VB.NET and C# Comparison

Program Structure

Imports System

Namespace Hello

Class HelloWorld

Overloads Shared Sub Main(ByVal args() As String)

Dim name As String = "VB.NET"

'See if an argument was passed from the command line

If args.Length = 1 Then name = args(0)

Console.WriteLine("Hello, " & name & "!")

End Sub

End Class

End Namespace

using System;

namespace Hello {

public class HelloWorld {

public static void Main(string[] args) {

string name = "C#";

// See if an argument was passed from the command line

if (args.Length == 1)

name = args[0];

Console.WriteLine("Hello, " + name + "!");

}

}

}

Comments

' Single line only

REM Single line only

''' <summary>XML comments</summary>

// Single line

/* Multiple

line */

/// <summary>XML comments on single line</summary>

/** <summary>XML comments on multiple lines</summary> */

Data Types

Value Types

Boolean

Byte, SByte

Char

Short, UShort, Integer, UInteger, Long, ULong

Single, Double

Decimal

Date (alias of System.DateTime)

Reference Types

Object

String

Initializing

Dim correct As Boolean = True

Dim b As Byte = &H2A 'hex or &O52 for octal

Dim person As Object = Nothing

Dim name As String = "Dwight"

Dim grade As Char = "B"c

Dim today As Date = #12/31/2010 12:15:00 PM#

Dim amount As Decimal = 35.99@

Dim gpa As Single = 2.9!

Dim pi As Double = 3.14159265

Dim lTotal As Long = 123456L

Dim sTotal As Short = 123S

Dim usTotal As UShort = 123US

Dim uiTotal As UInteger = 123UI

Dim ulTotal As ULong = 123UL

Implicitly Typed Local Variables

Dim s = "Hello!"

Dim nums = New Integer() {1, 2, 3}

Dim hero = New SuperHero With {.Name = "Batman"}

Type Information

Dim x As Integer

Console.WriteLine(x.GetType()) ' Prints System.Int32

Console.WriteLine(GetType(Integer)) ' Prints System.Int32

Console.WriteLine(TypeName(x)) ' Prints Integer

Dim c as New Circle

If TypeOf c Is Shape Then _

Console.WriteLine("c is a Shape")

Type Conversion / Casting

Dim d As Single = 3.5

Dim i As Integer = CType(d, Integer) ' set to 4 (Banker's rounding)

i = CInt(d) ' same result as CType

i = Int(d) ' set to 3 (Int function truncates the decimal)

Dim o As Object = 2

i = DirectCast(o, Integer) ' Throws InvalidCastException if type cast fails

Dim s As New Shape

Dim c As Circle = TryCast(s, Circle) ' Returns Nothing if type cast fails

Value Types

bool

byte, sbyte

char

short, ushort, int, uint, long, ulong

float, double

decimal

DateTime (not a built-in C# type)

Reference Types

object

string

Initializing

bool correct = true;

byte b = 0x2A; // hex

object person = null;

string name = "Dwight";

char grade = 'B';

DateTime today = DateTime.Parse("12/31/2010 12:15:00 PM");

decimal amount = 35.99m;

float gpa = 2.9f;

double pi = 3.14159265;

long lTotal = 123456L;

short sTotal = 123;

ushort usTotal = 123;

uint uiTotal = 123;

ulong ulTotal = 123;

Implicitly Typed Local Variables

var s = "Hello!";

var nums = new int[] { 1, 2, 3 };

var hero = new SuperHero() { Name = "Batman" };

Type Information

int x;

Console.WriteLine(x.GetType()); // Prints System.Int32

Console.WriteLine(typeof(int)); // Prints System.Int32

Console.WriteLine(x.GetType().Name); // prints Int32

Circle c = new Circle();

if (c is Shape)

Console.WriteLine("c is a Shape");

Type Conversion / Casting

float d = 3.5f;

i = Convert.ToInt32(d); // Set to 4 (rounds)

int i = (int)d; // set to 3 (truncates decimal)

object o = 2;

int i = (int)o; // Throws InvalidCastException if type cast fails

Shape s = new Shape();

Circle c = s as Circle; // Returns null if type cast fails

Constants

Const MAX_STUDENTS As Integer = 25

' Can set to a const or var; may be initialized in a constructor

ReadOnly MIN_DIAMETER As Single = 4.93

const int MAX_STUDENTS = 25;

