VB.NET and C# 语法比较手册

VB.NET

C#

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

Value TypesBooleanByteChar   (example: "A"c)Short, Integer, LongSingle, DoubleDecimalDate

Reference TypesObjectString

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

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

Value Typesboolbyte, sbytechar   (example: 'A')short, ushort, int, uint, long, ulongfloat, doubledecimalDateTime   (not a built-in C# type)

Reference Typesobjectstring

int x;Console.WriteLine(x.GetType());    // Prints System.Int32Console.WriteLine(typeof(int));      // Prints System.Int32

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

Comparison=  <  >  <=  >=  <>

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

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

BitwiseAnd  AndAlso  Or  OrElse  Not  <<  >>

LogicalAnd  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 lineIf 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

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

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 loopingDim names As String() = {"Fred", "Sue", "Barney"} For Each s As String In names   Console.WriteLine(s) Next

// no "until" keywordwhile (i < 10)   i++;for (i = 2; i < = 10; i += 2)   Console.WriteLine(i);

Post-test Loop:do   i++; while (i < 10);// Array or collection loopingstring[] 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 elementsDim 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) = 4.5Dim 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 arraystring[] names = new string[5];names[0] = "David";names[5] = "Bobby";   // Throws System.IndexOutOfRangeException // C# doesn't 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 SubSayHello("Strangelove", "Dr.")SayHello("Madonna")

int a = 1, b = 1, c;  // c doesn't need initializingTestFunc(a, ref b, out c);Console.WriteLine("{0} {1} {2}", a, b, c);  // 1 2 5

// Accept variable number of argumentsint 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 handlingOn Error GoTo MyErrorHandler...MyErrorHandler: Console.WriteLine(Err.Description)Dim ex As New Exception("Something is really wrong.") Throw  ex 

Try   y = 0  x = 10 / yCatch 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

Import Harding.Compsci.Graphics

namespace Harding.Compsci.Graphics {  ...}

// or

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

using Harding.Compsci.Graphics;

Accessibility keywords PublicPrivateFriend                    ProtectedProtected FriendShared

' InheritanceClass FootballGame  Inherits Competition  ...End Class 

' Interface definitionInterface IAlarmClock   ...End Interface

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

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

Accessibility keywords publicprivateinternalprotectedprotected internalstatic

// Inheritanceclass FootballGame : Competition {  ...}

// Interface definitioninterface IAlarmClock {  ...}

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

// Interface implementationclass 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' orSuperHero.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" constructhero.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 BobConsole.WriteLine(stu2.name);   // Prints Sue

Private _size As IntegerPublic 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 implicitlyEvent MsgArrivedEvent(ByVal message As String)

AddHandler MsgArrivedEvent, AddressOf My_MsgArrivedCallback ' Won't throw an exception if obj is NothingRaiseEvent MsgArrivedEvent("Test message") RemoveHandler MsgArrivedEvent, AddressOf My_MsgArrivedCallback

Imports System.Windows.Forms

Dim WithEvents MyButton As Button   ' WithEvents can't be used on local variableMyButton = 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 nullMsgArrivedEvent -= 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 constantsvbCrLf, 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);// orConsole.WriteLine(name + " is " + age + " years old.");

int c = Console.Read();  // Read single charConsole.WriteLine(c);    // Prints 65 if user enters "A"

Imports System.IO

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()

using System.IO;

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();