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VB.Net - Nested嵌套循环

2022-06-02 15:13 更新

VB.Net允许在另一个循环内使用一个循环。以下部分显示了几个例子来说明这个概念。

语法：

VB.Net中嵌套For循环语句的语法如下：

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中嵌套While循环语句的语法如下：

While condition1
    While condition2
    ...
    End While
End While

VB.Net中嵌套Do ... While循环语句的语法如下：

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

关于循环嵌套的最后一点是，你可以把任何类型的循环放在任何其他类型的循环里面。例如，for循环可以在while循环内，反之亦然。

示例：

以下程序使用嵌套for循环来查找从2到100的素数：

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

当上述代码被编译和执行时，它产生以下结果：

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

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