Comment #1

LANTERN — Thu, 07 Apr 2011 03:53:52 GMT

I had some problems posting all that stuff right, it was some kind of format problem, the lines were spaced out from each other a lot.

Original Blog Entry: 5th Part: "Nostalgia" "Old" Basic Language interpreters, Commodore 64 Basic Interpreter # 1.

LANTERN — Thu, 07 Apr 2011 03:20:15 GMT

Commodore BASIC Character Set

BLANK - separates keywords and variable names

; SEMI-COLON - used in variable lists to format output

= EQUAL SIGN - value assignment and relationship testing

+ PLUS SIGN - arithmetic addition or string concatenation

(concatenation: linking together in a chain)

- MINUS SIGN - arithmetic subtraction, unary minus

* ASTERISK - arithmetic multiplication

/ SLASH - arithmetic division

^ UP ARROW - arithmetic exponentiation

( LEFT PARENTHESIS - expression evaluation and functions

) RIGHT PARENTHESIS - expression evaluation and functions

% PERCENT - declares variable name as an integer

# NUMBER - comes before logical file number in input/

output statements

$ DOLLAR SIGN - declares variable name as a string

, COMMA - used in variable lists to format output; also

separates command parameters

. PERIOD - decimal point in floating point constants

QUOTATION MARK - encloses string constants

: COLON - separates multiple BASIC statements in a line

? QUESTION MARK - abbreviation for the keyword PRINT

LESS THAN - used in relationship tests

GREATER THAN - used in relationship tests

{pi} PI - the numeric constant 3.141592654

-------------------------------------------------------------------------------

Always type NEW and hit RETURN-ENTER before starting a new program.

-------------------------------------------------------------------------------

A person should really read the:

COMMODORE 64 PROGRAMMER'S REFERENCE GUIDE

http://www.commodore.ca/manuals/c64_programmers_reference/c64-programmers_reference.htm

http://www.commodore.ca/manuals/c64_users_guide/c64-users_guide.htm

http://project64.c64.org/hw/c64.html

Anyhow read:

Hierarchy of Operations ..................................... 15

And 10 to 17 pages

---------------------------------------------------------------------------

Read about the PRINT and the PRINT# keywords on pages 70 to 76

--------------------

EXPONENTIATION

Use the up arrow (^) to raise a number to a power. Press the RETURN

key after you type the calculation. For example, to find 12 to the fifth

power, type this:

PRINT 12^5 Key in this and RETURN

248832 The computer displays this

This is the same as:

PRINT 12*12*12*12*12

248832

--------------------

3.3. MULTIPLE CALCULATIONS ON ONE LINE

The last example shows that you can perform more than one calculation

on a line. You can also perform different kinds of calculations on the

same line. For example:

PRINT 3 * 5 - 7 + 2 Key in this and RETURN

10 The computer displays this

So far our examples have used small numbers and simple problems. But

the 64 can do much more complex calculations. The next example adds large

numbers.

Notice that 78956.87 doesn't have a comma between the 8 and the 9. You

can't use commas this way in BASIC. BASIC thinks commas indicate new

numbers, so it would think 78,956.87 is two numbers: 78 and 956.87.

Remember to press RETURN after you type the problem.

PRINT 1234.5 + 3457.8 + 78956.87

83649.17

The next example uses a ten digit number. The 64 can work with numbers

that have up to ten digits, but can only display nine digits in the

answer. So the 64 rounds numbers that are more than nine digits. Numbers

five and over are rounded up, and numbers four and under are rounded

down. This means that 12123123.45 is rounded to 12123123.5. Because of

rounding, the computer doesn't give the same answer you'd get if you

added these numbers by hand. In this case, the answer is 12131364.817.

You can see the difference rounding makes.

PRINT 12123123.45 + 345.78 + 7895.687

12131364.9

The 64 prints numbers between 0.01 and 999,999,999 using standard

notation, except for leaving out commas in large numbers. Numbers outside

this range are printed using scientific notation. Scientific notation

lets you express a very large or very small number as a power of 10. For

example:

PRINT 123000000000000000

1.23E+17

Another way of expressing this number is 1.23 * 10 ^ 17. The 64 uses

scientific notation for numbers with lots of digits to make them easier

to read.

There is a limit to the numbers the computer can handle, even using

scientific notation. These limits are:

Largest numbers : +/- 1.70141183E+38

Smallest numbers: +/- 2.93873588E-39

3.4. EXECUTION ORDER IN CALCULATIONS

If you tried to perform some mixed calculations of your own, you might

not have gotten the results you expected. This is because the computer

performs calculations in a certain order.

