCATE ppl Cursor position and visibility remain unchanged Sets the cursor to appear at the bottom of the character starting and ending on scan line 7 40 LOCATE 5 1 1 0 7 Moves the cursor to line 5 column 1 and turns the cursor on The cursor covers an entire character cell starting at scan line O and ending on scan line 7 file Cl D
125. cess file that has been opened for input or output the entire file is locked regardless of any record range specified This is not considered an error The specification of a range in the LOCK statement regarding the sequential file will simply be disregarded The LOCK statement should be executed on a file or record range within a file before attempting to read or write to that file The locked file or record range should be unlocked before the file is closed Failure to execute the UNLOCK statement can jeopardize future access to that file in a network environment file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LOCK html 1 of 2 28 03 2004 21 29 37 GW BASIC User s Guide It is expected that the time in which files or regions within files are locked will be short and thus the suggested usage of the LOCK statement is within short term paired LOCK UNLOCK statements Examples The following sequence demonstrates how the LOCK UNLOCK statements should be used LOCK 1 1 TO 4 LOCK 1 5 TO 8 UNLOCK 1 1 TO 4 UNLOCK 1 5 TO 8 The following example is illegal LOCK 1 1 TO 4 LOCK 1 5 TO 8 UNLOCK 1 1 TO 8 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LOCK html 2 of 2 28 03 2004 21 29 37 GW BASIC User s Guide LOF Function Purpose To return the length number of bytes allocated to the file Syntax LOF file number Comments file number is the number of the file that the
126. converting programs written in BASIC to GW BASIC Appendix F Communications describes the GW BASIC statements required to support RS 232 asynchronous communications with other computers and peripheral devices Appendix G Hexadecimal Equivalents lists decimal and binary equivalents to hexadecimal values Appendix H Key Scan Codes lists and illustrates the key scan code values used in GW BASIC Appendix I Characters Recognized by GW BASIC describes the GW BASIC character set file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 1 html 2 of 3 28 03 2004 21 28 56 GW BASIC User s Guide The Glossary defines words and phrases commonly used in GW BASIC and data processing 1 5 Bibliography This manual is a guide to the use of the GW BASIC Interpreter it makes no attempt to teach the BASIC programming language The following texts may be useful for those who wish to learn BASIC programming Albrecht Robert L LeRoy Finkel and Jerry Brown BASIC 2d ed New York Wiley Interscience 1978 Coan James Basic BASIC Rochelle Park N J Hayden Book Company 1978 Dwyer Thomas A and Margot Critchfield BASIC and the Personal Computer Reading Mass Addison Wesley Publishing Co 1978 Ettlin Walter A and Gregory Solberg The MBASIC Handbook Berkeley Calif Osborne McGraw Hill 1983 Knecht Ken Microsoft BASIC Portland Oreg Dilithium Press 1982 file Cl Documents 20and 20Se
127. d A term that refers to a diskette that can contain data on both surfaces of the diskette drive A device that holds and manipulates magnetic media so that the CPU can read data from or write data to them end of file mark EOF A symbol or machine equivalent that indicates that the last record of a file has been read erase To remove or replace magnetized spots from a storage medium error message An audible or visual indication of hardware or software malfunction or of an illegal data entry attempt execute To carry out an instruction or perform a routine exponent A symbol written above a factor and on the right telling how many times the factor is repeated In the example of A2 A is the factor and 2 is the exponent A means A times A A x A extension A one to three character set that follows a filename The extension further defines or clarifies the filename It is separated from the filename by a period field An area of a record that is allocated for a specific category of data file A collection of related data or programs that is treated as a unit by the computer file protection The devices or procedures that prevent unintentional erasure of data on a storage device such as a diskette file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 8 of 17 28 03 2004 21 29 08 GW BASIC User s Guide file structure A conceptual representation of how data values records and files are rela
128. d angle parameters are radian arguments between 27 and 27 which specify where the drawing of the ellipse is to begin and end If st art or end is negative the ellipse is connected to the center point with a line and the angles are treated as if they are positive note that this is different from adding 27 aspect describes the ratio of the x radius to the y radius x y The default aspect ratio depends on the screen mode but gives a visual circle in either graphics mode assuming a standard monitor screen aspect ratio of 4 3 If the aspect ratio is less than 1 then the radius is given in x pixels If it is greater than 1 the radius is given in y pixels In many cases an aspect ratio of 1 gives better ellipses in the medium resolution mode This also causes the ellipse to be drawn faster The start angle may be less than the end angle Example 1 10 SCREENL CIRCLE 100 100 50 Draws a circle of radius 50 centered at graphics points 100x and 100y Example 2 1 This will draw 17 ellipses TO CLS 20 SCREEN 1 30 FOR R 160 TO 0 STEP 10 40 CIRCLE 160 100 Ry gt 5 718 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CIRCLE html 1 of 2 28 03 2004 21 29 15 GW BASIC User s Guide 50 NEXT Example 3 10 This will draw 5 spheres 20 GOTO 160 50 IF VERT GOTO 100 60 CIRCLE X Y Rr Crpe cl 70 FOR I 1 TO 5 90 CIRCLE XY Rp Cryo 1 sZINExXT I 90 IF VERT THEN RETURN 100 CIRCLE X t RpCrep isd
129. d only if the function key is off Examples 100 X SCREEN 10 10 If the character at 10 10 is A then X is 65 110 X SCREEN 1 1 1 Returns the color attribute of the character in the upper left corner of the screen file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SCREENF htm128 03 2004 21 29 46 GW BASIC User s Guide SGN Function Purpose To return the sign of x Syntax SGN x Comments x is any numeric expression If x is positive SGN x returns 1 If xis 0 SGN x returns 0 If x is negative SGN x returns 1 This statement is similar to but not the same as SIN x which returns a trigonometric function in radians rather than in ones and zeros Examples 10 INPUT Enter value x 20 ON SGN X 2 GOTO 100 200 300 GW BASIC branches to 100 if X is negative 200 if X is 0 and 300 if X is positive file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SGN htm128 03 2004 21 29 46 GW BASIC User s Guide SIN Function Purpose To calculate the trigonometric sine of x in radians Syntax SIN x Comments SIN x is calculated in single precision unless the d switch is used when GW BASIC is executed To obtain SIN x when x is in degrees use SIN x m 180 Examples PRINT sis 143 9974931 The sine of 1 5 radians is 9974951 single precision file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SIN htm128 03 2004 21 29 46
130. d so on The DATA statement lines 110 120 may be placed anywhere in the program they may even be placed ahead of the READ statement 5 PRINT 10 PRINT CITY STATE Ere 20 READ Co Ss Z 30 DATA DENVER COLORADO 80211 40 PRINT C S Z RUN CITY STATE ZIP DENVER COLORADO 80211 This program reads string and numeric data from the DATA statement in line 30 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic READ html 2 of 2 28 03 2004 21 29 21 GW BASIC User s Guide DATES Statement and Variable Purpose To set or retrieve the current date Syntax As a statement DATES vS As a variable vS DATES Comments v is a valid string literal or variable vs can be any of the following formats when assigning the date mm dd yy mm dd yy mm dd yyyy mm dd yyyy If vs is not a valid string a Type Mismatch error results Previous values are retained If any of the values are out of range or missing an Illegal Function Call error is issued Any previous date is retained The current date as assigned when the operating system was initialized is fetched and assigned to the string variable if DATES is the expression in a LET or PRINT statement The current date is stored if DATES 1s the target of a string assignment With vS DATES DATES returns a 10 character string in the form mm dd yyyy mm is the month O1 to 12 ddis the day 01 to 31 and yyyy is the year 1980 to 2099
131. data bits plus a parity bit and represents either one alphabetic or special character two decimal digits or eight binary bits Byte is also used to file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 4 of 17 28 03 2004 21 29 08 GW BASIC User s Guide refer to a sequence of eight binary digits handled as a unit It is usually encoded in the ASCH format calculation A series of numbers and mathematical signs that when entered into a computer is executed according to a series of instructions central processor CPU The heart of the computer system where data is manipulated and calculations are performed The CPU contains a control unit to interpret and execute the program and an arithmetic logic unit to perform computations and logical processes It also routes information controls input and output and temporarily stores data chaining The use of a pointer in a record to indicate the address of another record logically related to the first character Any single letter of the alphabet numeral punctuation mark or other symbol that a computer can read write and store Character is synonymous with the term byte COBOL Acronym for COmmon Business Oriented Language a computer language suitable for writing complicated business applications programs It was developed by CODASYL a committee representing the U S Department of Defense certain computer manufacturers and major users of data processing
132. ding in the argument list the variable name that receives the result 5 If the argument is a string the parameter offset points to three bytes called the string descriptor Byte 0 of the string descriptor contains the length of the string 0 to 255 Bytes 1 and 2 respectively are the lower and upper eight bits of the string starting address in string space Note The called routine must not change the contents of any of the three bytes of the string descriptor 6 Strings may be altered by user routines but their length must not be changed GW BASIC cannot correctly manipulate strings if their lengths are modified by external routines 7 If the argument is a string literal in the program the string descriptor points to program text Be careful not to alter or destroy your program this way To avoid unpredictable results add to the string literal in the program For example the following line forces the string literal to be copied into string space allocated outside of program memory space 20 AS BASIC The string can then be modified without affecting the program Examples 100 DEF SEG amp H2000 110 ACC amp H7FA 120 CALL ACC A BS C Line 100 sets the segment to 2000 hex The value of variable ACC is added into the address as the low word after the DEF SEG value is left shifted four bits this is a function of the microprocessor not of GW BASIC Here ACC is set to amp H7FA so that the call to ACC file C
133. displayed on the screen and all characters except the following are passed to the program CTRL BREAK CTRL NUM LOCK CTRL ALT DEL CTRL PRTSCR PRTSCR Examples 10 CLS PRINI PRESS RETURN 20 TIMELIMIT S 1000 30 GOSUB 1010 40 IF TIMEOUTS THEN PRINT TOO LONG ELSE PRINT GOOD SHOW 50 PRINT RESPONSES 60 END 1000 REM TIMED INPUT SUBROUTINE 1010 RESPONSES 1020 FOR N 1 TO TIMELIMITS 1030 AS INKEYS IF LEN AS 0 THEN 1060 1040 IF ASC AS 13 THEN TIMEOUT S 0 RETURN 1050 RESPONSES RESPONSES AS 1060 NEXT N file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic INKEYS html 1 of 2 28 03 2004 21 29 30 GW BASIC User s Guide 1070 TIMEOUT 1 RETURN When this program is executed and if the RETURN key is pressed before 1000 loops are completed then GOOD SHOW is printed on the screen Otherwise TOO LONG is printed Since an INKEYS statement scans the keyboard only once place INKEYS statements within loops to provide adequate response times for the operator file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic INKEYS html 2 of 2 28 03 2004 21 29 30 GW BASIC User s Guide INP Function Purpose To return the byte read from machine port n Syntax INP n Comments n represents a valid machine port number within the range of 0 to 65535 The INP function is one way in which a peripheral device may communicate with a GW BASIC program INP is the complementary function to
134. e a KEY n statement When KEY n OFF is executed no key capture occurs and no keystrokes are retained If KEY n STOP is executed no key capture occurs but if a specified key is pressed the keystroke is retained so that immediate keystroke capture occurs when a KEY n ON is executed For further information on key trapping see the ON KEY n statement file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic KEYN htm128 03 2004 21 28 59 GW BASIC User s Guide Appendix F Communications This appendix describes the GW BASIC statements necessary to support RS 232 asynchronous communications with other computers and peripheral devices F 1 Opening Communications Files The OPEN COM statement allocates a buffer for input and output in the same manner as the OPEN statement opens disk files F 2 Communications I O Since the communications port is opened as a file all I O statements valid for disk files are valid for COM COM sequential input statements are the same as those for disk files INPUT LINE INPUT INPUTS COM sequential output statements are the same as those for diskette PRINT PRINT USING See the GW BASIC User s Reference for more information on these statements F 3 The COM I O Functions The most difficult aspect of asynchronous communications is processing characters as quickly as they are received At rates above 2400 baud bps it is necessary to suspend character transmission from the ho
135. e bad garbage out global search Used in reference to a variable character or command a global search causes the computer to locate all occurrences of that variable file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 9 of 17 28 03 2004 21 29 08 GW BASIC User s Guide graphics A hardware software capability to display objects in pictures rather than words usually on a graphic CRT display terminal with line drawing capability and permitting interaction such as the use of a light pen hard copy A printed copy of computer output in a readable form such as reports checks or plotted graphs hardware The physical equipment that comprises a system hexadecimal A number system with a base or radix of 16 The symbols used in this system are the decimal digits 0 through 9 and six additional digits which are generally represented as A B C D E and F hidden files Files that cannot be seen during normal directory searches hierarchical directories See tree structured directories housekeeping functions Routine operations that must be performed before the actual processing begins or after it is complete information Facts and knowledge derived from data The computer operates on and gen erates data The meaning derived from the data is information That is information results from data the two words are not synonymous although they are often used interchangeably interpreter A prog
136. e following command deletes the GW BASIC file RAINING from the subdirectory dogs KILL CATS DOGS RAINING BAS file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic KILL htm128 03 2004 21 29 33 GW BASIC User s Guide LEFTS Function Purpose To return a string that comprises the left most n characters of x Syntax LEFTS x n Comments n must be within the range of 0 to 255 If n is greater than LEN x the entire string x will be returned If n equals zero the null string length zero is returned see the MID and RIGHT substring functions Example 10 A BASIC 20 BS LEFTS AS 3 30 PRINT BS RUN BAS The left most three letters of the string BASIC are printed on the screen file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LEFTS htm128 03 2004 21 29 34 GW BASIC User s Guide MIDS Function Purpose To return a string of m characters from x beginning with the nth character Syntax MIDS x n m Comments n must be within the range of 1 to 255 m must be within the range of 0 to 255 If mis omitted or if there are fewer than m characters to the right of n all rightmost characters beginning with n are returned If n gt LEN x MIDS function returns a null string If m equals 0 the MID function returns a null string If either n or mis out of range an Illegal function call error is returned For more information and examples see the LEFT and
137. e last point referenced to the point x2 y2 in the foreground color Examples LINE 0 100 639 100 Draws a horizontal line which divides the screen in half from top to bottom in SCREEN 2 LINE 160 0 160 199 Draws a vertical line which divides the screen in half from left to right in SCREEN 1 makes a one quarter three quarter division in SCREEN 2 LINE 0 0 319 199 Draws a diagonal line from the top left to lower right corner of the screen in SCREEN 1 and from the upper left corner to the center bottom of the screen in SCREEN 2 LENE 10 10 20720 p2 Draws a line in color 2 if SCREEN 1 is previously specified see the COLOR statement 10 CLS 20 LINE RND 319 RND 199 RND 4 30 GOTO 20 Draw lines forever using random attributes 10 FOR X 0 TO 319 20 LINE X 0 X 199 X AND 1 30 NEXT Draws an alternating pattern line on line off lo CES 20 LINE RND 639 RND 199 RND 2 BF 30 GOTO 20 Draws lines all over the screen LINE 0 0 Cl00 175 pB Draws a square box in the upper left corner of the screen file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LINE html 2 of 3 28 03 2004 21 29 17 GW BASIC User s Guide LINE 0 0 100 175 BF Draws the same box and fills it in LINE 0 0 100 175 2 2F Draws the same filled box in magenta in SCREEN 1 LINE 0 0 100 350 s E Draws the same box if SCREEN 2 is specified 400 SCREEN 1 410 LINE 160 100 160 199 8HC
138. e note and so on n may be from 1 to 64 Length may also follow the note to change the length for that note only A16 is equivalent to LIGA Music foreground PLAY and SOUND statements are to run in foreground That is each subsequent note or sound is not started until the previous note or sound is finished This is the initial default Music background PLAY and SOUND statements are to run in background That is each note or sound is placed in a buffer allowing the BASIC program to continue execution while music plays in the background As many as 32 notes or rests can be played in background at one time Music normal Each note plays seven eighths of the time determined by L length Music legato Each note plays the full period set by L Music staccato Each note plays three quarters of the time determined by L Play note n n may range from 0 to 84 In the 7 possible octaves there are 84 notes n set to 0 indicates a rest Octave 0 sets the current octave There are 7 octaves 0 through 6 Default is 4 Middle C is at the beginning of octave 3 Pause P may range from 1 64 Tempo T sets the number of L4s in a minute n may range from 32 255 Default is 120 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PLA Y html 1 of 2 28 03 2004 21 29 41 GW BASIC User s Guide period A period after a note increases the playing time of the note by 3 2 times the period determined by L length of note times T temp
139. e number 4 replaces the number 3 in the statement Now press the RETURN key and then the F2 key Your screen displays the following Ok 10 X 4 RUN 6 Ok 3 5 Saving Your Program File Creating a program is like creating a data file The program is a file that contains specific instructions or statements for the computer In order to use the program again you must save it just as you would a data file file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 203 html 4 of 5 28 03 2004 21 28 59 GW BASIC User s Guide To save a file in GW BASIC use the following procedure 1 Press the F4 key The command word SAVE appears on your screen 2 Type a name for the program and press the RETURN key The file is saved under the name you specified To recall a saved file use the following procedure 1 Press the F3 key The command load LOAD appears on your screen 2 Type the name of the file 3 Press RETURN The file is loaded into memory and ready for you to list edit or run file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 203 html 5 of 5 28 03 2004 21 28 59 GW BASIC User s Guide Chapter 6 Constants Variables Expressions and Operators After you have learned the fundamentals of programming in GW BASIC you will find that you will want to write more complex programs The information in this chapter will help you learn more about the use of constants variable
140. e original media 2 On site or remote equipment available to complete an operation in the event of primary equipment failure BASIC Acronym for Beginner s All purpose Symbolic Instruction Code BASIC is a computer programming language developed at Dartmouth College as an instructional tool in teaching fundamental programming concepts This language has since gained wide acceptance as a time sharing language and is considered one of the easiest programming languages to learn batch processing A method of operating a computer so that a single program or set of related programs must be completed before the next type of program is begun baud A unit of measurement of data processing speed The speed in bauds is the number of signal elements per second Since a signal element can represent more than one bit baud is not synonymous with bits per second Typical baud rates are 110 300 1200 2400 4800 and 9600 binary 1 A characteristic or property involving a choice or condition in which there are two possibilities 2 A numbering system which uses 2 as its base instead of 10 as in the decimal system The file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 3 of 17 28 03 2004 21 29 08 GW BASIC User s Guide binary system uses only two digits 0 and 1 in its written form 3 A device whose design uses only two possible states or levels to perform its functions A computer executes programs in binary form
141. e sign of the step If STEP is negative the final value of the counter is set to be less than the initial value The counter is decremented each time through the loop and the loop is executed until the counter is less than the final value Nested Loops FOR NEXT loops may be nested that is a FOR NEXT loop may be placed within the context of another FOR NEXT loop When loops are nested each loop must have a unique variable name as file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic FORNEXT html 1 of 2 28 03 2004 21 29 27 GW BASIC User s Guide its counter The NEXT statement for the inside loop must appear before that for the outside loop If nested loops have the same end point a single NEXT statement may be used for all of them The variable s in the NEXT statement may be omitted in which case the NEXT statement will match the most recent FOR statement If a NEXT statement is encountered before its corresponding FOR statement a NEXT without FOR error message is issued and execution is terminated Examples The following example prints integer values of the variable I from 1 to 10 in steps of z For fastest execution I is declared as an integer by the sign 10 K 10 20 FOR I 1 TO K STEP 2 30 PRINT I 40 NEXT RUN On si Ot Goi In the following example the loop does not execute because the initial value of the loop exceeds the final value Nothing is printed by this example 10 R 0 20
142. e than 10 parameters will be accessed In line 20 the initial number of parameters is established as 1 In lines 30 through 70 a series of statements are used to adjust and correct the parameter numbers Line 71 deletes the present environment Lines 72 through 80 create a new environment Line 74 deletes the string Lines 80 through 100 store the new environment Lines 1000 through 1030 repeat the procedure by deleting the present environment and restore the parameters established in the first part of the program file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic EN VIRONS html 2 of 2 28 03 2004 21 29 24 GW BASIC User s Guide SHELL Statement Purpose To load and execute another program or batch file When the program finishes control returns to the GW BASIC program at the statement following the SHELL statement A program executed under control of GW BASIC is referred to as a child process Syntax SHELL string Comments string is a valid string expression containing the name of a program to run and optionally command arguments The program name in string may have any extension that MS DOS COMMAND COM supports If no extension is supplied COMMAND will look for a COM file then an EXE file and finally a BAT file If none is found SHELL will issue a File not found error Any text separated from the program name by at least one blank space will be processed by COMMAND as program param
143. ed while the cursor is located in the middle or at the beginning of the line To truncate or cut off a line at the current cursor position type CTRL END or CTRL E followed by pressing the RETURN key If you have originally saved your program to a program file make sure that you save the edited version of your program If you do not do this your modifications will not be recorded 4 3 Special Keys The GW BASIC Interpreter recognizes nine of the numeric keys on the right side of your keyboard It also recognizes the BACKSPACE key ESC key and the CTRL key The following keys and key sequences have special functions in GW BASIC Key Function BACKSPACE Or CTRL H Deletes the last character typed or deletes the character to the left of the cursor All characters to the right of the cursor are moved left one position Subsequent characters and lines within the current logical line are moved up as with the DEL key CTRL BREAK Or CTRL C Returns to the direct mode without saving changes made to the current line It will also exit auto line numbering mode CTRL CURSOR LEFT Or CTRL B Moves the cursor to the beginning of the previous word The previous word is defined as the next character to the left of the cursor in the set A to Z or in the set 0 to 9 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 204 html 2 of 6 28 03 2004 21 28 57 GW BASIC User s Guide CTRL CURSOR RIGHT Or CTRL F CURSOR DOWN or CTRL