// Can set to a const or var; may be initialized in a constructor

readonly float MIN_DIAMETER = 4.93f;

Enumerations

Enum Action

Start

[Stop] ' Stop is a reserved word

Rewind

Forward

End Enum

Enum Status

Flunk = 50

Pass = 70

Excel = 90

End Enum

Dim a As Action = Action.Stop

If a <> Action.Start Then _

Console.WriteLine(a.ToString & " is " & a) ' Prints "Stop is 1"

Console.WriteLine(Status.Pass) ' Prints 70

Console.WriteLine(Status.Pass.ToString()) ' Prints Pass

enum Action {Start, Stop, Rewind, Forward};

enum Status {Flunk = 50, Pass = 70, Excel = 90};

Action a = Action.Stop;

if (a != Action.Start)

Console.WriteLine(a + " is " + (int) a); // Prints "Stop is 1"

Console.WriteLine((int) Status.Pass); // Prints 70

Console.WriteLine(Status.Pass); // Prints Pass

Operators

Comparison

= < > <= >= <>

Arithmetic

+ - * /

Mod

\ (integer division)

^ (raise to a power)

Assignment

= += -= *= /= \= ^= <<= >>= &=

Bitwise

And Or Xor Not << >>

Logical

AndAlso OrElse And Or Xor Not

Note: AndAlso and OrElse perform short-circuit logical evaluations

String Concatenation

&

Comparison

== < > <= >= !=

Arithmetic

+ - * /

% (mod)

/ (integer division if both operands are ints)

Math.Pow(x, y)

Assignment

= += -= *= /= %= &= |= ^= <<= >>= ++ --

Bitwise

& | ^ ~ << >>

Logical

&& || & | ^ !

Note: && and || perform short-circuit logical evaluations

String Concatenation

+

Choices

' Ternary/Conditional operator (Iff evaluates 2nd and 3rd expressions)

greeting = If(age < 20, "What's up?", "Hello")

' One line doesn't require "End If"

If age < 20 Then greeting = "What's up?"

If age < 20 Then greeting = "What's up?" Else greeting = "Hello"

' Use : to put two commands on same line

If x <> 100 AndAlso y < 5 Then x *= 5 : y *= 2

' Preferred

If x <> 100 AndAlso y < 5 Then

x *= 5

y *= 2

End If

' Use _ to break up long single line or implicit line break

If whenYouHaveAReally < longLine And

itNeedsToBeBrokenInto2 > Lines Then _

UseTheUnderscore(charToBreakItUp)

'If x > 5 Then

x *= y

ElseIf x = 5 OrElse y Mod 2 = 0 Then

x += y

ElseIf x < 10 Then

x -= y

Else

x /= y

End If

Select Case color ' Must be a primitive data type

Case "pink", "red"

r += 1

Case "blue"

b += 1

Case "green"

g += 1

Case Else

other += 1

End Select

// Ternary/Conditional operator

greeting = age < 20 ? "What's up?" : "Hello";

if (age < 20)

greeting = "What's up?";

else

greeting = "Hello";

// Multiple statements must be enclosed in {}

if (x != 100 && y < 5) {

x *= 5;

y *= 2;

}

No need for _ or : since ; is used to terminate each statement.

if (x > 5)

x *= y;

else if (x == 5 || y % 2 == 0)

x += y;

else if (x < 10)

x -= y;

else

x /= y;

// Every case must end with break or goto case

switch (color) { // Must be integer or string

case "pink":

case "red": r++; break;

case "blue": b++; break;

case "green": g++; break;

default: other++; break; // break necessary on default

}

Loops

' Array or collection looping

Dim names As String() = {"Fred", "Sue", "Barney"}

For Each s As String In names

Console.WriteLine(s)

Next

' Breaking out of loops

Dim i As Integer = 0

While (True)

If (i = 5) Then Exit While

i += 1

End While

' Continue to next iteration

For i = 0 To 4

If i < 4 Then Continue For

Console.WriteLine(i) ' Only prints 4

Next

Arrays

Dim nums() As Integer = {1, 2, 3}

For i As Integer = 0 To nums.Length - 1

Console.WriteLine(nums(i))

