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C Programming

Rob Miles Edition 2

Department of Computer Science University of Hull

Contents Introduction


Computers and Programs 1

Our Case Study: Friendly Bank

Structures and References

Advanced Programming 5


58 Arrays

Creating Solutions 4

A First C# Program

Creating Programs 3


Simple Data Processing 2

Generics and Collections

Structured Error Handling

Glossary of Terms


184 Base

184 Call

184 Class

186 Event

188 Member

188 Method

190 Public

190 Static

190 Stream

191 This

The University of Hull

All rights reserved

No reproduction,

copy or transmission of this publication may be made without written permission

The author can be contacted at: The Department of Computer Science,

Robert Blackburn Building The University of Hull,

Cottingham Road HULL HU6 7RX UK Department: www

uk Email: [email protected] Blog: www

com If you find a mistake in the text please report the error to [email protected] and I will take a look

Edition 2



Introduction Welcome Welcome to the Wonderful World of Rob Miles™

This is a world of bad jokes,

In this book I'm going to give you a smattering of the C# programming language

If you have programmed before I'd be grateful if you'd still read the text

It is worth it just for the jokes and you may actually learn something

If you have not programmed before,

Programming is not rocket science it is,

The bad news about learning to program is that you get hit with a lot of ideas and concepts at around the same time when you start,

The keys to learning programming are: Practice – do a lot of programming and force yourself to think about things from a problem solving point of view Study – look at programs written by other people

You can learn a lot from studying code which other folk have created

Figuring out how somebody else did the job is a great starting point for your solution

And remember that in many cases there is no best solution,

just ones which are better in a particular context,

Persistence – writing programs is hard work

And you have to work hard at it

The principle reason why most folks don't make it as programmers is that they give up

Not because they are stupid


If you haven't solved a programming problem in 30 minutes you should call time out and seek help

Or at least walk away from the problem and come back to it

Staying up all night trying to sort out a problem is not a good plan

It just makes you all irritable in the morning

We will cover what to do when it all goes wrong later in section 5

Reading the notes These notes are written to be read straight through,

and then referred to afterwards

They contain a number of Programming Points

These are based on real programming experience and are to be taken seriously

There are also bits written in a Posh These are really important and should be learnt by heart

If you have any comments on how the notes can be made even better (although I of course consider this highly unlikely) then feel free to get in touch Above all,

Rob Miles [email protected] www

Getting a copy of the notes These notes are made freely available to Computer Science students at the University of Hull

The website for the book is at http://www

C# Programming © Rob Miles 2010

Computers and Programs


You will discover what you should do when starting to write a program,

to ensure that you achieve a ―happy ending‖ for you and your customer

Finally you will take a look at programming in general and the C# language in particular

we are going to consider computers

This is an important thing to do,

because it sets the context in which all the issues of programming itself are placed

? Ans: Because it doesn't know the words

One way of describing a computer is as an electric box which hums

can lead to significant amounts of confusion,

particularly amongst those who then try to program a fridge

A better way is to describe it as:

A device which processes information according to instructions it has been given

This general definition rules out fridges but is not exhaustive

However for our purposes it will do

The instructions you give to the computer are often called a program

The business of using a computer is often called programming

This is not what most people do with computers

Most people do not write programs

They use programs written by other people

We must therefore make a distinction between users and programmers

A user has a job which he or she finds easier to do on a computer running the appropriate program

A programmer has a masochistic desire to tinker with the innards of the machine

One of the golden rules is that you never write your own program if there is already one available,

a keen desire to process words with a computer should not result in you writing a word processor

because you will often want to do things with computers which have not been done before,

and further because there are people willing to pay you to do it,

we are going to learn how to program as well as use a computer

Before we can look at the fun packed business of programming though it is worth looking at some computer terminology:

The box,

must also have sufficient built-in intelligence to understand simple commands to do things

At this point we must draw a distinction between the software of a computer system and the hardware

Hardware is the physical side of the system

Essentially if you can kick it,

and it stops working when immersed in a bucket of water,

Hardware is the impressive pile of lights and switches in the corner that the salesman sold you

