1. C# B 1 CSC 298 Writing a C# application

2. C# B 2 A first C# application // Display Hello, world on the screen public class HelloWorld { public static void Main() { System.Console.WriteLine("Hello, world") ; } comment class definition class method use the System.Console class to write some text to the console every C# statement ends with a semi colon ;

3. C# B 3 Code organization  In C# (as in Java), no stand alone function  Code is written inside of blocks {} that are class definitions  public class HelloWorld { // my code is here … }  for now always write public class. More on this later  Good habits from Java (not required in C#)  Name the file that contains the definition of the public class HelloWorld: HelloWorld.cs  Write only one public class per C# file

4. C# B 4 Comments  Ignored by the computer. Essential for the reader.  2 types of comments: // and /* */  Everything between // and the end of the line is a comment  Everything between /* and */ is a comment. It can be used on several lines. You can't nest these comments (/* blabla /* blabla */ blabla */ gives an error)  Examples  // this is a comment  /* this is a comment that can be written on several lines */  Also XML comments /// (see VS.NET doc)

5. C# B 5 The Main method  An application always start executing with the Main method (note the capital M)  The Main method must be static  It can be of type void or return an int  It can take no arguments or an array of strings  It can be of any visibility (public, private…) public static int Main() static void Main(String[] args) // default to private

6. C# B 6 Console Input/Output in C#  Console: a class to access I/O functionalities for the console (=DOS window)  In: input stream, Out: output stream  important static methods: Write, WriteLine, ReadLine  Console is available in the namespace System Console.Write ("Enter your name: "); String name = Console.ReadLine(); Console.WriteLine("Welcome " + name);

7. C# B 7 System.Windows.Forms  A namespace that contains many classes to build graphical user interfaces  We will see many examples  Here is a simple example MessageBox.Show("Hello, world!", "Message");

8. C# B 8 The using statement  Define a shortcut to write the names of classes of the FCL in our programs.  using System.Windows.Forms means:  get access to all of the classes in the namespace System.Windows.Forms  In the program, to access the class System.Windows.Forms.MessageBox just type MessageBox

9. C# B 9 Formatting output  To concatenate strings (=sequence of characters), use +  Write("Hello, " + "World") prints Hello, World  Write(""+1+2) is not the same as Write(1+2). Why?  For tabs and newlines, use '\t' and '\n'  Write("Hello\tWorld") prints Hello World  Write("Hello\nWorld") prints Hello World  See later for other ways