Next

' 4 is the index of the last element, so it holds 5 elements

Dim names(4) As String

names(0) = "David"

names(5) = "Bobby" ' Throws System.IndexOutOfRangeException

' Resize the array, keeping the existing values (Preserve is optional)

ReDim Preserve names(6)

Dim twoD(rows-1, cols-1) As Single

twoD(2, 0) = 4.5

Dim jagged()() As Integer = { _

New Integer(4) {}, New Integer(1) {}, New Integer(2) {} }

jagged(0)(4) = 5

int[] nums = {1, 2, 3};

for (int i = 0; i < nums.Length; i++)

Console.WriteLine(nums[i]);

// 5 is the size of the array

string[] names = new string[5];

names[0] = "David";

names[5] = "Bobby"; // Throws System.IndexOutOfRangeException

// C# can't dynamically resize an array. Just copy into new array.

string[] names2 = new string[7];

Array.Copy(names, names2, names.Length); // or names.CopyTo(names2, 0);

float[,] twoD = new float[rows, cols];

twoD[2,0] = 4.5f;

int[][] jagged = new int[3][] {

new int[5], new int[2], new int[3] };

jagged[0][4] = 5;

Functions

' Pass by value (in, default), reference (in/out), and reference (out)

Sub TestFunc(ByVal x As Integer, ByRef y As Integer, ByRef z As Integer)

x += 1

y += 1

z = 5

End Sub

Dim a = 1, b = 1, c As Integer ' c set to zero by default

TestFunc(a, b, c)

Console.WriteLine("{0} {1} {2}", a, b, c) ' 1 2 5

' Accept variable number of arguments

Function Sum(ByVal ParamArray nums As Integer()) As Integer

Sum = 0

For Each i As Integer In nums

Sum += i

Next

End Function ' Or use Return statement like C#

Dim total As Integer = Sum(4, 3, 2, 1) ' returns 10

' Optional parameters must be listed last and must have a default value

Sub SayHello(ByVal name As String, Optional ByVal prefix As String = "")

Console.WriteLine("Greetings, " & prefix & " " & name)

End Sub

SayHello("Strangelove", "Dr.")

SayHello("Mom")

// Pass by value (in, default), reference (in/out), and reference (out)

void TestFunc(int x, ref int y, out int z) {

x++;

y++;

z = 5;

}

int a = 1, b = 1, c; // c doesn't need initializing

TestFunc(a, ref b, out c);

Console.WriteLine("{0} {1} {2}", a, b, c); // 1 2 5

// Accept variable number of arguments

int Sum(params int[] nums) {

int sum = 0;

foreach (int i in nums)

sum += i;

return sum;

}

int total = Sum(4, 3, 2, 1); // returns 10

/* C# 4.0 supports optional parameters. Previous versions required function overloading. */

void SayHello(string name, string prefix = "") {

Console.WriteLine("Greetings, " + prefix + " " + name);

}

SayHello("Strangelove", "Dr.");

SayHello("Mom");

Strings

Special character constants (all also accessible from ControlChars class)

vbCrLf, vbCr, vbLf, vbNewLine

vbNullString

vbTab

vbBack

vbFormFeed

vbVerticalTab

""

' String concatenation (use & or +)

Dim school As String = "Harding" & vbTab

school = school & "University" ' school is "Harding (tab) University"

' Chars

Dim letter As Char = school.Chars(0) ' letter is H

letter = "Z"c ' letter is Z

letter = Convert.ToChar(65) ' letter is A

letter = Chr(65) ' same thing

Dim word() As Char = school.ToCharArray() ' word holds Harding

' No string literal operator

Dim msg As String = "File is c:\temp\x.dat"

' String comparison

Dim mascot As String = "Bisons"

If (mascot = "Bisons") Then ' true

If (mascot.Equals("Bisons")) Then ' true

If (mascot.ToUpper().Equals("BISONS")) Then ' true

If (mascot.CompareTo("Bisons") = 0) Then ' true

' String matching with Like - Regex is more powerful

If ("John 3:16" Like "Jo[Hh]? #:*") Then 'true

' Substring

s = mascot.Substring(2, 3)) ' s is "son"

' Replacement

s = mascot.Replace("sons", "nomial")) ' s is "Binomial"