Software is what makes the machine tick

If a computer has a soul it keeps it in its software

Software uses the physical ability of the hardware,

C# Programming © Rob Miles 2010

Computers and Programs


It is called software because it has no physical existence and it is comparatively easy to change

Software is the voice which says "Computer Running" in a Star Trek film

All computers are sold with some software

Without it they would just be a novel and highly expensive heating system

The software which comes with a computer is often called its Operating System

The Operating System makes the machine usable

It looks after all the information held on the computer and provides lots of commands to allow you to manage things

It also lets you run programs,

ones you have written and ones from other people

You will have to learn to talk to an operating system so that you can create your C# programs and get them to go

Windows 7 is an operating system

It gives computer programs a platform on which they can execute

They seem to think that one means the other

I regard data and information as two different things: Data is the collection of ons and offs which computers store and manipulate

Information is the interpretation of the data by people to mean something

Strictly speaking computers process data,

An example,

the computer could hold the following bit pattern in memory somewhere: 11111111 11111111 11111111 00000000

You could regard this as meaning: "you are 256 pounds overdrawn at the bank" or "you are 256 feet below the surface of the ground" or "eight of the thirty two light switches are off" The transition from data to information is usually made when the human reads the output

So why am I being so pedantic

? Because it is vital to remember that a computer does not "know" what the data it is processing actually means

As far as the computer is concerned data is just patterns of bits,

it is the user who gives meaning to these patterns

Remember this when you get a bank statement which says that you have £8,388,608 in your account

Data Processing Computers are data processors

Information is fed into them

and then generate further information

A computer program tells the computer what to do with the information coming in

A computer works on data in the same way that a sausage machine works on meat,

and something comes out of the other end:

This makes a computer a very good "mistake amplifier",

as well as a useful thing to blame


A program is unaware of the data it is processing in the same way that a sausage machine is unaware of what meat is

Put a bicycle into a sausage machine and it will try to make sausages out of it

Put duff data into a computer and it will do equally useless things

It is only us people who actually give meaning to the data (see above)

As far as the computer is concerned data is just stuff coming in which has to be manipulated in some way

A computer program is just a sequence of instructions which tell a computer what to do with the data coming in and what form the data sent out will have

C# Programming © Rob Miles 2010

Computers and Programs

Programs and Programming

Note that the data processing side of computers,

which you might think is entirely reading and writing numbers,

examples of typical data processing applications are: Digital Watch: A micro-computer in your watch is taking pulses from a crystal and requests from buttons,

processing this data and producing a display which tells you the time

Car: A micro-computer in the engine is taking information from sensors telling it the current engine speed,

setting of the accelerator etc and producing voltages out which control the setting of the carburettor,

to optimise the performance of the engine

CD Player: A computer is taking a signal from the disk and converting it into the sound that you want to hear

At the same time it is keeping the laser head precisely positioned and also monitoring all the buttons in case you want to select another part of the disk

Games Console: A computer is taking instructions from the controllers and using them to manage the artificial world that it is creating for the person playing the game

Note that some of these data processing applications are merely applying technology to existing devices to improve the way they work

However the CD player and games console could not be made to work without built-in data processing ability

Most reasonably complex devices contain data processing components to optimise their performance and some exist only because we can build in intelligence

It is into this world that we,

as software writers are moving

It is important to think of business of data processing as much more than working out the company payroll,

reading in numbers and printing out results

These are the traditional uses of computers

Note that this "raises the stakes" in that the consequences of software failing could be very damaging

As software engineers it is inevitable that a great deal of our time will be spent fitting data processing components into other devices to drive them

You will not press a switch to make something work,

you will press a switch to tell a computer to make it work

These embedded systems will make computer users of everybody,

and we will have to make sure that they are not even aware that there is a computer in there

! You should also remember that seemingly innocuous programs can have life threatening possibilities

For example a doctor may use a spread sheet to calculate doses of drugs for patients

In this case a defect in the program could result in illness or even death (note that I don't think that doctors actually do this – but you never know

Programmer’s Point: At the bottom there is always hardware It is important that you remember your programs are actually executed by a piece of hardware which has physical limitations

You must make sure that the code you write will actually fit in the target machine and operate at a reasonable speed