144. efore the file is closed Failure to execute the UNLOCK statement can jeopardize future access to that file in a network environment In the case of files opened in random mode if a range of record numbers is specified this range must match exactly the record number range given in the LOCK statement The Permission denied message will appear if a syntactically correct UNLOCK request cannot be granted The UNLOCK statement must match exactly the paired LOCK statement It is expected that the time in which files or regions within files are locked will be short and thus the suggested usage of the LOCK statement is within shortterm paired LOCK UNLOCK statements file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic UNLOCK html 1 of 2 28 03 2004 21 29 40 GW BASIC User s Guide Examples The following demonstrates how the LOCK UNLOCK statements should be used LOCK 1 1 TO 4 LOCK 1 5 TO 8 UNLOCK 1 1 TO 4 UNLOCK 1 5 TO 8 The following example is illegal LOCK 1 1 TO 4 LOCK 1 5 TO 8 UNLOCK 1 1 TO 8 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic UNLOCK html 2 of 2 28 03 2004 21 29 40 GW BASIC User s Guide OPEN COM n Statement Purpose To allocate a buffer to support RS 232 asynchronous communications with other computers and peripheral devices in the same manner as OPEN for disk files Syntax OPEN COM n speed parity data stop RS CS n DS n CD n LF
145. el coordinate The range is within 0 to 199 Returns the character row position when PEN was last activated The range is within 1 to 24 Returns the character column position when PEN was last activated The range is within 1 to 40 or 1 to 80 depending on the screen width Returns the last known valid character row The range is within 1 to 24 Returns the last known valid character column position The range is within 1 to 40 or 1 to 80 depending on the screen width For execution speed improvements turn the pen off with a PEN OFF statement for those programs not using the light pen When the pen is in the border area of the screen the values returned will be inaccurate Examples 50 60 70 80 90 PEN ON FOR I L to 500 X PEN 0 X1 PEN 3 PRINT xy X1 NEXT 100 PEN OFF This example prints the pen value since the last poll and the current value file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PEN html 2 of 2 28 03 2004 21 29 41 GW BASIC User s Guide PLAY Statement Purpose To play music by embedding a music macro language into the string data type Syntax PLAY string expression Comments The single character commands in PLAY are as follows A G A G are notes or following a note produces a sharp produces a flat MF MB Any note followed by or must refer to a black key on a piano Sets the length of each note L4 is a quarter note L1 is a whol
146. ement such as the following DIM A I J which dimensions a string array for J elements of length I should be converted to the following statement DIM A J Some GW BASIC languages use a comma or ampersand for string concatenation Each of these must be changed to a plus sign which is the operator for GW BASIC string concatenation In GW BASIC the MIDS RIGHTS and LEFTS functions are used to take substrings of strings Forms such as A I to access the Ith character in A or A I J to take a substring of A from position I to position J must be changed as follows Other BASICGW BASIC X A I Xe MIDS AS 1 1 XS AS I J XS MIDS AS 1 J I 1 If the substring reference is on the left side of an assignment and X is used to replace characters in A convert as follows Other BASICGW BASIC AS I X MIDS AS 1I 1 X A I J X MIDS A 1I J I 1 x E 2 Multiple Assignments Some GW BASIC languages allow statements of the following form to set B and C equal to zero 10 LET B C 0 GW BASIC would interpret the second equal sign as a logical operator and set B equal to 1 if C equaled 0 Convert this statement to two assignment statements 10 C 0 B 0 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20E html 1 of 2 28 03 2004 21 29 06 GW BASIC User s Guide E 3 Multiple Statements Some GW BASIC languages use a backslash to separate multiple statements on a line With GW BA
147. ements are actually what are called attributes in this discussion This color argument specifies the way that text characters appear on the display screen Under a common initial palette setting points colored with the attribute 0 appear as black on the display screen Using the PALETTE statement you could for example change the mapping of attribute 0 from black to white Remember that a PALETTE statement executed without any parameters assigns all attributes their default colors The following table lists attribute and color ranges for various monitor types and screen modes Table 1 SCREEN Color and Attribute Ranges SCREEN Attribute Color Mode Monitor Attached Adapter Range Range 0 Monochrome MDPA NA NA Monochrome EGA 0 15 0 2 Color CGA NA 0 31a Color Enhanced4 EGA 0 31a 0 15 1 Color CGA NA 0 3 Color Enhanced4 EGA 0 3 0 15 2 Color CGA NA 0 1 Color Enhanced4 EGA 0 1 0 15 7 Color Enhanced4 EGA 0 15 0 15 8 Color Enhanced EGA 0 15 0 15 9 Enhanced EGAb 0 3 0 15 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PALETTE html 2 of 3 28 03 2004 21 29 16 GW BASIC User s Guide Enhanced 4 EGAS 0 15 0 63 10 Monochrome EGA 0 3 0 8 4 Attributes 16 31 refer to blinking versions of colors 0 15 b With 64K of EGA memory c With greater than 64K of EGA memory d IBM Enhanced Color Display NA Not Applicable CGA IBM Color Graphics Adapter EGA IBM Enhanced Graphics Adapter MDPA IBM Monochrome Display a
148. ential file is opened for input GW BASIC initially reads the first sector of the file In this case the Loc function returns the character before any input is allowed If the file was opened but no disk input output was performed LOC returns a zero Examples 200 IF LOC 1 gt 50 THEN STOP The program stops after 51 records are read or written file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LOC htm128 03 2004 21 29 36 GW BASIC User s Guide LOCATE Statement Purpose To move the cursor to the specified position on the active screen Optional parameters cause the cursor to blink on and off and define the start and stop raster lines for the cursor A raster line is the vertical or horizontal distance between two adjacent addressable points on your screen Syntax LOCATE row col Leursor start etep Comments row is the screen line number a numeric expression within the range of to 25 col is the screen column number a numeric expression within the range of 1 to 40 or 1 to 80 depending upon screen width cursor is a Boolean value indicating whether the cursor is visible zero is off nonzero is on start is the cursor start scan line a numeric expression within the range of 0 to 31 stop is the cursor stop scan line a numeric expression within the range of 0 to 31 When the cursor is moved to the specified position subsequent PRINT statements begin placing characters at this lo
149. equipment COBOL is designed to express data manipulations and processing problems in English narrative form in a precise and standard manner code 1 To write instructions for a computer system 2 To classify data according to arbitrary tables 3 To use a machine language 4 To program command A pulse signal word or series of letters that tells a computer to start stop or continue an operation in an instruction Command is often used incorrectly as a synonym for instruction compatible A description of data programs or equipment that can be used between different kinds of file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 5 of 17 28 03 2004 21 29 08 GW BASIC User s Guide computers or equipment compiler A computer program that translates a program written in a problem oriented language into a program of instructions similar to or in the language of the computer computer network A geographically dispersed configuration of computer equipment connected by communication lines and capable of load sharing distributive processing and automatic communication between the computers within the network concatenate To join together data sets such as files in a series to form one data set such as one new file The term concatenate literally means to link together A concatenated data set is a collection of logically connected data sets configuration In hardware a group of interrelated dev
150. er than I 0 A or R File already open A sequential output mode OPEN is issued for a file that is already open or a KILL is given for a file that is open Unprintable error An error message is not available for the error condition which exists This is usually caused by an error with an undefined error code Device I O Error Usually a disk I O error but generalized to include all I O devices It is a fatal error that is the operating system cannot recover from the error File already exists The filename specified in a NAME statement is identical to a filename already in use on the diskette file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20A html 4 of 7 28 03 2004 21 29 03 GW BASIC User s Guide 59 60Unprintable error 61 62 63 64 65 66 67 68 No error message is available for the existing error condition This is usually caused by an error with an undefined error code Disk full All disk storage space is in use Input past end An INPUT statement is executed after all the data in the file has been input or for a null empty file To avoid this error use the EOF function to detect the end of file Bad record number In a PUT or GET statement the record number is either greater than the maximum allowed 16 777 215 or equal to zero Bad filename An illegal form is used for the filename with LOAD SAVE KILL or OPEN for example a filename with too many characters
151. erases the character at the current cursor position and moves the cursor one character to the right The CURSOR RIGHT key moves the cursor one character to the right but does not delete the character When Insert Mode is off pressing the TAB key moves the cursor over characters until the next tab stop is reached Tab stops occur every eight character positions When Insert Mode is on characters following the cursor are moved to the right as typed characters are inserted before them at the current cursor position After each keystroke the cursor moves one position to the right Line wrapping is observed That is as characters move off the right side of the screen they are inserted from the left on subsequent lines Insertions increase logical line length When Insert Mode is on pressing the TAB key causes blanks to be inserted from current cursor position to the next tab stop Line wrapping is observed as above Places the computer in a pause state To resume operation press any other key Causes characters printed on the screen to echo to the line printer Ipt1 In other words you will be printing what you type on the screen Pressing CTRL PRTSC a second time turns off the echoing of characters to Ipt1 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 204 html 4 of 6 28 03 2004 21 28 57 GW BASIC User s Guide SHIFT PRTSC Sends the current screen contents to the printer effectively creating a sn
152. error is reset by subsequent inputs but the character causing the error is lost A Device fault error occurs if data set ready DSR is lost during I O A Parity error occurs if the PE parity enable option was used in the OPEN COM statement and incorrect parity was received F 5 The INPUT Function The INPUTS function is preferred over the INPUT and LINE INPUT statements for reading COM files because all ASCII characters may be significant in communications INPUT is least desirable because input stops when a comma or an enter is seen LINE INPUT terminates when an enter is seen INPUTS allows all characters read to be assigned to a string INPUTS returns x characters from the y file The following statements then are most efficient for reading a COM file 10 WHILE NOT EOF 1 20 AS INPUTS LOC 1 1 OU esa 40 Process data returned in AS 50 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20F html 2 of 7 28 03 2004 21 28 59 GW BASIC User s Guide 60 WEND This sequence of statements translates As long as something is in the input queue return the number of characters in the queue and store them in A If there are more than 255 characters only 255 are returned at a time to prevent string overflow If this is the case EOF 1 is false and input continues until the input queue is empty GET and PUT Statements for COM Files Purpose To allow fixed length I O for COM Syntax
153. es The following examples simulate error 15 the code for String too long 10 S 10 20 T 5 30 ERROR S T 40 END RUN String too long in 30 Or in direct mode ERROR 15 you type this line String too long GW BASIC types this line file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ERROR html 1 of 2 28 03 2004 21 29 25 GW BASIC User s Guide The following example includes a user defined error code message 110 ON ERROR GOTO 400 120 INPUT WHAT IS YOUR BEI 130 IF B gt 5000 THEN ERROR 210 400 IF ERR 210 THEN PRINT HOUSE LIMIT IS 5000 410 IF ERL 130 THEN RESUME 120 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ERROR html 2 of 2 28 03 2004 21 29 25 GW BASIC User s Guide EXP Function Purpose To return e the base of natural logarithms to the power of x Syntax EXP x Comments x must be less than 88 02969 If EXP overflows the Overflow error message appears machine infinity with the appropriate sign is supplied as the result and execution continues EXP x is calculated in single precision unless the d switch is used when GW BASIC is executed Examples 10 X 5 20 PRINT EXP X 1 RUN 54259315 Prints the value of e to the 4th power file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic EXP htm128 03 2004 21 29 26 GW BASIC User s Guide EXTERR Function Purpose To return extended error information Syntax EXTERR n
154. es the first 20 positions bytes in the random file buffer to the string variable N the next 10 positions to ID and the next 40 positions to ADD FIELD 1 20 AS NS 10 AS IDS 40 AS ADDS FIELD only allocates space it does not place any data in the random file buffer The total number of bytes allocated in a FIELD statement must not exceed the record length specified when the file was opened Otherwise a Field overflow error occurs the default record length is 128 Any number of FIELD statements may be executed for the same file and all FIELD statements executed are in effect at the same time Note Do not use a fielded variable name in an INPUT or LET statement Once a variable name is fielded it points to the correct place in the random file buffer If a subsequent INPUT or LET statement with that variable name is executed the variable s pointer is moved to string space see LSET RSET and GET statements file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic FIELD htm128 03 2004 21 29 26 GW BASIC User s Guide LSET and RSET Statements Purpose To move data from memory to a random file buffer and left or right justify it in preparation for a PUT statement Syntax LSET string variable string expression RSET string variable string expression Comments If string expression requires fewer bytes than were fielded to string variable LSET left justifies the string in the field and RSET right justif
155. essed returns nA AUNE CO 1 if trigger A2 is currently pressed returns 1 if trigger Al was pressed since the last STRIG 0 statement returns 0 if not 0 if not 1 if trigger B1 was pressed since the last STRIG 2 statement returns 0 if not 0 if not 1 if trigger A2 was pressed since the last STRIG 4 statement returns 0 if not 0 if not file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic STRIG htm128 03 2004 21 29 49 GW BASIC User s Guide STRIG n Statement Purpose To allow the use of a joystick by enabling or disabling the trapping of its buttons Syntax STRIG n ON STRIG n OFF STRIG n STOP Comments nis 0 2 4 or 6 corresponding to the buttons on the joystick where 0 is button Al 2 is button B1 4 is button A2 6 is button B2 Examples STRIG n ON Enables trapping of the joystick buttons After this statement is executed GW BASIC checks to see if this button has been pressed before executing following statements STRIG n OFF Disables GW BASIC from checking the state of the button STRIG n STOP Disables trapping of a given button through the ON STRIG n statement But any pressings are remembered so that trapping may take place once it is reenabled file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic STRIGN htm128 03 2004 21 29 49 GW BASIC User s Guide SWAP Statement Purpose To exchange the values of two variables Syntax
156. eters GW BASIC remains in memory while the child process is running When the child process finishes GW BASIC continues at the statement following the SHELL statement SHELL with no string will go to MS DOS You may now do anything that COMMAND allows When ready to return to GW BASIC type the MS DOS command EXIT Examples SHELL ADIR A gt EXIT Write some data to be sorted use SHELL SORT to sort it then read the sorted data to write a report 10 OPEN SORTIN DAT FOR OUTPUT AS 1 20 write data to be sorted 1000 CLOSE 1 1010 SHELL SORT lt SORTIN DAT gt SORTOUT DAT file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SHELL html 1 of 2 28 03 2004 21 29 24 GW BASIC User s Guide 1020 OPEN SORTOUT DAT FOR INPUT AS 1 1030 Process the sorted data file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SHELL html 2 of 2 28 03 2004 21 29 24 GW BASIC User s Guide EOF Function Purpose To return 1 true when the end of a sequential or a communications file has been reached or to return 0 if end of file EOF has not been found Syntax vV EOF file number Comments If a GET is done past the end of the file EOF returns 1 This may be used to find the size of a file using a binary search or other algorithm With communications files a 1 indicates that the buffer is empty Use EOF to test for end of file while inputting to avoid Input Past End errors Examples 10 O
157. ettings Lorenzo Desktop GW 20Basic DEFSEG html 1 of 2 28 03 2004 21 29 22 GW BASIC User s Guide DEF and SEG must be separated by a space Otherwise GW BASIC will interpret the statement DEFSEG 100 to mean assign the value 100 to the variable DEFSEG file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DEFSEG html 2 of 2 28 03 2004 21 29 22 GW BASIC User s Guide PEEK Function Purpose To read from a specified memory location Syntax PEEK a Comments Returns the byte decimal integer within the range of 0 to 255 read from the specified memory location a a must be within the range of 0 to 65535 The DEF SEG statement last executed determines the absolute address that will be peeked into PEEK is the complementary function to the POKE statement Examples 10 A PEEK amp H5A00 The value of the byte stored in user assigned hex offset memory location 5A00 23040 decimal will be stored in the variable A file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PEEK htm128 03 2004 21 29 22 GW BASIC User s Guide POKE Statement Purpose To write poke a byte of data into a memory location Syntax POKE a b Comments a and b are integer expressions The integer expression a is the offset address of the memory location to be poked The DEF SEG statement last executed determines the address GW BASIC does not check any offsets that are specified The integer expression b is t
158. ext or graphics currently displayed on the screen using attribute 3 are instantaneously changed to color 2 All text or graphics subsequently displayed with attribute 3 will also be displayed in color 2 The new palette of colors will contain 0 1 2 and 2 With the USING option all entries in the palette can be modified in one PALETTE statement The integer array name argument is the name of an integer array and the arrayindex specifies the index of the first array element in the integer array name to use in setting your palette Each attribute in the palette is assigned a corresponding color from this integer array The file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PALETTE html 1 of 3 28 03 2004 21 29 16 GW BASIC User s Guide array must be dimensioned large enough to set all the palette entries after arrayindex For example if you are assigning colors to all 16 attributes and the index of the first array element given in your PALETTE USING statement is 5 then the array must be dimensioned to hold at least 20 elements since the number of elements from 5 20 inclusive is 16 DIM PALS 20 PALETTE USING PAL 5 If the color argument in an array entry is 1 then the mapping for the associated attribute is not changed All other negative numbers are illegal values for color You can use the color argument in the COLOR statement to set the default text color Remember that color arguments in other BASIC stat
159. f in this mode Mode 9 allows the highest resolution possible for the EGA Enhanced Color Display configuration Programs written for this mode will not work for any other hardware configuration EGA with Monochrome Display Mode 10 The IBM Monochrome Display can be used to display monochrome graphics at a very high resolution in this mode Programs written for this mode will not work for any other hardware configuration Arguments The mode argument is an integer expression with legal values 0 1 2 7 8 9 and 10 All other values are illegal Selection of a mode argument depends primarily on your program s anticipated display hardware as described above Each of the SCREEN modes is described individually in the following paragraphs SCREEN 0 e Text mode only e Either 40 x 25 or 80 x 25 text format with character box size of 8 x 8 8 x 14 with EGA e Assignment of 16 colors to any of 2 attributes e Assignment of 16 colors to any of 16 attributes with EGA SCREEN 1 e 320 x 200 pixel medium resolution graphics e 80 x 25 text format with character box size of 8 x 8 e Assignment of 16 colors to any of 4 attributes e Supports both EGA and CGA e 2 bits per pixel SCREEN 2 e 640 x 200 pixel high resolution graphics e 40 x 25 text format with character box size of 8 x 8 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SCREENS html 2 of 7 28 03 2004 21 29 16 GW BASIC User s Guide e Assignment of 16 colors
160. fault attributes for SCREEN 10 monochrome display Attribute Value Displayed Pseudo Color 0 Off 1 On normal intensity 2 Blink 3 On high intensity The following are color values for SCREEN 10 monochrome display Color Value Displayed Pseudo Color 0 Off 1 Blink off to on 2 Blink off to high intensity 3 Blink on to off 4 On 5 Blink on to high intensity 6 Blink high intensity to off 7 Blink high intensity to on 8 High intensity For both composite monitors and TVs the colorswitch is a numeric expression that is either true non zero or false zero A value of zero disables color and permits display of black and white images only A nonzero value permits color The meaning of the colorswitch argument is inverted in SCREEN mode 0 For hardware configurations that include an EGA and enough memory to support multiple screen pages two arguments are available These apage and vpage arguments determine the active and visual memory pages The active page is the area in memory where graphics statements are written the visual page is the area of memory that is displayed on the screen Animation can be achieved by alternating the display of graphics pages The goal is to display the file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SCREENS html 4 of 7 28 03 2004 21 29 16 GW BASIC User s Guide visual page with completed graphics output while executing graphics statements in one or more active pages A pa
161. fer with a disk file or device This association exists until a CLOSE or CLOSE file number statement is executed file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic OPEN html 1 of 5 28 03 2004 21 29 39 GW BASIC User s Guide reclen is an integer expression within the range of 1 32767 that sets the record length to be used for random files If omitted the record length defaults to 128 byte records When reclen is used for sequential files the default is 128 bytes and reclen cannot exceed the value specified by the s switch A disk file must be opened before any disk I O operation can be performed on that file OPEN allocates a buffer for I O to the file and determines the mode of access that is used with the buffer More than one file can be opened for input or random access at one time with different file numbers For example the following statements are allowed OPEN B TEMP FOR INPUT AS 1 OPEN B TEMP FOR INPUT AS 2 However a file may be opened only once for output or appending For example the following statements are illegal OPEN TEMP FOR OUTPUT AS 1 OPEN TEMP FOR OUTPUT AS 2 Note Be sure to close all files before removing diskettes from the disk drives see CLOSE and RESET A device may be one of the following nee Be Crops Disk Drive KYBD Keyboard input only SCRN Screen output only LPT1 Line Printer 1 LPT2 Line Printer 2 LPT3 Line Printer 3 COMI RS 232 Communications 1
162. file was opened under With communications files LOF returns the amount of free space in the input buffers Examples The following sequence gets the last record of the random access file file big and assumes that the file was created with a default record length of 128 bytes 10 OPEN RR 1 FILE BIG 20 GET 1 LOF 1 128 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LOF htm128 03 2004 21 29 37 GW BASIC User s Guide LOG Function Purpose To return the natural logarithm of x Syntax LOG x Comments x must be a number greater than zero LOG x is calculated in single precision unless the d switch is used when GW BASIC is executed Examples PRINT LOG 2 6931471 PRINT LOG 1 0 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LOG htm128 03 2004 21 29 37 GW BASIC User s Guide LPOS Function Purpose To return the current position of the line printer print head within the line printer buffer Syntax LPOS x Comments LPOS does not necessarily give the physical position of the print head x is a dummy argument If the printer has less than the 132 characters per line capability it may issue internal line feeds and not inform the computer internal line printer buffer If this has happened the value returned by LPOS x may be incorrect LPOS x simply counts the number of printable characters since the last line feed was issued Examples
163. filename offset Comments filename is a valid string expression containing the device and filename offset is a valid numeric expression within the range of 0 to 65535 This is the offset into the segment declared by the last DEF SEG statement where loading is to start If offset is omitted the offset specified at BSAVE is assumed that is the file is loaded into the same location it was saved from Note BLOAD does not perform an address range check It is possible to BLOAD anywhere in memory You must not BLOAD over the GW BASIC stack space a GW BASIC program or the GW BASIC variable area While BLOAD and BSAVE are useful for loading and saving machine language programs they are not restricted to them The DEF SEG statement lets you specify any segment as the source or target for BLOAD and BSAVE For example this allows the video screen buffer to be read from or written to the diskette BLOAD and BSAVE are useful in saving and displaying graphic images Examples 10 DEF SEG amp HB800 20 BLOAD PICTURE 0 The DEF SEG statement in line 10 points the segment at the screen buffer The DEF SEG statement in line 10 and the offset of 0 in line 20 guarantee that the correct address is used The BLOAD command in line 20 loads the file named picture into the screen buffer Note file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic BLOAD html 1 of 2 28 03 2004 21 29 13 GW BASIC User s Guide The BSAVE
