GENCALC

by David F.M. Carmichael

from ZX Computing Feb/Mar.1985



A brilliant program from David F M Carmichael of Glasgow.





This program has been devised so that the ZX Spectrum and ZX

printer can be used to carry out and annotate a wide range

of calculations without the necessity of having to write

specialised programs for each case. The program operates in

a number of different modes which can be selected by codes

entered at the key board.



The main operating modes (with their appropriate codes) are:-



"type": Typewriting mode allowing full typewriting

facilities in columns 1-30 of the display with various

delete options.



"calc": Calculator mode allowing typewriting facilities

similar to the above but only in columns 1-15, while

allowing the right-hand side of the screen to be used as a

calculator. Easy interchange is possible between the typing

and calculating sub-modes.



"table": User defined formula driven table calculator which

can be used with complex arithmetical expressions with up to

3 variables. Optional total facility is available.



Two other modes are available:



"copy": Copies the screen and gives option to take a further

copy if required.



"newpage": Copies the screen as above but on completion

scrolls the display to the next page.



All the above codes are initialised in the program so that

in the event of a crash or break in the program, it can be

restarted without disturbing the display by using the

command GO TO "(whatever code appropriate)".



On running the program the prompt "Enter required mode" will

appear and the appropriate code should be entered from the

keyboard. The computer will not accept spurious codes and

will beep to indicate the fact. (Indeed all through the

program spurious entries will get the same treatment, with

one notable exception in "table" mode).



Detailed instructions for each mode are as follows:



"type": Flashing "T" cursor displayed initially. Simulates

typewriter for all key entries (except for those below). A

warning beep is given when the cursor reaches column 25 and

a double beep at column 30. The cursor automatically moves

on to the next line but there is no autorepeat for key

entry.



Special key entries (with shift where appropriate) are:-



'DELETE'   : Autorepeat backspace/delete

'ENTER'    : Autorepeat new line

'EDIT'     : Gives "Enter required mode" prompt

'STOP'     : Stop program

'Cursor    : Gives line delete cursor

 Left'      (flashing "*" in column 0).



With line delete cursor the following key entries (with

shift where appropriate) can be used.



Cursor Up    Moves cursor in appropriate

Cursor Down  direction (autorepeat).

'DELETE'     Deletes whole line to the right of the cursor.

Cursor Right Returns to normal typewriter state with "T" cursor on

             column 1 of the line to the right of the cursor.



NOTE: When the bottom of the screen is reached either by

normal typing or by use of the newline command the screen

prompt "Screen full - go to next page?" will appear. If the

'N' key is pressed this prompt will disappear and the option

of obtaining and using the delete cursor is open. If the 'Y'

key is pressed an automatic copy/newpage sequence is

initiated.



'note'    Flashing 'N' cursor shows initially. Simulates typewriter

sub-mode  as in "type" mode but only in left hand side of screen. The

          delete cursor is a flashing "+" and will only delete one

          half of the line. All control key entries are the same as

          for "type" mode with the following additions:

"N"       Cursor right goes to 'calculator' sub-mode. A flashing

cursor    "<" cursor will appear on the right of the screen

          marking the print line.

"+"       Provided that no calculation is in progress the key

cursor    entry "Cursor Left" will move the delete cursor

          (behind the screen as it were) to the right side of the

          screen. Here it can be used to delete any entries on that

          side. At this point "Cursor Right" will return the cursor to

          the left hand side of the screen. It is not possible to go

          to the calculator sub-mode directly with the "+" cursor

          on the right hand side.





"Calculator" sub-mode



The prompt will ask for number or operator entry. Number of

entries must be no more than 8 characters long. Spurious

entries will be beeped.



Relevant operators are:



"+"     for addition

"-"     for subtraction

"*"     for multiplication

"/"     for division

"+%"    calculates % and adds result to running total

"-%"    calculates % and subtracts result from running total

"sub"   gives subtotal (marked with symbol ">")

"total" gives total

"note"  returns to "note" sub-mode.