The power and capacity of modern computers makes this less of an issue than in the past,

but you should still be aware of these aspects

I will mention them when appropriate

Programming is a black art

It is the kind of thing that you grudgingly admit to doing at night with the blinds drawn and nobody watching

Tell people that you program computers and you will get one of the following responses: 1

C# Programming © Rob Miles 2010

A blank stare

followed by a long description of the double glazing that they have just had fitted

Asked to solve every computer problem that they have ever had,

A look which indicates that you can't be a very good one as they all drive Ferraris and tap into the Bank of England at will

Computers and Programs

Programs and Programming

Programming is defined by most people as earning huge sums of money doing something which nobody can understand

Programming is defined by me as deriving and expressing a solution to a given problem in a form which a computer system can understand and execute

One or two things fall out of this definition: 

You need to be able to solve the problem yourself before you can write a program to do it

The computer has to be made to understand what you are trying to tell it to do

? I like to think of a programmer as a bit like a plumber

! A plumber will arrive at a job with a big bag of tools and spare parts

Having looked at it for a while,

he will open his bag and produce various tools and parts,

fit them all together and solve your problem

Programming is just like this

You are given a problem to solve

You have at your disposal a big bag of tricks,

in this case a programming language

You look at the problem for a while and work out how to solve it and then fit the bits of the language together to solve the problem you have got

The art of programming is knowing which bits you need to take out of your bag of tricks to solve each part of the problem

And remember just how much plumbers earn…

From Problem to Program The art of taking a problem and breaking it down into a set of instructions you can give a computer is the interesting part of programming

Unfortunately it is also the most difficult part of programming as well

If you think that learning to program is simply a matter of learning a programming language you are very wrong

In fact if you think that programming is simply a matter of coming up with a program which solves a problem you are equally wrong

Programming is not about mathematics,

it is about organization and structure

There are many things you must consider when writing a program

not all of them are directly related to the problem in hand

I am going to start on the basis that you are writing your programs for a customer

He or she has problem and would like you to write a program to solve it

We shall assume that the customer knows even less about computers than we do

! Initially we are not even going to talk about the programming language,

type of computer or anything like that

we are simply going to make sure that we know what the customer wants

Solving the Wrong Problem Coming up with a perfect solution to a problem the customer has not got is something which happens surprisingly often in the real world

Many software projects have failed because the problem that they solved was the wrong one

The developers of the system quite simply did not find out what was required,

but instead created what they thought was required

The customers assumed that,

since the developers had stopped asking them questions,

the right thing was being built,

and only at the final handover was the awful truth revealed

It is therefore very important that a programmer holds off making something until they know exactly what is required

The worst thing you can say to a customer is "I can do that"

Instead you should think "Is that what the customer wants

This is a kind of self-discipline

Programmers pride themselves on their ability to come up with solutions,

so as soon as they are given a problem they immediately start thinking of ways to solve it,

What you should do is think "Do I really understand what the problem is

?" Before you solve a problem you should make sure that you have a watertight definition of what the problem is,

which both you and the customer agree on

In the real world such a definition is sometimes called a Functional Design Specification or FDS

This tells you exactly what the customer wants

Both you and the

C# Programming © Rob Miles 2010

Computers and Programs

Programs and Programming

and the bottom line is that if you provide a system which behaves according to the design specification the customer must pay you

Once you have got your design specification,

then you can think about ways of solving the problem

You might think that this is not necessary if you are writing a program for yourself

there is no customer to satisfy

This is not true

Writing some form of specification forces you to think about your problem at a very detailed level

It also forces you to think about what your system is not going to do and sets the expectations of the customer right at the start

Programmer’s Point: The specification must always be there I have written many programs for money

I would never write a program without getting a solid specification first

This is true even (or perhaps especially) if I do a job for a friend

Modern development techniques put the customer right at the heart of the development,

and involve them in the design process

These work on the basis that it is very hard (and actually not that useful) to get a definitive specification at the start of a project

You as a developer don’t really know much about the customer’s business and they don’t know the limitations and possibilities of the technology

With this in mind it is a good idea to make a series of versions of the solution and discuss each with the customer before moving on to the next one

This is called prototyping

you are sitting in your favourite chair in the pub contemplating the universe when you are interrupted in your reverie by a friend of yours who sells double glazing for a living

