This is the first of two
Variable utility programs. The second VARSORT2 which allows you to add
descriptions to the variables and which can be accessed from this
program will be published next issue. Whilst written for disk users, the
program can be easily converted for cassette.
When writing a program
which uses quite a lot of variables, it is very easy to forget which
variables you have already used. It is possible to obtain a list of
these from the computer itself but they will be in the order of
entering. This program is 'ENTERed' from disc and tacks itself on to the
end of your program (its line numbers run from 32000 upwards). When 'ENTERed'
type 'GOTO 32000' and the program will clear the screen and print, in
three columns, all the variables you have used so far. You will then be
asked to press any key for a 'sort'. The sort section is the one used in
a program published in Page 6 some time ago although in this version you
can watch its progress on the screen. When completed, the sorted list of
variables is displayed on screen, again in three columns. You are then
asked if you want to print them or put them to disk - the filename is
fixed. Finally you have the option to call 'VARSORT2' or finish. A word
of warning - whichever option you choose will erase your original
program from memory - so SAVE IT FIRST !!!.
The program runs as
follows:-
FETCHING THE VARIABLES
Line
32000 dimensions the strings and array used. The array is cleared.
Line
32010 sets the mode to zero: sets the colours: clears the cursor.
Line
32020 prints the heading asking you to wait for the variables to be
fetched.
Line
32030 sets a TRAP: OPENs a channel for input from keyboard.
Line
32040 sets a loop 'XX' which will run from the address contained within
memory locations 130 and 131 to that in 132 and 133 LESS 47. The
first is the beginning of the variable list - the last is the end minus
1. Why 47 then? The variables used in this program occupy 46 bytes and,
as we don't want them listed we stop the list just before they are
reached.
(A
word of explanation - the variables are listed nose to tail with no gaps
in between. What makes it easy to pick out each separate variable is the
way in which the last character is stored - as an INVERSE character. The
ATASCII number for an Inverse
Character is 128 greater than that for a normal one).
Line
32050 looks at the value contained in 'XX', if less than 128 then its
value is passed on to 'XXX': GOSUB's line 32100 and on returning GOTO's
32070.
Line
32060 is only reached when a PEEK at 'XX' is greater than 128 and when
this is so then 'XXX' is made equal to 'XX' but less 128: GOSUB's 32100
and, on return, is immediately GOSUBbed again to line 32110, for it is
obvious that a complete variable name has been obtained.
Line
32070 sends you back for another pass through the loop until finally the
list is exhausted whereupon the program GOSUB's to line 32440 (the
screen print-out).
Line
32080 prints the request to press any key for the sort to begin and then
waits for your input.
Line
32090 clears the screen and GOTO's line 32150.
Line
32100 adds the individual characters of the variable (in 'XXX') to a
string 'XX$'.
Line
32110 is brought into use when the complete variable is contained in 'XX$',
the string is then checked for length, if not 10 characters then it has
a dot added until it is. As the final string will contain all the
variables, each sub string must be of a fixed length so that we can
extract it!
Line
32120 adds 'XX$' to that final 'long' string, 'XAR$' and 'XX$' are then
cleared ready for the next variable.
Line
32130 is the error line which the TRAP, when sprung, sends the program
to.
Line
32140 sends you back to line 32010 to have another try.
THE SORT
Line
32150 is the first line of the sort section. The bell is rung, warning
you of the start: 'XX' is used again, this time to represent the length
of each variable sub string. A loop is started - 'XZX1 ' - running from
1 to the length of 'XAR$' divided by 'XX', this of course gives you the
number of variables in the string: 'XX1' is equalled to the pass through
the loop 'XZX1' times 'XX': 'XROW' is equalled to the number of
variables in the string.
Line
32160 Another loop 'XZX2' is started running from 1 to the number of
variables: 'XX2' is equalled to 'XZX2' times 'XX'. This second loop
completes a whole cycle whilst the first loop is stationary on one item
at a time. This is used by the line 32180.
Line
32170 prints the loop positions as they are executed.
Line
32180 compares the variable in the first loop (using 'XX1' to split it
from the long string) with the variables as they appear in the second.
When the first variable is 'less' (alphabetically speaking!) than that
in the second loop then 'XROW' (initially representing the total number
of variables) is reduced by one.
Line
32190 goes back for another pass through loop 'XZX2' until this is
completed.
Line
32200 comes into effect when loop 'XZX2' has completed its cycle,
checking each of its items against the single item of loop 'XZX1'. 'XROW
now holds the actual position which the loop 'XZX1' item will hold in
the new string. This is now placed in the array 'XROW', the position
within the array being determined by the pass through loop 'XZX1'.