In this calculation:

20 + 8 / 2

the answer is 14 if you add 20 to 8 first, and then divide 28 by 4. But

the answer is 24 if you first divide 8 by 2, and then add 20 and 4.

On the 64, you always get 24 because the computer always performs

calculations in the same order. Problems are solved from left to right,

but within that general movement, some types of calculations take

precedence over others. Here is the order of precedence:

First : - minus sign for negative numbers, not for subtraction.

Second: ^ exponentiation, left to right

Third : * / multiplication and division, left to right

Fourth: + - addition and subtraction, left to right

This means that the computer checks the whole calculation for negative

numbers before doing anything else. Then it looks for exponents; then it

performs all multiplication and division; then it adds and subtracts.

This explains why 20 + 8 / 2 is 24: 8 is divided by 2 before 20 is

added because division has precedence over addition.

There is an easy way to override the order of precedence: enclose any

calculation you want solved first in parentheses. If you add parentheses

to the equation shown above, here's what happens:

PRINT (20 + 8) / 2

14

You get 14 because the parentheses allow 20 and 8 to be added before

the division occurs.

Here's another example that shows how you can change the order, and the

answer, with parentheses:

PRINT 30 + 15 * 2 - 3

57

PRINT (30 + 15) * 2 - 3

87

PRINT 30 + 15 * (2 - 3)

15

PRINT (30 + 15) * (2 - 3)

-45

The last example has two calculations in parentheses. As usual, they're

evaluated from left to right, and then the rest of the problem is solved.

When you have more than one calculation in parentheses, you can further

control the order by using parentheses within parentheses. The problem in

the innermost parentheses is solved first. For example:

PRINT 30 + (15 * (2 - 3))

15

In this case, 3 is subtracted from 2, then 15 is multiplied by -1, and

-15 is added to 30. As you experiment with solving calculations, you'll

get familiar with the order in which mixed calculations are solved.

3.5. COMBINING PRINT'S CAPABILITIES

The 64 computers let you combine the two types of print statements that

you've read about in this book. Remember that anything you enclose in

quotation marks is displayed exactly as you type it.

The next example shows how you can combine the types of PRINT

statements. The equation enclosed in quotes is displayed without being

solved. The equation not in quotes is solved. The semicolon separates the

two parts of the PRINT statement (semicolon means no space).

PRINT 5 * 9 = ; 5 * 9 You key in this and RETURN

5 * 9 = 45 The computer displays this

Remember, only the second part of the statement actually solves the

calculation. The two parts are separated by a semicolon. You always have

to separate the parts of a mixed PRINT statement with some punctuation

for it to work the way you want it to. If you use a comma instead of a

semicolon, there is more space between the two parts when they're

displayed. A semicolon leaves out space.

The 64's screen is organized into 4 zones of 10 columns each. When you

use a comma to separate parts of a PRINT statement, the comma works as a

tab, sending each result into the next zone. For example:

PRINT TOTAL: ;95, SHORTAGE: ;15

TOTAL: 95 SHORTAGE: 15

If you have more than four results, they are automatically displayed on

the next line. For example:

PRINT 2 * 3,4 - 6,2 ^ 3,6 / 4,100 + (-48)

6 -2 8 1.5

52

Here's the difference when you use semicolons:

PRINT 2 * 3;4 - 6;2 ^ 3;6 / 4;100 + (-48)

6 -2 8 1.5 52

You can use the difference between the comma and the semicolon in

formatting PRINT statements to create complex displays.

--------------------------------------------------

So next the END KEYWORD

NEW

10 REM How to use the END keyword command

12 PRINT RED , BROWN , GREEN

14 END

-----

Copy that and then paste onto the C64 program and then type RUN and hit ENTER

Get:

RED BROWN GREEN

READY.

------------

Also it can work like this:

10 REM How to use the END keyword

12 PRINT RED :PRINT BROWN :PRINT GREEN :END

Copy that and then paste onto the program and then type RUN and hit Enter and the get:

RED

BROWN

GREEN

READY.

-------------

All of that also works on DIRECT Mode, without line numbers.

----------------------------------

Well you already know about the LIST keyword, it will LIST a program loaded into memory into the C64 Interpreter.

----------------------------

If you already have a program listing into the program's memory and want to delete a line for example:

Line 10

10 REM How to use the END keyword command

12 PRINT RED , BROWN , GREEN

14 END

Type line 10 without anything on it like this:

10

Then hit the Enter key.

Now list the program's lines:

LIST

And you will see that line 10 is now gone:

12 PRINT RED , BROWN , GREEN

14 END

--------------

To change a line for example line 12 type it again:

12 PRINT RED , BROWN

14 END

Now if you RUN it you will get:

RED BROWN

READY.

---------------------

Well that is all for today.

... [ More ]