He knows you are a programmer of sorts and would like your help in solving a problem which he has: He has just started making his own window units and is looking for a program which will do the costing of the materials for him

He wants to just enter the dimensions of the window and then get a print out of the cost to make the window,

in terms of the amount of wood and glass required

"This looks like a nice little earner" you think,

and once you have agreed to a price you start work

The first thing you need to do is find out exactly what the customer wants you to do

Specifying the Problem When considering how to write the specification of a system there are three important things:   

What information flows into the system

What flows out of the system

What the system does with the information

There are lots of ways of representing this information in the form of diagrams,

for now we will stick with written text when specifying each of the stages:

Information going in In the case of our immortal double glazing problem we can describe the information as:  

The width of a window

The height of the window

Information coming out The information that our customer wants to see is:  

C# Programming © Rob Miles 2010

the area of glass required for the window the length of wood required to build a frame

Computers and Programs

Programs and Programming

You can see what we need if you take a look at the diagram below:

Height of Window

Width of Window

The area of the glass is the width multiplied by the height

To make the frame we will need two pieces of wood the width of the window,

and two pieces of wood the height of the window

Programmer’s Point: metadata is important Information about information is called metadata

The word meta in this situation implies a "stepping back" from the problem to allow it to be considered in a broader context

In the case of our window program the metadata will tell us more about the values that are being used and produced,

specifically the units in which the information is expressed and the valid range of values that the information may have

For any quantity that you represent in a program that you write you must have at least this level of metadata

What the program actually does The program can derive the two values according to the following equations: glass area = width of window * height of window wood length = (width of window + height of window) * 2

Putting in more detail We now have a fairly good understanding of what our program is going to do for us

Being sensible and far thinking people we do not stop here,

we now have to worry about how our program will decide when the information coming in is actually valid

This must be done in conjunction with the customer,

he or she must understand that if information is given which fits within the range specified,

your program will regard the data as valid and act accordingly

In the case of the above we could therefore expand the definition of data coming in as:  

The width of the window,

in metres and being a value between 0

The height of the window,

in metres and being a value between 0

Note that we have also added units to our description,

in which case our output description should read:   Note that both you and the customer must understand the document

C# Programming © Rob Miles 2010

The area of glass required for the window,

Remember that we are selling double glazing,

The length of wood required for the frame,

given in feet using the conversion factor of 3

Having written this all up in a form that both you and the customer can understand,

we must then both sign the completed specification,

Computers and Programs

Programs and Programming

Proving it Works In a real world you would now create a test which will allow you to prove that the program works,

you could for example say: “If I give the above program the inputs 2 metres high and 1 metre wide the program should tell me I need 4 square metres of glass and 19

” The test procedure which is designed for a proper project should test out all possible states within the program,

including the all-important error conditions

In a large system the person writing the program may have to create a test harness which is fitted around the program and will allow it to be tested

Both the customer and the supplier should agree on the number and type of the tests to be performed and then sign a document describing these

Testing is a very important part of program development

There is even one development technique where you write the tests before you write the actual program that does the job

This is actually a good idea,

In terms of code production,

you can expect to write as much code to test your solution as is in the solution itself

Remember this when you are working out how much work is involved in a particular job

Getting Paid At this point the supplier knows that if a system is created which will pass all the tests the customer will have no option but to pay for the work

! Note also that because the design and test procedures have been frozen,

there is no ambiguity which can lead to the customer requesting changes to the work although of course this can still happen

Better yet,

set up a phased payment system so that you get some money as the system is developed

The good news for the developer is that if changes are requested these can be viewed in the context of additional work,

for which they can be expect to be paid

Customer Involvement Note also in a "proper" system the customer will expect to be consulted as to how the program will interact with the user,

sometimes even down to the colour of the letters on the display

! Remember that one of the most dangerous things that a programmer can think is "This is what he wants"

! The precise interaction with the user

how the information is presented etc

is something which the customer is guaranteed to have strong opinions about

Ideally all this information should be put into the specification,

which should include layouts of the screens and details of which keys should be pressed at each stage

Quite often prototypes will be used to get an idea of how the program should look and feel

