Object Oriented Programming

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Object Oriented Programming

• Introduction to C

Dr. Mike Spann m.spann_at_bham.ac.uk
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Contents

• Introducing C
• Writing applications in C
• Visual Studio .NET
• Basic C language concepts

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Introducing C

• C (C-sharp) is a language that targets one and
  only one platform, namely .NET
• That doesnt mean its restricted to Windows
• There are now .NET implementations on other
  operating systems including Linux
• As long as we get to grips with object oriented
  programming, C is a simple language to master

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Introducing C

• C derives its power from .NET and the framework
  class library
• The most similar language to C is Java
• There are a number of striking similarities
• BUT there is one fundamental difference
• Java runs on a virtual machine and is interpreted
• C programs runs in native machine code
• This is because of the power of .NET and leads to
  much more efficient programs

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Writing applications in C

• An application in C can be one of three types
• Console application (.exe)
• Windows application (.exe)
• Library of Types (.dll)
• The .dll is not executable
• These 3 types exclude the more advanced web-based
  applications

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Writing applications in C

• Before we look at the more detailed structure and
  syntax of C programs, we will show a simple
  example of each type
• In each case we will use the command line
  compiler (csc) to create the binary (assembly)
• Later in this lecture we will look at using
  Visual Studio to create our applications

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Writing applications in C

• Example 1 A console application
• This example inputs a number from the console and
  displays the square root back to the console
• Uses a simple iterative algorithm rather than
  calling a Math library function

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Writing applications in C
using System class Square_Root static void
Main(string args) double
a,root do Console.Write("Enter
a number ") aConvert.ToDouble(Console.Re
adLine()) if (alt0)
Console.WriteLine(Enter a positive
number!") while (alt0) roota/2
double root_old do
root_oldroot root(root_olda/root_old)
/2 while (Math.Abs(root_old-root)gt1.0E-6)
Console.WriteLine("The square root of " a
" is " root)
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Writing applications in C
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Writing applications in C

• We can see that everything in a C application is
  in a class
• In this case the class defines a program entry
  point Main
• This makes the application binary an executable
• Note the use of the System namespace
• Classes referred to, such as Console and Math,
  are actually System.Console and System.Math

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Writing applications in C

• Example 2 A windows application
• A simple GUI displaying a menu
• This example displays a window with couple of
  menu buttons
• Clicking on a menu button displays a pop-up
  dialog box
• The code listing demonstrates the simplicity of
  GUI programming in C

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Writing applications in C
using System using System.Drawing using
System.Windows.Forms class App public
static void Main() Application.Run(new
MenuForm()) class MenuFormForm
public MenuForm()
this.ContextMenu new ContextMenu(SetupMenu())
this.Menu new MainMenu(SetupMenu())
MenuItem SetupMenu()
MenuItem file new MenuItem("File")
file.MenuItems.Add("Exit", new
EventHandler(OnExit)) MenuItem messages
new MenuItem("Message Boxes")
EventHandler handler new EventHandler(OnMessag
eBox) messages.MenuItems.Add("Message
Box 1", handler) messages.MenuItems.Add("
Message Box 2", handler) return new
MenuItemfile, messages void
OnExit(Object sender, EventArgs args)
this.Close() void
OnMessageBox(Object sender, EventArgs args)
MenuItem item sender as MenuItem
MessageBox.Show(this, "You selected menu item -
"item.Text)
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Writing applications in C
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Writing applications in C
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Writing applications in C

• This program is considerably more complex than
  the previous example
• It uses the System.Drawing and System.Windows.Form
  s namespaces
• The (System.Windows.Forms).Form class is a
  standard outer graphics container for most
  windows/GUI applications
• It also uses event handling to respond to user
  interaction (menu button clicks)

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Writing applications in C

• Example 3 A library
• We can take some of the code from example 1 for
  computing the square root and make it a library
• It will not have a Main method
• We indicate that we are compiling to a .dll using
  the /Targetlibrary option

