Sinclair ZX81 User Manual page 10

PRINT 3*(2+2)
gives the answer 3*4 = 12.
A combination like this is called an expression - in this case, an arithmetic or numeric expression
because the answer is a number. In general, whenever the computer is expecting a number from you, you
can give it an expression instead and it will work out the answer.
You can write numbers with decimal points (use the full stop), & you can also use scientific notation - as
is quite common on pocket calculators. In this, after an ordinary number (with or without a decimal point),
you can write an exponent part consisting of the letter E, then maybe + or -, & then a number without a
decimal point. The E here means '*10
2.34E0 = 2.34 * 10**0 = 2.34
2.34E3 = 2.34 * 10**3 = 2340
2.34E-2 = 2.34 * 10**-2 = 0.0234
(Try printing these out on the ZX81.)
The easiest way of thinking of this is to imagine the exponent part shifting the decimal point along to the
right (for a positive exponent) or to the left (for a negative exponent).
You can also print more than one thing at once, separating them either with commas (,) or semicolons (;
or shifted X). If you use a comma, then the next number will be displayed starting either at the left hand
margin, or in the middle of the line in the 16th column. If you use a semicolon, then the next number will be
displayed immediately following the last one.
Try
PRINT 1;2;3;4;5;6;7;8;9;10
&
PRINT 1,2,3,4,5,6,7,8,9,10
to see the differences. You can mix commas & semicolons within a single PRINT statement if you want.
Summary
Statements: PRINT , with commas & semicolons
Operations: +,-,*,/,
Expressions, scientific notation
Exercises
1. Try
PRINT 2.34E0
PRINT 2.34E1
PRINT 2.34E2
and so on up to
PRINT 2.34E15
You will see that after a while the ZX81 also starts using scientific notation. This is because it never
takes more than 14 spaces to write a number in. Similarly, try
PRINT 2.34E-1
PRINT 2.34E-2
& so on.
2. Try
PRINT 1,,2,,3,,,4,,,,5
**
' ('times ten to the power of'), so that
**
& so on.