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VB.NET and C# 语法比较手册
发布日期：2021-06-30 19:00:52 浏览次数：3 分类：技术文章

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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();

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