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.

Comments
Data Types
Constants
Enumerations
Operators Choices
Loops
Arrays
Functions
andling">Exception Handling Namespaces
Classes / Interfaces
Constructors / Destructors
Objects
Structs Properties
andevents">Delegates / Events
Console I/O
File I/O

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 TypesValue 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)
ConstantsConst MAX_STUDENTS As Integer = 25const int MAX_STUDENTS = 25;EnumerationsEnum 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 PassOperatorsComparison
= < > <= >= <>
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);

// 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; [i]// 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, "");
}
andling>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 / DestructorsClass 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 Classclass 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[/b]
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[/b]
if (hero == null)
hero = new SuperHero();

Object obj = new SuperHero();
if (obj is SuperHero)
Console.WriteLine("Is a SuperHero object.");
StructsStructure 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
PropertiesPrivate _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++;
andevents>Delegates / EventsDelegate 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/OSpecial 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
,

/
"
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/OImports 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();
Page last modified: 01/14/2004 05:34:59
Please send any corrections or comments to fmccown@harding.edu.
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