Sinclair ZX81 - Page 11

A comma always moves you on a bit for the next number. Now try
PRINT
1;;2;;3;;;4;;;;5
Why is a string of semicolons no different from a single one?
3.
PRINT
gives only 8 significant digits. Try
PRINT
4294967295, 4294967295 -429E7
This proves that the computer can hold all the digits of 4294967295, even though it is not prepared to
display them all at once.
4. If you've got some log tables, then test out this rule:
Raising 10 to the power of a number is the same as taking the antilog of that number.
For instance, type
PRINT
10
**
0.3010
& look up the antilog of 0.3010. Why are the answers not exactly equal?
5. The ZX81 uses floating point arithmetic, which means that it keeps separate the digits of a number (its
mantissa) and the position of the point (the exponent). This is not always exact, even for whole numbers.
Type
PRINT
1E10+1-1E10,1E10-1E10+1
Numbers are held to about 9 1/2 digits accuracy, so 1E10 is too big to be held exactly right. The inaccuracy
(actually about 2) is more than 1, so the numbers 1E10 & 1E10+1 appear to the computer to be equal.
For an even more peculiar example, type
PRINT
5E9+1-5E9
Here the inaccuracy in 5E9 is only about 1, & the 1 to be added on in fact gets rounded up to 2. Here the
numbers 5E9+1 & 5E9+2 appear to the computer to be equal.
The larger integer (whole number) that can be held completely accurately is 2
32
-1 (4,294,967,295).