c#.NET和VB.NET语法的比较

VB.NET

C#

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 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)

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 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

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

+

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

}

' Array or collection looping

Dim names As String() = {"Fred", "Sue", "Barney"}

For Each s As String In names

Console.WriteLine(s)

Next

// 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);

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;

' 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")

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, "");

}

' 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

}

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

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 {

...

}

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

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 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 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

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

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);

}

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"

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();