' Split

Dim names As String = "Michael,Dwight,Jim,Pam"

Dim parts() As String = names.Split(",".ToCharArray()) ' One name in each slot

' Date to string

Dim dt As New DateTime(1973, 10, 12)

Dim s As String = "My birthday: " & dt.ToString("MMM dd, yyyy") ' Oct 12, 1973

' Integer to String

Dim x As Integer = 2

Dim y As String = x.ToString() ' y is "2"

' String to Integer

Dim x As Integer = Convert.ToInt32("-5") ' x is -5

' Mutable string

Dim buffer As New System.Text.StringBuilder("two ")

buffer.Append("three ")

buffer.Insert(0, "one ")

buffer.Replace("two", "TWO")

Console.WriteLine(buffer) ' Prints "one TWO three"

Escape sequences

\r // carriage-return

\n // line-feed

\t // tab

\\ // backslash

\" // quote

// String concatenation

string school = "Harding\t";

school = school + "University"; // school is "Harding (tab) University"

// Chars

char letter = school[0]; // letter is H

letter = 'Z'; // letter is Z

letter = Convert.ToChar(65); // letter is A

letter = (char)65; // same thing

char[] word = school.ToCharArray(); // word holds Harding

// String literal

string msg = @"File is c:\temp\x.dat";

// same as

string msg = "File is c:\\temp\\x.dat";

// String comparison

string mascot = "Bisons";

if (mascot == "Bisons") // true

if (mascot.Equals("Bisons")) // true

if (mascot.ToUpper().Equals("BISONS")) // true

if (mascot.CompareTo("Bisons") == 0) // true

// String matching - No Like equivalent, use Regex

// Substring

s = mascot.Substring(2, 3)) // s is "son"

// Replacement

s = mascot.Replace("sons", "nomial")) // s is "Binomial"

// Split

string names = "Michael,Dwight,Jim,Pam";

string[] parts = names.Split(",".ToCharArray()); // One name in each slot

// Date to string

DateTime dt = new DateTime(1973, 10, 12);

string s = dt.ToString("MMM dd, yyyy"); // Oct 12, 1973

// int to string

int x = 2;

string y = x.ToString(); // y is "2"

// string to int

int x = Convert.ToInt32("-5"); // x is -5

// Mutable string

System.Text.StringBuilder buffer = new System.Text.StringBuilder("two ");

buffer.Append("three ");

buffer.Insert(0, "one ");

buffer.Replace("two", "TWO");

Console.WriteLine(buffer); // Prints "one TWO three"

Regular Expressions

Imports System.Text.RegularExpressions

' Match a string pattern

Dim r As New Regex("j[aeiou]h?. \d:*", RegexOptions.IgnoreCase Or _

RegexOptions.Compiled)

If (r.Match("John 3:16").Success) Then 'true

Console.WriteLine("Match")

End If

' Find and remember all matching patterns

Dim s As String = "My number is 305-1881, not 305-1818."

Dim r As New Regex("(\d+-\d+)")

Dim m As Match = r.Match(s) ' Matches 305-1881 and 305-1818

While m.Success

Console.WriteLine("Found number: " & m.Groups(1).Value & " at position " _

& m.Groups(1).Index.ToString)

m = m.NextMatch()

End While

' Remeber multiple parts of matched pattern

Dim r As New Regex("(\d\d):(\d\d) (am|pm)")

Dim m As Match = r.Match("We left at 03:15 pm.")

If m.Success Then

Console.WriteLine("Hour: " & m.Groups(1).ToString) ' 03

Console.WriteLine("Min: " & m.Groups(2).ToString) ' 15

Console.WriteLine("Ending: " & m.Groups(3).ToString) ' pm

End If

' Replace all occurrances of a pattern

Dim r As New Regex("h\w+?d", RegexOptions.IgnoreCase)

Dim s As String = r.Replace("I heard this was HARD!", "easy") ' I easy this was easy!