164. finity with the sign of the numerator is supplied as the result of the division and execution continues If the evaluation of an exponentiation results in zero being raised to a negative power the Division by zero error message appears positive machine infinity is supplied as the result of the exponentiation and execution continues If overflow occurs the Overflow error message appears machine infinity with the algebraically correct sign is supplied as the result and execution continues The errors that occur in overflow and division by zero will not be trapped by the error trapping function 6 4 2 Relational Operators Relational operators let you compare two values The result of the comparison is either true 1 or false 0 This result can then be used to make a decision regarding program flow Table 6 1 displays the relational operators Table 6 1 Relational Operators OperatorRelation Tested Expression Equality X Y lt gt Inequality X lt gt Y Less than XSI Greater than X gt Y lt Less than or equal to X lt Y file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 6 html 8 of 12 28 03 2004 21 29 00 GW BASIC User s Guide vm Greater than or equal toX gt Y The equal sign is also used to assign a value to a variable See the LET statement in the GW BASIC User s Reference When arithmetic and relational operators are combined in one expression the arithmetic is always performed firs
165. following special functions FILIST F2 RUNH F3LOAD F4 SAVE FSCONTA Fo p LETLI gl F7TRONA F8 TROFFI FOKEY FIOSCREEN 0004 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic KEY html 1 of 3 28 03 2004 21 28 58 GW BASIC User s Guide Note _ arrow means that you do not have to press RETURN after each of these keys has been pressed Any one or all of the 10 keys may be redefined When the key is pressed the data assigned to it will be input to the program KEY key number string expression Assigns the string expression to the specified key KEY LIST List all 10 key values on the screen All 15 characters of each value are displayed KEY ON Displays the first six characters of the key values on the 25th line of the screen When the display width is set at 40 five of the 10 keys are displayed When the width is set at 80 all 10 are displayed KEY OFF Erases the key display from the 25th line making that line available for program use KEY OFF does not disable the function keys If the value for key number is not within the range of 1 to 10 or 15 to 20 an Illegal function call error occurs The previous KEY assignment is retained Assigning a null string length 0 disables the key as a function key When a function key is redefined the INKEYS function returns one character of the assigned string per invocation If the function key is disabled INKEYS returns a string of two characters the f
166. following uses 64K bytes of memory and three files Allocates 512 bytes to RS 232 receive buffers and 128 bytes to transmit buffers and loads and executes the program file tty bas A gt gwbasic TTY C 512 For more information about RS 232 Communications see Appendix F Redirection of Standard Input and Output When redirected all INPUT LINE INPUT INPUTS and INKEYS statements are read from the specified input file instead of the keyboard All PRINT statements write to the specified output file instead of the screen Error messages go to standard output and to the screen File input from KYBD is still read from the keyboard File output to SCRN still outputs to the screen GW BASIC continues to trap keys when the ON KEY n statement is used Typing CTRL BREAK when output is redirected causes GW BASIC to close any open files issue the message Break in line nnnn to standard output exit GW BASIC and return to MS DOS When input is redirected GW BASIC continues to read from this source until a CTRL Z is detected This condition can be tested with the end of file EOF function If the file is not terminated by a CTRL Z or if a GW BASIC file input statement tries to read past the end of file then any open files are closed and GW BASIC returns to MS DOS file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 202 html 4 of 8 28 03 2004 21 28 57 GW BASIC User s Guide For further information about these
167. g File 1 is opened for asynchronous I O at 1200 bits second No parity is to be produced or checked 10 OPEN COM1 1200 N 8 AS 1 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic OPENCOMN html 2 of 2 28 03 2004 21 29 40 GW BASIC User s Guide OUT Statement Purpose To send a byte to a machine output port Syntax OUT h j Comments hand j are integer expressions h may be within the range of 0 to 65535 j may be within the range of 0 to 255 h is a machine port number and j is the data to be transmitted OUT is the complementary statement to the INP function Examples 100 OUT 12345 225 Outputs the decimal value 225 to port number 12345 In assembly language this is equivalent to the following MOV DX 12345 MOV AL 255 OUT DX AL file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic OUT htm128 03 2004 21 29 41 GW BASIC User s Guide PCOPY Command Purpose To copy one screen page to another in all screen modes Syntax PCOPY sourcepage destinationpage Comments The sourcepage is an integer expression in the range 0 to n where n is determined by the current video memory size and the size per page for the current screen mode The dest inationpage has the same requirements as the sourcepage For more information see CLEAR and SCREEN Examples This copies the contents of page 1 to page 2 PCOPY 1 2 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20B
168. g the GOSUB entry that the trap created When a trap is made for a particular event the trap automatically causes a STOP on that event so that recursive traps can never take place The RETURN from the trap routine automatically does an ON unless an explicit OFF has been performed inside the trap routine The non local RETURN must be used with care Any GOSUB WHILE or FOR statement active at the time of the trap remains active file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic RETURN htm128 03 2004 21 29 45 GW BASIC User s Guide RMDIR Command Purpose To delete a subdirectory Syntax RMDIR pathname Comments pathname is a string expression not exceeding 63 characters identifying the subdirectory to be removed from its parent The subdirectory to be deleted must be empty of all files except and ora Path file access error is given Examples Referring to the sample directory structure illustrated in CHDIR the following command deletes the subdirectory report RMDIR SALES JOHN REPORT file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic RMDIR htm128 03 2004 21 29 45 GW BASIC User s Guide RUN Command Purpose To execute the program currently in memory or to load a file from the diskette into memory and run it Syntax RUN line number r RUN filename r Comments RUN or RUN line number runs the program currently in memory If line number is spec
169. ge is displayed only when graphics output to that page is complete Thus the following program fragment is typical SCREEN Je Ly 2 work in page 1 Graphics output to page 1 while viewing page 2 SCREEN 7 721 work in page 2 Graphics output to page 2 while viewing page 1 show page 1 show page 2 The number of pages available depends on the SCREEN mode and the amount of available memory as described in the following table Table 2 SCREEN Mode Specifications Mode 0 1 10 4 Numbers in the range 16 31 are blinking versions of the colors 0 15 Resolution Attribute Color Range 40 column text NA 80 column text NA 320x200 640x200 320x200 640x200 640x350 640x350 0 36 0 1 0 15 0 15 0 3 0 15 0 15 0 3 Range 0 15a 0 15a 0 3 0 1 0 15 0 15 0 15 0 63 0 63 0 8 b Attributes applicable only with EGA Attributes and Colors EGA Memory Pages NA NA NA NA 64K 128K 256K 64K 128K 256K 64K 128K 256K 128K 256K 1 NOR Re BRN RK OO BN KF Ke N Page Size 2K 4K 16K 16K 32K 64K 64K 128K 128K file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SCREENS html 5 of 7 28 03 2004 21 29 16 GW BASIC User s Guide For various screen modes and display hardware configurations different attribute and color settings exist See the PALETTE statement for a discussion of attribute and color number The majorit
170. gher numbered lines 1inenumber lists lines from the beginning of the program through the specified line The period can replace either 1 inenumber to indicate the current line Any listing may be interrupted by pressing ctrl break Examples List Lists all lines in the program LIST 20 Lists lines 1 through 20 LIST 10 20 Lists lines 10 through 20 LIST 20 Lists lines 20 through the end of the program file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LIST htm128 03 2004 21 29 35 GW BASIC User s Guide LLIST Command Purpose To list all or part of the program currently in memory to the line printer Syntax LLIST line number line number LLIST line number Comments GW BASIC always returns to command level after a LLIST is executed The line range options for LLIST are the same as for LIST Examples See the examples in the LIST statement file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LLIST htm128 03 2004 21 29 35 GW BASIC User s Guide LOAD Command Purpose To load a file from diskette into memory Syntax LOAD filename r Comments filename is the filename used when the file was saved If the extension was omitted BAS will be used LOAD closes all open files and deletes all variables and program lines currently residing in memory before it loads the designated program If the r option is used with LOAD the program runs after it
171. h file requires 194 bytes for the File Control Block FCB plus 128 bytes for the data buffer The data buffer size may be altered with the s switch If the switch is omitted the maximum number of open files defaults to 3 This switch is ignored unless the i switch is also specified on the command line i makes GW BASIC statically allocate space required for file operations based on the s and switches s n sets the maximum record length allowed for use with files The record length option in the OPEN statement cannot exceed this value If the s switch is omitted the record length defaults to 128 bytes The maximum record size is 32767 c n controls RS 232 communications If RS 232 cards are present c 0 disables RS 232 support and any subsequent I O attempts for each RS 232 card present If the c switch is omitted 256 bytes are allocated for the receive buffer and 128 bytes for the transmit buffer for each card present The c switch has no affect when RS 232 cards are not present The c n switch allocates n bytes for the receive buffer and 128 bytes for the transmit buffer for each RS 232 card present m n n sets the highest memory location first n and maximum block size second n used by GW BASIC GW BASIC attempts to allocate 64K bytes of memory for the data and stack segments If machine language subroutines are to be used with GW BASIC programs use the m switch to set the highest location that GW BASIC
172. he data to be poked b must be within the range of 0 to 255 a must be within the range of 0 to 65535 The complementary function to POKE is PEEK The argument to PEEK is an address from which a byte is to be read POKE and PEEK are useful for efficient data storage loading assembly language subroutines and for passing arguments and results to and from assembly language subroutines Examples 20 POKE amp H5A00 amp HFF Places the decimal value 255 amp HFF into the hex offset location 23040 decimal See PEEK function example file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic POKE htm128 03 2004 21 29 22 GW BASIC User s Guide DELETE Command Purpose To delete program lines or line ranges Syntax DELETE line numberi line number2 DELETE line number1 Comments line number1 is the first line to be deleted line number2 is the last line to be deleted GW BASIC always returns to command level after a DELETE command is executed Unless at least one line number is given an Illegal Function Call error occurs The period may be used to substitute for either line number to indicate the current line Examples DELETE 40 Deletes line 40 DELETE 40 100 Deletes lines 40 through 100 inclusively DELETE 40 Deletes all lines up to and including line 40 DELETE 40 Deletes all lines from line 40 to the end of the program file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic D
173. he decimal equivalent of the ASCII symbol for the minus sign file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PRINT html 2 of 2 28 03 2004 21 29 31 GW BASIC User s Guide STRING Function Purpose To return e astring of length n whose characters all have ASCII code j or e the first character of x Syntax STRINGS n j STRINGS n x Comments STRINGS is also useful for printing top and bottom borders on the screen or the printer n and j are integer expressions in the range 0 to 255 Examples 10 XS STRINGS 10 45 20 PRINT X MONTHLY REPORT X RUN MONTHLY REPORT 45 is the decimal equivalent of the ASCII symbol for the minus sign Appendix C in the GW BASIC User s Guide lists ASCII character codes file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic STRINGS htm128 03 2004 21 29 31 GW BASIC User s Guide LPRINT and LPRINT USING Statements Purpose To print data at the line printer Syntax LPRINT list of expressions LPRINT USING string exp list of expressions Comments list of expressions consists of the string or numeric expression separated by semicolons string expressions is a String literal or variable consisting of special formatting characters The formatting characters determine the field and the format of printed strings or numbers These statements are the same as PRINT and PRINT USING except that output goes to the li
174. he left SHIFT key is pressed TER amp HOI The right SHIFT key is pressed For trapping shifted keys you may use the value amp HO1 amp H02 or amp H03 The left and right SHIFT keys are coupled when amp H03 is used Refer to the KEY n statement for more information No type of trapping is activated when GW BASIC is in direct mode Function keys resume their standard expansion meaning during input A key that causes a trap is not available for examination with the INPUT or INKEYS statement so the trap routine for each key must be different if a different function is desired If CTL PRTSCR is trapped the line printer echo toggle is processed first Defining CTL PRTSCR as a key trap does not prevent characters from being echoed to the printer if CTL PRTSCR is pressed Function keys 1 through 14 are predefined Therefore setting scan codes 59 68 72 75 77 or 80 has no effect PLAY Trapping A PLAY event trap is issued only when playing background music PLAY MB PLAY event music traps are not issued when running in MUSIC foreground default case or PLAY MF Choose conservative values for n An ON PLAY 32 statement will cause event traps so often that there will be little time to execute the rest of your program The ON PLAY n statement causes an event trap when the background music queue goes from n to n 1 notes file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ONCOMN html 3 of 5 28 03 2004 21
175. hen an Assembly Language Subroutine is called the GW BASIC program execution is paused and control is transferred to the Assembly Language program When that program is executed control is returned to the GW BASIC program at the point of interruption Examples 190 DEF SEG 0 200 DEF USRO 24000 210 X USRO Y 2 2 82 Lines 190 and 200 set the absolute address Line 210 calls the USR routine located at that address and passes the integer value of the expression contained within the parentheses to the user program see USR Note This statement is given here primarily to provide compatibility with other GW BASIC file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DEFUSR html 1 of 2 28 03 2004 21 29 05 GW BASIC User s Guide implementations The more versatile CALL statement should be used if this downward compatibility is unimportant file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DEFUSR html 2 of 2 28 03 2004 21 29 05 GW BASIC User s Guide USR Function Purpose To call an assembly language subroutine Syntax v USR n argument Comments n specifies which USR routine is being called argument can be any numeric or string expression Although the CALL statement is recommended for calling assembly language subroutines the USR function call may also be used See Appendix D in the GW BASIC User s Guide for a comparison of CALL and USR and for a detailed discussion of calling assembl
176. iables using VARPTRS variable Example 1 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DRA W html 2 of 3 28 03 2004 21 29 17 GW BASIC User s Guide To draw a box in medium resolution 10 SCREEN 1 20 A 20 30 DRAW U A R A D A L A Example 2 The aspect ratio to draw a square on a standard screen is 4 3 as shown below To draw a 96 pixel wide square on a 640 x 200 pixel screen SCREEN 2 do the following calculations Horizontal value 96 Vertical value 96 200 640 4 3 or Vertical value 40 Horizontal value 40 640 200 3 4 The horizontal values equals 4 3 of the vertical values Example 3 To draw a triangle in medium resolution 10 CLS 20 SCREEN 1 30 PSET 60 125 40 DRAW E100 F100 L199 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DRA W html 3 of 3 28 03 2004 21 29 17 GW BASIC User s Guide LINE Statement Purpose To draw lines and boxes on the screen Syntax LINE xi vi 2 2 attribute B F lystviel Comments x1 y1 and x2 y2 specify the end points of a line Resolution mode is determined by the SCREEN statement attribute specifies color or intensity of the displayed pixel see the COLOR and PALETTE statements B box draws a box with the points x1 y1 and x2 y2 at opposite corners BF filled box draws a box as B and fills in the interior with points Note If attribute is n
177. icant digit if printed will not always be accurate You should be very careful when making conversions between integer single precision and double precision variables The following variable is a single precision value by default ABC Variables beginning with FN are assumed to be calls to a user defined function file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 6 html 3 of 12 28 03 2004 21 29 00 GW BASIC User s Guide The GW BASIC statements DEF INT DEFSTR DEFSNG and DEFDBL may be included in a program to declare the types of values for certain variable names 6 2 3 Array Variables An array is a group or table of values referenced by the same variable name Each element in an array is referenced by an array variable that is a subscripted integer or an integer expression The subscript is enclosed within parentheses An array variable name has as many subscripts as there are dimensions in the array For example V 10 references a value in a one dimensional array while T 1 4 references a value in a two dimensional array The maximum number of dimensions for an array in GW BASIC is 255 The maximum number of elements per dimension is 32767 Note If you are using an array with a subscript value greater than 10 you should use the DIM statement Refer to the GW BASIC User s Reference for more information If a subscript greater than the maximum specified is used you will receive the error me
178. ices that constitute a system In software the total of the software modules and their interrelationships constant A never changing value or data item coprocessor A microprocessor device connected to a central microprocessor that per forms specialized computations such as floating point arithmetic much more efficiently than the CPU alone cursor A blinking line or box on a computer screen that indicates the next location for data entry data A general term used to signify all the basic information elements that can be produced or processed by a computer See information data element The smallest named physical data unit data file A collection of related data records organized in a specific manner Data files contain computer records which contain information as opposed to containing data handling information or a program file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 6 of 17 28 03 2004 21 29 08 GW BASIC User s Guide debug The process of checking the logic of a computer program to isolate and remove mistakes from the program or other software default An action or value that the computer automatically assumes unless a different instruction or value is given delimit To establish parameters to set a minimum and a maximum delimiter A character that marks the beginning or end of a unit of data on a storage medium Commas semi colons periods and spaces are used as delimiters to
179. idth setting WIDTH LPTI 512e file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic WIDTH html 1 of 2 28 03 2004 21 29 32 GW BASIC User s Guide A statement of the following form recognizes this stored width value OPEN LPT1 FOR OUTPUT AS number and uses it while the file is open WIDTH file number size If the file is open to Ipt1 line printer width is immediately changed to the new size specified This allows the width to be changed at will while the file is open This form of WIDTH has meaning only for Ipt1 After outputting the indicated number of characters from the open file GW BASIC inserts a carriage return at the end of the line and wraps the output if the width is less than the length of the record Valid widths for the line printer are 1 through 255 Specifying WIDTH 255 for the line printer Iptl enables line wrapping This has the effect of infinite width Any value entered outside of these ranges results in an Illegal function call error The previous value is retained Using the WIDTH statement on a communications file causes a carriage return to be sent after the number of characters specified by the size attribute It does not alter either the receive or transmit buffer Examples 10 WIDTH LETI 75 20 OPEN LPT1 FOR OUTPUT AS 1 6020 WIDTH 1 40 Line 10 stores a line printer width of 75 characters per line Line 20 opens file 1 to the line printer and sets the width to 75 f
180. ies the string spaces are used to pad the extra positions If the string is too long for the field characters are dropped from the right To convert numeric values to strings before the LSET or RSET statement is used see the MKI MKS and MKD functions LSET or RSET may also be used with a nonfielded string variable to left justify or right justify a string in a given field Examples 110 AS SPACES 20 120 RSET AS N These two statements right justify the string N in a 20 character field This can be valuable for formatting printed output file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LSET htm128 03 2004 21 29 26 GW BASIC User s Guide GET Statement Files Purpose To read a record from a random disk file into a random buffer Syntax GET file number record number Comments file number is the number under which the file was opened record number is the number of the record within the range of 1 to 16 777 215 If record number is omitted the next record after the last GET is read into the buffer After a GET statement INPUT and LINE INPUT may be used to read characters from the random file buffer GET may also be used for communications files record number is the number of bytes to be read from the communications buffer record number cannot exceed the buffer length set in the OPEN COM n statement Examples The following example opens the vendor file for random access
181. if the error was on a character device It will contain the 2 byte block device name A B etc if the device was not a character device Examples Installed device driver Ipt2 caused a Printer out of paper error via INT 24H ERDEV contains the error number 9 in the lower 8 bits while the upper 8 bits contain the upper byte of the Device Header word attributes ERDEVS contains LPT2 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ERDEV htm128 03 2004 21 29 25 GW BASIC User s Guide ERR and ERL Variables Purpose To return the error code ERR and line number ERL associated with an error Syntax v ERR v ERL Comments The variable ERR contains the error code for the last occurrence of an error All the error codes and their definitions are listed in Appendix A of the GW BASIC User s Guide The variable ERL contains the line number of the line in which the error was detected The ERR and ERL variables are usually used in IF THEN or ON ERROR GOTO or GOSUB statements to direct program flow in error trapping If the statement that caused the error was a direct mode statement ERL will contain 65535 To test if an error occurred in a direct mode statement use a line of the following form IF 65535 ERL THEN Otherwise use the following 10 IF ERR error code THEN GOSUB 4000 20 IF ERL line number THEN GOSUB 4010 Note If the line number is not on the right side of the relational oper
182. ified execution begins on that line Otherwise execution begins at the lower line number If there is no program in memory when RUN is executed GW BASIC returns to command level RUN filename closes all open files and deletes the current memory contents before loading the specified file from disk into memory and executing it The r option keeps all data files open If you are using the speaker on the computer please note that executing the RUN command will turn off any sound that is currently running and will reset to Music Foreground Also the PEN and STRIG Statements are reset to OFF Examples RUN NEWFIL R Runs NEWFIL BAS without closing data files file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic RUN htm128 03 2004 21 29 45 GW BASIC User s Guide SAVE Command Purpose To save a program file on diskette Syntax SAVE filename a SAVE filename p Comments filename is a quoted string that follows the normal MS DOS naming conventions If filename already exists the file will be written over If the extension is omitted bas will be used The a option saves the file in ASCII format Otherwise GW BASIC saves the file in a compressed binary format ASCII format takes more space on the diskette but some diskette access commands for example the MERGE command and some MS DOS commands such as TYPE may require an ASCII format file The p option protects the file by saving it in an e
183. ill not have the current directory information written on the directory track RESET closes all open files on all drives and writes the directory track to every diskette with open files file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic RESET htm128 03 2004 21 29 40 GW BASIC User s Guide UNLOCK Statement Purpose To release locks that have been applied to an opened file This is used in a multi device environment often referred to as a network or network environment Syntax UNLOCK n record number TO record number Comments n is the number that was assigned the file as it was originally numbered in the program record number is the number of the individual record that is to be unlocked Or if a range of records are to be unlocked record number designates the beginning and ending record of the specified range The range of legal record numbers is 1 to 232 1 The limit on record size is 32767 bytes The record range specified must be from lower to the same or higher record numbers If a starting record number is not specified the record number 1 is assumed If an ending record number is not specified then only the specified record is unlocked The following are legal UNLOCK statements UNLOCK n unlocks the entire file n UNLOCK n X unlocks record x only UNLOCK n TO Y unlocks records through y UNLOCK n X TO Y unlocks records x through Y The locked file or record range should be unlocked b