Notes



The calculator will only work if numbers are displayed in

normal notation. Where subtotals or totals are such that the

computer would require to use exponent notation for display

then a series of beeps will occur and the total or subtotal

will appear as a line of asterisks.



Automatic subtotalling takes place where this will clarify

the display.



Where the screen is filled in the 'note' sub-mode the option

to continue or to select the line delete cursor is given as

for 'type'. However if the screen is filled in 'calculator'

sub-mode the copy/newpage sequence is automatically

initiated.



2, 3 or 4 columns can be chosen and after entering the

number required the code letters for the columns are

displayed ('a' 'b' 'c' and 'd' with the right hand column

always being 'd'). Column descriptions up to seven

characters long can now be systematically entered (and

corrected if necessary).



The formula is now entered. This can be any arithmetical

expression up to 30 characters long but must use the code

letters of the columns. The computer will display "d =" and

only the right hand side of the equation is entered.



The calculator is normally set to give a max of six decimal

places but the opportunity is now given to alter this.



Entry prompts will now appear systematically (using the

column descriptions already entered). Entries with more than

seven characters will be refused (and beeped). Any non

numeric entry will also be beeped but will be accepted (for

reasons noted below). The opportunity is given to check all

entries before computation of the value in column (d) is

carried out. Non numeric entries are acceptable provided the

column is not being included in the calculation (eg. if

formula is d = b * c then column (a) can be used as columns

used for computation will result in an error. As in "calc"

any total in column (d) outwith normal numeric display will

be printed as asterisks (with appropriate beeps).



After each line the opportunity is given to continue the

calculation or to stop and if the latter the option of a

total of column (d) is given. Unlike the intermediate line

totals the total of column (d) can be displayed in either

normal or exponent notation and thus can be any number

within the range of the computer. On completion of all

calculations the computer displays the "Enter required mode"

prompt.



NOTE: If on first selecting the "table" mode the print

cursor is below line 15 the computer will automatically give

a new page. Subsequent automatic copy/newpage sequences will

take place at line 19 and the current column headings will

be displayed automatically at the top of the new page.





Technical notes



'Descriptive' variables are used throughout the program and

most of these are self explanatory.



Various flags are also used and these are noted below:



notec  :  Determines which prompt is given in 'calculator' sub-mode

          of "calc" when changing from 'note' sub-mode. (If 0 then

          'number' is prompted. If 1 then 'operator' is prompted).

subtf  :  Controls whether automatic subtotalling will take place on

          entry of certain operators. If 0 then no subtotalling

          takes place. The subtotal routine automatically resets

          this flag to 0.

calcf  :  Controls whether automatic subtotalling takes place

          after calculation. In the case of addition + subtraction

          this remains 0 but other operators such as "*" or

          "/" set this to 1. Like subtf this is reset to 0 after

          subtotalling.

cursf  :  Is set to 1 as soon as calculation starts and controls

          movement of line delete cursor to right hand side of

          screen (which can only happen when this flag = 0).

totf   :  Determines whether total is in normal or exponent

          notation and sets print position accordingly.

nof    :  Set at 1 by "no check" routine (Line 9700) if

          entry is non-numeric; otherwise 0.





Variables



The following non-descriptive variables are used:



a$,b$       General purpose non-dimensioned.

d$(4,7)     Column descriptions in 'table' mode.

e$(4,7)     Input information in 'table' mode.

a,b,c,d,e,f General purpose variables.

t           'table' total

x,y         General print position controls.

z           Special print position control used in 'table' mode

            (see line 4220 and similar).





Functions



Two used defined functions are included:



Line 9800   Controls no. of decimal points.

Line 9810   % function used in 'calc' mode.





--

Another Fine Product transcribed by:

Jim Grimwood (jimg@globalnet.co.uk), Weardale, England

--