' Replace matched patterns

Dim s As String = Regex.Replace("123 < 456", "(\d+) . (\d+)", "$2 > $1") ' 456 > 123

' Split a string based on a pattern

Dim names As String = "Michael, Dwight, Jim, Pam"

Dim r As New Regex(",\s*")

Dim parts() As String = r.Split(names) ' One name in each slot

using System.Text.RegularExpressions;

// Match a string pattern

Regex r = new Regex(@"j[aeiou]h?. \d:*", RegexOptions.IgnoreCase |

RegexOptions.Compiled);

if (r.Match("John 3:16").Success) // true

Console.WriteLine("Match");

// Find and remember all matching patterns

string s = "My number is 305-1881, not 305-1818.";

Regex r = new Regex("(\\d+-\\d+)");

// Matches 305-1881 and 305-1818

for (Match m = r.Match(s); m.Success; m = m.NextMatch())

Console.WriteLine("Found number: " + m.Groups[1] + " at position " +

m.Groups[1].Index);

// Remeber multiple parts of matched pattern

Regex r = new Regex("@(\d\d):(\d\d) (am|pm)");

Match m = r.Match("We left at 03:15 pm.");

if (m.Success) {

Console.WriteLine("Hour: " + m.Groups[1]); // 03

Console.WriteLine("Min: " + m.Groups[2]); // 15

Console.WriteLine("Ending: " + m.Groups[3]); // pm

}

// Replace all occurrances of a pattern

Regex r = new Regex("h\\w+?d", RegexOptions.IgnoreCase);

string s = r.Replace("I heard this was HARD!", "easy")); // I easy this was easy!

// Replace matched patterns

string s = Regex.Replace("123 < 456", @"(\d+) . (\d+)", "$2 > $1"); // 456 > 123

// Split a string based on a pattern

string names = "Michael, Dwight, Jim, Pam";

Regex r = new Regex(@",\s*");

string[] parts = r.Split(names); // One name in each slot

Exception Handling

' Throw an exception

Dim ex As New Exception("Something is really wrong.")

Throw ex

' Catch an exception

Try

y = 0

x = 10 / y

Catch ex As Exception When y = 0 ' Argument and When is optional

Console.WriteLine(ex.Message)

Finally

Beep()

End Try

' Deprecated unstructured error handling

On Error GoTo MyErrorHandler

...

MyErrorHandler: Console.WriteLine(Err.Description)

// Throw an exception

Exception up = new Exception("Something is really wrong.");

throw up; // ha ha

// Catch an exception

try {

y = 0;

x = 10 / y;

}

catch (Exception ex) { // Argument is optional, no "When" keyword

Console.WriteLine(ex.Message);

}

finally {

Microsoft.VisualBasic.Interaction.Beep();

}

Namespaces

Namespace Harding.Compsci.Graphics

...

End Namespace

' or

Namespace Harding

Namespace Compsci

Namespace Graphics

...

End Namespace

End Namespace

End Namespace

Imports Harding.Compsci.Graphics

namespace Harding.Compsci.Graphics {

...

}

// or

namespace Harding {

namespace Compsci {

namespace Graphics {

...

}

}

}

using Harding.Compsci.Graphics;

Classes / Interfaces

Access Modifiers

Public

Private

Friend

Protected

Protected Friend

Class Modifiers

MustInherit

NotInheritable

Method Modifiers

MustOverride

NotInheritable

Shared

Overridable

' All members are Shared

Module

' Partial classes

Partial Class Competition

...

End Class

' Inheritance

Class FootballGame

Inherits Competition

...

End Class

' Interface definition

Interface IAlarmClock

Sub Ring()

Property TriggerDateTime() As DateTime

End Interface

' Extending an interface

Interface IAlarmClock

Inherits IClock

...

End Interface

' Interface implementation

Class WristWatch

Implements IAlarmClock, ITimer

Public Sub Ring() Implements IAlarmClock.Ring

Console.WriteLine("Wake up!")

End Sub

Public Property TriggerDateTime As DateTime Implements IAlarmClock.TriggerDateTime

...

End Class

Access Modifiers

public

private

internal

protected

protected internal

Class Modifiers

abstract

sealed

static

Method Modifiers

abstract

sealed

static

virtual

No Module equivalent - just use static class

// Partial classes

partial class Competition {

...

}

// Inheritance

class FootballGame : Competition {

...

}

// Interface definition

interface IAlarmClock {

void Ring();

DateTime CurrentDateTime { get; set; }

}

// Extending an interface

interface IAlarmClock : IClock {

...

