嵌套循环

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：

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
        Proj.MsgDebug.Add("{0} is prime", i)
    End If
Next i
    
'返回结果:2 Is prime
'返回结果:3 Is prime
'返回结果:5 Is prime
'返回结果:7 Is prime
'返回结果:11 Is prime
'返回结果:13 Is prime
'返回结果:17 Is prime
'返回结果:19 Is prime
'返回结果:23 Is prime
'返回结果:29 Is prime
'返回结果:31 Is prime
'返回结果:37 Is prime
'返回结果:41 Is prime
'返回结果:43 Is prime
'返回结果:47 Is prime
'返回结果:53 Is prime
'返回结果:59 Is prime
'返回结果:61 Is prime
'返回结果:67 Is prime
'返回结果:71 Is prime
'返回结果:73 Is prime
'返回结果:79 Is prime
'返回结果:83 Is prime
'返回结果:89 Is prime
'返回结果:97 Is prime