Transcript 2.4 - Nature & Capabilities of Software

Creating a Program
In today’s lesson we will look at:
• what programming is
• different types of programs
• how we create a program
• installing an IDE to get ready for
programming in Python
What is Programming?
• Put very simply, programming is telling the
computer what to do!
• Programs can be applications on your computer or
apps on your phone, but also lots of other things
such as macros, web-pages, etc.
• Some types programs – e.g. Word – run on their
own, others – e.g. Scratch or macros – need
another program or web-site to make them run.
• Almost every program that you use will have been
“written” by a person – or more likely a team of
people.
Different Types of Program
Computers don’t understand Python or BASIC or
Scratch, so before a program is run, it needs to be
converted into a form that the computer can understand,
called machine code:
• Some programs are compiled – the programmer uses a
tool called a compiler to convert their program into an
executable file that runs on its own.
• Some programs are interpreted – the interpreter converts
the program, possibly line-by-line (or block-by-block in the
case of Scratch), as it actually runs.
• Early programmers also used assemblers to convert lowlevel instructions into programs, and Java is an exception –
it’s half-compiled and then interpreted.
Compilers
• Most programs that run on PCs are compiled –
examples include things like web-browsers, office
software and graphics applications.
• Compiled Windows applications are usually in files that
end in .exe – they can be run without the compiler.
• Programs created in programs such as C/C++ or
VisualBasic are compiled – the user doesn’t get to see
the original code written by the programmers.
• Compiled programs usually run more quickly as you
don’t have to wait for them to be interpreted. That’s
why Android Lollipop compiles apps when you install
them – previous versions interpreted them at run-time.
Interpreters
• Sometimes programming languages that are
interpreted are called scripting languages – the
program, or script, is often just written in a text file.
• Examples include JavaScript, VBScript or PHP for
web-pages, VBA for Office macros, JustBasic, Scratch
and Python.
• The program that you write can’t be run without the
interpreter – e.g. you can’t create a standalone
application in JavaScript; it needs the web-browser.
• Because interpreters have to convert the script into a
language and then run it, interpreted programs
traditionally run more slowly than compiled ones.
High or Low Level?
• Where the commands in a
programming language
resemble words to in English
to describe what you want to
do, e.g. print, input, if, etc.,
then the language is described
as high-level.
• Where the commands are less
recognisable, and are mainly
concerned with technical detail
(such as using memory
addresses), then the language
is described as low-level.
Integrated Development Environment
Programmers often use an integrated development
environment (IDE) to create programs.
An IDE will usually include:
• an editor, to allow you to create your programs – often they
will colour-code aspects of your program, or even suggest
which command or symbol might come next
• debugging tools – e.g. the ability to add breakpoints (where
your program will stop and you can look at the value of the
variables, etc.)
• a way of running the program to see if it works
Examples include Microsoft Visual Studio and IDLE…
Integrated Development Environment
Which Language is Best?
• Actually, learning to program isn’t just about
learning the language.
• All languages include things like:
– Variables
– Decisions
– Repetition
– Events
• The real skill is being able to take an idea for a
program and to use these things to create it
Events
• We won’t spend much time looking at events
to begin with, but events are things that can
happen to your program, e.g.
– mouse clicks and movements
– key presses
– screen touches
– objects colliding
– controls/form fields, etc. getting “focus”
• You will need to decide what your program
should do when these things happen.
Can We Start Now?
• For this section of the course, we’re going
to be looking at the Python programming
language.
• Python is an interpreted language – the
programs themselves are just text files so
you can use Notepad.
• It’s much easier, however, to use an IDE
– there is a free one called IDLE that
works well with Python.
Downloading IDLE and Python
• Python can be downloaded from:
https://www.python.org/download
• There are two current versions – 2.7.x
and 3.4.x – you won’t notice much
difference at this stage
• There are versions for 32-bit Windows
and 64-bit Windows – if you’re not sure
what you’re using, the 32-bit version will
work on both.