}

// Interface implementation

class WristWatch : IAlarmClock, ITimer {

public void Ring() {

Console.WriteLine("Wake up!");

}

public DateTime TriggerDateTime { get; set; }

...

}

Constructors / Destructors

Class SuperHero

Private powerLevel As Integer

Public Sub New()

powerLevel = 0

End Sub

Public Sub New(ByVal powerLevel As Integer)

Me.powerLevel = powerLevel

End Sub

Shared Sub New()

' Shared constructor invoked before 1st instance is created

End Sub

Protected Overrides Sub Finalize()

' Destructor to free unmanaged resources

MyBase.Finalize()

End Sub

End Class

class SuperHero {

private int powerLevel;

public SuperHero() {

powerLevel = 0;

}

public SuperHero(int powerLevel) {

this.powerLevel = powerLevel;

}

static SuperHero() {

// Static constructor invoked before 1st instance is created

}

~SuperHero() {

// Destructor implicitly creates a Finalize method

}

}

Using Objects

Dim hero As SuperHero = New SuperHero

' or

Dim hero As New SuperHero

With hero

.Name = "SpamMan"

.PowerLevel = 3

End With

hero.Defend("Laura Jones")

hero.Rest() ' Calling Shared method

' or

SuperHero.Rest()

Dim hero2 As SuperHero = hero ' Both reference the same object

hero2.Name = "WormWoman"

Console.WriteLine(hero.Name) ' Prints WormWoman

hero = Nothing ' Free the object

If hero Is Nothing Then _

hero = New SuperHero

Dim obj As Object = New SuperHero

If TypeOf obj Is SuperHero Then _

Console.WriteLine("Is a SuperHero object.")

' Mark object for quick disposal

Using reader As StreamReader = File.OpenText("test.txt")

Dim line As String = reader.ReadLine()

While Not line Is Nothing

Console.WriteLine(line)

line = reader.ReadLine()

End While

End Using

SuperHero hero = new SuperHero();

// No "With" construct

hero.Name = "SpamMan";

hero.PowerLevel = 3;

hero.Defend("Laura Jones");

SuperHero.Rest(); // Calling static method

SuperHero hero2 = hero; // Both reference the same object

hero2.Name = "WormWoman";

Console.WriteLine(hero.Name); // Prints WormWoman

hero = null ; // Free the object

if (hero == null)

hero = new SuperHero();

Object obj = new SuperHero();

if (obj is SuperHero)

Console.WriteLine("Is a SuperHero object.");

// Mark object for quick disposal

using (StreamReader reader = File.OpenText("test.txt")) {

string line;

while ((line = reader.ReadLine()) != null)

Console.WriteLine(line);

}

Structs

Structure StudentRecord

Public name As String

Public gpa As Single

Public Sub New(ByVal name As String, ByVal gpa As Single)

Me.name = name

Me.gpa = gpa

End Sub

End Structure

Dim stu As StudentRecord = New StudentRecord("Bob", 3.5)

Dim stu2 As StudentRecord = stu

stu2.name = "Sue"

Console.WriteLine(stu.name) ' Prints Bob

Console.WriteLine(stu2.name) ' Prints Sue

struct StudentRecord {

public string name;

public float gpa;

public StudentRecord(string name, float gpa) {

this.name = name;

this.gpa = gpa;

}

}

StudentRecord stu = new StudentRecord("Bob", 3.5f);

StudentRecord stu2 = stu;

stu2.name = "Sue";

Console.WriteLine(stu.name); // Prints Bob

Console.WriteLine(stu2.name); // Prints Sue

Properties

' Auto-implemented properties are new to VB10

Public Property Name As String

Public Property Size As Integer = -1 ' Default value, Get and Set both Public

' Traditional property implementation

Private mName As String

Public Property Name() As String

Get

Return mName

End Get

Set(ByVal value As String)

mName = value

End Set

End Property

' Read-only property

Private mPowerLevel As Integer

Public ReadOnly Property PowerLevel() As Integer

Get

Return mPowerLevel

End Get

End Property

' Write-only property

Private mHeight As Double

Public WriteOnly Property Height() As Double

Set(ByVal value As Double)

mHeight = If(value < 0, mHeight = 0, mHeight = value)

