VB.NET and C# 差异

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VB.NET and C# 差异

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(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

// 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", no "Else" If language = "VB.NET" Then langType = "verbose"

' 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

' 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 && y < 5) { // 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 }

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

' Breaking out of loops Dim i As Integer = 0 While (True) If (i = 5) Then Exit While i += 1 End While

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++; }

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") Console.WriteLine(s)

' 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.")

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.");

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();

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