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VB.NET

C#

Reference Types
Object
String
　

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

' Type conversion
Dim numDecimal As Single = 3.5
Dim numInt As Integer
numInt = CType(numDecimal, Integer)   ' set to 4 (Banker's rounding)
numInt = CInt(numDecimal)  ' same result as CType
numInt = Int(numDecimal)    ' set to 3 (Int function truncates the decimal)

Reference Types
object
string
　

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

// Type conversion
double numDecimal = 3.5;
int numInt = (int) numDecimal;   // set to 3  (truncates decimal)

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
&

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
+

' 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 Then x *= 5 : y *= 2  

' 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

if (x != 100) {    // 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 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

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;

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("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, "");
}

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
　

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
}

' or

Namespace Harding
  Namespace Compsci
    Namespace Graphics 
      ...
    End Namespace
  End Namespace
End Namespace

Import Harding.Compsci.Graphics

// or

namespace Harding {
  namespace Compsci {
    namespace Graphics {
      ...
    }
  }
}

using Harding.Compsci.Graphics;

' 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 

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

// Interface definition
interface IAlarmClock {
  ...
}

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

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

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.")

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.");

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

foo.Size += 1

foo.Size++;

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

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);
}

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"

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"

Dim writer As StreamWriter = File.CreateText("c:\myfile.txt")
writer.WriteLine("Out to file.")
writer.Close()

Dim reader As StreamReader = File.OpenText("c:\myfile.txt")
Dim line As String = reader.ReadLine()
While Not line Is Nothing
  Console.WriteLine("line=" & line)
  line = reader.ReadLine()
End While
reader.Close()

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()

Dim binReader As New BinaryReader (File.OpenRead("c:\myfile.dat"))
str = binReader.ReadString()
num = binReader.ReadInt32()
binReader.Close()

StreamWriter writer = File.CreateText("c:\\myfile.txt");
writer.WriteLine("Out to file.");
writer.Close();

StreamReader reader = File.OpenText("c:\\myfile.txt");
string line = reader.ReadLine();
while (line != null) {
  Console.WriteLine(line);
  line = reader.ReadLine();
}
reader.Close();

string str = "Text data";
int num = 123;
BinaryWriter binWriter = new BinaryWriter(File.OpenWrite("c:\\myfile.dat"));
binWriter.Write(str);
binWriter.Write(num);
binWriter.Close();

BinaryReader binReader = new BinaryReader(File.OpenRead("c:\\myfile.dat"));
str = binReader.ReadString();
num = binReader.ReadInt32();
binReader.Close();

    在向你挥舞的各色花帕中
    是谁的手突然收回
    紧紧捂住了自己的眼睛
    当人们四散离去, 谁
    还站在船尾
    衣裙漫飞, 如翻涌不息的云
    江涛
    高一声
    低一声

    美丽的梦留下美丽的忧伤
    人间天上, 代代相传
    但是, 心
    真能变成石头吗
    为了眺望天上来鸿
    而错过无数人间月明

    沿着江峰
    金光菊和女贞子的洪流
    正煽动着新的背叛
    与其在悬崖上展览千年
    不如在爱人肩头痛哭一晚

1981年6月于长江