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Writing applications in C
using System public class Square_Root_Class p
ublic static double calcRoot(double number)
double root rootnumber/2
double root_old do
root_oldroot root(root_oldnumber/root
_old)/2 while (Math.Abs(root_old-root)gt1.
0E-6) return root
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Writing applications in C
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Writing applications in C

• We can now write a simple program containing a
  Main method which uses this library class
• The only thing we need to do is to reference the
  library .dll using the /r switch when we compile
  the application

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Writing applications in C
using System class Square_Root static
void Main(string args) double
a,root do
Console.Write("Enter a number ")
aConvert.ToDouble(Console.ReadLine())
if (alt0) Console.WriteLine("Please
enter a positive number!") while
(alt0) rootSquare_Root_Class.ca
lcRoot(a) Console.WriteLine("The square root
of " a " is " root)
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Writing applications in C
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Visual Studio .NET

• VS.NET is an Integrated Development Environment
  or IDE
• It includes a source code editors (usually pretty
  fancy ones containing language help features)
• Software project management tools
• Online-help and
• Debugging
• GUI design tools
• And lots more......

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Visual Studio .NET

• Creating a new project gives the user the option
  of the language and project type
• Visual Basic, C, C, J
• Console, Windows, Class Library, Active Web Page
  or Web Service

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Visual Studio .NET
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Visual Studio .NET

• We can group our projects under a common solution
• Each application has just one solution but may
  comprise many projects
• A single solution can comprise projects written
  in different languages
• Each project contains a number of files including
  source files, executables and xml files
  containing information about the project and
  resources

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Visual Studio .NET

• We can add each of our previous 3 example
  applications (projects) to a single solution
  Learning C Sharp
• Its a simple matter to flip between them and view
  the code from each project by selecting the
  appropriate tab
• Each project must be built (compiled) before
  executing and any of the projects in a solution
  can be selected to be executed

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Visual Studio .NET
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Visual Studio .NET

• It is a simple matter to reference a .dll from a
  project
• We can check all the references that a project
  makes by expanding the References menu item in
  the solution explorer
• Notice for the windows project, lots of FCL
  classes are referenced

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Visual Studio .NET
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Visual Studio .NET

• An important feature of VS is its ability to
  enable visual programming
• Essentially we can create fairly sophisticated
  GUIs without writing a line of code
• We simply add GUI components to an outer window
  (a Form) and set up the properties of the
  components to get the required look and feel
• VS allows us to easily switch between code and
  design views
• We will look more into visual programming in a
  future lecture

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Basic C language concepts

• C has a rich C-based syntax much like C or
  Java
• The concepts of variables, program statements,
  control flow, operators, exceptions etc are the
  same in C as in C and Java
• Like Java, everything in C is inside a class
• We will only look at those C language issues
  which differ from those we are already familiar
  with

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Basic C language concepts

• Primitive types
• These are types representing the basic types we
  are familiar with integers, floats, characters
  etc
• In C they are part of the FCL so they are
  treated as Objects (unlike in Java!) but are used
  in the same way as normal primitive types
• So, for example, we can apply the normal
  arithmetic operators to them

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Basic C language concepts
C Primitive C Alias Description
Boolean bool Indicates a true or false value. The if, while, and do-while constructs require expressions of type Boolean.
Byte byte Numeric type indicating an unsigned 8-bit value.
Char char Character type that holds a 16-bit Unicode character.
Decimal decimal High-precession numerical type for financial or scientific applications.
Double double Double precision floating point numerical value.
Single float Single precision floating point numerical value.
Int32 int Numerical type indicating a 32-bit signed value.
Int64 long Numerical type indicating a 64-bit signed value.
SByte sbyte Numerical type indicating an 8-bit signed value.
Int16 short Numerical type indicating a 16-bit signed value.
UInt32 uint Numerical type indicating a 32-bit unsigned value.
UInt64 ulong Numerical type indicating a 64-bit unsigned value.
UInt16 ushort Numerical type indicating a 16-bit unsigned value.
String string Immutable string of character values
Object object The base type of all type in any managed code.
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Basic C language concepts

• Reference Types and Value Types
• When we declare a variable in a C program it is
  either a reference or a value type
• All non-primitive types are reference types
• Essentially the variable name is a reference to
  the memory occupied by the variable
• But primitive types can be either
• Even though all primitive types are treated as
  objects (unlike in Java)!!

