C# B 1

CSC 298

Writing a C# application

C# B 2

A first C# application// Display Hello, world on the screenpublic 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# statementends with a semi colon ;

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

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)

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

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);

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");

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 classSystem.Windows.Forms.MessageBox

just type MessageBox

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

HelloWorld

See later for other ways