184. ine All physical screen lines are erased until the terminating RETURN is found Moves the cursor to the end of the logical line Characters typed from this position are added to the line Moves the cursor to the beginning of the next screen line This lets you create logical program lines which are longer than the physical screen width Logical lines may be up to 255 characters long This function may also be used as a line feed Enters a line into the GW BASIC program It also moves the cursor to the next logical line Erases the entire logical line on which the cursor is located file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 204 html 3 of 6 28 03 2004 21 28 57 GW BASIC User s Guide CTRL G CTRL K or HOME CTRL HOME or CTRL L CTRL R or INS CTRL NUM LOCK or CTRL S CTRL PRTSC Causes a beep to emit from your computer s speaker Moves the cursor to the upper left corner of the screen The screen contents are unchanged Clears the screen and positions the cursor in the upper left corner of the screen Turns the Insert Mode on and off Insert Mode is indicated by the cursor blotting the lower half of the character position In Graphics Mode the normal cursor covers the whole character position When Insert Mode is active only the lower half of the character position is blanked by the cursor When Insert Mode is off characters typed replace existing characters on the line The SPACEBAR
185. ings Lorenzo Desktop GW 20Basic MKDIR htm128 03 2004 21 29 38 GW BASIC User s Guide NAME Command Purpose To change the name of a disk file Syntax NAME old filename AS new filename Comments old filename must exist and new filename must not exist otherwise an error results After a NAME command the file exists on the same diskette in the same disk location with the new name Examples NAME ACCTS AS LEDGER The file formerly named ACCTS will now be named LEDGER The file content and physical location on the diskette is unchanged file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic NAME htm128 03 2004 21 29 38 GW BASIC User s Guide NEW Command Purpose To delete the program currently in memory and clear all variables Syntax NEW Comments NEW is entered at command level to clear memory before entering a new program GW BASIC always returns to command level after a NEW is executed Examples NEW Or 980 PRINT Do You Wish To Quit Y N 990 ANSS INKEYS IF ANSS THEN 990 1000 IF ANSS Y THEN NEW 1010 IF ANSS N THEN 980 1020 GOTO 990 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic NEW htm128 03 2004 21 29 38 GW BASIC User s Guide ON ERROR GOTO Statement Purpose To enable error trapping and specify the first line of the error handling subroutine Syntax ON ERROR GOTO line number Comments Once error trapping has been enabled all err
186. into a string variable ignoring delimiters Syntax LINE INPUT prompt string string variable Comments prompt string is a string literal displayed on the screen that allows user input during program execution A question mark is not printed unless it is part of prompt string string variable accepts all input from the end of the prompt to the carriage return Trailing blanks are ignored LINE INPUT is almost the same as the INPUT statement except that it accepts special characters such as commas in operator input during program execution If a line feed carriage return sequence this order only is encountered both characters are input and echoed Data input continues If LINE INPUT is immediately followed by a semicolon pressing the RETURN key will not move the cursor to the next line A LINE INPUT may be escaped by typing CTRL BREAK GW BASIC returns to command level and displays Ok Typing CONT resumes execution at the LINE INPUT line Example 100 LINE INPUT A Program execution pauses at line 100 and all keyboard characters typed thereafter are input to string A until RETURN CTRL M CTRL C Or CTRL BREAK is entered file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LINEINPUT htm128 03 2004 21 29 35 GW BASIC User s Guide LINE INPUT Statement Purpose To read an entire line up to 255 characters without delimiters from a sequential disk file to a string variable Syntax LIN
187. ion FIELD Statement Copyright Microsoft Corporation 1986 1987 All rights reserved Portions copyright COMPAQ Computer Corporation 1985 Simultaneously published in the United States and Canada Microsoft MS DOS GW BASIC and the Microsoft logo are registered trademarks of Microsoft Corporation EGA and IBM are registered trademarks of International Business Machines Corporation Document Number 410130013 330 RO2 0787 Introduction This manual is an alphabetical reference to GW BASIC instructions statements functions commands and variables The name and type of each instruction is listed at the top of the page and is followed by Purpose The purpose of the instruction Syntax The complete notation of the instruction Comments Pertinent information about the instruction and what happens when it is encountered by GW BASIC An illustration of the instruction as it might Examples appear in a program Notes Any special information about the instruction file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic index html 2 of 6 28 03 2004 21 28 55 GWBASIC User s Manual FILES Command FIX Function FOR Statement FRE Function GET Statement Files GET Statement Graphics GOSUB RETURN Statement GOTO Statement HEX Function IF Statement INKEY Variable INP Function INPUT Statement INPUT Statement INPUT Function INSTR Function INT Function IOCTL Statement I
188. ion keys may be redefined For more information see the KEY and ON KEY statements in the GW file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 204 html 5 of 6 28 03 2004 21 28 57 GW BASIC User s Guide BASIC User s Reference file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 204 html 6 of 6 28 03 2004 21 28 57 GW BASIC User s Guide KEY Statement Purpose To allow rapid entry of as many as 15 characters into a program with one keystroke by redefining GW BASIC special function keys Syntax KEY key number string expression KEY n CHRS hex code CHR scan code KEY ON KEY OFF KEY LIST Comments key number is the number of the key to be redefined key number may range from 1 20 string expression is the key assignment Any valid string of 1 to 15 characters may be used If a string is longer than 15 characters only the first 15 will be assigned Constants must be enclosed in double quotation marks scan code is the variable defining the key you want to trap Appendix H in the GW BASIC User s Guide lists the scan codes for the keyboard keys hex code is the hexadecimal code assigned to the key shown below Key Hex code EXTENDED amp H80 CAPS LOCK amp H40 NUM LOCK amp H20 ALT amp HO08 CTRL amp HO04 SHIFT amp HO1 amp HO2 amp H03 Hex codes may be added together such as amp H03 which is both shift keys Initially the function keys are assigned the
189. ion of each item printed is determined by the punctuation used to separate the items in the list Separator Print Position r Beginning of next zone Immediately after last value space s Immediately after last value If a comma semicolon or SPC or TAB function ends an expression list the next PRINT statement begins printing on the same line accordingly spaced If the expression list ends without a comma semicolon or SPC or TAB function a carriage return is placed at the end of the lines GW BASIC places the cursor at the beginning of the next line A carriage return line feed is automatically inserted after printing width characters where width is 40 or 80 as defined in the WIDTH statement This results in two lines being skipped when you print exactly 40 or 80 characters unless the PRINT statement ends in a semicolon When numbers are printed on the screen the numbers are always followed by a space Positive number are preceded by a space Negative numbers are preceded by a minus sign Single precision numbers are represented with seven or fewer digits in a fixed point or integer format file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PRINT html 1 of 2 28 03 2004 21 29 31 GW BASIC User s Guide See the LPRINT and LPRINT USING statements for information on sending data to be printed on a printer Examples 10 XS STRINGS 10 45 20 PRINT XS MONTHLY REPORT XS RUN MONTHLY REPORT 45 is t
190. irst is binary zero the second is the key scan code Examples 10 KEY 1 MENU CHRS 13 Displays a menu selected by the operator each time key 1 is pressed 1 KEY OFF Turns off the key display 10 DATA KEY1 KEY2 KEY3 KEY4 KEY5 20 FOR N 1 TO 5 READ SOFTKEYS n 30 KEY N SOFTKEYSS I 40 NEXT N 50 KEY ON file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic KEY html 2 of 3 28 03 2004 21 28 58 GW BASIC User s Guide Displays new function keys on line 25 of the screen 2 REY Ly Ti Disables function key 1 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic KEY html 3 of 3 28 03 2004 21 28 58 GW BASIC User s Guide Appendix H Key Scan Codes Key Code Key Code Esc 0l U 16 1 02 I 17 2 03 O 18 3 04 P 19 A 05 1A 5 06 V 1B 6 07 ENTER 1C 7 amp 08 CTRL 1D 8 09 A 1E 9 OA S 1F 0 OB D 20 _ OC F 21 OD G 22 BACKSPACEQE H 23 TAB OF J 24 Q 10 K 25 W 11 L 26 E 12 27 R 13 ae 28 T 14 29 Y 15 LEFT SHIFT2A Key Code 2B Z 2C X 2D C 2E V 2F B 30 N 31 M 32 lt 33 IN 35 RIGHT SHIFT36 PRTSCR 37 ALT 38 SPACE 39 CAPS LOCK 3A F1 3B F2 3C F3 3D F4 3E F5 3F F6 40 Key Code F7 41 F8 42 F9 43 F10 44 NUM LOCK 45 SCROLLLOCK 46 7 HOME 47 8 CURSORUP 48 9 PG UP 49 4A 4 CURSOR LEFT 4B 5 4C 6 CURSOR RIGHT4D 4E 1 END 4F 2 CURSOR DOWNSO 3 PG DN 51 O INS 52 DEL 53 file Cl Documents 20and 20Settings Lorenzo Desktop
191. is loaded and all open data files are kept open LOAD with the r option lets you chain several programs or segments of the same program Information can be passed between the programs using the disk data files Examples LOAD STRIRK R Loads the file strtrk bas and runs it retaining all open files and variables from a previous program intact file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LOAD htm128 03 2004 21 29 36 GW BASIC User s Guide LOC Function Purpose To return the current position in the file Syntax LOC file number Comments file number is the file number used when the file was opened When transmitting or receiving a file through a communication port LOC returns the number of characters in the input buffer waiting to be read The default size for the input buffer is 256 characters but can be changed with the c option on the GW BASIC command line If there are more than 255 characters in the buffer LOC returns 255 Since a string is limited to 255 characters this practical limit alleviates the need to test for string size before reading data into it If fewer than 255 characters remain in the buffer then LOC returns the actual count With random disk files Loc returns the record number just read from or written to with a GET or PUT statement With sequential files LOC returns the number of 128 byte blocks read from or written to the file since it was opened When the sequ
192. is the first line number to be used in the new sequence The default is 10 old number is the line in the current program where renumbering is to begin The default is the first line of the program increment 1s the increment to be used in the new sequence The default is 10 RENUM also changes all line number references following ELSE GOTO GOSUB THEN ON GOTO ON GOSUB RESTORE RESUME and ERL statements to reflect the new line numbers If a nonexistent line number appears after one of these statements the error message Undefined line x in y appears The incorrect line number reference x is not changed by RENUM but line number y may be changed RENUM cannot be used to change the order of program lines for example RENUM 15 30 when the program has three lines numbered 10 20 and 30 or to create line numbers greater than 65529 An Illegal function call error results Examples RENUM Renumbers the entire program The first new line number will be 10 Lines increment by 10 RENUM 300 30 Renumbers the entire program The first new line number will be 300 Lines increment by 50 RENUM 1000 900 20 Renumbers the lines from 900 up so they start with line number 1000 and are incremented by 20 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic RENUM htm128 03 2004 21 29 44 GW BASIC User s Guide RESUME Statement Purpose To continue program execution after an error recovery procedure has been perfo
193. ization of This Manual The GW BASIC User s Guide is divided into six chapters nine appendixes and a glossary Chapter 1 Welcome to GW BASIC describes this manual Chapter 2 Getting Started with GW BASIC is an elementary guideline on how to begin programming Chapter 3 Reviewing and Practicing GW BASIC lets you use the principles of GW BASIC explained in Chapter 2 Chapter 4 The GW BASIC Screen Editor discusses editing commands that can be used when inputting or modifying a GW BASIC program It also explains the unique properties of the ten re definable function keys and of other keys and keystroke combinations Chapter 5 Creating and Using Files tells you how to create files and to use the diskette input output I O procedures Chapter 6 Constants Variables Expressions and Operators defines the elements of GW BASIC and describes how you will use them Appendix A Error Codes and Messages is a summary of all the error codes and error messages that you might encounter while using GW BASIC Appendix B Mathematical Functions describes how to calculate certain mathematical functions not intrinsic to GW BASIC Appendix C ASCII Character Codes lists the ASCII character codes recognized by GW BASIC Appendix D Assembly Language Machine Code Subroutines shows how to include assembly language subroutines with GW BASIC Appendix E Converting BASIC Programs to GW BASIC provides pointers on
194. key assign to it instead e Press the F1 key e Press RETURN Your program should appear on the screen To run the program simply press the F2 key which is assigned to the RUN command As you learn more commands you ll learn how to use keys F3 through F10 Chapter 4 The GW BASIC Screen Editor contains more information about keys used in GW BASIC file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 203 html 3 of 5 28 03 2004 21 28 59 GW BASIC User s Guide 3 4 Editing Lines There are two basic ways to change lines You can e Delete and replace them e Alter them with the EDIT command To delete a line simply type the line number and press the RETURN key For example if you type 12 and press the RETURN key line number 12 is deleted from your program To use the EDIT command type the command EDIT followed by the number of the line you want to change For example type the following and press the RETURN key edit 10 You can then use the following keys to perform editing Key Function CURSOR UP Moves the cursor within the statement CURSOR DOWN CURSOR LEFT CURSOR RIGHT BACKSPACE Deletes the character to the left of the cursor DELETE DEL Deletes the current character INSERT INS Lets you insert characters to the left of the cursor For example to modify statement line 10 to read x 4 use the CURSOR RIGHT control key to move the cursor under the 3 and then type a 4 Th
195. ks or string delimiter Period dot or decimal point Single quotation mark apostrophe or remark indicator Semicolon or carriage return suppressor Colon or line statement delimiter Ampersand or descriptor for hexadecimal and octal number conversion Question mark Less than symbol Greater than symbol Backslash or integer division symbol At sign o0 x 20 46 Ca NV A a file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20L html 1 of 2 28 03 2004 21 29 07 GW BASIC User s Guide Underscore BACKSPACEDeletes last character typed ESC Erases the current logical line from the screen TAB Moves print position to next tab stop Tab stops are every eight columns CURSOR Moves cursor to next physical line Terminates input to a line and moves cursor to beginning of the next line or executes RETURN aa statement in direct mode file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20L html 2 of 2 28 03 2004 21 29 07 GW BASIC User s Guide Glossary abend An acronym for abnormal end of task An abend is the termination of computer processing on a job or task prior to its completion because of an error condition that cannot be resolved by programmed recovery procedures access The process of seeking reading or writing data on a storage unit access methods Techniques and programs used to move data between main memory and input output devices accuracy
196. l Documents 20and 20Settings Lorenzo Desktop GW 20Basic Appendix 20D html 3 of 8 28 03 2004 21 29 05 GW BASIC User s Guide executes the subroutine at location 2000 7FA hex Upon entry only 16 bytes eight words remain available within the allocated stack space If the called program requires additional stack space then the user program must reset the stack pointer to a new allocated space Be sure to restore the stack pointer adjusted to the start of the calling sequence on return to GW BASIC The following assembly language sequence demonstrates access of the parameters passed and storage of a return result in the variable C Note The called program must know the variable type for numeric parameters passed In these examples the following instruction copies only two bytes MOVSW This is adequate if variables A and C are integer It would be necessary to copy four bytes if they were single precision or copy eight bytes if they were double precision MOV BP SP Gets the current stack position in BP MOV BX 8 BP Gets the address of B description MOV CL BX Gets the length of B in CL MOV DxX 1 BX Gets the address of B string descriptor in DX MOV SI 10 BP Gets the address of A in SI MOV DI 6 BP Gets the pointer to C in DI MOVSW Stores variable A in C RET 6 Restores stack returns D 3 USR Function Calls Although the CALL statement is the recommended way of calling assembly language subroutines the USR fu
197. lace so that results can be used to guide the physical process remote A term used to refer to devices that are located at sites away from the central computer reverse video A display of characters on a background opposite of the usual display ROM Acronym for read only memory RS 232 A standard communications interface between a modem and terminal devices that complies with EIA Standard RS 232 serial output Sending only one bit at a time to and from interconnected devices file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 15 of 17 28 03 2004 21 29 08 GW BASIC User s Guide single density The standard recording density of a diskette Single density diskettes can store approximately 3400 bits per inch bpi single precision value The number of words or storage positions used to denote a number in a computer Single precision arithmetic is the use of one word per number double precision arithmetic is the use of two words per number and so on For variable word length computers precision is the number of digits used to denote a number The higher the precision the greater the number of decimal places that can be carried single sided A term used to describe a diskette that contains data on one side only software A string of instructions that when executed direct the computer to perform certain functions stack architecture An architecture wherein any portion of the external memory can
198. le 1 the field read is defined in line 70 and converts the first four bytes N into a single precision number assigned to the variable Y Since a single precision number can contain as many as seven ASCII characters seven bytes writing a file using MKSS conversion and reading with the CVS conversion as many as three bytes per number recorded are saved on the storage medium Even more may be saved if double precision numbers are required MKD and CVD conversions would be used in this case file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic C VL htm128 03 2004 21 29 20 GW BASIC User s Guide MKI MKS MKD Functions Purpose To convert numeric values to string values Syntax MKIS integer expression MKSS single precision expression MKDS double precision expression Comments MKI converts an integer to a 2 byte string MKSS converts a single precision number to a 4 byte string MKDS converts a double precision number to an 8 byte string Any numeric value placed in a random file buffer with a LSET or a RSET statement must be converted to a string see CVI CVS CVD for the complementary functions These functions differ from STR because they change the interpretations of the bytes not the bytes themselves Examples 90 AMT K T 100 FIELD 1 8 AS De 20 AS NS 110 LSET DS MKSS AMT 120 LSET Ne A5 130 PUT 1 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic MKI
199. licated Use the CLEAR statement to set aside more stack space or memory area file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20A html 1 of 7 28 03 2004 21 29 03 GW BASIC User s Guide 8 10 Li iz L3 14 15 16 17 Undefined line number A line reference in a GOTO GOSUB IF THEN ELSE or DELETE is a nonexistent line Subscript out of range An array element is referenced either with a subscript that is outside the dimensions of the array or with the wrong number of subscripts Duplicate Definition Two DIM statements are given for the same array or a DIM statement is given for an array after the default dimension of 10 has been established for that array Division by zero A division by zero is encountered in an expression or the operation of involution results in zero being raised to a negative power Machine infinity with the sign of the numerator is supplied as the result of the division or positive machine infinity is supplied as the result of the involution and execution continues Illegal direct A statement that is illegal in direct mode is entered as a direct mode command Type mismatch A string variable name is assigned a numeric value or vice versa a function that expects a numeric argument is given a string argument or vice versa Out of string space String variables have caused GW BASIC to exceed the amount of free memory remaining GW BASIC allocates s
200. lue of MENU Key E 60 XOFFS CHRS 19 XONS CHRS 17 100 10 120 130 140 200 210 220 230 240 250 260 270 280 300 310 400 410 420 430 440 500 310 520 520 540 550 600 610 620 630 640 650 1000 1010 1020 1030 LOCATE 25 1 PRINI Asyne TTY Program LOCATE 1 1 LINE INPUT Speed SPEEDS COMP lLse COM1 4 5PEERBDSe B 7 OPEN COMFILS AS 1 OPEN SCRN FOR OUTPUT AS 3 PAUSE FALSE AS INKEYS IF AS THEN 230 IF ASC AS MENU THEN 300 ELSE PRINT 1 AS IF EOF 1 THEN 210 IF LOC 1 gt 128 THEN PAUSE TRUE PRINT 1 XOFFS AS INPUTS LOC 1 1 PRINT 3 A IF LOC 1 gt 0 THEN 240 IF PAUSE THEN PAUSE FALSE PRINT 1 XONG GOTO 210 LOCATE 1 1 PRINT STRINGS 30 32 LOCATE 1 1 LINE INPUT FILE DSKFIL LOCATE 1 1 PRINT STRINGS 30 32 LOCATE 1 1 LINE INPUT T ransmit or R eceive TXRX IF TXRXS T THEN OPEN DSKFILS FOR INPUT AS 2 GOTO 1000 OPEN DSKFILS FOR OUTPUT AS 2 PRINT 1 CHRS 13 IF EOF 1 THEN GOSUB 600 IF LOC 1 gt 128 THEN PAUSE TRUE PRINT 1 XOFFS AS INPUTS LOC 1 1 PRINT 2 A5 21F LOC 1 gt 0 THEN 510 IF PAUSE THEN PAUSE FALSE PRINT 1 XONS GOTO 500 FOR I 1 TO 5000 IF NOT EOF 1 THEN I 9999 NEXT I IF I gt 9999 THEN RETURN CLOSE 27 CLS LOCATE 25 10 PRINT Download complete RETURN 200 WHILE NOT EOF 2 AS INPUTS 1 2 PRINT 1 AS WEND file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Appendix 20F html 4 of 7 28 03 2004 21 28 59 GW
201. ly or may be the result of calculations in your program If a variable is assigned no value GW BASIC assumes the variable s value to be zero 6 2 1 Variable Names and Declarations GW BASIC variable names may be any length up to 40 characters are significant The characters allowed in a variable name are letters numbers and the decimal point The first character in the variable name must be a letter Special type declaration characters are also allowed Reserved words all the words used as GW BASIC commands statements functions and operators can t be used as variable names However if the reserved word is embedded within the variable name it will be allowed Variables may represent either numeric values or strings 6 2 2 Type Declaration Characters Type declaration characters indicate what a variable represents The following type declaration characters are recognized CharacterType of Variable S String variable Integer variable Single precision variable iF Double precision variable The following are sample variable names for each type Variable Type Sample Name String variable NS Integer variable LIMITS Single precision variable MINIMUM Double precision variable 1 The default type for a numeric variable name is single precision Double precision while very accurate uses more memory space and more calculation time Single precision is sufficiently accurate for most applications However the seventh signif
202. m file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DEFINT htm128 03 2004 21 29 22 GW BASIC User s Guide DEF SEG Statement Purpose To assign the current segment address to be referenced by a subsequent BLOAD BSAVE CALL PEEK POKE or USR Syntax DEF SEG address Comments address is a numeric expression within the range of 0 to 65535 The address specified is saved for use as the segment required by BLOAD BSAVE PEEK POKE and CALL statements Entry of any value outside the address range 0 65535 results in an Illegal Function Call error and the previous value is retained If the address option is omitted the segment to be used is set to GW BASIC s data segment DS This is the initial default value If you specify the address option base it on a 16 byte boundary Segment addresses are shifted 4 bits to the left so to get the segment address divide the memory location by 16 For BLOAD BSAVE PEEK POKE or CALL statements the value is shifted left four bits this is done by the microprocessor not by GW BASIC to form the code segment address for the subsequent call instruction see the BLOAD BSAVE CALL PEEK and POKE statements GW BASIC does not perform additional checking to assure that the resultant segment address is valid Examples 10 DEF SEG amp HB800 Sets segment to screen buffer 20 DEF SEG Restores segment to BASIC DS Note file Cl Documents 20and 20S
