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[转]c#.NET和VB.NET语法的比较

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本文转自：/article/5795713.html

c#.NET和VB.NET语法的比较

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 = 25const 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();

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