
ALPHABET (16K ZX-81)
DISCOUNTING (1K ZX-81)
MARK UP (1K ZX-81)
SCROLL (1K ZX-81)


ALPHABET (16K ZX-81)
by P Styles
from Sinclair Programs 3, September/October 1982, page 29

Alphabet is a teaching aid for students - so if you can't read this, read on.
The program runs initially in FAST mode, then the screen clears and display
the alphabet in random order.

The student has a laser base and has to blast the letters in their correct
order. The distance of the laser from the letters is decided by the level of
difficulty selected and the laser is moved with the usual keys 5 and 8.

The program was sent by P Styles of Rotherham. It runs on an expanded ZX-81.

[The game suffers from two bugs. It fails to reset variable R back to 38 when
restarting the game after missing a letter. This can be fixed with the
addition of the following line:

   445 LET R=38

Also, it is possible to move too far to the right and cause the program to
crash when fire is pressed. This can be resolved by changing the value 27 in
line 130 to 25.]


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DISCOUNTING (1K ZX-81)
from Sinclair Programs 3, September/October 1982, page 48

Following our program for Compound Interest in the July/August issue, we are
proud and privileged to present a method of calculating Discounting - i.e.,
compounding in reverse.

The program will tell you how much to invest to earn a given amount in a
certain period. Stay with Sinclair Programs and you will always have money to
invest.


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MARK UP (1K ZX-81)
by David Eddison
from Sinclair Programs 3, September/October 1982, page 32

Probably the most frequent criticism of personal computers is that they are
toys for big boys and of no practical use.

Mark Up shows that an unexpanded ZX-81 can be of use in business, as a means
of computing retail selling prices.

The program, submitted by David Eddison of Manchester, can calculate VAT and
operates with a choice of five pre-determined mark-up rates, including, for
the especially greedy, a boost of 100 percent.

It is straightforward enough, though Eddison reports that whenever INPUT
appears in a PRINT statement he saved memory by entering THEN INPUT and
afterwards deleting THEN. [This is not how the listing appears else a space
would be present before every INPUT word]


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QUADRATIC EQUATIONS (1K ZX-81)
by Richard Harris
from Sinclair Programs 3 (September/October 1982), page 24

A neat program for solving quadratic equations on an unexpanded ZX-81 has
been sent by Richard Harris of Eastleigh, Hampshire.

The program invites you to enter the co-efficients of the equation and then
displays the equation with the known values inserted, followed by the roots.
It also points-out when a negative square root occurs.


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SCROLL (1K ZX-81)
by A A Ryan
from Sinclair Programs 3 (September/October 1982), page 39

From A A Ryan of Wallasey, Merseyside, a short routine for the ZX-81 allows you
to scroll sideways. A good deal of care is needed when entering the listing, as
the first line is so long that if mistakes are made it takes a long time to
correct. Our reviewer discovered that, which is why causes in the first line is
spelt caues.

The first line is only to show what can be done, so it can be shorter; and the
spaces are not limited to the two sets of five and 20 shown in the listing.

Once entered and running, the scrolling can be stopped by pressing BREAK and
then it starts again when CONT is pressed.