203. m in execution toggle Alternation of function between two stable states track A specific area on a moving storage medium such as a diskette disk or tape cartridge that can be accessed by the drive heads tree structured directory A file organization structure consisting of directories and subdirectories that when diagrammed resembles a tree truncation To end a computation according to a specified rule for example to drop numbers at the end of a line instead of rounding them off or to drop characters at the end of a line when a file is copied upgrade To expand a system by installing options or using revised software utility function Computer programs dedicated to one particular task that are helpful in using the computer For example FDISK for setting up partitions on the fixed disk variable A quantity that can assume any of a set of values as a result of processing data volume label The name for the contents of a diskette or a partition on a fixed disk word The set of bits comprising the largest unit that the computer can handle in a single operation write protect notch A cut out opening in the sealed envelope of a diskette that when covered prevents writing or adding text to the diskette but allows information to be read from the diskette file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 17 of 17 28 03 2004 21 29 08 GW BASIC User s Guide ABS Function Purpose To
204. mal 10 OPEN I 1 DATA 20 IF EOF 1 THEN 50 30 PRINT HEX ASC INPUTS 1 1 40 GOTO 20 50 PRINT 60 END Example 2 In the following program the program pauses awaiting a keyboard entry of either P or S Line 130 continues to loop back to line 100 if the input is other than P or S file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic INPUTS html 1 of 2 28 03 2004 21 29 32 GW BASIC User s Guide 100 PRINT TYPE P TO PROCEED OR S TO STOP 110 XS INPUTS 1 120 IF X P THEN 500 130 IF X 9 THEN 700 ELSE 100 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic INPUTS html 2 of 2 28 03 2004 21 29 32 GW BASIC User s Guide INSTR Function Purpose To search for the first occurrence of string y in x and return the position at which the string is found Syntax INSTR n XS y Comments Optional offset n sets the position for starting the search The default value for n is 1 If n equals zero the error message Illegal argument in line number is returned n must be within the range of 1 to 255 If n is out of this range an Illegal Function Call error is returned INSTR returns 0 if e n gt LEN lt xS e xSis null e ys cannot be found If ys is null INSTR returns n x and y may be string variables string expressions or string literals Examples 10 XS ABCDEBXYZ 20 B 30 PRINT INSTR X Y INSTR 4 X Y RUN 2 6 The interpreter
205. mber or range of numbers to be edited The lines will appear on your screen 4 2 1 Editing the Information in a Program Line You can make changes to the information in a line by positioning the cursor where the change is to be made and by doing one of the following e Typing over the characters that are already there e Deleting characters to the left of the cursor using the BACKSPACE key e Deleting characters at the cursor position using the DEL key on the number pad e Inserting characters at the cursor position by pressing the INS key on the number pad This file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 204 html 1 of 6 28 03 2004 21 28 57 GW BASIC User s Guide moves the characters following the cursor to the right making room for the new information e Adding to or truncating characters at the end of the program line If you have changed more than one line be sure to press RETURN on each modified line The modified lines will be stored in the proper numerical sequence even if the lines are not updated in numerical order Note A program line will not actually have changes recorded within the GW BASIC program until the RETURN key is pressed with the cursor positioned somewhere on the edited line You do not have to move the cursor to the end of the line before pressing the RETURN key The GW BASIC Interpreter remembers where each line ends and transfers the whole line even if RETURN is press
206. me or a different file number A CLOSE statement with no file number specified closes all open files and devices A CLOSE statement sent to a file or device opened for sequential output writes the final buffer of output to that file or device The END NEW RESET SYSTEM or RUN and LOAD without r option statements always close all files or devices automatically STOP does not close files Examples 250 CLOSE This closes all open devices and files 300 CLOSE 1 2 3 Closes all files and devices associated with file numbers 1 2 and 3 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CLOSE htm128 03 2004 21 29 18 GW BASIC User s Guide CLS Statement Purpose To clear the screen Syntax CLS n Comments n is one of the following values Value ofn Effect 0 Clears the screen of all text and graphics 1 Clears only the graphics viewport 2 Clears only the text window If the graphics viewport is active CLS without argument clears only the viewport If the graphics viewport is inactive CLS clears the text window If the screen is in alpha mode the active page is cleared to the currently selected background color see the SCREEN and COLOR statements If the screen is in graphics mode the entire screen buffer is cleared to background color The screen may also be cleared by pressing CTRL HOME or by changing the screen mode with the SCREEN or WIDTH statements CLS returns the cursor to the u
207. medium medium The physical material on which data is recorded and stored Magnetic tape punched cards and diskettes are examples of media memory The high speed work area in the computer where data can be held copied and retrieved menu A list of choices from which an operator can select a task or operation to be performed by the computer microprocessor A semiconductor central processing unit CPU in a computer modem Acronym for modulator demodulator A modem converts data from a computer to analog signals that can be transmitted through telephone lines or converts the signals from telephone lines into a form the computer can use MS DOS Acronym for Microsoft Disk Operating System nested programs or subroutines A program or subroutine that is incorporated into a larger routine to permit ready execution or file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 12 of 17 28 03 2004 21 29 08 GW BASIC User s Guide access of each level of the routine For example nesting loops involves incorporating one loop of instructions into another loop null Empty or having no members This is in contrast to a blank or zero which indicates the presence of no information For example in the number 540 zero contains needed information numeric A reference to numerals as opposed to letters or other symbols octal number system A representation of values or quantities with octal numbers The octal num
208. ment is used in conjunction with the CHAIN statement COMMON statements may appear anywhere in a program although it is recommended that they appear at the beginning Any number of COMMON statements may appear in a program but the same variable cannot appear in more than one COMMON statement To pass all variables using the CHAIN statement use the all option and omit the COMMON statement Place parentheses after the variable name to indicate array variables Examples 100 COMMON A B C D GS 110 CHAIN A PROG3 This example chains to program PROG3 BAS on disk drive A and passes the array D along with the variables A B C and string G file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic COMMON htm128 03 2004 21 29 19 GW BASIC User s Guide CONT Command Purpose To continue program execution after a break Syntax CONT Comments Resumes program execution after CTRL BREAK STOP or END halts a program Execution continues at the point where the break happened If the break took place during an INPUT statement execution continues after reprinting the prompt CONT is useful in debugging in that it lets you set break points with the STOP statement modify variables using direct statements continue program execution or use GOTO to resume execution at a particular line number If a program line is modified CONT will be invalid file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CON
209. ments in a loop as long as a given condition is true Syntax WHILE expression loop statements END Comments If expression is nonzero true loop statements are executed until the WEND statement is encountered GW BASIC then returns to the WHILE statement and checks expression If it is still true the process is repeated If it is not true execution resumes with the statement following the WEND statement WHILE and WEND loops may be nested to any level Each WEND matches the most recent WHILE An unmatched WHILE statement causes a WHILE without WEND error An unmatched WEND statement causes a WEND without WHILE error Examples 90 BUBBLE SORT ARRAY AS 100 FLIPS 1 110 WHILE FLIPS 115 FLIP Ss 0 120 FOR N 1 TO J 1 130 IF AS N gt AS N 1 THEN SWAP AS N AS N 1 FLIPS 1 140 NEXT N 150 WEND file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic WHILEWEND htm128 03 2004 21 29 52 GW BASIC User s Guide WINDOW Statement Purpose To draw lines graphics and objects in space not bounded by the physical limits of the screen Syntax WINDOW SCREEN x1 y1 x2 y2 Comments x1 y1 x2 y2 are the coordinates defined by the user These coordinates called the world coordinates may be any single precision floating point number They define the world coordinate space that graphics statements map into the physical coordinate space as defined by the VIEW statement WINDOW is
210. mmas expression is an expression that performs the operation of the function It is limited to one statement In the DEF FN statement arguments serve only to define the function they do not affect program variables that have the same name A variable name used in a function definition may or may not appear in the argument If it does the value of the parameter is supplied when the function is called Otherwise the current value of the variable is used The variables in the argument represent on a one to one basis the argument variables or values that are to be given in the function call User defined functions may be numeric or string If a type is specified in the function name the value of the expression is forced to that type before it is returned to the calling statement If a type is specified in the function name and the argument type does not match a Type Mismatch error occurs A user defined function may be defined more than once in a program by repeating the DEF FN statement A DEF FN statement must be executed before the function it defines may be called If a function is called before it has been defined an Undefined User Function error occurs DEF FN is illegal in the direct mode Recursive functions are not supported in the DEF FN statement Examples file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DEFFN html 1 of 2 28 03 2004 21 29 01 GW BASIC User s Guide 400 R 1 S 2 410 DEF FNA
211. n as the first red pixel is drawn By specifying red CHRS amp HAA as the background attribute the red line is drawn over the red background You cannot specify more than two consecutive bytes in the tile string that match the background attribute Specifying more than two results in an Illegal function call error Examples 10 CLS 20 SCREEN 1 30 LINE 0 Oj 100 150 2 B 40 PAINT 50 SU ly 2 90 LOCATE 20 1 The PAINT statement in line 40 fills in the box drawn in line 30 with color 1 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PAINT html 3 of 3 28 03 2004 21 29 17 GW BASIC User s Guide PRESET and PSET Statements Purpose To display a point at a specified place on the screen during use of the graphics mode Syntax PRESET x y color PSET x y color Comments x y represents the coordinates of the point color is the color of the point Coordinates can be given in either absolute or relative form Absolute Form absolute x absolute y is more common and refers directly to a point without regard to the last point referenced For example 10 10 Relative Form STEP x offset y offset isa point relative to the most recent point referenced For example STEP 10 10 Coordinate values can be beyond the edge of the screen However values outside the integer range 32768 to 32767 cause an Overflow error 0 0 is always the upper left corne
212. n be read back into two string variables CAMERA 93604 1 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PRINTF html 2 of 2 28 03 2004 21 29 42 GW BASIC User s Guide PUT Statement Files Purpose To write a record from a random buffer to a random disk file Syntax PUT file number record number Comments file number is the number under which the file was opened record number is the number of the record If it is omitted the record has the next available record number after the last PUT The largest possible record number is 232 1 This will allow you to have large files with short record lengths The smallest possible record number is 1 The PRINT PRINT USING LSET RSET or WRITE statements may be used to put characters in the random file buffer before a PUT statement In the case of WRITE GW BASIC pads the buffer with spaces up to an enter Any attempt to read or write past the end of the buffer causes a Field overflow error PUT can be used for communications files Here record number is the number of bytes written to the file Record number must be less than or equal to the length of the buffer set in the OPEN COM n statement file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PUTF htm128 03 2004 21 29 43 GW BASIC User s Guide PUT Statement Graphics Purpose To transfer graphics images to the screen Syntax PUT x Y array yaction verb
213. nal Standards Institute ANSI It uses 7 binary bits for information and the 8th bit for parity purposes assembler A computer program that produces a machine language program which may then be directly executed by the computer assembly language A symbolic language that is machine oriented rather than problem oriented A program in an assembly language is converted by an assembler to a machine language program Symbols file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 2 of 17 28 03 2004 21 29 08 GW BASIC User s Guide representing storage locations are converted to numerical storage locations symbolic operation codes are converted to numeric operation codes asynchronous 1 Not having a regular time or clocked relationship See synchronous 2 A type of computer operation in which a new instruction is initiated when the former instruction is completed Thus there is no regular time schedule or clock with respect to instruction sequence The current instruction must be complete before the next is begun regardless of the length of time the current instruction takes asynchronous communication A way of transmitting data serially from one device to another in which each transmitted character is preceded by a start bit and followed by a stop bit This is also called start stop transmission back up 1 A second copy of data on a diskette or other medium ensuring recovery from loss or destruction of th
214. ncoded binary format When a protected file is later run or loaded any attempt to list or edit it fails When the p option is used make an additional copy under another name or diskette to facilitate future program maintenance Examples The following command saves the file com2 bas in the ASCII format SAVE COM2 A The following command saves the file prog bas in binary format and protects access SAVE PROG P file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SA VE htm128 03 2004 21 29 46 GW BASIC User s Guide SCREEN Function Purpose To return the ASCII code 0 255 for the character at the specified row line and column on the screen Syntax X SCREEN row col zZ Comments x is a numeric variable receiving the ASCII code returned row is a valid numeric expression within the range 1 to 25 col is a valid numeric expression 1 to 40 or 1 to 80 depending upon screen width setting See the WIDTH statement z 1s a valid numeric expression with a true or false value It may be used only in alpha mode The ordinal of the character at the specified coordinates is stored in the numeric variable In alpha mode if the optional parameter z is given and is true nonzero the color attribute for the character is returned instead of the ASCII code for the character see the COLOR statement Any values entered outside of the range indicated result in an Illegal function call error Row 25 may be reference
215. nction call is still available for compatibility with previously written programs Syntax USR n argument n is a number from 0 to 9 which specifies the USR routine being called see DEF USR statement If n is omitted USRO is assumed argument is any numeric or string expression In GW BASIC a DEF SEG statement should be executed prior to a USR function call to ensure file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20D html 4 of 8 28 03 2004 21 29 05 GW BASIC User s Guide that the code segment points to the subroutine being called The segment address given in the DEF SEG statement determines the starting segment of the subroutine For each USR function call a corresponding DEF USR statement must have been executed to define the USR function call offset This offset and the currently active DEF SEG address determine the starting address of the subroutine When the USR function call is made register AL contains the number type flag NTF which specifies the type of argument given The NTF value may be one of the following NTF ValueSpecifies 2 a two byte integer two s complement format 3 a string 4 a single precision floating point number 8 a double precision floating point number If the argument of a USR function call is a number AL lt gt 73 the value of the argument is placed in the floating point accumulator FAC The FAC is 8 bytes long and is in the GW BASIC data segment Register
216. nd Printer Adapter See the SCREEN statement reference page for the list of colors available for various SCREEN mode monitor and graphics adapter combinations Examples PALETTE 0 2 Changes all points colored with attribute 0 to color 2 PALETTE 0 1 Does not modify the palette PALETTE USING A 0 Changes each palette entry Since the array is initialized to zero when it is first declared all attributes are now mapped to display color zero The screen will now appear as one single color However it will still be possible to execute BASIC statements PALETTE Sets each palette entry to its appropriate initial display color Actial initial colors depend on your screen hardware configuration file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PALETTE html 3 of 3 28 03 2004 21 29 16 GW BASIC User s Guide DRAW Statement Purpose To draw a figure Syntax DRAW string expression Comments The DRAW statement combines most of the capabilities of the other graphics statements into an object definition language called Graphics Macro Language GML A GML command is a single character within a string optionally followed by one or more arguments The DRAW statement is valid only in graphics mode Movement Commands Each of the following movement commands begins movement from the current graphics position This is usually the coordinate of the last graphics point plotted with another GML
217. ne printer For more information about string and numeric fields and the variables used in them see the PRINT and PRINT USING statements The LPRINT and LPRINT USING statements assume that your printer is an 80 character wide printer To reset the number of characters that you can print across the printed page assuming that your printer is wider than 80 characters see the WIDTH statement file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LPRINT htm128 03 2004 21 29 31 GW BASIC User s Guide PRINT USING Statement Purpose To print strings or numbers using a specified format Syntax PRINT USING string expressions list of expressions Comments string expressions is a String literal or variable consisting of special formatting characters The formatting characters determine the field and the format of printed strings or numbers list of expressions consists of the string or numeric expressions separated by semicolons String Fields The following three characters may be used to format the string field Specifies that only the first character in the string is to be printed n spaces Specifies that 2 n characters from the string are to be printed If the backslashes are typed with no spaces two characters are printed if the backslashes are typed with one space three characters are printed and so on If the string is longer than the field the extra characters are ignored If the field is longer
218. ng the nth parameter from the environment string table If there is no nth parameter then a null string is returned The ENVIRONS function distinguishes between upper and lowercase Examples The following lines ENVIRON PATH A SALES A ACOUNTING B MKT Create entry PRINT ENVIRONS PATH Print entry will print the following string A SALES A ACCOUNTING B MKT The following line will print the first string in the environment PRINT ENVIRONS 1 The following program saves the environment string table in an array so that it can be modified for a child process After the child process completes the environment is restored 10 DIM ENVTBLS 10 20 NPARMS 1 30 WHILE LEN ENVIRONS NPARMS gt 0 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic EN VIRONS html 1 of 2 28 03 2004 21 29 24 GW BASIC User s Guide 40 ENVTBLS NPARMS ENVIRONS NPARMS 50 NPARMS NPARMS 1 60 WEND 70 NPARMS NPARMS 1 72 WHILE LEN ENVIRONS 1 gt 0 73 AS MIDS ENVIRONS 1 1 INSTR ENVIRONS 1 74 ENVIRON AS 75 WEND 90 ENVIRON MYCHILDPARM1 SORT BY NAME 100 ENVIRON MYCHILDPARM2 LIST BY NAME 1000 1002 1003 1004 1005 1010 1020 1030 SHELL MYCHILD RUNS MYCHILD EXE WHILE LEN ENVIRON 1 gt 0 AS MIDS ENVIRONS 1 1 INSTR ENVIRONS ENVIRON AS WEND FOR I 1 TO NPARMS ENVIRON ENVTBLS I NEXI I Joy ep ee The DIM statement in line 10 assumes no mor
219. ngs Lorenzo Desktop GW 20Basic VIEWPRINT htm128 03 2004 21 29 52 GW BASIC User s Guide WAIT Statement Purpose To suspend program execution while monitoring the status of a machine input port Syntax WAIT port number n j Comments port number represents a valid machine port number within the range of 0 to 65535 n and j are integer expressions in the range of 0 to 255 The WAIT statement causes execution to be suspended until a specified machine input port develops a specified bit pattern The data read at the port is XORed with the integer expression j and then ANDed with n If the result is zero GW BASIC loops back and reads the data at the port again If the result is nonzero execution continues with the next statement When executed the WAIT statement tests the byte n for set bits If any of the bits is set then the program continues with the next statement in the program WAIT does not wait for an entire pattern of bits to appear but only for one of them to occur It is possible to enter an infinite loop with the WAIT statement You can exit the loop by pressing CTRL BREAK or by resetting the system If j is omitted zero is assumed Examples 100 WAIT 32 2 Suspends machine operation until port 32 receives 2 as input file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic W AIT htm128 03 2004 21 29 52 GW BASIC User s Guide WHILE WEND Statement Purpose To execute a series of state
220. nstrated in the TTY programming example to turn transmit off long enough to catch up e Use a lower baud rate for transmit and receive Permission Denied This is one of three hard disk errors returned from the diskette controller e An attempt has been made to write onto a diskette that is write protected e Another process has attempted to access a file already in use e The UNLOCK range specified does not match the preceding LOCK statement Disk not Ready Occurs when the diskette drive door is open or a diskette is not in the drive Use an ON ERROR GOTO statement to recover Disk media error Occurs when the diskette controller detects a hardware or media fault This usually indicates damaged media Copy any existing files to a new diskette and reformat the damaged diskette FORMAT maps the bad tracks in the file allocation table The remainder of the diskette is now usable Advanced Feature An attempt was made to use a reserved word that is not available in this version of GW BASIC Rename across disks Occurs when an attempt is made to rename a file to a new name declared to be on a disk other than the disk specified for the old name The naming operation is not performed file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20A html 6 of 7 28 03 2004 21 29 03 GW BASIC User s Guide TS Path File Access Error During an OPEN MKDIR CHDIR or RMDIR operation MS DOS is unable to make a correc
221. nts 20and 20Settings Lorenzo Desktop GW 20Basic Appendix 20D html 7 of 8 28 03 2004 21 29 05 GW BASIC User s Guide Example 2 places the assembly language subroutine in the specified area Example 2 10 I 0 JC 0 100 DIM A 23 150 MEM S VARPTR Ab 1 200 FOR I 1 TO 23 300 READ JC 400 POKE MEM JC 450 MEMS MEM S 1 500 NEXT 600 C1 2 C2 3 C3 0 700 TWOSUM VARPTR Ab 1 800 CALL TWOSUM C1 C23 C3 900 PRINT C35 950 END 1000 DATA amp H55 amp H8b amp Hec amp H8b amp H76 amp HO8 amp H8b amp H04 amp H8b amp H76 1100 DATA amp H0a amp H03 amp H04 amp H8b amp H7e amp H06 amp H89 amp HO5 amp H5d 1200 DATA amp Hca amp H06 amp HO0O oO file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Appendix 20D html 8 of 8 28 03 2004 21 29 05 GW BASIC User s Guide DEF USR Statement Purpose To specify the starting address of an assembly language subroutine to be called from memory by the USR function Syntax DEF USR n integer Comments n may be any digit from 0 to 9 The digit corresponds to the USR routine address being specified If nis omitted DEF USRO is assumed integer is the offset address of the USR routine If more than 10 USR routines are required DEF USR n may appear in the program as many times as necessary to redefine the USR n starting address Add the current segment value to the integer to get the starting address of the user routine W
222. o Multiple periods can appear after a note and the playing time is scaled accordingly For example A will cause the note A to play one and half times the playing time determined by L length of the note times T the tempo two periods placed after A A will cause the note to be played at 9 4 times its ascribed value an A with three periods A at 27 8 etc Periods may also appear after a P pause and increase the pause length as described above Xstring Executes a substring where string is a variable assigned to a string of PLAY commands Because of the slow clock interrupt rate some notes do not play at higher tempos for example 1 64 at T255 These note tempo combinations must be determined through experimentation gt n A greater than symbol preceding the note n plays the note in the next higher octave lt n A less than symbol preceding the note n plays the note in the next lower octave Note Numeric arguments follow the same syntax described under the DRAW statement n as an argument can be a constant or it can be a variable with in front of it variable A semicolon is required after the variable and also after the variable in Xst ring file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PLA Y html 2 of 2 28 03 2004 21 29 41 GW BASIC User s Guide PLAY n Function Purpose To return the number of notes currently in the background music queue Syntax PLAY n Comments nis a