Line
32210 now returns for the next pass through loop 'XZX1' (just one item
before going through loop 'XZX2' again). 'XROW' is automatically
reinitialized to the total number of variables before the loop 'XZX2'
starts. This continues until the whole of loop 'XZX1' has been compared
with the items shown by loop 'XZX2', and the 'XROW' array contains the
new positions.
Line
32220 starts a loop 'XZX1' running as before. 'XX1' is set as before.
Line
32230 starts loop 'XZX2' as before. 'XX2' is set as before.
Line
32240 prints the state of the loops to screen (alongside the other).
Line
32250 checks the first loop 'XZX1 ' and if the pass is equal to 'XROW'
array as defined by the pass through the loop 'XZX2' then the new string
has the variable shown in that pass through 'XZX2' transferred to the
new string in the position which 'XZX1' and 'XROW (XZX1)' agree
upon.
Line
32260 goes back for another loop through 'XZX2' and line 32270 through
'XZX1'.
Line
32280 When all is finished and the new string 'XAR1$' contains the
sorted list then this line sets about restoring the original string. 'XAR$'
is first emptied, then 'XAR$' is made equal to 'XAR1$', finally 'XAR1$'
is emptied.
Line
32290 prints the fact that the sort has been completed and line 32300
pauses for a while, clears the screen and GOSUB's line 32440 for a print
out
PRINT
IT?
Line
32320 asks you if you wish to print the list - waits for an answer Y or
N. An ' N' would send the program to line 32380.
Line
32330 sets a TRAP in case the printer is not switched
on: does an exploratory LPRINT, which if OK then passes on to line
32350.
Line
32340 is the error routine which prints the message to switch the
printer on.
Line
32345 sends you back to line 32330 so creating a loop, this will
continue (ringing the bell in the process) until the printer is switched
on.
Line
32350 sets the printer to the Condensed Print and 8 lines to the inch
mode. This should be changed to suit your own printer.
Line
32360 sets 'XX' to equal 10: starts a loop 'XZX1' running from 1 to the
number of variables as before: sets 'XX1' as before: prints to paper the
variables out of XAR$ as defined by 'XX': goes back for another pass:
clears the printer settings.
Line
32380 asks if you wish to record to Disc. An 'N' would send you to line
32420. The variables would be filed under the name D:XXX.DAT and can be
used by the program VARSORT2.
Line
32390 sets a TRAP to close the channel when finished: OPENs a channel to
write data to the above file.
Line
32400 prints the data to disc.
Line
32410 closes the channel.
Line
32420 asks you if you wish to call the program VARSORT2. A 'Y' would
cause VARSORT2 to be run, so erasing both your own program and VARSORT1
in the process. The moral being SAVE IT!!
Line
32430 An' N' would close the keyboard input channel and issue a NEW
instruction, with the same effect as above with regard to your program.
PUT
IT ON SCREEN
Line
32440 sets 'XX' to equal 10: 'XXXLIN' (line counter) to 5: 'XZX1'
(screen print position) to zero.
Line
32450 starts a loop 'XX2' as before: 'XX1 ' is set as before: at a
position defined by 'XZX1' and 'XXXLIN' the variables are printed: 'XXXLIN'
has 1 added to it.
Line
32460 'XXXLIN' is checked, if 19 and 'XZX2' equals 1 the 'XXXLIN' is
reset to 5: 'XZX1 ' to 14: 'XZX2' to 2: the program then GOTO's line
32490.
Line
32470 checks 'XXXLIN', if 19 and and 'XZX2' equals 2 then 'XXXLIN' is
reset to 5: 'XZX1' to 28: 'XZX2' to 3: and goto's line 32490.
Line
32480 checks 'XXXLIN', if 19 and 'XZX2' equals 3 then 'XXXLIN' is reset
to 5: 'XZX1' to zero: 'XZX2' to 1: and GOTO's line 32500.
Line
32490 sends you back for another pass through the loop. When the loop is
finished the program RETURNS to a position immediately after the
original GOSUB.
Line
32500 asks you to press a key for the next page and then waits for an
input.
Line
32510 uses a loop 'XXX' to print a line of blanks from lines 19 to 5:
returns to line 32490.
Even
if you do not type it in I hope that the line by line explanation will
help you to understand the structure of the program and will help you to
write your own utilities. VARSORT2 will follow in the next issue.
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