End Set

End Property

// Auto-implemented properties

public string Name { get; set; }

public int Size { get; protected set; } // Set default value in constructor

// Traditional property implementation

private string name;

public string Name {

get {

return name;

}

set {

name = value;

}

}

// Read-only property

private int powerLevel;

public int PowerLevel {

get {

return powerLevel;

}

}

// Write-only property

private double height;

public double Height {

set {

height = value < 0 ? 0 : value;

}

}

Delegates / Events

Delegate Sub MsgArrivedEventHandler(ByVal message As String)

Event MsgArrivedEvent As MsgArrivedEventHandler

' or to define an event which declares a delegate implicitly

Event MsgArrivedEvent(ByVal message As String)

AddHandler MsgArrivedEvent, AddressOf My_MsgArrivedCallback

' Won't throw an exception if obj is Nothing

RaiseEvent MsgArrivedEvent("Test message")

RemoveHandler MsgArrivedEvent, AddressOf My_MsgArrivedCallback

Imports System.Windows.Forms

Dim WithEvents MyButton As Button ' WithEvents can't be used on local variable

MyButton = New Button

Private Sub MyButton_Click(ByVal sender As System.Object, _

ByVal e As System.EventArgs) Handles MyButton.Click

MessageBox.Show(Me, "Button was clicked", "Info", _

MessageBoxButtons.OK, MessageBoxIcon.Information)

End Sub

delegate void MsgArrivedEventHandler(string message);

event MsgArrivedEventHandler MsgArrivedEvent;

// Delegates must be used with events in C#

MsgArrivedEvent += new MsgArrivedEventHandler(My_MsgArrivedEventCallback);

MsgArrivedEvent("Test message"); // Throws exception if obj is null

MsgArrivedEvent -= new MsgArrivedEventHandler(My_MsgArrivedEventCallback);

using System.Windows.Forms;

Button MyButton = new Button();

MyButton.Click += new System.EventHandler(MyButton_Click);

private void MyButton_Click(object sender, System.EventArgs e) {

MessageBox.Show(this, "Button was clicked", "Info",

MessageBoxButtons.OK, MessageBoxIcon.Information);

}

Generics

' Enforce accepted data type at compile-time

Dim numbers As New List(Of Integer)

numbers.Add(2)

numbers.Add(4)

DisplayList(Of Integer)(numbers)

' Subroutine can display any type of List

Sub DisplayList(Of T)(ByVal list As List(Of T))

For Each item As T In list

Console.WriteLine(item)

Next

End Sub

' Class works on any data type

Class SillyList(Of T)

Private list(10) As T

Private rand As New Random

Public Sub Add(ByVal item As T)

list(rand.Next(10)) = item

End Sub

Public Function GetItem() As T

Return list(rand.Next(10))

End Function

End Class

' Limit T to only types that implement IComparable

Function Maximum(Of T As IComparable)(ByVal ParamArray items As T()) As T

Dim max As T = items(0)

For Each item As T In items

If item.CompareTo(max) > 0 Then max = item

Next

Return max

End Function

// Enforce accepted data type at compile-time

List<int> numbers = new List<int>();

numbers.Add(2);

numbers.Add(4);

DisplayList<int>(numbers);

// Function can display any type of List

void DisplayList<T>(List<T> list) {

foreach (T item in list)

Console.WriteLine(item);

}

// Class works on any data type

class SillyList<T> {

private T[] list = new T[10];

private Random rand = new Random();

public void Add(T item) {

list[rand.Next(10)] = item;

}

public T GetItem() {

return list[rand.Next(10)];

}

}

// Limit T to only types that implement IComparable

T Maximum<T>(params T[] items) where T : IComparable<T> {

T max = items[0];

foreach (T item in items)

if (item.CompareTo(max) > 0)

max = item;

return max;

}

LINQ

Dim nums() As Integer = {5, 8, 2, 1, 6}

' Get all numbers in the array above 4

Dim results = From value In nums

Where value > 4

Select value

Console.WriteLine(results.Count()) ' 3

Console.WriteLine(results.First()) ' 5

Console.WriteLine(results.Last()) ' 6

Console.WriteLine(results.Average()) ' 6.33333

' Displays 5 8 6

For Each n As Integer In results

Console.Write(n & " ")