223. o down load a file Get filename e If the character A is not the MENU key send it by writing to the communications file PRINT 1 3 If no character is waiting check to see if any characters are being received 4 At 230 see if any characters are waiting in COM buffer If not go back file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20F html 5 of 7 28 03 2004 21 28 59 GW BASIC User s Guide 300 320 400 420 430 500 510 520 530 540 550 600 650 1000 1060 and check the keyboard 5 At 240 if more than 128 characters are waiting set PAUSE flag to indicate that input is being suspended Send XOFF to host stopping further transmission 6 At 250 260 read and display contents of COM buffer on screen until empty Continue to monitor size of COM buffer in 240 Suspend transmission if reception falls behind 7 Resume host transmission by sending XON only if suspended by previous XOFF 8 Repeat process until the MENU key is pressed Get disk filename to be down loaded to Open the file as number 2 Asks if file named is to be transmitted uploaded or received down loaded Receive routine Sends a RETURN to the host to begin the down load This program assumes that the last command sent to the host was to begin such a transfer and was missing only the terminating return If a DEC system is the host such a command might be COPY TTY MANUAL MEM MENU Key if the
224. ocuments 20and 20Settings Lorenzo Desktop GW 20Basic LOCATE html 2 of 2 28 03 2004 21 29 36 GW BASIC User s Guide LOCK Statement Purpose To restrict the access to all or part of a file that has been opened by another process This is used in a multi device environment often referred to as a network or network environment Syntax LOCK n record number TO record number Comments n is the number that was assigned to the file as it was originally numbered in the program record number is the number of the individual record that is to be locked Or if a range of records are to be locked record number designates the beginning and ending record of the specified range The range of legal record numbers is 1 to 232 1 The limit on record size is 32767 bytes The record range specified must be from lower to the same or higher record numbers If a starting record number is not specified the record number 1 is assumed If an ending record number is not specified then only the specified record is locked The following are examples of legal LOCK statements LOCK n locks the entire file n LOCK n X locks record x only LOCK n TO Y locks records 1 through Y LOCK n X TO Ylocks records X through Y With a random access file the entire opened file or a range of records within an opened file may be locked thus denying access to those records to any other process which has also opened the file With a sequential ac
225. omes out of a subroutine any attempt to continue loops outside the subroutine results ina NEXT without FOR error Special Notes about Each Type of Trap COM Trapping Typically the COM trap routine will read an entire message from the COM port before returning It is recommended that you not use the COM trap for single character messages since at high baud rates the overhead of trapping and reading for each individual character may allow the interrupt buffer for COM to overflow KEY Trapping Trappable keys 15 to 20 are defined by the following statement KEY n CHR hex code CHR scan code n is an integer expression within the range of 15 to 20 defining the key to be trapped file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ONCOMN html 2 of 5 28 03 2004 21 28 58 GW BASIC User s Guide hex code is the mask for the latched key CAPS LOCK NUM LOCK ALT CTRL LEFT SHIFT RIGHT SHIFT scan code is the number identifying one of the 83 keys to trap Refer to Appendix H in the GW BASIC User s Guide for key scan codes The appropriate bit in hex code must be set in order to trap a key that is shifted control shifted or alt shifted hex code values are as follows Mask Hex code Indicates that EXTENDED amp H80 Key is extended CAPS LOCK amp H40 CAPS LOCK is active NUM LOCK amp H20 NUM LOCK is active ALT amp HO08 The ALT key is pressed CTRL amp H04 The CTRL key is pressed LEFT SHIFT amp H02 T
226. omment HELLO on the 24 line of the screen The LOCATE statement in line 50 restores the position of the cursor to the original line and column file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CSRLIN html28 03 2004 21 29 20 GW BASIC User s Guide POS Function Purpose To return the current cursor position Syntax POS c Comments The leftmost position is 1 cis a dummy argument Examples 10 CLS 20 WIDTH 80 30 AS INKEYS IF AS THEN GOTO 30 ELSE PRINT AS 40 IF POS X gt 10 THEN PRINT CHRS 13 50 GOTO 30 Causes a carriage return after the 10th character is printed on each line of the screen file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic POS htm128 03 2004 21 29 20 GW BASIC User s Guide CVI CVS CVD Functions Purpose To convert string values to numeric values Syntax CVI 2 byte string CVS 4 byte string CVD 8 byte string Comments Numeric values read in from a random access disk file must be converted from strings back into numbers if they are to be arithmetically manipulated CVI converts a 2 byte string to an integer MKIS is its complement CVS converts a 4 byte string to a single precision number MKS is its complement CVD converts an 8 byte string to a double precision number MKD is its complement See MKI MKS and MKD Examples 70 FIELD 1 4 Ae NS 127 AS BS 80 GET 1 90 Y CVS NS Line 80 reads a field from fi
227. on are 1 The numbered lines 2 The use of the run command These features let the computer know that all the statements have been typed and the computation can be carried out from beginning to end It is the numbering of the lines that first signals the computer that this is a program not a calculation and that it must not do the actual computation file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 203 html 2 of 5 28 03 2004 21 28 59 GW BASIC User s Guide until the RUN command is entered In other words calculations are done under the direct mode Programs are written under the indirect mode To display the entire program again type the LIST command and press the RETURN key LISE Your screen should look like this Ok 10 x 3 20 Princ 27x run Ok 5 Ok List 10 X 3 40 PRINT 2 X Ok You ll notice a slight change in the program The lowercase letters you entered have been converted into uppercase letters The LIST command makes this change automatically 3 3 Function Keys Function keys are keys that have been assigned to frequently used commands The ten function keys are located on the left side of your keyboard A guide to these keys and their assigned commands appears on the bottom of the GW BASIC screen To save time and keystrokes you can press a function key instead of typing a command name For example to list your program again you needn t type the LIST command you can use the function
228. or subsequent PRINT 1 statements Line 6020 changes the current line printer width to 40 characters per line file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic WIDTH html 2 of 2 28 03 2004 21 29 32 GW BASIC User s Guide INPUT Statement Purpose To read data items from a sequential file and assign them to program variables Syntax INPUT file number variable list Comments file number is the number used when the file was opened for input variable list contains the variable names to be assigned to the items in the file The data items in the file appear just as they would if data were being typed on the keyboard in response to an INPUT statement The variable type must match the type specified by the variable name With INPUT no question mark is printed as it is with INPUT Numeric Values For numeric values leading spaces and line feeds are ignored The first character encountered not a space or line feed is assumed to be the start of a number The number terminates on a space carriage return line feed or comma Strings If GW BASIC is scanning the sequential data file for a string leading spaces and line feeds are ignored If the first character is a double quotation mark the string will consist of all characters read between the first double quotation mark and the second A quoted string may not contain a double quotation mark as a character The second double quotation mark alwa
229. ors can be selected with the integers 0 15 A blinking version of each color can be selected by adding 16 to the color number for example a blinking color 7 is equal to 7 16 or 23 Thus the legal integer range for foreground is 0 31 The background color must be an integer expression in the range 0 7 and is the color of the background for each text character Blinking colors are not permitted The border color is an integer expression in the range 0 15 and is the color used when drawing the screen border Blinking colors are not permitted If no arguments are provided to COLOR then the default color for background and border is black COLOR 0 and for foreground is as described in the SCREEN statement reference pages file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic COLOR html 1 of 3 28 03 2004 21 29 16 GW BASIC User s Guide SCREEN 1 SCREEN 2 SCREEN 7 SCREEN 10 In mode 1 the COLOR statement has a unique syntax that includes a palette argument which is an odd or even integer expression This argument determines the set of display colors to use when displaying particular color numbers For hardware configurations that do not have an IBM Enhanced Graphics Adapter EGA the default color settings for the palette parameter are equivalent to the following COLOR p Same as the next three PALETTE statements 1 green 2 red 3 yellow COLOR p1 Same as the next three PALETTE statements l cy
230. ors detected by GW BASIC including direct mode errors for example syntax errors cause GW BASIC to branch to the line in the program which begins the specified error handling subroutine GW BASIC branches to the line specified by the ON ERROR statement until a RESUME statement is found If line number does not exist an Undefined line error results To disable error trapping execute the following statement ON ERROR GOTO 0 Subsequent errors print an error message and halt execution An ON ERROR GOTO 0 statement in an error trapping subroutine causes GW BASIC to stop and print the error message for the error that caused the trap It is recommended that all error trapping subroutines execute an ON ERROR GOTO 0 if an error is encountered for which there is no recovery action If an error occurs during execution of an error handling subroutine the GW BASIC error message is printed and execution terminated Error trapping does not occur within the error handling subroutine Examples 10 ON ERROR GOTO 1000 1000 A ERR B ERL 1010 PRINT A B 1020 RESUME NEXT Line 1010 prints the type and location of the error on the screen see the ERR and ERL variables file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ONERROR html 1 of 2 28 03 2004 21 29 39 GW BASIC User s Guide Line 1020 causes program execution to continue with the line following the error file Cl Documents 20and 20Settings Lorenzo Desktop GW
231. ot specified two commas must be used before B or BF LINE supports the additional argument style style is a 16 bit integer mask used when putting down pixels on the screen This is called line styling Each time LINE stores a point on the screen it uses the current circulating bit in style If that bit is 0 no store will be done If the bit is a 1 then a normal store is done After each point the next bit position in style is selected Since a 0 bit in st yle does not clear out the old contents you may wish to draw a background line before a styled line in order to force a known background style is used for normal lines and boxes but is illegal for filled boxes If the BF parameter is used with the style parameter a Syntax error will occur When out of range values are given in the LINE statement the coordinates that are out of range are not visible on the screen This is called line clipping In the syntax shown here the coordinate form STEP x offset y offset is not shown However this form can be used wherever a coordinate is used file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic LINE html 1 of 3 28 03 2004 21 29 17 GW BASIC User s Guide In a LINE statement if the relative form is used on the second coordinate it is relative to the first coordinate After a LINE statement the last referenced point is x2 y2 The simplest form of LINE is the following LINE XZ yZ This draws a line from th
232. other COM I O statements to the file Any coding errors within the filename string result in Bad file name errors An indication as to which parameters are in error is not given number is the maximum number of bytes which can be read from the communications buffer file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic OPENCOMN html 1 of 2 28 03 2004 21 29 40 GW BASIC User s Guide when using GET or PUT default of 128 bytes A Device timeout error occurs if data set ready DSR is not detected The RS CS DS DC LF and PE options affect the line signals as follows Option Function RS suppresses RTS request to send CS n controls CTS clear to send DS n controls DSR data set ready CDn controls CD carrier detect LF sends a line feed at each return PE enables parity checking nis the number of milliseconds to wait 0 65535 for that signal before a device timeout error occurs Defaults are CS1000 DS1000 and CDO If RS was specified then CSO is the default If n is omitted then timeout is set to 0 See Appendix F in the GW BASIC User s Guide for more information about communications Examples In the following File 1 is opened for communications with all defaults speed at 300 bps even parity seven data bits and one stop bit 10 OPEN COM1 AS 1 In the following File 2 is opened for communications at 2400 bps Parity and number of data bits are defaulted 20 OPEN COM1 2400 AS 2 In the followin
233. out NEXT A FOR was encountered without a matching NEXT Out of Paper The printer is out of paper or a printer fault Unprintable error No error message is available for the existing error condition This is usually caused by an error with an undefined error code WHILE without WEND A WHILE statement does not have a matching WEND WEND without WHILE A WEND was encountered without a matching WHILE file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20A html 3 of 7 28 03 2004 21 29 03 GW BASIC User s Guide 31 49Unprintable error 50 Jd 52 J3 54 oo 56 57 58 No error message is available for the existing error condition This is usually caused by an error with an undefined error code FIELD overflow A FIELD statement is attempting to allocate more bytes than were specified for the record length of a random file Internal error An internal malfunction has occurred in GW BASIC Report to your dealer the conditions under which the message appeared Bad file number A statement or command references a file with a file number that is not open or is out of range of file numbers specified at initialization File not found A LOAD KILL NAME FILES or OPEN statement references a file that does not exist on the current diskette Bad file mode An attempt is made to use PUT GET or LOF with a sequential file to LOAD a random file or to execute an OPEN with a file mode oth
234. owing statement IF ABS A 1 0 lt 1 0E 6 THEN This test returns true if the value of A is 1 0 with a relative error of less than 1 0E 6 Examples The following statement gets record number N if N is not zero 200 IF N THEN GET 1 N In the following example a test determines if N is greater than 10 and less than 20 If N is within this range DB is calculated and execution branches to line 300 If N is not within this range execution continues with line 110 100 IF N lt 20 and N gt 10 THEN DB 1979 1 GOTO 300 110 PRINT OUT OF RANGE The next statement causes printed output to go either to the terminal or the line printer depending on the value of a variable OFLAG If IOFLAG is zero output goes to the line printer otherwise output goes to the terminal 210 IF IOFLAG THEN PRINT AS ELSE LPRINT AS file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic IF html 2 of 2 28 03 2004 21 29 29 GW BASIC User s Guide INKEY Variable Purpose To return one character read from the keyboard Syntax vS INKEYS Comments If no character is pending in the keyboard buffer a null string length zero is returned If several characters are pending only the first is returned The string will be one or two characters in length Two character strings are used to return the extended codes described in Appendix C of the GW BASIC User s Guide The first character of a two character code is zero No characters are
235. pper left corner of the screen and sets the last point referenced to the center of the screen If the VIEW statement has been used CLS clears only the last viewport specified Examples 1 CLS This clears the screen file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CLS htm128 03 2004 21 29 18 GW BASIC User s Guide COM n Statement Purpose To enable or disable trapping of communications activity to the specified communications adapter Syntax COM n ON COM n OFF COM n STOP Comments n is the number of the communications adapter 1 or 2 Execute a COM n ON statement before ON COM n statement to allow trapping After COM n ON if a nonzero number is specified in the ON COM n statement BASIC checks every new statement to see if any characters have come in the communication adapter With COM n OFF no trapping takes place and all communications activity will be lost With COM n STOP no trapping takes place However any communication that takes place will be remembered so that immediate trapping will occur when COM n ON is executed file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic COMN htm128 03 2004 21 29 19 GW BASIC User s Guide COMMON Statement Purpose To pass variables to a chained program Syntax COMMON variables Comments variables are one or more variables separated by commas that you want to pass to the chained program The COMMON state
236. pressions consists of the numeric and or string expressions to be written to the file Double quotation marks are used as delimiters for numeric and or string expressions The first double quotation mark opens the line for input the second double quotation mark closes it If numeric or string expressions are to be printed as they are input they must be surrounded by double quotation marks If the double quotation marks are omitted the value assigned to the numeric or string expression is printed If no value has been assigned 0 is assumed The double quotation marks do not appear on the screen For example 10 PRINT 1 A 10 A 26 20 PRINT 1 A 26 10 A 26 20 PRINT 1 A A If double quotation marks are required within a string use CHRS 34 the ASCII character for double quotation marks For example 100 PRINT 1 He said Hello I think He said 0 I think because the machine assigns the value 0 the variable Hello 100 PRINT 1 He said CHRS 34 Hello CHRS 34 I think He said Hello I think file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PRINTF html 1 of 2 28 03 2004 21 29 42 GW BASIC User s Guide If the strings contain commas semicolons or significant leading blanks surround them with double quotation marks The following example will input CAMERA to A and AUTOMATIC 93604 1 to B 10 AS CAMERA AUTOMATIC BS 93604 1 20 PRINT 1 AS BS 30 INPUT 1 AS BS To sep
237. r and 0 199 is the lower left corner in both high resolution and medium resolution See the COLOR and PALETTE statements for more information If the value for color is greater than 3 an Illegal function call error is returned Example 1 The following draws a diagonal line from 0 0 to 100 100 10 CLS 20 SCREEN 1 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PRESET html 1 of 2 28 03 2004 21 29 18 GW BASIC User s Guide 30 FOR I 0 TO 100 40 PSET I TI 50 NEXT 60 LOCATE 14 1 Example 2 The following clears out the line by setting each pixel to 0 40 FOR I 100 TO 0 STEP 1 90 PeET iz1 0 60 NEXT I file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PRESET html 2 of 2 28 03 2004 21 29 18 GW BASIC User s Guide CLEAR Command Purpose To set all numeric variables to zero all string variables to null and to close all open files Options set the end of memory and reserve the amount of string and stack space available for use by GW BASIC Syntax CLEAR expressionl expression2 Comments expressionl is a memory location that if specified sets the maximum number of bytes available for use by GW BASIC expression2 sets aside stack space for GW BASIC The default is the previous stack space size When GW BASIC is first executed the stack space is set to 512 bytes or one eighth of the available memory whichever is smaller GW BASIC allocates string space d
238. r s Guide 8 9 10 11 12 13 14 15 aA Gira o oo 18 19 1A 1B 1C 1D 1E 1F 24 25 26 27 28 29 30 31 90 AO BO CO DO EO FO 144 160 176 192 208 224 240 900 A00 BOO C00 DOO E00 FOO 2304 2560 2816 3072 3328 3584 3840 9000 A000 B000 C000 D000 E000 F000 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Appendix 20G html 2 of 2 28 03 2004 21 29 06 36864 40960 45056 49152 53248 57344 61440 GW BASIC User s Guide Appendix I Characters Recognized by GW BASIC The GW BASIC character set includes all characters that are legal in GW BASIC commands statements functions and variables The set comprises alphabetic numeric and special characters The alphabetic characters in GW BASIC are the uppercase and lowercase letters of the alphabet The numeric characters in GW BASIC are the digits 0 through 9 The following special characters and terminal keys are recognized by GW BASIC Character Description Blank Equal sign or assignment symbol Plus sign or string concatenation Minus sign Asterisk or multiplication symbol Slash or division symbol Caret exponentiation symbol or CTRL key Left parenthesis Right parenthesis Percent or integer declaration Number sign or double precision declaration Dollar sign or string declaration Exclamation point or single precision declaration Left bracket Right bracket r Comma ii Double quotation mar
239. r s Guide READ Statement Purpose To read values from a DATA statement and assign them to variables Syntax READ Jist of variables Comments A READ statement must always be used with a DATA statement READ statements assign variables to DATA statement values on a one to one basis READ statement variables may be numeric or string and the values read must agree with the variable types specified If they do not agree a Syntax error results A single READ statement may access one or more DATA statements They are accessed in order Several READ statements may access the same DATA statement If the number of variables in list of variables exceeds the number of elements in the DATA statement s an Out of data message is printed If the number of variables specified is fewer than the number of elements in the DATA statement s subsequent READ statements begin reading data at the first unread element If there are no subsequent READ statements the extra data is ignored To reread DATA statements from the start use the RESTORE statement Examples 80 FOR I 1 TO 10 90 READ A T 100 NEXT I 110 DATA 3 08 5 19 3 12 3 98 4 24 120 DATA 508 5 55 4 00 3 16 3 37 This program segment reads the values from the DATA statements into array A After execution file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic READ html 1 of 2 28 03 2004 21 29 21 GW BASIC User s Guide the value of A 1 is 3 08 an
240. r the foreground background and border colors discussed above See the PALETTE statement reference pages for more details file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic COLOR html 2 of 3 28 03 2004 21 29 16 GW BASIC User s Guide SCREEN Examples The following series of examples show COLOR statements and their effects in the various screen modes SCREEN 0 COLOR 1 2 3 foreground 1 background 2 border 3 SCREEN 1 COLOR i 0 foreground 1 even palette number COLOR 2 1 foreground 2 odd palette number SCREEN 7 COLOR 3 5 foreground 3 background 5 SCREEN 8 COLOR 6G 7 foreground 6 background 7 SCREEN 9 COLOR 1 2 foreground 1 background 2 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic COLOR html 3 of 3 28 03 2004 21 29 16 GW BASIC User s Guide SCREEN Statement Purpose To set the specifications for the display screen Syntax SCREEN mode colorswitch apage vpage Comments The SCREEN statement is chiefly used to select a screen mode appropriate for a particular display hardware configuration Supported hardware configurations and screen modes are described below MDPA with Monochrome Display Mode 0 The IBM Monochrome Display and Printer Adapter MDPA is used to connect only to a monochrome display Programs written for this configuration must be text mode only CGA with Color Display Modes 0 1 and 2 The IBM Color Graphics
241. ram that reads translates and executes a user s program such as one written in the BASIC language one line at a time A compiler on the other hand reads and translates the entire user s program before executing it input 1 The process or device concerning the entry of data into a computer 2 Actual data being entered into a computer input output file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 10 of 17 28 03 2004 21 29 08 GW BASIC User s Guide A general term for devices that communicate with a computer Input output is usually abbreviated as I O instruction A program step that tells the computer what to do next Instruction is often used incorrectly as a synonym for command integer A complete entity having no fractional part The whole or natural number For example 65 is an integer 65 1 is not integrated circuit A complete electronic circuit contained in a small semiconductor component interface An information interchange path that allows parts of a computer computers and external equipment such as printers monitors or modems or two or more computers to communicate or interact VO The acronym for input output job A collection of tasks viewed by the computer as a unit K The symbol signifying the quantity 210 which is equal to 1024 K is sometimes confused with the symbol k kilo which is equal to 1000 logarithm A logarithm of a given number is the value of
242. reen you must use VIEW to disable the viewports Then use CLS to clear the screen CLS does not move the cursor to home Press CTRL HOME to send the cursor home and clear the screen Examples The following defines a viewport such that the statement PSET 0 0 3 would set down a point at the physical screen location 10 10 VIEW 10 1LO 200 100 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic VIEW html 1 of 2 28 03 2004 21 29 52 GW BASIC User s Guide The following defines a viewport such that the point designated by the statement PSET 0 0 3 would not appear because 0 0 is outside of the viewport PSET 10 10 3 would be within the viewport VIEW SCREEN 10 10 200 100 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic VIEW html 2 of 2 28 03 2004 21 29 52 GW BASIC User s Guide VIEW PRINT Statement Purpose To set the boundaries of the screen text window Syntax VIEW PRINT topline TO bottomline Comments VIEW PRINT without topline and bottomline parameters initializes the whole screen area as the text window The whole screen area consists of lines 1 to 24 by default line 25 is not used Statements and functions that operate within the defined text window include CLS LOCATE PRINT and SCREEN The screen editor will limit functions such as scroll and cursor movement to the text window For more information see VIEW file Cl Documents 20and 20Setti
