Blix the Programmer
An Introduction to Programming
1.1
We program time
So you are eager to
learn programming, ok let’s code a time machine!
Imagine you are a
programmer like Blix above. Our goal is to make him look cute nerdy, he looks
very busy working with his dual monitor setup and his pile of books. I hope you
guys love The Programmer as our guide as much as we do.
You've always wanted
to learn how to build software (or just whip up an occasional script) but never
knew where to start. Today you do that first step.
1.2 First we need a tool
A tool is needed to type
some code and run it. What you think is coding? Coding is not only writing or
typing. After all we don’t write software, we build it!
This reminds me of a
true “Dilbert moment” a few years ago, when my (obviously non-technical) boss
commented that he never understood why it took months to develop software. “After
all”, he said, “it's just typing.” ;-(
Luckily, the web is
full of free resources that can turn you into a programmer.
Now we download such
a free resource, called maXbox:
http://sourceforge.net/projects/maxbox/files/
The tool you will
use is split up into the toolbar at the top, the editor or code part in middle
and the output window (console) at the bottom with an interface part on the
right. Change that in the menu /View at our own style.
G In maXbox you will execute just
the script, all libraries and units are already built in.
POnce the download
has finished, unzip the file, making sure that you preserve the folder
structure as it is. If you double-click maxbox3.exe the box opens a default demo program. Test it with F9 / F2 or press Compile on the toolbar and you should
hear a sound and a browser will open. So far so good now we’ll prepare our
first program, nowadays called an app:
Click on File/New and a template is loaded. You can run this template with Compile and the app writes three times “hi world of code” in the console at the
bottom of the box.
Keep in mind we want
to program a clock in several steps. Its good practise to name and store our
script file with Save
As…, for example to
myfirstclock.txt
If you want
to look at the whole script you can find the file at:
http://www.softwareschule.ch/examples/341_blix_clock.txt
Now let’s take a
look at the code of this first part project. Our first line is
01 Program myClock;
We name it, means
the program’s name is above. Don’t confuse it with the filename stored on your
disk myfirstclock.txt, the program name is just an internal name defined.
FThis example
requires also objects, but we won’t go deeper into object oriented programming,
we just use objects. At the end of this doc you’ll find links to maXbox tutorials.
Next we learn how a constant works. Constants are fixed
numeric or character values represented by a name. In line 4 we set a name and
the content of a constant:
02 Const
03//<Constant declarations>
04 TEXTOUT = ' hi
world of code ';
A constant is called
a const[1]
because you can’t change it during the program.
The next
lines of the program declare a variable
i of type
integer. In line 11 we first declare name and type to use. This variable has a numeric type.
F A type is essentially a name for a kind of data. When you declare a
variable you must specify its type, which determines the range and storage of
values the variable can hold and the operations that can be performed on it.
09 Var
10//<Variable declarations>
11 i: integer;
You see in this primer, we don’t deal with own types, function or
procedure. The next lines are simply comments in your
code and are ignored by the compiler
(the part that translates your code into instructions a computer can understand
before executing it).
13 //<FUNCTION>
14 //<PROCEDURE>
Line 16 ff is much
of interest. A program must have a main routine between begin and end. The main routine
is run once and once only at the start of the program (after you compiled).
Here will you place general instructions and the main control of the app.
//Main routine
16 Begin
17 //<Executable statements>
18 for
i:= 1 to
3 do //iteration
19 Writeln(TEXTOUT);
20 //<Definitions>
21 End.
1.3 Time will come
So we are ready to
change our first line. The easiest way to try your hand at coding for your Win,
Linux or Mac desktop is to start with a script or macro program and change
something.
Our plan is to
change the output and add time information in a loop. Right, a loop is similar
to iteration. The “for statement” in line 18 implements an iterative loop.
After each iteration of the loop, the counter variable i is incremented. Therefore,
i is the loop
counter.
In this line we add
the actual time:
19
Writeln(TEXTOUT + TimeToStr(Time));
Time is our first function called, you guess it, Time. We say we call a function. Because functions return a value, we get the
time and send it to the output with Writeln().
But first we have to
convert it to a string with another function, TimeToStr. Compile it!
But wait a second,
as you can see we don’t see the difference, because the loop is too fast. What
about to delay the loop and get the seconds in between as clockwork. No problem
at all, we add a new line 20 with the procedure Delay:
19
Writeln(TEXTOUT + TimeToStr(Time));
20 Delay(1000); //milliseconds
Something is still missing in our design. We have to extend the scope of
the loop with a building block; means the loop runs between begin and end. Also
each begin must have and end ;-).
18
for i:= 1 to 3 do begin
19 Writeln(TEXTOUT) + TimeToStr(Time));
20 Delay(1000)
21 end;
7 Now it’s up to you: produce a clock output that
runs for 15 seconds.
Right you simply
change the loop counter from 3 to 15:
18
for i:= 1 to 15 do begin
As a control, the
runtime output (in yellow window) is about 15 seconds more or less, depending
on the CPU performance at the moment. A one hour clock has to be set to 3600!
