vb.net For 循环步骤 -1
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For Loop Step -1
提问by Iswanto San
I want to know why this loop doesn't show anything in VB.NET.
我想知道为什么这个循环在 VB.NET 中没有显示任何内容。
I think this code will create an infinite loop. But it doesn't show anything.
我认为这段代码将创建一个无限循环。但它没有显示任何东西。
Dim i as Integer
For i = 1 to 3 Step - 1
MessageBox.Show(i)
Next
Is that loop different with this code (in java/c#) ?
该循环与此代码（在 java/c# 中）不同吗？
for(int i = 1;i <= 3;i--)
{
// print i
}
回答by JamesH
http://msdn.microsoft.com/en-us/library/5z06z1kb.aspxWith a negative step size the loop only executes if counter >= end. So in this case with i = 1, that is less than the ending value so the loop doesn't execute at all.
http://msdn.microsoft.com/en-us/library/5z06z1kb.aspx对于负步长，循环仅在 counter >= end 时执行。因此，在 i = 1 的情况下，它小于结束值，因此循环根本不执行。
回答by Sam Axe
It doesn't show anything because you are running the counter backwards without reversing the start and end conditions.
它没有显示任何内容，因为您在不反转开始和结束条件的情况下向后运行计数器。
Think of the loop like this:
想想这样的循环：
Dim counter As Int32 = 1
Do
If counter <= 1 Then
Exit Do
End If
Console.WriteLine("The counter is at " & counter)
counter +=1
Loop
Obviously this won't work properly. You need to reverse the start and end conditions:
显然这不会正常工作。您需要颠倒开始和结束条件：
For counter = 3 To 1 Step -1
Console.WriteLine("counter: " & counter)
Next
回答by cf stands with Monica
For i = 1 to 3 Step - 1
It won't create an infinite loop. The loop will simply be skipped, because you can't get from 1 to 3 with a step value of -1.
它不会造成无限循环。循环将被简单地跳过，因为您无法使用 -1 的步长值从 1 到 3。
Is that loop different with this code (in java/c#) ?
该循环与此代码（在 java/c# 中）不同吗？
This loop will also end immediately, because the initial value (i = 1) meets the exit condition (i <= 3).
此循环也会立即结束，因为初始值 ( i = 1) 满足退出条件 ( i <= 3)。