Fact: If you expect to derive the specification as the project goes on either you will fail to do the job,

or you will end up performing five times the work

If this seems that you are getting the customer to help you write the program then you are exactly right

! Your customer may have expected you to take the description of the problem and go into your back room

This is not going to happen

What will happen is that you will come up with something which is about 60% right

The customer will tell you which bits look OK and which bits need to be changed

You then go back into your back room,

and emerge with another system to be approved

Rob's law says that 60% of the duff 40% will now be OK,

so you accept changes for the last little bit and again retreat to your keyboard

The customer thinks that this is great,

reminiscent of a posh tailor who produces the perfect fit after numerous alterations

All the customer does is look at something,

suggests changes and then wait for the next version to find something wrong with

They will get a bit upset when the delivery deadline goes by without a finished product appearing but they can always cheer themselves up again by suing you


we have come full circle here,

because I did mention earlier that prototyping is a good way to build a system when you are not clear on the initial specificaiton


if you are going to use prototypes it is a good thing to plan for this from the

C# Programming © Rob Miles 2010

Computers and Programs

Programming Languages

start rather than ending up doing extra work because your initial understanding of the problem was wrong

Fact: More implementations fail because of inadequate specification than for any other reason

If your insistence on a cast iron specification forces the customer to think about exactly what the system is supposed to do and how it will work,

The customer may well say "But I am paying you to be the computer expert,

I know nothing about these machines"

This is no excuse

Explain the benefits of "Right First Time" technology and if that doesn't work produce a revolver and force the issue

if I could underline in red I would: All the above apply if you are writing the program for yourself

You are your own worst customer

! You may think that I am labouring a point here

the kind of simple systems we are going to create as we learn to program are going to be so trivial that the above techniques are far too long winded

You are wrong

One very good reason for doing this kind of thing is that it gets most of the program written for you

When we start with our double glazing program we now know that we have to: read in the width verify the value read in the height verify the value calculate width times height times 2 and print it calculate ( width + height ) * 2 * 3

The programming portion of the job is now simply converting the above description into a language which can be used in a computer

Programmer’s Point: Good programmers are good communicators The art of talking to a customer and finding out what he/she wants is just that,

If you want to call yourself a proper programmer you will have to learn how to do this

One of the first things you must do is break down the idea of "I am writing a program for you" and replace it with "We are creating a solution to a problem"

You do not work for your customers,

This is very important,

particularly when you might have to do things like trade with the customer on features or price

and how we are going to determine whether it has worked or not (test) we now need to express our program in a form that the computer can work with

You might ask the question "Why do we need programming languages,

why can we not use something like English

?" There are two answers to this one: 1

Computers are too stupid to understand English

English would make a lousy programming language

Please note that this does not imply that tape worms would make good programmers

To take the first point

We cannot make very clever computers at the moment

Computers are made clever by putting software into them,

and there are limits to the size of program that we can create and the speed at which it can talk to us

At the moment,

by using the most advanced software and hardware,

we can make computers which are about as clever as a tape worm

Tape worms do not speak very good English

therefore we cannot make a computer which can understand English

The best we can do is to get a computer to make sense of a very limited language which we use to tell it what to do

Time Flies like an Arrow

Fruit Flies like a Banana

To take the second point

English as a language is packed full of ambiguities

It is very hard to express something in an unambiguous way using English

If you do not believe me,

C# Programming © Rob Miles 2010

Computers and Programs

Programming languages get around both of these problems

They are simple enough to be made sense of by computer programs and they reduce ambiguity

Programmer’s Point: The language is not that important There are a great many programming languages around,

during your career you will have to learn more than just one

C# is a great language to start programming in,

but do not think that it is the only language you will ever learn

you will need to know at least 3

We are going to learn a language called C# (pronounced C sharp)

If you ever make the mistake of calling the language C hash you will show your ignorance straight away

! C# is a very flexible and powerful programming language with an interesting history

It was developed by Microsoft Corporation for a variety of reasons,

some political and others marketing

C# bears a strong resemblance to the C++ and Java programming languages,

having borrowed (or improved) features provided by these languages

The origins of both Java and C++ can be traced back to a language called C,

which is a highly dangerous and entertaining language which was invented in the early 1970s

