Teaching with C Sharp Rob Miles

Overview  Introduction >My perspective  C# and Java >Broad overview of the languages  Significant C# Features >C# features from a teaching perspective  Conclusion >..and possibly a sing song?

Introduction  The material is based on my experience teaching C# to two student cohorts  It is necessarily coloured by my teaching philosophy  It has been presented in targeted sections so that you can use those components which suit your purpose  There are number of sample projects for each section which form the basis of the lab work

Presentation Notes  A full set of notes is provided for this presentation  The notes are broken down in the same sequence as the items given here  Each section is followed by a number of practical examples along with some ideas for investigation

Bonus Materials  As this is the “collectors edition” of the course >Just like every other edition…  It is supplied with bonus materials in the form of a copy of “C# from Java”  This provides an FAQ for a number of conversion issues

Teaching Philosophy  At Hull we teach an “algorithms first” course  This concentrates on program construction in semester one and introduces objects in semester two  Everything is placed in the strongest possible “real world” context and I make heavy use of analogies

Objects  Objects are presented as a solution to structure and design  I try to make a logical transition from structures to components: >Encapsulation >Business Objects >Test driven development >Component based design >Hierarchies for code reuse

Teaching and C#  I have found that C# matches with our teaching philosophy  It would also match with an objects first approach, at least as well as Java does  The points made later are applicable to both teaching approaches

C# and Java  C# is heavily based on Java  Conversion from C# to Java (or back) is not difficult  C# programs seem to run faster on the PC platform  C# is not being positioned as Microsoft proprietary >But the language development is Microsoft driven, in the same way that Java development is Sun driven

C# Versions  There are now two versions of C#  Version 2 adds a number of features: >Partial classes >Generics  There are few breaking changes moving from C# Version 1 to Version 2  This presentation is Version 1 compliant

Development Tools  A command line compiler kit is available >Directly analogous to the JDK  Visual Studio 2005 is available under the Academic Alliance  Visual Studio 2005 Express Edition is available for free >David will give more details of these later

C# Language Features  We can consider some specific C# features: >User input/Output >Value Types and Structures >Exception Handling >Reference Parameters >Event Handling/Delegates >Program Linking and Deployment >Properties >Generics  They will be placed into a teaching context

User input/output  The System.Console object provides a range of input/output actions  There is no need to create a stream object  There is also no need to trap exceptions

demo demo  Simple Input/Output >Text Read and Write and colour manipulation  Console Power >Moving dot game

Value Types  In Java a type is either primitive or reference:  Primitive >Managed by value >Primitive types do not support methods or properties  Reference >Managed by reference >Support methods and properties >Slower to manipulate

Java Primitive Problems  For a student learning to program the primitive-reference distinction is hard to grasp  It also brings a need to describe the use of wrapper classes >Students do not like to have to learn the difference between int and Integer  This knowledge is not that relevant to other languages

C# value types  C# uses a different approach: >All types are objects >Some types are “value” types, i.e. manipulated by value not reference >But they all support methods and properties >The “box” operation performs conversion from value to reference as required  The C# student need not be aware of any distinction at the start of the course

demo demo  Value type behaviour in.NET 1.1 and.NET 2.0 >Using ildasm to look at the IL

Boxing in Action static void Main(string[] args) { int a, b; a = 99; b = a; b = 100; Console.WriteLine("a is {0} b is {1}", a, b); }

Boxing Assembler

Structures as value types  C# supports a struct type  This type is directly analogous to the struct in C  A struct is manipulated as a value type  This allows data to be grouped together without a need to cover objects and references  It also allows for more complex exercises

C# Structs  A struct in C# is managed by value.  However, they do behave a lot like objects >They can support methods and properties >They can have constructors >They can even implement an interface  But they do not support inheritance

demo demo  Structures in C# >Simple structures >Structure “housekeeping” >Arrays of structures