243. return the absolute value of the expression n Syntax ABS n Comments n must be a numeric expression Examples PRINT ABS 7 3 35 Prints 35 as the result of the action file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ABS htm128 03 2004 21 29 11 GW BASIC User s Guide ASC Function Purpose To return a numeric value that is the ASCII code for the first character of the string xs Syntax ASC x5 Comments If x is null an Illegal Function Call error is returned If x begins with an uppercase letter the value returned will be within the range of 65 to 90 If x begins with a lowercase letter the range is 97 to 122 Numbers 0 to 9 return 48 to 57 sequentially See the CHR function for ASCII to string conversion See Appendix C in the GW BASIC User s Guide for ASCII codes Examples 10 XS TEN 20 PRINT ASC XS RUN 84 84 is the ASCII code for the letter T file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic ASC htm128 03 2004 21 29 12 GW BASIC User s Guide CHR Function Purpose To convert an ASCII code to its equivalent character Syntax CHRS n Comments nis a value from 0 to 255 CHRS is commonly used to send a special character to the terminal or printer For example you could send CHRS 7 to sound a beep through the speaker as a preface to an error message or you could send a form feed CHRS 12 to the printer See the AS
244. rings with double quotation marks Positive numbers are not preceded by blank spaces WRITE outputs numeric values using the same format as the PRINT statement Examples 10 B e0 B 90 CS THAT S ALL 20 WRITE A B C RUN 80 90 THAT S ALL file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic WRITE html28 03 2004 21 29 53 GW BASIC User s Guide WRITE Statement Purpose To write data to a sequential file Syntax WRITE filenum list of expressions Comments filenum is the number under which the file was opened for output list of expressions is a list of string and or numeric expressions separated by commas or semicolons The WRITE and PRINT statements differ in that WRITE inserts commas between the items as they are written and delimits strings with quotation marks making explicit delimiters in the list unnecessary Another difference is that WRITE does not put a blank in front of a positive number After the last item in the list is written a carriage return line feed sequence is inserted Examples Let A CAMERA and B 93604 1 The following statement WRITE 1 AS BS writes the following image to disk CAMERA 93604 1 A subsequent INPUTS statement such as the following would input CAMERA to A and 93604 1 to B INPUT 1 AS BS file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic WRITEF htm128 03 2004 21 29 53
245. rmed Syntax RESUME RESUME 0 RESUME NEXT RESUME line number Comments Any one of the four formats shown above may be used depending upon where execution is to resume Syntax Result RESUME or RESUME 0 Execution resumes at the statement that caused an error RESUME NEXT Execution resumes at the statement immediately following the one that caused an error RESUME line number Execution resumes at the specified line number A RESUME statement that is not in an error trapping routine causes a RESUME without error message to be printed Examples 10 ON ERROR GOTO 900 900 IF ERR 230 AND ERL 90 THEN PRINT TRY AGAIN RESUME 80 If an error occurs after line 10 is executed the action indicated in line 900 is taken and the program continues at line 80 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic RES UME htm128 03 2004 21 29 44 GW BASIC User s Guide RETURN Statement Purpose To return from a subroutine Syntax RETURN line number Comments The RETURN statement causes GW BASIC to branch back to the statement following the most recent GOSUB statement A subroutine may contain more than one RETURN statement to return from different points in the subroutine Subroutines may appear anywhere in the program RETURN line number is primarily intended for use with event trapping It sends the event trapping routine back into the GW BASIC program at a fixed line number while still eliminatin
246. rogram performs When you type in the desired function number line 230 branches to the appropriate subroutine Example 6 120 129 130 135 140 150 160 170 180 220 225 230 240 250 260 270 RETURN 280 2 90 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450 460 470 OPEN R 1 INVEN DAT 39 FIELD 1 1 AS F 30 AS DS 2 AS 05 2 AS RS 4 AS P PRINT PRINT FUNCTIONS PRINT PRINT 1 INITIALIZE FILE PRINT 2 CREATE A NEW ENTRY PRINT 3 DISPLAY INVENTORY FOR ONE PART PRINT 4 ADD TO STOCK PRINT 5 SUBTRACT FROM STOCK PRINT 6 DISPLAY ALL ITEMS BELOW REORDER LEVEL PRINT PRINT INPUT FUNCTION FUNCTION oO Ol S G NO S IF FUNCTION lt 1 OR FUNCTION gt 6 THEN PRINT BAD FUNCTION NUMBER GOTO 130 ON FUNCTION GOSUB 900 250 390 480 560 680 GOTO 220 REM BUILD NEW ENTRY GOSUB 840 IF ASC FS lt gt 255 THEN INPUT OVERWRITE AS IF AS lt gt y LSET FS CHRS 0 NPUT DESCRIPTION DESCS SET DS DESCS UT QUANTITY IN STOCK 202 SET QS MKIS 0 UT REORDER LEVEL R SET RS MKIS RS UT UNIT PRICE P SET PS MKSS P UT 1 PART RETURN REM DISPLAY ENTRY GOSUB 840 IF ASC FS 255 THEN PRINT NULL ENTRY RETURN PRINT USING PART NUMBER PARTS PRINT DS PRINT USING QUANTITY ON HAND CVI QS PRINT USING REORDER LEVEL CVI RS PRINT USING UNIT PRICE S CVS PS RETURN Z ja E H EH Z ja
247. rray are as follows e 2 for integer e 4 for single precision e 8 for double precision file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic GETG html 1 of 2 28 03 2004 21 29 28 GW BASIC User s Guide The number of bytes required to get a 10 by 12 image into an integer array is 4 INT 10 2 7 8 12 or 40 bytes An integer array with at least 20 elements is necessary If OPTION BASE equals zero an integer array can be used to examine the x and y dimensions and the data The x dimension is in element 0 of the array and the y dimension is in element 1 Integers are stored low byte first then high byte but data is transferred high byte first left most then low byte It is possible to get an image in one mode and put it in another although the effect may be quite strange because of the way points are represented in each mode Examples 10 CLS SCREEN 1 20 PSET L30 120 30 DRAW U25 E7 R20 D327 L6 Ulz L14 40 DRAW D12 L6 PSET 137 102 50 DRAW U4 E4 R8 D8 L12 60 PSET 137 88 70 DRAW E47 R20 D327 G4 PAINT 139 87 80 DIM A 500 90 GET 125 130 170p 60 a4 100 FOR I 1 TO 1000 NEXT I 116 PUT 20 20 A POSET 120 FOR I 1 TO 1000 NEXT I 130 GET 125 120 L170 30 A 140 FOR I 1 TO 1000 NEXT I 150 PUT 220 130 A PRESET file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic GETG html 2 of 2 28 03 2004 21 29 28 GW BASIC User
248. s expressions and operators in GW BASIC and how they can be used to develop more sophisticated programs 6 1 Constants Constants are static values the GW BASIC Interpreter uses during execution of your program There are two types of constants string and numeric A string constant is a sequence of 0 to 255 alphanumeric characters enclosed in double quotation marks The following are sample string constants HELLO 525 000 00 Number of Employees Numeric constants can be positive or negative When entering a numeric constant in GW BASIC you should not type the commas For instance if the number 0 000 were to be entered as a constant it would be typed as 0000 There are five types of numeric constants integer fixed point floating point hexadecimal and octal Constant Description Integer Whole numbers between 32768 and 32767 They do not contain decimal points Fixed Point Positive or negative real numbers that contain decimal points Floating Point Constants Positive or negative numbers represented in exponential form similar to scientific notation A floating point constant consists of an optionally signed integer or fixed point number the mantissa followed by the letter and an optionally signed integer the exponent The allowable range for floating point constants is 3 0x10 39 to 1 7x1038 For example 250 986E 7 0000235988 2359E6 2359000000 file Cl Documents 20and 20Settings Lorenzo Desktop G
249. s Guide GOSUB RETURN Statement Purpose To branch to and return from a subroutine Syntax GOSUB line number RETURN line number Comments line number is the first line number of the subroutine A subroutine may be called any number of times in a program and a subroutine may be called from within another subroutine Such nesting of subroutines is limited only by available memory A RETURN statement in a subroutine causes GW BASIC to return to the statement following the most recent GOSUB statement A subroutine can contain more than one RETURN statement should logic dictate a RETURN at different points in the subroutine Subroutines can appear anywhere in the program but must be readily distinguishable from the main program To prevent inadvertent entry precede the subroutine by a STOP END or GOTO statement to direct program control around the subroutine Examples 10 GOSUB 40 20 PRINT BACK FROM SUBROUTINE 30 END 40 PRINT SUBROUTINE 50 PRINT IN 60 PRINT PROGRESS 70 RETURN RUN SUBROUTINE IN PROGRESS BACK FROM SUBROUTINE The END statement in line 30 prevents re execution of the subroutine file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic GOSUB htm128 03 2004 21 29 28 GW BASIC User s Guide GOTO Statement Purpose To branch unconditionally out of the normal program sequence to a specified line number Syntax GOTO line number Comments line number is
250. s sign at the beginning or end of the format string causes the sign of the number plus or minus to be printed before or after the number z A minus sign at the end of the format field causes negative numbers to be printed with a trailing minus sign For example PRINT USING f tt 7 68 95 2 4 95 6 9 Ro F240 t3960 0s 90 PRINT USING 68 95 22 449 7 01 60 95 22 45 Ts01 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PRINTUSING html 2 of 4 28 03 2004 21 29 32 GW BASIC User s Guide kK RAKRA A double asterisk at the beginning of the format string causes leading spaces in the numeric field to be filled with asterisks The also specifies two more digit positions For example PRINT USING 712 39 0 9 76901 12 4 097 65 1 A double dollar sign at the beginning of the format string causes a dollar sign to be printed to the immediate left of the formatted number The specifies two more digit positions one of which is the dollar sign The exponential format cannot be used with Negative numbers cannot be used unless the minus sign trails to the right For example PRINT USING SS 456 78 S456 76 The at the beginning of a format string combines the effects of the above two symbols Leading spaces are filled with asterisks and a dollar sign is printed before the number S specifies three more digit positions one of which is the dollar sign For example PRINT
251. sembly language subroutine The GW BASIC stack space must be restored however before returning from the subroutine file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20D html 1 of 8 28 03 2004 21 29 05 GW BASIC User s Guide D 2 CALL Statement CALL variablename arguments variablename contains the offset in the current segment of the subroutine being called arguments are the variables or constants separated by commas that are to be passed to the routine For each parameter in arguments the 2 byte offset of the parameter s location within the data segment DS is pushed onto the stack The GW BASIC return address code segment CS and offset IP are pushed onto the stack A long call to the segment address given in the last DEF SEG statement and the offset given in variablename transfers control to the user s routine The stack segment SS data segment DS extra segment ES and the stack pointer SP must be preserved Figure D 1 shows the state of the stack at the time of the CALL statement Figure 1 Figure D 1 Stack Layout When the CALL Statement is Activated not shown The user s routine now has control Parameters may be referenced by moving the stack pointer SP to the base pointer BP and adding a positive offset to BP Upon entry the segment registers DS ES and SS all point to the address of the segment that contains the GW BASIC interpreter code The code segment register CS
252. single precision value only the first seven digits rounded of the converted number are valid This is because only seven digits of accuracy were supplied with the single precision value The absolute value of the difference between the printed double precision number and the original single precision value is less than 6 3E 8 times the original single precision value For example 10 A 2 04 20 BE A 30 PRINT A B RUN 2 04 2039999961853027 6 4 Expressions and Operators An expression may be simply a string or numeric constant a variable or it may combine constants and variables with operators to produce a single value Operators perform mathematical or logical operations on values The operators provided by GW BASIC are divided into four categories e Arithmetic e Relational file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 6 html 6 of 12 28 03 2004 21 29 00 GW BASIC User s Guide e Logical e Functional 6 4 1 Arithmetic Operators The following are the arithmetic operators recognized by GW BASIC They appear in order of precedence OperatorOperation i Exponentiation Negation a Multiplication Floating point Division Addition 3 Subtraction Operations within parentheses are performed first Inside the parentheses the usual order of precedence is maintained The following are sample algebraic expressions and their GW BASIC counterparts Algebraic ExpressionBASIC Expression X Z Y
253. ssage Subscript out of range Multidimensional arrays more than one subscript separated by commas are useful for storing tabular data For example A 1 4 could be used to represent a two row five column array such as the following Column O 1 2 3 4 Row 0 10 20 30 40 50 Row 1 60 70 80 90 100 In this example element A 1 2 80 and A 0 3 40 Rows and columns begin with 0 not 1 unless otherwise declared For more information see the OPTION BASE statement in the GW BASIC User s Reference 6 2 4 Memory Space Requirements for Variable Storage The different types of variables require different amounts of storage Depending on the storage file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 6 html 4 of 12 28 03 2004 21 29 00 GW BASIC User s Guide and memory capacity of your computer and the size of the program that you are developing these can be important considerations Variable Required Bytes of Storage Integer 2 Single precision 4 Double precision8 Arrays Required Bytes of Storage Integer 2 per element Single precision 4 per element Double precision8 per element Strings Three bytes overhead plus the present contents of the string as one byte for each character in the string Quotation marks marking the beginning and end of each string are not counted 6 3 Type Conversion When necessary GW BASIC converts a numeric constant from one type of variable to another according to the follo
254. st long enough for the receiver to catch up This can be done by sending XOFF CTRL S to the host to temporarily suspend transmission and XON CTRL Q to resume if the application supports it GW BASIC provides three functions which help to determine when an overrun condition is imminent file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20F html 1 of 7 28 03 2004 21 28 59 GW BASIC User s Guide LOC x Returns the number of characters in the input queue waiting to be read The input queue can hold more than 255 characters determined by the e switch If there are more than 255 characters in the queue LOC x returns 255 Since a string is limited to 255 characters this practical limit alleviates the need for the programmer to test for string size before reading data into it LOF x Returns the amount of free space in the input queue that is e size number of characters in the input queue LOF may be used to detect when the input queue is reaching storage capacity EOF x True 1 indicates that the input queue is empty False 0 is returned if any characters are waiting to be read F 4 Possible Errors A Communications buffer overflow error occurs if a read is attempted after the input queue is full that is LOC x returns 0 A Device I O error occurs if any of the following line conditions are detected on receive overrun error OE framing error FE or break interrupt BI The
255. standard coordinate attributes 0 0 320 0 639 0J sl y increases 320 100 0 199 320 199 639 199 Example 2 If you type WINDOW 1 1 1 1 the screen uses the Cartesian coordinates i 1 O 1 iy L T y increases 0 0 y decreases ele 1 Op 1 ih SL Example 3 If you type WINDOW SCREEN 1 1 1 1 the screen uses the non inverted coordinate l 0 1 Ly 1 T y decreases 0 0 L y increases 1 1 0 1 fy 1 RUN SCREEN and WINDOW with no attributes disable any WINDOW definitions and return the screen to its normal physical coordinates file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic WINDOW html 2 of 2 28 03 2004 21 29 53 GW BASIC User s Guide WRITE Statement Purpose To output data to the screen Syntax WRITE list of expressions Comments If list of expressions is omitted a blank line is output If list of expressions is included the values of the expressions are output at the terminal The expressions in the list may be numeric and or string expressions and must be separated by commas or semicolons When printed items are output each item will be separated from the last by a comma Printed strings are delimited by double quotation marks After the last item in the list is printed GW BASIC inserts a carriage return line feed The difference between WRITE and PRINT is that WRITE inserts commas between displayed items and delimits st
256. stitute for 1ine number to indicate the current line If line number is followed by a comma and increment is not specified the last increment specified in an AUTO command is assumed If AUTO generates a line number that is already being used an asterisk appears after the number to warn that any input will replace the existing line However pressing return immediately after the asterisk saves the line and generates the next line number AUTO is terminated by entering CTRL BREAK or CTRL C GW BASIC will then return to command level Note The line in which CTRL BREAK or CTRL C is entered is not saved To be sure that you save all desired text use CTRL BREAK and CTRL C only on lines by themselves Examples AUTO 100 50 Generates line numbers 100 150 200 and so on AUTO Generates line numbers 10 20 30 40 and so on file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A UTO htm128 03 2004 21 29 12 GW BASIC User s Guide BEEP Statement Purpose To sound the speaker at 800 Hz 800 cycles per second for one quarter of a second Syntax BEEP Comments BEEP CTRL G and PRINT CHRS 7 have the same effect Examples 2340 IF X gt 20 THEN BEEP If X is out of range the computer beeps file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic BEEP htm128 03 2004 21 29 13 GW BASIC User s Guide BLOAD Command Purpose To load an image file anywhere in user memory Syntax BLOAD
257. subdirectory via different paths it is nearly impossible for GW BASIC to know that it is the same file simply by looking at the path For this reason GW BASIC does not let you open the file for OUTPUT or APPEND if it is on the same disk even if the path is different For example if mary is your working directory the following statements all refer to the same file OPEN REPORT OPEN SALES MARY REPORT OPEN MARY REPORT OPEN MARY REPORT At any one time it is possible to have a particular diskette filename open under more than one file number Each file number has a different buffer so several records from the same file may be kept in memory for quick access This allows different modes to be used for different purposes or for program clarity different file numbers to be used for different modes of access If the LEN reclen option is used reclen may not exceed the value set by the s reclen switch option in the command line In a network environment the use of the OPEN statement is based upon two different sets of circumstances e Devices may be shared on a network for specific purposes only so that OPEN statements may be restricted to specific modes among those which might be requested such as INPUT OUTPUT APPEND and default random file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic OPEN html 3 of 5 28 03 2004 21 29 39 GW BASIC User s Guide e Files may be restricted by the implementation
258. t X Y lt T 1 2Z This expression is true if the value of X plus Y is lessthan the value of T 1 divided by Z 6 4 3 Logical Operators Logical operators perform tests on multiple relations bit manipulation or Boolean operations The logical operator returns a bit wise result which is either true not zero or false zero In an expression logical operations are performed after arithmetic and relational operations The outcome of a logical operation is determined as shown in the following table The operators are listed in order of precedence Table 6 2 Results Returned by Logical Operations Operation Value Value Result NOT X NOT X T F F T AND x y X AND Y T T T T F F F T F F F F OR X Y X OR Y T T T T F T F T T F F F XOR x y X XOR Y T T F T F T F T T F F F file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 6 html 9 of 12 28 03 2004 21 29 00 GW BASIC User s Guide EQV EQV Y IMP IMP Y MHeteacmenda A7HHax Daas HHmMHx lt H OTH Just as the relational operators can be used to make decisions regarding program flow logical operators can connect two or more relations and return a true or false value to be used in a decision For example IF D lt 200 AND F lt 4 THEN 80 IF I gt 10 OR K lt O THEN 50 IF NOT P THEN 100 Logical operators convert their operands to 16 bit signed two s complement integers within the range of 32768 to 32767 if the operands are not within this r
259. t mode GW BASIC statements and commands are executed as they are entered Results of arithmetic and logical operations can be displayed immediately and or stored for later use but the instructions themselves are lost after execution This mode is useful for debugging and for using GW BASIC as a calculator for quick computations that do not require a complete program file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 202 html 1 of 8 28 03 2004 21 28 57 GW BASIC User s Guide 2 2 2 Indirect Mode The indirect mode is used to enter programs Program lines are always preceded by line numbers and are stored in memory The program stored in memory is executed by entering the RUN command 2 3 The GW BASIC Command Line Format The GW BASIC command line lets you change the environment or the conditions that apply while using GW BASIC Note When you specify modifications to the operating environment of GW BASIC be sure to maintain the parameter sequence shown in the syntax statement To skip a parameter insert a comma This will let the computer know that you have no changes to that particular parameter GW BASIC uses a command line of the following form gwbasic filename lt stdin gt gt stdout n i s n e n m n n d filename is the name of a GW BASIC program file If this parameter is present GW BASIC proceeds as if a RUN command had been given If no extension is provided for the
260. t path to filename connection The operation is not completed 76 Path not found During an OPEN MKDIR CHDIR or RMDIR operation MS DOS is unable to find the path specified The operation is not completed file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20A html 7 of 7 28 03 2004 21 29 03 GW BASIC User s Guide Appendix B Mathematical Functions Mathematical functions not intrinsic to GW BASIC can be calculated as follows GW ay Equivalent Function Secant Cosecant Cotangent Inverse Sine Inverse Cosine Inverse Secant Inverse Cosecant Inverse Cotangent Hyperbolic Sine Hyperbolic Cosine Hyperbolic Tangent Hyperbolic Secant Hyperbolic Cosecant Hyperbolic Cotangent Inverse Hyperbolic Sine Inverse Hyperbolic Cosine Inverse Hyperbolic Tangent Inverse Hyperbolic Cosecant Inverse Hyperbolic Secant Inverse Hyperbolic Cotangent SEC X 1 COS CSC 1 SIN COT 4 1 TAN ARCSIN X AT ARCCOS X AT ARCSEC X AT ARCCSC X ATI ARCCOT X AT SINH X EXP COSH X EXP TANH X EXP SECH X 2 E CSCH X 2 E COTH X EXP ARCSINH X LO ARCCOSH X LO ARCTANH X LO ARCCSCH X LO ARCSECH X LO ARCCOTH X LO0 X X X N X SQR X X 1 N X SQR X X 1 PI 2 N X SQOR X X 1 SGN SGN X 1 PI 2 N X SQR X X 1 SGN X 1 PI 2 N X PI 2 X EXP X 72 X EXP X 2 X EXP X EXP X EXP X XP X
261. tatement and USR function see Appendix D in the GW BASIC User s Guide Example 1 100 DEF SEG amp H2000 110 ARK 0 120 CALL ARK A B C Line 100 sets the segment to hex 2000 ARK is set to zero so that the call to ARK executes the subroutine at location 2000 0 Example 2 The following sequence of 8086 Assembly Language demonstrates access of the parameters passed and stored in variable C PUSH BP MOV BP SP Gets current stack position in BP MOV BX 8 BP Gets address of BS descriptor file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CALL html 2 of 3 28 03 2004 21 29 13 GW BASIC User s Guide MOV CL BX Gets length of BS in CL MOV DX 1 BX Gets address of BS text in DX MOV SI 10 BP Gets address of A in SI MOV DI 6 BP Gets pointer to C in DI MOVSW Stores variable A in C RET 6 Restores stack and returns MOVSW copies only two bytes This is sufficient if variables A and C are integer Four bytes must be copied if they are single precision eight bytes if they are double precision Example 3 100 DEF SEG amp H2000 110 ACC amp H7FA 120 CALL ACC A BS C Line 100 sets the segment to hex 2000 The value of variable ACC is added into the address as the low word after the DEF SEG value is shifted four bits to the left this is a function of the microprocessor not of GW BASIC Here ACC is set to amp H7FA so that the call to ACC executes the subroutine at the location