C is famous as the language the UNIX operating system was written in,

and was specially designed for this

So what do I mean by that

Rob Miles,

want to use a chain saw I will hire one from a shop

As I am not an experienced chain saw user I would expect it to come with lots of built in safety features such as guards and automatic cut outs

These will make me much safer with the thing but will probably limit the usefulness of the tool,

because of all the safety stuff I might not be able to cut down certain kinds of tree

If I was a real lumberjack I would go out and buy a professional chain saw which has no safety features whatsoever but can be used to cut down most anything

If I make a mistake with the professional tool I could quite easily lose my leg,

something the amateur machine would not let happen

In programming terms what this means is that C lacks some safety features provided by other programming languages

This makes the language much more flexible


if I do something stupid C will not stop me,

so I have a much greater chance of crashing the computer with a C program than I do with a safer language

Programmer’s Point: Computers are always stupid I reckon that you should always work on the basis that any computer will tolerate no errors on your part and anything that you do which is stupid will always cause a disaster

! This concentrates the mind wonderfully

A C# program can contain managed or unmanaged parts

The managed code is fussed over by the system which runs it

This makes sure that it is hard (but probably not impossible) to crash your computer running managed code


all this fussing comes at a price,

causing your programs to run more slowly

To get the maximum possible performance,

and enable direct access to parts of the underlying computer system,

you can mark your programs as unmanaged

An unmanaged program goes faster,

but if it crashes it is capable of taking the computer

C# Programming © Rob Miles 2010

Computers and Programs

Switching to unmanaged mode is analogous to removing the guard from your new chainsaw because it gets in the way

C# is a great language to start learning with as the managed parts will make it easier for you to understand what has happened when your programs go wrong

Objects are an organisational mechanism which let you break your program down into sensible chunks,

each of which is in charge of part of the overall system

Object Oriented Design makes large projects much easier to design,

It also lets you create programs which can have a high degree of reliability and stability

I am very keen on object oriented programming,

but I am not going to tell you much about it just yet

This is not because I don't know much about it (honest) but because I believe that there are some very fundamental programming issues which need to be addressed before we make use of objects in our programs

The use of objects is as much about design as programming,

and we have to know how to program before we can design larger systems

C# is a compiled programming language

The computer cannot understand the language directly,

so a program called a compiler converts the C# text into the low level instructions which are much simpler

These low level instructions are in turn converted into the actual commands to drive the hardware which runs your program

We will look in more detail at this aspect of how C# programs work a little later,

for now the thing to remember is that you need to show your wonderful C# program to the compiler before you get to actually run it

A compiler is a very large program which knows how to decide if your program is legal

The first thing it does is check for errors in the way that you have used the language itself

Only if no errors are found by the compiler will it produce any output

The compiler will also flag up warnings which occur when it notices that you have done something which is not technically illegal,

but may indicate that you have made a mistake somewhere

An example of a warning situation is where you create something but don't use it for anything

The compiler would tell you about this,

in case you had forgotten to add a bit of your program

The C# language is supplied with a whole bunch of other stuff (to use a technical term) which lets C# programs do things like read text from the keyboard,

set up network connections and the like

These extra features are available to your C# program but you must explicitly ask for them

They are then located automatically when your program runs

Later on we will look at how you can break a program of your own down into a number of different chunks (perhaps so several different programmers can work on it)

which is a great place to write programs

It comprises the compiler,

along with an integrated editor,

It is provided in a number of versions with different feature sets

There is a free version,

called Visual Studio Express edition,

which is a great place to get started

Another free resources is the Microsoft

NET Framework

This provides a bunch of command line tools,

things that you type to the command prompt,

which can be used to compile and run C# programs

How you create and run your programs is up to you

C# Programming © Rob Miles 2010

Computers and Programs

I'm not going to go into details of how to download and install the

NET framework

I am going to assume that you are using a computer which has a text editor (usually Notepad) and the

NET framework installed

The Human Computer Of course initially it is best if we just work through your programs on paper

I reckon that you write programs best when you are not sitting at the computer,

the best approach is to write (or at least map out) your solution on paper a long way away from the machine

Once you are sitting in front of the keyboard there is a great temptation to start pressing keys and typing something in which might work