Next

results = results.Intersect({5, 6, 7}) ' 5 6

results = results.Concat({5, 1, 5}) ' 5 6 5 1 5

results = results.Distinct() ' 5 6 1

Dim Students() As Student = {

New Student With {.Name = "Bob", .GPA = 3.5},

New Student With {.Name = "Sue", .GPA = 4.0},

New Student With {.Name = "Joe", .GPA = 1.9}

}

' Get an ordered list of all students by GPA with GPA >= 3.0

Dim goodStudents = From s In Students

Where s.GPA >= 3.0

Order By s.GPA Descending

Select s

Console.WriteLine(goodStudents.First.Name) ' Sue

int[] nums = { 5, 8, 2, 1, 6 };

// Get all numbers in the array above 4

var results = from value in nums

where value > 4

select value;

Console.WriteLine(results.Count()); // 3

Console.WriteLine(results.First()); // 5

Console.WriteLine(results.Last()); // 6

Console.WriteLine(results.Average()); // 6.33333

// Displays 5 8 6

foreach (int n in results)

Console.Write(n + " ");

results = results.Intersect(new[] {5, 6, 7}); // 5 6

results = results.Concat(new[] {5, 1, 5}); // 5 6 5 1 5

results = results.Distinct(); // 5 6 1

Student[] Students = {

new Student{ Name = "Bob", GPA = 3.5 },

new Student{ Name = "Sue", GPA = 4.0 },

new Student{ Name = "Joe", GPA = 1.9 }

};

// Get an ordered list of all students by GPA with GPA >= 3.0

var goodStudents = from s in Students

where s.GPA >= 3.0

orderby s.GPA descending

select s;

Console.WriteLine(goodStudents.First().Name); // Sue

Console I/O

Console.Write("What's your name? ")

Dim name As String = Console.ReadLine()

Console.Write("How old are you? ")

Dim age As Integer = Val(Console.ReadLine())

Console.WriteLine("{0} is {1} years old.", name, age)

' or

Console.WriteLine(name & " is " & age & " years old.")

Dim c As Integer

c = Console.Read() ' Read single char

Console.WriteLine(c) ' Prints 65 if user enters "A"

Console.Write("What's your name? ");

string name = Console.ReadLine();

Console.Write("How old are you? ");

int age = Convert.ToInt32(Console.ReadLine());

Console.WriteLine("{0} is {1} years old.", name, age);

// or

Console.WriteLine(name + " is " + age + " years old.");

int c = Console.Read(); // Read single char

Console.WriteLine(c); // Prints 65 if user enters "A"

File I/O

Imports System.IO

' Write out to text file

Dim writer As StreamWriter = File.CreateText("c:\myfile.txt")

writer.WriteLine("Out to file.")

writer.Close()

' Read all lines from text file

Dim reader As StreamReader = File.OpenText("c:\myfile.txt")

Dim line As String = reader.ReadLine()

While Not line Is Nothing

Console.WriteLine(line)

line = reader.ReadLine()

End While

reader.Close()

' Write out to binary file

Dim str As String = "Text data"

Dim num As Integer = 123

Dim binWriter As New BinaryWriter(File.OpenWrite("c:\myfile.dat"))

binWriter.Write(str)

binWriter.Write(num)

binWriter.Close()

' Read from binary file

Dim binReader As New BinaryReader(File.OpenRead("c:\myfile.dat"))

str = binReader.ReadString()

num = binReader.ReadInt32()

binReader.Close()

using System.IO;

// Write out to text file

StreamWriter writer = File.CreateText("c:\\myfile.txt");

writer.WriteLine("Out to file.");

writer.Close();

// Read all lines from text file

StreamReader reader = File.OpenText("c:\\myfile.txt");

string line = reader.ReadLine();

while (line != null) {

Console.WriteLine(line);

line = reader.ReadLine();

}

reader.Close();

// Write out to binary file

string str = "Text data";

int num = 123;

BinaryWriter binWriter = new BinaryWriter(File.OpenWrite("c:\\myfile.dat"));

binWriter.Write(str);

binWriter.Write(num);

binWriter.Close();

// Read from binary file

BinaryReader binReader = new BinaryReader(File.OpenRead("c:\\myfile.dat"));

str = binReader.ReadString();

num = binReader.ReadInt32();

binReader.Close();