VB.NET and C# 语法比较手册

VB.NET and C# Comparison This is a quick reference guide to highlight some key syntactical differences between VB.NETand C#. Hope you find this useful! Thank you to Tom Shelton, Fergus Cooney, and others for your input.

VB.NET C# Comments ' Single line only Rem Single line only

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

Data Types

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 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)

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

Constants Const MAX_STUDENTS As Integer = 25 const int MAX_STUDENTS = 25; 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)     ' Prints 1 Console.WriteLine(Status.Pass)     ' Prints 70 Dim s As Type = GetType(Status) Console.WriteLine([Enum].GetName(s, Status.Pass))    ' 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(Status.Pass);    // Prints Pass Operators

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 +

Choices

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 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 }

Loops Pre-test Loops: While c < 10   c += 1 End While

Do Until c = 10    c += 1 Loop

Do While c < 10   c += 1 Loop

For c = 2 To 10 Step 2   Console.WriteLine(c) Next

Post-test Loops: Do    c += 1 Loop While c < 10 Do    c += 1 Loop Until c = 10

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

Pre-test Loops:  

// 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);

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# 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;

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("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, ""); }

Exception Handling

' 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 }

Namespaces

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;

Classes / Interfaces

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 {    ... }

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   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   } }

Objects

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.");

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

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++;

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); }

Console I/O

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"

File I/O

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();