This is not good technique

You will almost certainly end up with something which almost works,

which you will then spend hours fiddling with to get it going

If you had sat down with a pencil and worked out the solution first you would probably get to a working system in around half the time

Programmer’s Point: Great Programmers debug less I am not impressed by hacking programmers who spend whole days at terminals fighting with enormous programs and debugging them into shape

I am impressed by someone who turns up,

types in the program and makes it work first time

? If your mum wanted to tell you how to make your favourite fruitcake she’d write the recipe down on a piece of paper

The recipe would be a list of ingredients followed by a sequence of actions to perform on them

A program can be regarded as a recipe,

but written for a computer to follow,

The ingredients will be values (called variables) that you want your program to work with

The program itself will be a sequence of actions (called statements) that are to be followed by the computer

Rather than writing the program down on a piece of paper you instead put it into a file on the computer,

This is what the compiler acts on

A source file contains three things:   

instructions to the compiler information about the structures which will hold the data to be stored and manipulated

instructions which manipulate the data

To take these in turn:

Controlling the Compiler The C# compiler needs to know certain things about your program

It needs to know which external resources your program is going to use

It also can be told about any options for the construction of your program which are important

Some parts of your program will simply provide this information to tell the compiler what to do

Storing the Data Programs work by processing data

The data has to be stored within the computer whilst the program processes it

All computer languages support variables of one form or another

A variable is simply a named location in which a value is held whilst the program runs

C# also lets you build up structures which can hold more than one item,

for example a single structure could hold all the information about a particular bank customer

As part of the program design process you will need to decide what items of data need to be stored

You must also decide on sensible names that you will use to identify these items

C# Programming © Rob Miles 2010

Computers and Programs

Describing the Solution The actual instructions which describe your solution to the problem must also be part of your program

A single,

instruction to do something is in a C# program is called a statement

A statement is an instruction to perform one particular operation,

for example add two numbers together and store the result

The really gripping thing about programs is that some statements can change which statement is performed next,

so that your program can look at things and decide what to do

In the case of C# you can lump statements together to form a lump of program which does one particular task

Such a lump is called a method

A method can be very small,

It can return a value which may or may not be of interest

It can have any name you like,

and your program can contain as many methods as you see fit

One method may refer to others

The C# language also has a huge number of libraries available which you can use

These save you from "re-inventing the wheel" each time you write a program

We will look at methods in detail later in these notes

Seasoned programmers break down a problem into a number of smaller ones and make a method for each

Identifiers and Keywords You give a name to each method that you create,

and you try to make the name of the function fit what it does,

for example ShowMenu or SaveToFile

The C# language actually runs your program by looking for a method with a special name,

This method is called when your program starts running,

The names that you invent to identify things are called identifiers

You also create identifiers when you make things to hold values

woodLength might a good choice when we want to hold the length of wood required

Later on we will look at the rules and conventions which you must observe when you create identifiers

The words which are part of the C# language itself are called keywords

In a recipe a keyword would be something like "mix" or "heat" or "until"

They would let you say things like "heat sugar until molten" or "mix until smooth"

In fact,

you'll find that programs look a lot like recipes

Keywords will appear blue in some of the listings in this text

Objects Some of the things in the programs that we write are objects that are part of the framework we are using

To continue our cooking analogy,

these are things like mixing bowls and ovens,

which are used during the cooking process

The names of objects will be given in a different shade of blue in some of the listings in this text

Text in a Computer Program There are two kinds of text in your program

There are the instructions that you want the computer to perform and there are the messages that you want the program to actually display in front of the user

Your mum might add the following instruction to her cake recipe: Now write the words “Happy Christmas” on top of the cake in pink icing

She is using double quote characters to mark the text that is to be drawn on the cake,

and C# works in exactly the same way

―Happy Christmas‖ is not part of the instructions

it is what needs to be written

These kinds of messages are coloured red in this text

Colours and Conventions The colours that I use in this text are intended to line up with the colours you will see when you edit your programs using a professional program editor such as the one supplied as part of Visual Studio

The colours just serve to make the programs easier to understand,

and do not have any special meaning

They are added automatically by the editor as you write your program

C# Programming © Rob Miles 2010

Simple Data Processing

A First C# Program

We will start by creating a very simple solution and investigating the C# statements that perform basic data processing