1.4 Time forever
Programmers never die,
they just GOSUB without return. You may also know, in the beginning there was
nothing which exploded ;). So let the jokes aside. Our last step is an eternal
clock that goes back in the time like I said before: we code a time machine.
When we travel in
past, present or future we change the logic from digital to trigital ;-).
So this piece of
code can then be translated and run on various platforms and frameworks as
well. There are several different kinds of software development you can do for
various platforms, from the web to a desktop to your smart phone to a command
line.
So what’s the
solution to run this time forever? Answer: a do forever loop or at least one
hour. With the call of another function we set the time one hour back in every
second (sign: –i).
18
for i:= 1 to 3600 do begin
19 Writeln(TEXTOUT + TimeToStr(AddHours(Time,-i)));
20 Delay(1000)
21 end;
Be careful, the loop
counter 3600 will last long, so change it step
by step on your own experience. The clock goes one hour back into the past every
second, but the seconds tick forward like a normal clock. In the film “back to
the future” they call it the flux-comparator.
IIf you want to stop or
break a loop, just override the loop
counter in line 18 and recompile (F9) it during the execution!
When you call the function AddHours that takes two argument and returns another time, then we say the function
call TimeToStr(AddHours(Time,-i)) is nested. A nested
call contains other functions within a statement. Let me explain:
First we call the time function, the result we pass to the AddHours function its result is passed to the TimeToStr function and the whole we pass again to Writeln!
When we want to travel
back to the past, maybe in the year of 1759, further information is missing.
Right, there is no date. Easier done than said ;-).
18
for i:= 1 to round(Power(2,4)) do begin
19 Writeln(TEXTOUT + DateTimeToStr(AddHours(Now,-i)));
Did you see the difference? We replaced the Time function with the Now function and the string converter to DateTimetoStr. And with Power big numbers are possible
(Power is like 2^4). Now we’re ready to go back to middle age.
7 NHow can you accelerate your time machine? One hour
back per second takes to much time, simply the loop must step faster.
You got it; we
change the parameter of the delay procedure:
20
Delay(10);
Remember: The clock
rate is still the same, but our time machine can go faster to the past. The time
is flushing by with this speed; the calculation of how many lines we get is
also interesting:
Suppose we have Power(2,12) as the for counter limit, how many lines we get?
Answer: 2^12 = 4096.
And the next by Power(2,30) could be also of interest, but its huge and your app runs long!:
Can you imagine
where in the past we are landing, middle age or stone age or maybe far out of
our history line?
The calculation is
simple: (2^30/24)/365 is rounded to 122573 years. This would be Stone Age!
How can you do that
in maXbox: 2^30 / (24*365) is another solution.
Writeln(intToStr(round(Power(2,30)/24/365)));
We come closer to
the end and had to refactor just one thing. Our last release looks like this:
for i:= 1
to round(Power(2,N)) do begin
Writeln(IntToStr(i)+TEXTOUT +
DateTimeToStr(AddHours(Now,-i)));
Delay(SN); //speed of time
machine
end;
As you can see I
introduced two parameters to be more flexible, the counter limit N and the speed of time machine SN. Means also 2 more variables to add in your code:
11 i, N, SN: integer;
18 N:= 4; SN:= 1000; //Assign a value to a variable
So far
we have learned something about functions in a loop, comments and the
difference between a constant and a variable. Now its time to reflect
over those used functions:
|
Function |
Explanation and Purpose… |
|
Writeln() |
Writes one or more lines as
string to an output. |
|
IntToStr() |
Converts an integer to a
string. |
|
DateTimeToStr() |
Converts a variable of
type TDateTime to a string. |
|
AddHours() |
Change the hours of a
TDateTime function. |
|
Now |
Returns the current date
and time. |
|
Power() |
Power raises Base to power
specified by Exponent. |
|
Round() |
Returns a value of a real
rounded to the nearest whole number. |
|
Delay() or Sleep() |
Pauses execution for a
specified number of microseconds. |
There are plenty
more functions, which can be found in Help/All Functions List.
This interface information
of RTL functions is contained in various unit files that are a standard part of
C++,
Time Travelling
from Middle Age to the ancient Greeks till Stone Age ;-)
eConclusion: A common pitfall for beginners is
getting stuck figuring out which programming language is best to learn first.
There are a lot of
opinions out there, but there's no one “best” language. Here's the thing to
consider: In the end, language doesn't matter THAT much. Understanding data and
control structures, algorithms, metrics, modelling and design patterns does
matter very much. Every language, even a simple scripting language, will have
elements that you'll use in other languages as well and will help your
understanding. maXbox is build on Object Pascal and is similar to Java or C++ a
well known and mighty language.
Script: Examples/336_digiclock2.txt
V1.2, Feedback
@
Literature:
Kleiner et al., Patterns konkret, 2003, Software &
Support
Proof
Links of
maXbox Tutorials:
http://www.softwareschule.ch/maxbox.htm
http://sourceforge.net/projects/maxbox
http://sourceforge.net/apps/mediawiki/maxbox/
http://en.wikipedia.org/wiki/Time_travel