VB.NET and C# 语法比较手册

''''  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")

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 {
   ...
}

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