Then we will use additional features of the C# language to improve the quality of the solution we are producing

This is the problem we set out to solve as described in section0

Here it is: using System

class GlazerCalc { static void Main() { double width,





woodLength = 2 * ( width + height ) * 3

glassArea = 2 * ( width * height )


WriteLine ( "The length of the wood is " + woodLength + " feet" )


WriteLine( "The area of the glass is " + glassArea + " square metres" )

Code Sample 1

If you gave it to a C# compiler it would compile,

The actual work is done by the two lines that I have highlighted

Broadly speaking the stuff before these two lines is concerned with setting things up and getting the values in to be processed

The stuff after the two lines is concerned with displaying the answer to the user

We can now go through each line in turn and try to see how it fits into our program

C# Programming © Rob Miles 2010

Simple Data Processing

A First C# Program

This is an instruction to the C# compiler to tell it that we want to use things from the System namespace

A namespace is a place where particular names have meaning

We have namespaces in our conversations too,

if I am using the "Football" namespace and I say “That team is really on fire” I'm saying something good

If I am using the "Firefighter" namespace I'm saying something less good

A big part of learning to program is learning how to use all the additional features of the system which support your programs

In the case of C# the System namespace is where lots of useful things are described

One of these useful things provided with C# is the Console object which will let me write things which will appear on the screen in front of the user

If I want to just refer to this as Console I have to tell the compiler I'm using the System namespace

This means that if I refer to something by a particular name the compiler will look in System to see if there is anything matching that name

We will use other namespaces later on

class GlazerCalc A C# program is made up of one or more classes

A class is a container which holds data and program code to do a particular job

In the case of our double glazing calculator the class just contains a single method which will work out our wood lengths and glass area,

but a class can contain much more than that if it needs to

Classes are the basis of object oriented programming,

You need to invent an identifier for every class that you create

I've called ours GlazerCalc since this reflects what it does

For now,

don't worry too much about classes

just make sure that you pick sensible names for the classes that you create

There is a convention that the name of the file which contains a particular class should match the class itself,

in other words the program above should be held in a file called GlazerCalc

static This keyword makes sure that the method which follows is always present,

the word static in this context means "is part of the enclosing class and is always here"

When we get to consider objects we will find that this little keyword has all kinds of interesting ramifications

But for now I'd be grateful if you'd just make sure that you put it here in order to make your programs work properly

In programming terms the void keyword means that the method we are about to describe does not return anything of interest to us

The method will just do a job and then finish

In some cases we write methods which return a result (in fact we will use such a method later in the program)


in order to stop someone else accidentally making use of the value returned by our Main method,

we are explicitly stating that it returns nothing

This makes our programs safer,

in that the compiler now knows that if someone tries to use the value returned by this method,

Main You choose the names of your methods to reflect what they are going to do for you

Except for Main

This method (and there must be one,

and only one such method) is where your program starts running

When your program is loaded and run the first method given control is the one called Main

If you miss out the Main method the system quite literally does not know where to start

C# Programming © Rob Miles 2010

Simple Data Processing

A First C# Program

() This is a pair of brackets enclosing nothing

This may sound stupid,

but actually tells the compiler that the method Main has no parameters

A parameter to a method gives the method something to work on

When you define a method you can tell C# that it works on one or more things,

for example sin(x) could work on a floating point value of angle x

We will cover methods in very great detail later in this document

As the name implies,

for every open brace there must be a matching close

Braces allow programmers to lump pieces of program together

Such a lump of program is often called a block

A block can contain the declaration of variable used within it,

followed by a sequence of program statements which are executed in order

In this case the braces enclose the working parts of the method Main

When the compiler sees the matching close brace at the end it knows that it has reached the end of the method and can look for another (if any)

The effects of an un-paired brace are invariably fatal

double By now you probably feel that you need a drink

But that is not what double means in this context

What it means is "double precision floating point number"

Our program needs to remember certain values as it runs

Notably it will read in values for the width and height of the windows and then calculate and print values for the glass area and wood length

C# calls the places where values are put variables

At the beginning of any block you can tell C# that you want to reserve some space to hold some data val

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