For beginners |
Topics | |
1. What is a programming language?
2. Who's playing? A threesome!
3. What programms look like
4. What are variables?
5. What are Subs?
6. What's a '\' character and what do I do with it? Character strings!
1. What is a programming language?
A programming language is a language that computers understand.
Humans can use this language to order computers to do whatever they want,
computers are slaves and that's politically correct!
I call this absolute freedom 'Computer Plasticity'. Indeed, as you can
turn a ball of plasticine into anything you want, so can you with
a computer.
However, computers are -so far, quite stupid. You can't use every day's
language to ask your computer to do something. That's why most of
the languages they use are simplifications of our human languages.
The main thing in computer languages is that they must be very precise.
A computer can not understand the sentance 'Put that there'. That's
too subtle.
Programms are stored in files.
2. A threesome
Sorry if you expected something more, ermmmm, more adult here,
but the threesome I'm talking about is this one, sorry...
3. What programms look like
Aptilis programms, like most programms, are text files. In Windows, that
means you can simply use the notepad to write a programm. In Unix, you'll
have the less friendly (but they say, more powerful once you know how to
use it...) vi.
Here's an example of a programm:
sub main print("Hello World!") end sub
If you want to try it, save this file as "test" with the notepad (test.txt under
Unix) in the directory where you put 'aptilis.exe', open a DOS box, go
to the directory where aptilis.exe is and at the command prompt, type:
aptilis test.txtUnix users should type ./aptilis.exe test.txt
4. Variables
Variables are boxes in which you put values, like a number.
You have probably heard about pi, that 'greek' number that knows how
to compute all things circular. Well, you don't want to type
'3.141592654' all the time. First, because you don't want to go into
a math encyclopedia every two lines of code and second, you want something shorter,
more readable. Let's see how to create a variable:
pi = 3.141592654
In aptilis, that means: put the value 3.141592654 into the variable 'pi'.
I hear someone ask: 'No declarations, then?'
Nope.
If you don't know what a declaration is don't worry, you don't need to,
unless you want to use Java or C.
5. Subs
Subs are pieces of programms, where you usually do one thing. By partitioning
your programms in subs, you'll make your task easier when it comes to find
bugs (errors). In all cases, you need at least one sub in Aptilis:
the main sub.
If there is no sub called main, then Aptilis will be lost and won't be able
to run your programme. The sub main is an agreed meeting point between you
and Aptilis.
Subs can also be seen as little factories: You feed them with raw materials
(the parameters) and they return a finished product (the return value).
This sub is fed the radius of a circle and returns its circumference:
sub circumference(r) return 2 * 3.141592654 * r end sub
There are two kinds of subs: predefined subs which have already been written
for you, like 'print', 'saveFile', etc... and the ones you will write, which are
simply called 'subs'.
6. The '\' character, and how to put a " in a string, etc.
You put a string into a variable as follows:
name = "John Doe" $
Now how could you insert a double quote? Because double quotes mark the begining and the end of the string, if you inserted one or more of them within the string, that would first cut it and then confuse the Aptilis parser and you would get an error. The trick is to say: 'Hey! Attention please! There's gonna be a special character!!". You do that by typing a '\', in other words, a back-slash. For my fellow dyslexic programmers, that's the one on the left of the keyboard, not far from the 'Caps Lock' key. Here's what it's looking like:
name = "John \"Duck Face\" Doe" $
Now, if the back slash is reserved to indicate special characters, how do you type the backslash itself?? Here's the solution:
path = "c:\\directory" $
You just type two of them.
Here are all the special characters Aptilis knows:
\n Line Feed (print to next line)
\r Carriage return, might be needed for DOS files before a '\n'
\t Tab character
\" double quotes
\\ backslash
\0 ASCII 0
Aptilis also understands the '\xHH' notation where HH is a hexadecimal number,
from 0 to 255, so that you can get the whole ASCII set.