C Programming Yellow Book

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.
{
This is a brace. As the name implies, braces come in packs of two, i.e. 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 variables 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....
A double variable can hold a
very wide range of values to a
very high precision.
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 values. Each item can hold a particular kind of value. Essentially, C# can
handle three types of data, floating point numbers, integer numbers and text (i.e. letters,
digits and punctuation). The process of creating a variable is called declaring the
variable.
You declare some variables of a particular type by giving the type of the data,
followed by a list of the names you want the variables to have. We are using the type
double for now. Later we will use other types.
width, height, woodLength, glassArea
This is a list. A list of items in C# is separated by , (comma) characters. In this case it
is a list of variable names. Once the compiler has seen the word double (see above) it
is expecting to find the name of at least one variable to be created. The compiler works
its way through the list, creating boxes which can hold values of type double and
giving them the appropriate names. From this point on we can refer to the above
names, and the compiler will know that we are using that particular variable.
Programmer’s Point: Know where your data comes from
In fact, given the limitations in the accuracy to which people can read tape measures, and the fact that we are not
going to make any windows as wide as the universe, a double precision floating point number is overkill for this
application. You would instead ask the customer if it is OK to just express the dimensions in millimetres instead. We
will look at the considerations driving the choice of particular variable types a bit later on. All these decisions are
driven by the metadata (data about data) that you gather when you are finding out about the system you are creating.
C# Programming © Rob Miles 2015 16