<b>Using Python</b>

For the next set of exercises I will assume you have a properly installed version of Python on your computer. If not, go fetch the latest version from the Python web site and follow the install instructions for your platform.

Now from a command prompt type python and the Python prompt should appear looking something like this:

Python 2.3 (#46, Jul 29 2003, 18:54:32) [MSC v.1200 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>

Alternatively you might find a shortcut to something called IDLE, or the Python GUI, in your start menus. If you start IDLE instead of the command line version you will get a similar prompt but in a window of its own and with some pretty font colors! Danny Yoo has written a pretty good IDLE Tutorial to get you started with IDLE and I recommend you pay it a visit if you want to stick with it rather than the basic command prompt. It duplicates some of the early material here but repetition of the basics is no bad thing!

The full manual for IDLE is found here. For now I'd recommend you stick with Danny's tutor.

One interesting thing about IDLE is that it is itself a Python program, so it's a very good demonstration of just what is possible using Python

If you got your version of Python from ActiveState or if you downloaded the Windows specific extensions (the winall package), you also have access to another GUI programming environment, very similar to IDLE but perhaps a little more polished, called Pythonwin. Either Pythonwin or IDLE make far better programming environments than the standard DOS prompt, but at the very beginning I prefer to use the most basic tools to focus on the underlying principles rather than the toys.
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<b>A word about error messages</b>
If you type in the commands as we go through them then sooner or later you will get an error message. It will look something like this:

<img src="http://www.freenetpages.co.uk/hp/alan.gauld/tutstart.htm">

>>> print 'fred' + 7
Traceback (most recent call last):
File "<input>", line 1, in ?
TypeError: cannot concatenate 'str' and 'int' objects

Don't worry about the exact meaning here just look at the structure.
The '>>> print ...' line is the erroneous command
The next 2 lines are describing where the error occurred:
'line 1 in ?' means line 1 in the command we are typing. If it were a longer program stored in a source file the <input> would be replaced by the file name.

The 'TypeError...' line tells you what the interpreter thinks is wrong and sometimes there will be a caret character(^) pointing to the part of the line that Python thinks is at fault.
Unfortunately this will often be wrong, usually the error is earlier in the line, or even in the (one or two) lines immediately preceding where Python says it is - remember computers are dumb!

Use the error information to figure out what's happening. Remember it's most likely to be you at fault not the computer. Remember again that computers are dumb. Probably you just mistyped something or forgot a quote sign or something similar. Check carefully.

In case you are wondering, the mistake I made was trying to add a number to a character string. You're not allowed to do that so Python objected and told me there was a TypeError. You'll need to wait till we get to the topic on the Raw Materials to understand what types are all about....

Whichever approach you've decided to take, command prompt or IDLE (or Pythonwin) we are ready to start creating some very simple Python programs.
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JavaScript
To create JavaScript programs in a browser we need to do a bit more work. We need to create an HTML file which we can load into a web browser. An HTML file is really just a plain text file which you can create in Notepad or any other text editor. The file will look like this:

<img src="http://www.freenetpages.co.uk/hp/alan.gauld/tutstart.htm">

<html>
<body>

<script language="JavaScript">

document.write('Hello World\n');

</script>

</body>
</html>

The bit between <script...> and </script> is our program. I won't be showing all the HTML tags every time in this tutorial so you need to copy that file each time as a template and then replace everything between the script tags with the code you want to try out.
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VBScript
VBScript is essentially the same as JavaScript with the single difference that you replace the name "JavaScript" in the language= bit with, surprisingly enough, "VBScript". Like this:

<img src="http://www.freenetpages.co.uk/hp/alan.gauld/tutstart.htm">

<html>
<body>

<script language="VBScript">

MsgBox "Hello World"

</script>

</body>
</html>

Once again the bit between the <script> tags is the program

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VBScript and JavaScript errors
In both VBScript and JavaScript you will get a dialog box pop up telling you the line number of an error. There will also be a fairly inscrutable error message. As with Python, treat the line number as a rough guide rather than an exact pointer. After finding and fixing the error you will need to reload (or refresh) the page in your web browser.

OK, Whichever language you choose you are ready to start.

Points to remember
Start python by typing python at a command prompt
Error messages are nothing to be scared of, read them carefully, they usually give a clue as to why you got them.
But it's only a clue... if in doubt check the lines immediately before the reported line

What is C?
C is a mid-level structured programming language.

It is low-level enough to allow the programmer to take complete control over program execution, meaning you can do pretty much whatever you want.

It is also high-level enough to make some tasks easier, such as loops, conditionals and function calls.

C does not stand for any abbreviation. The name comes as an evolution of the B language which is based on BCPL language.

There are C compilers for practically every platform, from Intel to Alpha and Sparc, from DOS to Windows, BSD, Linux, Macintosh, UNIX, VMS, Solaris, BeOS. It is not the most portable language, but it can very powerful in the hands of the right programmer.

What Can C Be Used For?
The two biggest are operating systems and scientific applications.

Most operating systems have at least some C in them, although some mix in assembly language and C++. Linux, for example, is mostly C except for the low-level parts that use assembly.

Scientific applications are mainly developed using C under UNIX or Linux environments. Games are often written in C, although more and more they are being written in C++.

Rather than reinventing the wheel, it makes sense to use both C and C++ libraries and ideas next to each other.

What Is The Syntax Like?
C programs start with headers.

They usually contain data definitions: for example, program constants, macros, prototypes, global variables, etc. but not actual logic.



The main block in a C program is the main() function which is a system function including the logic flow of the C program.

Inside the main(), all the local variables are first declared. Next comes the function calls and all the logic of the program.

C programs usually have several pieces that fit together to make a program. Usually you will have a group of source code files that are compiled separately, then linked together into a single executable file. Each source code file will have a header file that describes its contents

Your source code files contain all your code that actually does stuff, the program logic. Multiple files are used for all but the shortest of programs because it just isn't practical to have a single source code file with thousands or even millions of lines of code. It's too difficult to maintain.

Usually, similar functions are grouped together in a single file. For example, one file may contain your program's code for loading and saving its data to disk. Another file may contain the code for displaying the main window. The header files usually contain little or no program logic.

Functions are the cornerstone of C programming. Functions are cohesive blocks of code that perform common tasks. Code reuse is an important programming concept, and functions allow you, the programmer, to achieve this. Rather than typing out the same task a thousand times, you can put it in a function and use that function over and over again. Therefore, program size becomes smaller.

Another Facts is that C uses pointers extensively. It uses them freely than any other Programming Language. Pointers are variables which store the address of other variables. Using pointers U can literaly point to any addressing location of your system

An Example C Program
This is an example of a C program.

/* Include the Standard C functions for input and output */
#include <stdio.h>

/* This is the main function, where the program starts running */
int main (void)
{
/* Display a short message to the user */
printf ("I charge thee. Speak! \n");

/* Program is done now, return to the operating system */
return 0;
}

What Do I Need To Get Started?
You will need a C compiler. This is available for free with any UNIX-based operating system including Linux. You can download Borland C++ Builder (if you are using Windows) or GNU C++ Compiler (gcc) (if you are using Linux). These compilers can be used for both C and C++.


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