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Basic C language concepts

• For example String and Int32 are both primitive
  types
• BUT
• String is a reference type
• Int32 is a value type
• String variable s is a reference (memory address)
  of some memory which stores the string (which
  defaults to null)
• Int32 variable x is the actual value of the
  integer (which defaults to zero)

Int32 x10 String sHello
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Basic C language concepts

• Arrays
• Array declaration and initialization is similar
  to other languages

// A one dimensional array of 10 Bytes Byte
bytes new Byte10   // A two dimensional
array of 4 Int32s Int32, ints new
Int325,5   // A one dimensional array of
references to Strings String strings new
String10
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Basic C language concepts

• The array itself is an object
• The array is automatically derived from the Array
  class in the FCL
• This enables a number of useful methods of the
  Array class to be used
• Finding the length of an array
• Finding the number of dimensions of an array
• Arrays themselves are reference types although
  their elements can be value types, or reference
  types

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Basic C language concepts

• Control flow statements in C are the same as for
  C and Java
• if else
• for
• do while()
• etc
• However, there is one additional new one in C!
• foreach

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Basic C language concepts

• foreach simplifies the code for iterating through
  an array
• There is no loop counter
• If the loop counter variable is required in the
  loop, then a for construct must be used
• The type must match the type of elements in the
  array
• The array cannot be updated inside the loop

foreach (type identifier in arrayName)
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Basic C language concepts
using System public class ForEachTest
static void Main(string args)
int array 0, 2, 4, 6, 8, 10, 12, 14
int total 0 foreach (int n in
array) total n
Console.WriteLine("Array total " total)

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Basic C language concepts

• Expressions and operators
• C is a strongly typed language
• Variables are declared before use
• Implicit type conversions that dont lose
  precision will be carried out
• Unlike C (but like Java) C has a Boolean type
• Thus the following code generates a compilation
  error

Int32 x 10while(x--) DoSomething()
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Basic C language concepts

• C has the standard set of operators we are
  familiar with
• Also it has operators such as is and typeof for
  testing variable type information
• C provides operator overload functions (as does
  C but not Java) to enable standard operators to
  be applied to non-primitive types

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Basic C language concepts
Operator category Operators
Arithmetic - /
Logical (boolean and bitwise) ! true false
String concatenation
Increment, decrement   --
Shift ltlt gtgt
Relational ! lt gt lt gt
Assignment - / ltlt gtgt
Member access .
Indexing
Cast ()
Conditional (Ternary) ?
Delegate concatenation and removal -
Object creation New
Type information is sizeof typeof   
Overflow exception control checked unchecked
Indirection and Address -gt
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Basic C language concepts

• Error handling
• This is always done in C using structured
  exception handling
• Use of the try catch mechanism as in Java and
  C
• Functions should not return error conditions but
  should throw exceptions
• This is done universally by methods in FCL classes

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Basic C language concepts
public static void ExceptionExample() //
try-catch try Int32 index 10
while(index-- ! 0) Console.WriteLine(
100/index) catch(DivideByZeroException)
Console.WriteLine("A divide by zero
exception!") Console.WriteLine("Exceptio
n caught code keeps running")   //
try-finally try return
finally Console.WriteLine("Code in
finally blocks always runs")
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Summary

• We have looked at different types of simple C
  applications
• Console applications
• Windows applications
• Libraries (reusable types)
• We have looked at the basics of using Visual
  Studio.NET
• We have looked at some C language issues from
  the point of view of differences from C and Java