262. ted to each other The structure usually implies how the data is stored and how the data must be processed filename The unique name usually assigned by a user which is used to identify one file for all subsequent operations that use that file fixed disk A hard disk enclosed in a permanently sealed housing that protects it from environmental interference Used for storage of data floating point arithmetic A method of calculation in which the computer or program automatically records and accounts for the location of the radix point The programmer need not consider the radix location floating point routine A set of program instructions that permits a floating point mathematics operation in a computer which lacks the feature of automatically accounting for the radix point format A predetermined arrangement of data that structures the storage of information on an external storage device function A computer action as defined by a specific instruction Some GW BASIC functions are Cos EOF INSTR LEFTS and TAN function keys Specific keys on the keyboard that when pressed instruct the computer to perform a particular operation The function of the keys is determined by the applications program being used GIGO An informal term that indicates sloppy data processing an acronym for Garbage In Garbage Out The term GIGO is normally used to make the point that if the input data is bad garbage in then the output data will also b
263. than the string the string is left justified in the field and padded with spaces on the right For example 10 AS LOOK gt BS OUT 30 PRINT USING A B AQ PRINT USING A BS 50 PRINT USING y AS Bost t i RUN LO LOOKOUT LOOK OUT file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic PRINTUSING html 1 of 4 28 03 2004 21 29 32 GW BASIC User s Guide amp Specifies a variable length string field When the field is specified with the string is output exactly as input For example 10 A LOOK BS OUT 20 PRINT USING AS 30 PRINT USING amp BS RUN LOUT Numeric Fields The following special characters may be used to format the numeric field A pound sign is used to represent each digit position Digit positions are always filled If the number to be printed has fewer digits than positions specified the number is right justified preceded by spaces in the field A decimal point may be inserted at any position in the field If the format string specifies that a digit is to precede the decimal point the digit always is printed as 0 if necessary Numbers are rounded as necessary For example PRINT USING 78 0 78 PRINT USING 987 654 98765 PRINT USING 710 2 5 3 66 789 234 10 20 Des 0 CCT 023 In the last example three spaces were inserted at the end of the format string to separate the printed values on the line ji A plu
264. the OUT statement Examples 100 A INP 56 Upon execution variable A contains the value present on port 56 The number returned will be within the range of 0 to 255 decimal The assembly language equivalent to this statement is MOV DX 56 IN AL DX file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic INP htm128 03 2004 21 29 30 GW BASIC User s Guide INPUT Statement Purpose To prepare the program for input from the terminal during program execution Syntax INPUT prompt string list of variables INPUT prompt string list of variables Comments prompt stringis arequest for data to be supplied during program execution list of variables contains the variable s that stores the data in the prompt string Each data item in the prompt string must be surrounded by double quotation marks followed by a semicolon or comma and the name of the variable to which it will be assigned If more than one variable is given data items must be separated by commas The data entered is assigned to the variable list The number of data items supplied must be the same as the number of variables in the list The variable names in the list may be numeric or string variable names including subscripted variables The type of each data item input must agree with the type specified by the variable name Too many or too few data items or the wrong type of values for example numeric instead of string causes the
265. the exponent indicating the power required to raise a specified constant known as the base to produce that given number That is if B is the base N is the given number and L is the logarithm then BL N Since 103 1000 the logarithm to the base 10 of 1000 is 3 loop A series of computer instructions that are executed repeatedly until a desired result is obtained or a predetermined condition is met The ability to loop and reuse instructions eliminates countless repetitious instructions and is one of the most important attributes of stored programs M The symbol signifying the quantity 1 000 000 10 When used to denote storage it more file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Glossary html 11 of 17 28 03 2004 21 29 08 GW BASIC User s Guide precisely refers to 1 048 576 22 mantissa The fractional or decimal part of a logarithm of a number For example the logarithm of 163 is 2 212 The mantissa is 0 212 and the characteristic is 2 0 In floating point numbers the mantissa is the number part For example the number 24 can be written as 24 2 where 24 is the mantissa and 2 is the exponent The floating point number is read as 24 x 102 or 24 master file A data file composed of records having similar characteristics that rarely change A good example of a master file would be an employee name and address file that also contains social security numbers and hiring dates media The plural of
266. the hour 0 23 Minutes and seconds default to 00 hh mm sets the hour and minutes 0 59 Seconds default to 00 hh mm ss sets the hour minutes and seconds 0 59 If string exp is nota valid string a Type mismatch error results As you enter any of the above values you may omit the leading zero if any You must however enter at least one digit If you wanted to set the time as a half hour after midnight you could enter TIMES 0 30 but not TIMES 30 If any of the values are out of range an Illegal function call error is issued The previous time is retained The current time is stored if TIMES is the target of a string assignment The current time is fetched and assigned to the string variable if TIMES is the expression in a LET or PRINT statement If string exp TIMES TIMES returns an 8 character string in the form hh mm ss Examples The following example sets the time at 8 00 A M TIMES 08 00 PRINT TIMES file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic TIMES html 1 of 2 28 03 2004 21 29 50 GW BASIC User s Guide 08200305 The following program displays the current date and time on the 25th line of the screen and will sound on the minute and half minute 10 KEY OFF SCREEN 0 WIDTH 80 CLS 20 LOCATE 25 5 30 PRINT DATES TIMES 40 SEC VAL MIDS TIMES 7 2 50 IF SEC SSEC THEN 20 ELSE SSEC SEC 60 IF SEC 0 THEN 1010 70 IF SEC 30 THEN 1020 80 IF SEC lt 57 THEN 20 1000
267. the rectangular region in the world coordinate space It allows zoom and pan It allows the user to draw lines graphics and objects in space not bounded by the physical limits of the screen To do this the user specifies the world coordinate pairs x1 y1 and x2 y2 GW BASIC then converts the world coordinate pairs into the appropriate physical coordinate pairs for subsequent display within screen space Window inverts with the screen attribute omitted the y coordinate on subsequent graphics statements This places the x1 y1 coordinate in the lower left and the x2 y2 coordinate in the upper right of the screen This allows the screen to be viewed in true Cartesian coordinates The coordinates are not inverted when the SCREEN attribute is included This places the x1 y1 coordinate in the upper left and the x2 y2 coordinate in the lower right corner of the screen The WINDOW statement sorts the x and y argument pairs into ascending order For example WINDOW 30 30 10 19 becomes WINDOW 10 10 50 50 Or WINDOW 2 2 2 2 becomes WINDOW 2 2 2 2 All coordinate pairs of x and y are valid except that x1 cannot equal x2 and y1 cannot equal y2 WINDOW with no arguments disables previous window statements file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic WINDOW html 1 of 2 28 03 2004 21 29 53 GW BASIC User s Guide Example 1 If you type NEW SCREEN 2 the screen uses the
268. ther process Other processes are denied access to the file while it is open under default access Therefore it is functionally exclusive When an attempt is made to open a file that has been previously accessed by another process the error Permission Denied will result An example of a situation generating this error is when a process attempts to OPEN SHARED ona file that is already OPEN LOCK READ WRITE by another process If an OPEN statement fails because the mode is incompatible with network installed sharing access to a device the error generated is Path File Access Error An example of this is when a process is attempting to OPEN a file for output on a directory that has been shared for read only For more information about using files in a networking environment see the LOCK and UNLOCK statements Examples file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic OPEN html 4 of 5 28 03 2004 21 29 39 GW BASIC User s Guide 10 OPEN I 2 INVEN Opens file 2 inven for sequential input file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic OPEN html 5 of 5 28 03 2004 21 29 39 GW BASIC User s Guide RESET Command Purpose To close all disk files and write the directory information to a diskette before it is removed from a disk drive Syntax RESET Comments Always execute a RESET command before removing a diskette from a disk drive Otherwise when the diskette is used again it w
269. thin variable names Keywords are stored in the system as tokens 1 or 2 byte characters for the most efficient use of memory space 2 4 2 Commands Commands and statements are both executable instructions The difference between commands and statements is that commands are generally executed in the direct mode or command level of the interpreter They usually perform some type of program maintenance such as editing loading or saving programs When GW BASIC is invoked and the GW BASIC prompt Ok appears the file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 202 html 5 of 8 28 03 2004 21 28 57 GW BASIC User s Guide system assumes command level 2 4 3 Statements A statement such as ON ERROR GOTO is a group of GW BASIC keywords generally used in GW BASIC program lines as part of a program When the program is run statements are executed when and as they appear 2 4 4 Functions The GW BASIC Interpreter performs both numeric and string functions 2 4 4 1 Numeric Functions The GW BASIC Interpreter can perform certain mathematical arithmetical or algebraic calculations For example it calculates the sine SIN cosine COS or tangent TAN of angle x Unless otherwise indicated only integer and single precision results are returned by numeric functions 2 4 4 2 String Functions String functions operate on strings For example TIMES and DATES return the time and date known by the system
270. to any of 2 attributes e Supports both EGA and CGA e bit per pixel SCREEN 7 e 320 x 200 pixel medium resolution graphics e 40 x 25 text format with character box size of 8 x 8 e 2 4 or 8 memory pages with 64K 128K or 256K of memory respectively installed on the EGA e Assignment of any of 16 colors to 16 attributes e EGA required e 4 bit per pixel SCREEN 8 e 640 x 200 pixel high resolution graphics e 80 x 25 text format with character box size of 8 x 8 e 1 2 or 4 memory pages with 64K 128K or 256K of memory respectively installed on the EGA e Assignment of any of 16 colors to 16 attributes e EGA required e 4 bits per pixel SCREEN 9 e 640 x 350 pixel enhanced resolution graphics e 80 x 25 text format with character box size of 8 x 14 e Assignment of either 64 colors to 16 attributes more than 64K of EGA memory or 16 colors to 4 attributes 64K of EGA memory e Two display pages if 256K of EGA memory installed e EGA required e 2 bits per pixel 64K EGA memory 4 bits per pixel more than 64K EGA memory file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SCREENS html 3 of 7 28 03 2004 21 29 16 GW BASIC User s Guide SCREEN 10 e 640 x 350 enhanced resolution graphics e 80 x 25 text format with character box size of 8 x 14 e Two display pages if 256K of EGA memory installed e Assignment of up to 9 pseudo colors to 4 attributes e EGA required e 2 bits per pixel The following are de
271. tring space dynamically until it runs out of memory String too long An attempt is made to create a string more than 255 characters long String formula too complex A string expression is too long or too complex Break the expression into smaller expressions Can t continue An attempt is made to continue a program that e Has halted because of an error e Has been modified during a break in execution e Does not exist file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic A ppendix 20A html 2 of 7 28 03 2004 21 29 03 GW BASIC User s Guide LS 19 20 21 22 23 24 20 26 2T 28 29 30 Undefined user function A USR function is called before the function definition DEF statement is given No RESUME An error trapping routine is entered but contains no RESUME statement RESUME without error A RESUME statement is encountered before an error trapping routine is entered Unprintable error No error message is available for the existing error condition This is usually caused by an error with an undefined error code Missing operand An expression contains an operator with no operand following it Line butfer overflow An attempt is made to input a line that has too many characters Device Timeout GW BASIC did not receive information from an I O device within a predetermined amount of time Device Fault Indicates a hardware error in the printer or interface card FOR With
272. ttings Lorenzo Desktop GW 20Basic Chapter 1 html 3 of 3 28 03 2004 21 28 56 GW BASIC User s Guide Chapter 2 Getting Started with GW BASIC This chapter describes how to load GW BASIC into your system It also explains the two different types of operation modes line formats and the various elements of GW BASIC 2 1 Loading GW BASIC To use the GW BASIC language you must load it into the memory of your computer from your working copy of the MS DOS diskette Use the following procedure 1 Turn on your computer 2 Insert your working copy of the MS DOS diskette into Drive A of your computer and press RETURN 3 Type the following command after the A gt prompt and press RETURN gwbasic Once you enter GW BASIC the GW BASIC prompt Ok will replace the MS DOS prompt A gt On the screen the line XXXXX Bytes Free indicates how many bytes are available for use in memory while using GW BASIC The function key F1 F10 assignments appear on the bottom line of the screen These function keys can be used to eliminate key strokes and save you time Chapter 4 The GW BASIC Screen Editor contains detailed information on function keys 2 2 Modes of Operation Once GW BASIC is initialized loaded it displays the Ok prompt Ok means GW BASIC is at command level that is it is ready to accept commands At this point GW BASIC may be used in either of two modes direct mode or indirect mode 2 2 1 Direct Mode In the direc
273. u must save the work you have entered under GW BASIC or the work will be lost To return to MS DOS type the following after the Ok prompt and press RETURN system The system returns to MS DOS and the A gt prompt appears on your screen file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 202 html 8 of 8 28 03 2004 21 28 57 GW BASIC User s Guide Chapter 4 The GW BASIC Screen Editor You can edit GW BASIC program lines as you enter them or after they have been saved in a program file 4 1 Editing Lines in New Files If an incorrect character is entered as a line is being typed it can be deleted with the BACKSPACE or DEL keys or with CTRL H After the character is deleted you can continue to type on the line The Esc key lets you delete a line from the screen that is in the process of being typed In other words if you have not pressed the RETURN key and you wish to delete the current line of entry press the ESC key To delete the entire program currently residing in memory enter the NEW command NEW is usually used to clear memory prior to entering a new program 4 2 Editing Lines in Saved Files After you have entered your GW BASIC program and saved it you may discover that you need to make some changes To make these modifications use the LIST statement to display the program lines that are affected 1 Reload the program 2 Type the LIST command or press the F1 key 3 Type the line nu
274. wing rules e Ifa numeric constant of one type is set equal to a numeric variable of a different type the number is stored as the type declared in the variable name For example 10 AS 23 42 20 PRINT A RUN 23 If a string variable is set equal to a numeric value or vice versa a Type Mismatch error occurs e During an expression evaluation all of the operands in an arithmetic or relational operation are converted to the same degree of precision that is that of the most precise operand Also the result of an arithmetic operation is returned to this degree of precision For example 10 D 6 7 20 PRINT D RUN 8571428571428571 file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic Chapter 6 html 5 of 12 28 03 2004 21 29 00 GW BASIC User s Guide The arithmetic is performed in double precision and the result is returned in D as a double precision value 10 D 6 7 20 PRINT D RUN oo 1429 The arithmetic is performed in double precision and the result is returned to D single precision variable rounded and printed as a single precision value e Logical operators convert their operands to integers and return an integer result Operands must be within the range of 32768 to 32767 or an Overflow error occurs e When a floating point value is converted to an integer the fractional portion is rounded For example 10 Cs 55 88 20 PRINT C RUN 56 e If adouble precision variable is assigned a
275. y coordinate of joystick A x coordinate of joystick B 3 y coordinate of joystick B file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic STICK htm128 03 2004 21 29 48 GW BASIC User s Guide STOP Statement Purpose To terminate program execution and return to command level Syntax STOP Comments STOP statements may be used anywhere in a program to terminate execution When a STOP is encountered the following message is printed Break in line nnnnn Unlike the END statement the STOP statement does not close files GW BASIC always returns to command level after a STOP is executed Execution is resumed by issuing a CONT command Examples 10 INPUT A B C 20 KRaA 2 5 32 LHB s 26 30 STOP 40 M C K 100 PRINT M RUN gt dy 2p 3 BREAK IN 30 PRINT L 30 76923 CONT flees ee file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic STOP htm128 03 2004 21 29 48 GW BASIC User s Guide STR Function Purpose To return a string representation of the value of x Syntax STRS x Comments STRS x is the complementary function to VAL x see the VAL function Examples 5 REM ARITHMETIC FOR KIDS 10 INPUT TYPE A NUMBER N 20 ON LEN STRS N GOSUB 30 40 50 This program branches to various subroutines depending on the number of characters typed before the RETURN key is pressed file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic STRS htm128 03 2004 21 2
276. y language subroutines Only values 0 9 are valid for n If n is omitted USRO is assumed see DEF USR for the rules governing n If a segment other than the default segment GW BASIC data segment DS is used a DEF SEG statement must be executed prior to a USR call This ensures that the code segment points to the subroutine being called The segment address given in the DEF SEG statement determines the starting segment of the subroutine For each USR function a corresponding DEF USR statement must have been executed to define the USR call offset This offset and the currently active DEF SEG segment address determine the starting address of the subroutine If more than 10 user routines are required the value s of DEF USR may be redefined for the other starting addresses as many times as needed The type numeric or string of the variable receiving the function call must be consistent with the argument passed If no argument is required by the assembly language routine then a dummy argument must be supplied file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic USR htm128 03 2004 21 29 05 GW BASIC User s Guide Appendix E Converting BASIC Programs to GW BASIC Programs written in a BASIC language other than GW BASIC may require some minor adjustments before they can be run The following sections describe these adjustments E 1 String Dimensions Delete all statements used to declare the length of strings A stat
277. y of these attribute and color configurations are summarized in the following table Table 3 Default Attributes and Colors for Most Screen Modes Attributes for Mode Color Display Monochrome Display 19 2 0 7 8 9 Number Color Number Color 0 0 0 0 Black 0 Off 1 1 Blue Underlined 2 2 Green 1 On 3 3 Cyan 1 On 4 4 Red 1 Ona 5 5 Magenta 1 Ona 6 6 Brown 1 Ona 7 a White 1 Ona 8 8 Gray 0 Off High intensit 9 9 Light Blue a derlined y 10 10 Light Green 2 High intensity 1 11 11 Light Cyan 2 High intensity 12 12 Light Red 2 High intensity 2 13 13 Light Magenta 2 High intensity 14 14 Yellow 2 High intensity 3 1 15 15 High intensity White 0 Off a Off when used for background b With EGA memory gt 64K c Only for mode 0 monochrome The default foreground colors for the various modes are given in the following table Table 4 Default Foreground Colors Default foreground attribute Default foreground color Screen Color Extended Monochrome Color Extended Monochrome mode Display Display Display Display 0 7 7 7 1 1 3 NA 15 NA 2 1 NA 15 NA file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SCREENS html 6 of 7 28 03 2004 21 29 16 GW BASIC User s Guide 7 15 NA 15 NA 8 15 NA 15 NA 9 3b NA 63 NA 10 NA 3 NA 8 a IBM Enhanced Color Display b 15 if greater than 64K of EGA memory NA Not Applicable file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic SCREENS html 7 of 7 28 03 2004 21 29 16 GW BASIC
278. ynamically An Out of String Space error occurs only if there is no free memory left for GW BASIC to use The CLEAR command e Closes all files e Clears all COMMON and user variables e Resets the stack and string space e Releases all disk buffers e Turns off any sound e Resets sound to music foreground e Resets PEN to off e Resets STRIG to off e Disables ON ERROR trapping Examples CLEAR Zeroes variables and nulls all strings file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CLEAR html 1 of 2 28 03 2004 21 29 18 GW BASIC User s Guide CLEAR 32768 Zeroes variables nulls strings protects memory above 32768 does not change the stack space CLEAR 2000 Zeroes variables nulls strings allocates 2000 bytes for stack space and uses all available memory in the segment CLEAR 32768 2000 Zeroes variables nulls strings protects memory above 32768 and allocates 2000 bytes for stack space file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic CLEAR html 2 of 2 28 03 2004 21 29 18 GW BASIC User s Guide CLOSE Statement Purpose To terminate input output to a disk file or a device Syntax CLOSE filenumber filenumber Comments filenumber 1s the number under which the file was opened The association between a particular file or device and file number terminates upon execution of a CLOSE statement The file or device may then be reopened using the sa
279. ys terminates the string If the first character of the string is not a double quotation mark the string terminates on a comma carriage return line feed or after 255 characters have been read If end of the file is reached when a numeric or string item is being INPUT the item is terminated INPUT can also be used with random files file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic INPUTF htm128 03 2004 21 29 32 GW BASIC User s Guide INPUTS Function Purpose To return a string of x characters read from the keyboard or from file number Syntax INPUTS x file number Comments If the keyboard is used for input no characters will appear on the screen All control characters except CTRL BREAK are passed through CTRL BREAK interrupts the execution of the INPUTS function The INPUTS function is preferred over INPUT and LINE INPUT statements for reading communications files because all ASCII characters may be significant in communications INPUT is the least desirable because input stops when a comma or carriage return is seen LINE INPUT terminates when a carriage return is seen INPUTS allows all characters read to be assigned to a string INPUTS will return x characters from the file number or keyboard For more information about communications refer to Appendix F in the GW BASIC User s Guide Example 1 The following example lists the contents of a sequential file in hexadeci
280. ytes times 21 elements file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic DIM htm128 03 2004 21 29 00 GW BASIC User s Guide OPTION BASE Statement Purpose To declare the minimum value for array subscripts Syntax OPTION BASE n Comments nis 1 or 0 The default base is 0 If the statement OPTION BASE 1 is executed the lowest value an array subscript can have is 1 An array subscript may never have a negative value OPTION BASE gives an error only if you change the base value This allows chained programs to have OPTION BASE statements as long as the value is not changed from the initial setting Note You must code the OPTION BASE statement before you can define or use any arrays If an attempt is made to change the option base value after any arrays are in use an error results file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic OPTIONBASE htm128 03 2004 21 29 01 GW BASIC User s Guide FIX Function Purpose To truncate x to a whole number Syntax FIX x Comments FIX does not round off numbers it simply eliminates the decimal point and all characters to the right of the decimal point FIX x is equivalent to SGN x INT ABS x The major difference between FIX and INT is that FIX does not return the next lower number for negative x FIX is useful in modulus arithmetic Examples PRINT PIX 30273 58 PRINT PIX 360 75 50 file Cl Documents 20and
281. ze is determined by S switch VRECL bytes are transferred between BUFFER and FIELD on I O operations Use this offset to examine file data in random I O mode Example 1 100 X VARPTR Y When executed the variable X will contain an address that points to the storage space assigned to the variable Y Example 2 10 OPEN DATA FIL AS 1 20 FCBADR VARPTR 1 30 DATADR FCBADR 188 40 AS PEEK DATADR In line 20 FCBADR contains the start of FCB In line 30 DATADR contains the address of the data buffer In line 40 A contains the first byte in the data buffer file Cl Documents 20and 20Settings Lorenzo Desktop GW 20Basic VARPTR html 3 of 3 28 03 2004 21 29 51 GW BASIC User s Guide VARPTR Function Purpose To return a character form of the offset of a variable in memory Syntax VARPTRS variable Comments variable is the name of a variable that exists in the program Note Assign all simple variables before calling VARPTRS for an array element because the array addresses change when a new simple variable is assigned VARPTRS returns a three byte string of the following form Byte 0 Byte 1 Byte 2 Byte 0 contains one of the following variable types 2 integer 3 string 4 single precision 8 double precision Byte 1 contains the 8086 address format and is the least significant byte Byte 2 contains the 8086 address format and is the most significant byte Examples 100 X USR VARP

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