VB.Net - 巢狀迴圈

VB.Net 允許在一個迴圈內使用另一個迴圈。以下部分顯示了一些示例來說明這個概念。

語法

VB.Net 中巢狀 For 迴圈語句的語法如下：

For counter1 [ As datatype1 ] = start1 To end1 [ Step step1 ]
   For counter2 [ As datatype2 ] = start2 To end2 [ Step step2 ]
      ...
   Next [ counter2 ]
Next [ counter 1]

VB.Net 中巢狀 While 迴圈語句的語法如下：

While condition1
   While condition2
      ...
   End While
End While

VB.Net 中巢狀 Do...While 迴圈語句的語法如下：

Do { While | Until } condition1
   Do { While | Until } condition2
      ...
   Loop
Loop

關於迴圈巢狀的最後一點說明是，您可以在任何型別的迴圈內放入任何其他型別的迴圈。例如，For 迴圈可以在 While 迴圈內，反之亦然。

示例

以下程式使用巢狀 For 迴圈查詢 2 到 100 之間的素數：

Module loops
   Sub Main()
      ' local variable definition 
      Dim i, j As Integer
      For i = 2 To 100
         For j = 2 To i
            ' if factor found, not prime
            If ((i Mod j) = 0) Then
               Exit For
            End If
         Next j
            If (j > (i \ j)) Then
               Console.WriteLine("{0} is prime", i)
            End If
         Next i
      Console.ReadLine()
   End Sub
End Module

當以上程式碼編譯並執行時，它會產生以下結果：

2 is prime
3 is prime
5 is prime
7 is prime
11 is prime
13 is prime
17 is prime
19 is prime
23 is prime
29 is prime
31 is prime
37 is prime
41 is prime
43 is prime
47 is prime
53 is prime
59 is prime
61 is prime
67 is prime
71 is prime
73 is prime
79 is prime
83 is prime
89 is prime
97 is prime