VB与C#的区别（转载）

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 + "!");
                  }
               }
            }

‘ Single line only
Rem Single line only

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

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

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;

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

Comparison
            =  <  >  <=  >=  <>

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

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

Bitwise
            And   Or   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
            +

greeting = IIf(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 And y < 5 Then x *= 5 : y *= 2 

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

‘ To break up any long single line 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 (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) 
              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
            }

‘  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

Pre-test Loops:

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

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

Post-test Loop:

do 
              c++; 
while (c < 10);



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

// Breaking out of loops
            int i = 0;
            while (true) {
              if (i == 5)
                break;
              i++;
            }

// Continue to next iteration
            for (i = 0; i < 5; i++) {
              if (i < 4)
                continue;
              Console.WriteLine(i);   // Only prints 4
            }

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 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")

// 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# 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, ""); 
            }

Special character constants
            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 = 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

Console.WriteLine(mascot.Substring(2, 3)) ‘ Prints "son"

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

            Imports System.Text.RegularExpressions   ‘ More powerful than Like
            Dim r As New Regex("Jo[hH]. "d:*")
            If (r.Match("John 3:16").Success) Then   ‘true

‘ My birthday: Oct 12, 1973
            Dim dt As New DateTime(1973, 10, 12)
            Dim s As String = "My birthday: " & dt.ToString("MMM dd, yyyy")

‘ 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
            "n, "r
            "t
            ""
            "" 

// String concatenation
string school = "Harding"t"; 
            school = school + "University";   // school is "Harding (tab) University"

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

Console.WriteLine(mascot.Substring(2, 3));    // Prints "son"

// String matching
// No Like equivalent - use regular expressions 

            using System.Text.RegularExpressions;
Regex r = new Regex(@"Jo[hH]. "d:*");
            if (r.Match("John 3:16").Success)   // true

// My birthday: Oct 12, 1973
            DateTime dt = new DateTime(1973, 10, 12);
            string s = "My birthday: " + dt.ToString("MMM dd, yyyy");

// 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"

‘ 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 { 
              // Requires reference to the Microsoft.VisualBasic.dll 
  // assembly (pre .NET Framework v2.0) 
              Microsoft.VisualBasic.Interaction.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 _powerLevel As Integer 

              Public Sub New() 
                _powerLevel = 0 
              End Sub 

              Public Sub New(ByVal powerLevel As Integer) 
                Me._powerLevel = powerLevel 
              End Sub

              Protected Overrides Sub Finalize() 
               ‘ Desctructor code 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; 
              }

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

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 IsNothing 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);
            }

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

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

private int _size;

            public int Size { 
              get { 
                return _size; 
              } 
              set { 
                if (value < 0) 
                  _size = 0; 
                else 
                  _size = value; 
              } 
            }

            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, 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); 
            }

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"

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();