语言比较之： VB.NET 和 C#

VB.NET

Program Structure

C#

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 + "!");
      }
   }
}

VB.NET

Comments

C#

' Single line only
Rem Single line only

// Single line
/* Multiple
    line  */
/// XML comments on single line
/** XML comments on multiple lines */

VB.NET

Data Types

C#

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(GetType(Integer))   ' 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
Console.WriteLine(x.GetType().Name);   // prints Int32

// Type conversion
float d = 3.5f;
int i = (int)d;   // set to 3  (truncates decimal)

VB.NET

Constants

C#

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;

VB.NET

Enumerations

C#

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

VB.NET

Operators

C#

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
+

VB.NET

Choices

C#

greeting = IIf(age < 20, "What's up?", "Hello")

' One line doesn't require "End If"
If age < 20 Then greeting = "What's up?"
If age < 20 Then greeting = "What's up?" Else greeting = "Hello"

' 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

' To break up any long single line 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 (age < 20)
  greeting = "What's up?";
else
  greeting = "Hello";

// Multiple statements must be enclosed in {}
if (x != 100 && y < 5) {   
  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;

// Every case must end with break or goto case
switch (color) {                          // Must be integer or string
  case "pink":
  case "red":    r++;    break;
  case "blue":   b++;   break;
  case "green": g++;   break;
  default:    other++;   break;       // break necessary on default
}

VB.NET

Loops

C#

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

 

' Continue to next iteration
For i = 0 To 4
  If i < 4 Then Continue For
  Console.WriteLine(i)   ' Only prints 4
Next

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++;
}

// Continue to next iteration
for (i = 0; i < 5; i++) {
  if (i < 4)
    continue;
  Console.WriteLine(i);   // Only prints 4
}

VB.NET

Arrays

C#

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;

VB.NET

Functions

C#

' 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, "");
}

VB.NET

Strings

C#

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")

' 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"

VB.NET

Exception Handling

C#

' 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();
}

VB.NET

Namespaces

C#

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;

VB.NET

Classes / Interfaces

C#

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 {
   ...
}

VB.NET

Constructors / Destructors

C#

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
  }
}

VB.NET

Using Objects

C#

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 Is Nothing Then _
  hero = New SuperHero

Dim obj As Object = New SuperHero
If TypeOf obj Is SuperHero Then _
  Console.WriteLine("Is a SuperHero object.")

' Mark object for quick disposal
Using reader As StreamReader = File.OpenText("test.txt")
  Dim line As String = reader.ReadLine()
  While Not line Is Nothing
    Console.WriteLine(line)
    line = reader.ReadLine()
  End While
End Using

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.");

// Mark object for quick disposal
using (StreamReader reader = File.OpenText("test.txt")) {
  string line;
  while ((line = reader.ReadLine()) != null)
    Console.WriteLine(line);
}

VB.NET

Structs

C#

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

VB.NET

Properties

C#

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++;

VB.NET

Delegates / Events

C#

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);
}

VB.NET

Console I/O

C#

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"

VB.NET

File I/O

C#

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();