.net 基础知识大杂烩(3) ——循环语句

循环语句

C# VB 输出

int i = 0; while (i <= 2) { Console.WriteLine(i); i++; }; // 这个分号可有可无	Dim i As Integer = 0 While i <= 2 Console.WriteLine(i) i += 1 End While	0 1 2
int i = 0; do { Console.WriteLine(i); i++; } while (i <= 2); // 这个分号必须写	Dim i As Integer = 0 Do Console.WriteLine(i) i += 1 Loop While i <= 2	0 1 2
/	Dim i As Integer = 0 Do Console.WriteLine(i) i += 1 Loop Until i >= 3	0 1 2
/	Dim i As Integer = 0 Do While i <= 2 Console.WriteLine(i) i += 1 Loop	0 1 2
/	Dim i As Integer = 0 Do Until i >= 3 Console.WriteLine(i) i += 1 Loop	0 1 2
/	Do Console.WriteLine("Hello") Loop	Hello Hello Hello ……无限循环
for (; ; ) { Console.WriteLine("Hello"); }	/	Hello Hello Hello ……无限循环
for (int i = 2; i >= 0; i--) { Console.WriteLine(i); }; // 这个分号可有可无	For i As Integer = 2 To 0 Step -1 Console.WriteLine(i) Next	2 1 0
int i = 0; do { for (int j = 1; j <= 10; j++) { Console.WriteLine(i.ToString() + j.ToString()); if (j >= 2) { break; } if (i >= 3) { goto enddo; } } i++; } while (true); enddo: ;	Dim i As Integer = 0 Do For j As Integer = 1 To 10 Console.WriteLine(i & j) If j >= 2 Then Exit For End If If i >= 3 Then Exit Do End If Next i += 1 Loop	01 02 11 12 21 22 31
for (int i = 1; i <= 10; i++) { if (i % 2 == 0) { continue; } Console.WriteLine(i); }	For i As Integer = 1 To 10 If (i Mod 2 = 0) Then Continue For End If Console.WriteLine(i) Next	1 3 5 7 9
int[] a = new int[] { 2, 4, 6 }; foreach (int i in a) { Console.WriteLine(i); }	Dim a() As Integer = New Integer() {2, 4, 6} For Each i As Integer In a Console.WriteLine(i) Next	2 4 6

foreach 语句的本质

foreach是一个语法糖。

IList < int > a = new List < int > ();
foreach ( int i in a)
{
Console.WriteLine(i);
}

会被编译器转换成

IList < int > a = new List < int > ();
IEnumerator < int > e = a.GetEnumerator();
try
{
while (e.MoveNext())
{
Console.WriteLine(e.Current);
}
}
finally
{
if (e != null )
e.Dispose();
}

http://www.cnblogs.com/1-2-3/archive/2008/03/10/net-basic-knowledge-3-cs-vb-for-while-statement.html