Exception Handling  In Java you have to handle some exceptions (the checked ones) >These are thrown by lots of library methods, including input/output  In C# all exceptions are unchecked >If you don’t catch them the run time system will pick them up >This makes things like simple input/output much simpler

demo demo  Exceptions in C# >Simple exception handling >Creating your own exceptions

Reference Parameters  Unlike Java, where parameters are always passed by value, in C# reference parameters are allowed  This makes programming more efficient  It also allows discussion of the meaning of references without the need to consider objects

demo demo  Reference Parameters >ref parameters >in parameters

Event handling and delegates  C# provides a delegate type which can be used to create a typesafe reference to a method in an instance of a class  There is no need to create an instance of a class to receive events  Delegates are used to manage system events and the user interface

demo demo  Event handling with delegates >Simple form creation and event management >Using the Visual Studio 2005 Forms Designer

Delegates and Design  Delegates bring function pointers back into programming  However, they can be deployed in a typesafe manner in a properly managed environment  However, he biggest advantage over Java is that they make interacting with Forms components much easier

Program Linking and Deployment  In Java a program is built at run time >The classpath is used to locate the required components as the program runs >There is little attention paid at build time to linking issues  In C# the.exe file is an assembly which may make use of.dll library files >There is a distinct difference between an executable file and a library one >An exe file will refer to a specific version of a dll when it is built

C# Programs  Only one class in a C# program may contain a Main method to provide the entry point  During the build process the particular libraries to be used must be specifically identified and located >If you are using Visual Studio the metadata from the assembly can be used in interactive help

C# Linking and Teaching  I place great emphasis on Business Objects and Test Driven Development  The C# linking process fits well with this approach  The students are initially introduced to the process by means of compiler directives  Later they move on to use Visual Studio 2005

demo demo  Using Business Objects >Single workspace containing a number of Visual Studio Projects

The naming of components  Java provides a package mechanism by which a system can be broken down into components >this is linked to the physical position of the file in a directory hierarchy >only one public class can placed in each file, and the filename must match the class name  C# does not do this >A class is placed in a “namespace” which is not physically mapped to storage

C# Namespace  Namespaces are hierarchical  A single source file can contain components from a number of namespaces  A namespace can span multiple source files  Visual Studio 2005 provides a view of all the components in a namespace

Partial Classes  These are available in C# Version 2.0  A class can be made to span a number of source files  This allows the developer to partition the behaviours of a class into a number of separate source files >Hide the scary bits?  Visual Studio 2005 does this with forms

demo demo  Using Business Objects and Namespaces >Advanced multi-project workspace with business and control objects

Properties  Properties are “syntactic sugar”  They provide a convenient wrapper for get and set behaviour in objects  There is no need to use them >But all of the system library classes do  They are best explained in the context of “making life easier”

demo demo  Simple Properties >A book title class which uses properties to manage the name of the book

Properties and Assembler

Generics  Generics are new in Version 2.0  They let you create classes which work on classes  You don’t have to give the types of the classes when you write the code  Instead you use placeholders which are “filled in” at runtime in a typesafe manner

Generics and teaching  I would not teach about generics in the first part of a programming course  The fact that they are now present in C# means that we can use this language in later years

Generic Collections  The major advantage that generics brings for learner programmers is a better way to deploy collection classes  They remove the need to cast items read from the collection >Although I must admit I think that covering casting at this point is a good idea

demo demo  Using the List collection class >A typesafe list collection is created using the new System.Generics.List collection class

Using Generics  Generics do make it possible to talk about data structures without dwelling on the type of the data being manipulated  This can be rolled into discussions about generalisation which can take place in the latter parts of a first year course

demo demo  Creating and using a generic linked list class >A linked list generic which is deployed for both integers and string types

Conclusion  Students like C# >We have seen improved performance in both coursework and examinations  It is a more productive programming environment than Java >All of the language changes are soundly pragmatic >The toolset is very effective and now handles important issues like test driven development  C# will do very nicely. For now……

Questions  I can take any quick questions now  For more detailed ones please catch me in the break or during the labs