C Programming Yellow Book

Simple Data Processing
A First C# Program
()
A method call is followed by the parameters to the method. A parameter is something
that is passed into a method for it to work on. Think of it as raw materials for a process
of some kind. In the case of ReadLine it has no raw materials; it is going to fetch the
information from the user who will type it in. However, we still have to provide the list
of parameters even if it is empty.
;
We have seen the semi-colon before. It marks the end of a statement in our program.
width =
This is another assignment (Mr. Phelps/Hawke 1 ). The variable width is being given a
value. Many statements in your programs will simply be moving data around and
performing actions on it.
double.
But the rest of the statement looks a bit scary. In fact it is not too tricky. We are asking
Mr. double (the thing responsible holding for double precision floating point
numbers) to do a little job for us. In this case the little job is "take the string held by
widthString and convert it into a double precision floating point number". Mr.
double provides this ability by exposing a method called Parse.
Note that there is nothing wrong or naughty about something in C# exposing its
methods. It is how we get things done for us. When you come to design larger
programs you will find that the best way to do this is to create components which
expose methods to get the job done. The whole of the C# library set is provided as a
series of methods and one of the things that you will have to get to grips with is where
the methods are and how to use them. As with many things in life, the trick is knowing
who to ask…
Parse
The Parse method has the job of converting the string it has been given into a double
precision floating point number. To do this it must look along the string, pull out each
digit in turn and then calculate the actual value, as in "12" means a ten and two units.
This process of looking along things is often called parsing. Hence the name of the
method we are using. The method is given the string that is to be parsed and returns the
number that it has found.
Note that this gives significant potential for evil, in that if the user doesn’t type in a
value or types something like "Twenty Five" the Parse method call will not be able to
resolve a number and will fail as a result. How it fails, and how you can resolve this
failure, will be left for a future section in order to add more excitement to this text.
(widthString);
1
Obscure movie/TV show reference for you there folks.
We have seen that a call of a method must be followed by the raw materials
(parameters) for that method. In the case of ReadLine there are no parameters, but we
still need to supply an empty list to indicate this. In the case of Parse the method
needs to be given the string that it is to work on. We do this by putting the name of the
string variable containing the text (widthString) into the brackets as above. The
value of the information in widthString (i.e. the text that the user has typed in) is
passed into the Parse method for it to work on and extract the number from.
C# Programming © Rob Miles 2015 18