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VB.NET

C#

// Single line
/* Multiple
    line  */
/// XML comments on single line
/** XML comments on multiple lines */

Value Types
Boolean
Byte
Char   (example: "A"c)
Short, Integer, Long
Single, Double
Decimal
Date

Reference Types
Object
String

Dim x As Integer 
Console.WriteLine(x.GetType())     ' Prints System.Int32 
Console.WriteLine(TypeName(x))  ' Prints Integer

' Type conversion
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)

Value Types
bool
byte, sbyte
char   (example: 'A')
short, ushort, int, uint, long, ulong
float, double
decimal
DateTime   (not a built-in C# type)

Reference Types
object
string

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

// Type conversion 
float d = 3.5f; 
int i = (int) d;   // set to 3  (truncates decimal)

' Can be set to a const or a variable. May be initialized in a constructor. 
ReadOnly MIN_DIAMETER As Single = 4.93

// Can be set to a const or a variable. May be initialized in a constructor. 
readonly float MIN_DIAMETER = 4.93f;

Comparison
=  <  >  <=  >=  <>

Arithmetic
+  -  *  /
Mod
\  (integer division)
^  (raise to a power)

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

Bitwise
And  AndAlso  Or  OrElse  Not  <<  >>

Logical
And  AndAlso  Or  OrElse  Not

Note: AndAlso and OrElse are for short-circuiting 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
+

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

' One line doesn't require "End If", no "Else"
If language = "VB.NET" Then langType = "verbose"

' Use : to put two commands on same line
If x <> 100 And y < 5 Then x *= 5 : y *= 2  

' Preferred
If x <> 100 And y < 5 Then
  x *= 5 
  y *= 2
End If

' or to break up any long single command use _
If whenYouHaveAReally < longLine And itNeedsToBeBrokenInto2 > Lines Then _
  UseTheUnderscore(charToBreakItUp)

'If x > 5 Then 
  x *= y 
ElseIf x = 5 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

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

if (x != 100 && y < 5) {    // Multiple statements must be enclosed in {}
  x *= 5;
  y *= 2;
}

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

if (x > 5) 
  x *= y; 
else if (x == 5) 
  x += y; 
else if (x < 10) 
  x -= y; 
else 
  x /= y;

switch (color) {                          // Must be integer or string
  case "pink":
  case "red":    r++;    break;        // break is mandatory; no fall-through
  case "blue":   b++;   break;
  case "green": g++;   break;
  default:    other++;   break;       // break necessary on default
}

'  Array or collection looping
Dim names As String() = {"Fred", "Sue", "Barney"} 
For Each s As String In names 
  Console.WriteLine(s) 
Next

// no "until" keyword
while (i < 10) 
  i++;

for (i = 2; i < = 10; i += 2) 
  Console.WriteLine(i);

Post-test Loop:

do 
  i++; 
while (i < 10);



// Array or collection looping
string[] names = {"Fred", "Sue", "Barney"};
foreach (string s in names)
  Console.WriteLine(s);

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;

' 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 AsInteger()) 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, OptionalByVal prefix As String = "")
  Console.WriteLine("Greetings, " & prefix & " " & name) 
End Sub

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

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# doesn't support optional arguments/parameters.  Just create two different versions of the same function. */  
void SayHello(string name, string prefix) {
  Console.WriteLine("Greetings, " + prefix + " " + name);
} 

void SayHello(string name) { 
  SayHello(name, ""); 
}

' Deprecated unstructured error handling
On Error GoTo MyErrorHandler
...
MyErrorHandler: Console.WriteLine(Err.Description)

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

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

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

try { 
  y = 0; 
  x = 10 / y; 
} 
catch (Exception ex) {   // Argument is optional, no "When" keyword 
  Console.WriteLine(ex.Message); 
} 
finally { 
  // Must use unmanaged MessageBeep API function to beep 
}

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;

Accessibility keywords 
Public
Private
Friend                    
Protected
Protected Friend
Shared

' Inheritance
Class FootballGame
  Inherits Competition
  ...
End Class 

' Interface definition
Interface IAlarmClock 
  ...
End Interface

// Extending an interface 
Interface IAlarmClock 
  Inherits IClock
  ...
End Interface

// Interface implementation
Class WristWatch 
  Implements IAlarmClock, ITimer 
   ...
End Class 

Accessibility keywords 
public
private
internal
protected
protected internal
static

// Inheritance
class FootballGame : Competition {
  ...
}

// Interface definition
interface IAlarmClock {
  ...
}

// Extending an interface 
interface IAlarmClock : IClock {
  ...
}

// Interface implementation
class WristWatch : IAlarmClock, ITimer {
   ...
}

class SuperHero {
  private int _powerLevel;

  public SuperHero() {
     _powerLevel = 0;
  }

  public SuperHero(int powerLevel) {
    this._powerLevel= powerLevel; 
  }

  ~SuperHero() {
    // Destructor code to free unmanaged resources.
    // Implicitly creates a Finalize method
  }
}

Dim hero As SuperHero = 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 refer to 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.")

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 refer to 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.");

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

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

Private _size As Integer

Public Property Size() As Integer
  Get 
    Return _size 
  End Get 
  Set (ByVal Value As Integer) 
    If Value < 0 Then 
      _size = 0 
    Else 
      _size = Value 
    End If 
  End Set 
End Property

foo.Size += 1

foo.Size++;

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, AddressOfMy_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) HandlesMyButton.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); 
}

Special character constants
vbCrLf, vbCr, vbLf, vbNewLine 
vbNullString 
vbTab 
vbBack 
vbFormFeed 
vbVerticalTab
"" 
Chr(65)  ' Returns 'A'

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"

Escape sequences
\n, \r
\t
\\
\"

Convert.ToChar(65)  // Returns 'A' - equivalent to Chr(num) in VB
// or
(char) 65

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"

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 NewBinaryWriter(File.OpenWrite("c:\myfile.dat"))  
binWriter.Write(str)  
binWriter.Write(num) 
binWriter.Close()

' Read from binary file
Dim binReader As NewBinaryReader(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();