Visual Basic .substring錯誤

Question

我是VB新手，遇到以下代碼出現問題。

Dim random As String = "asfdgasfdgasfdgasfd11" 
    Dim length As Integer = Nothing 

    length = random.Length 
    Console.WriteLine(random.Length) 
    Console.WriteLine(length) 
    Console.WriteLine() 
    Console.WriteLine() 
    Console.ReadLine() 

    If length <= 20 Then 
     Console.WriteLine(random.Substring(0, length)) 
    ElseIf length <= 40 Then 
     Console.WriteLine(random.Substring(0, 20)) 
     Console.WriteLine(random.Substring(20, length)) 
    End If 

    Console.ReadLine() 

錯誤：

" An unhandled exception of type 'System.ArgumentOutOfRangeException' occurred in mscorlib.dll

Additional information: Index and Length must refer to a location within the string "

我認爲該錯誤發生由於（20，length））。我試圖給變量分配長度，所以程序不會崩潰，除非嘗試是特定數量的字符。

我試圖讓任何給定長度的變量，如果它大於20個字符，那麼每行只能打印20個字符。

Answer 1

Additional information: Index and Length must refer to a location within the string

這就是要點。在你的第二個WriteLine中，你要求打印從第20個字符開始的random字符串（開始索引ok，有21個字符），但它要求打印21個字符（長度= 21）。
是，則startIndex +長度= 41，這是出字符串限制

的

你可以嘗試修復線與

Console.WriteLine(random.Substring(20, length - 20)) 

或引入while循環在時間打印20個字符

length = random.Length 
Console.WriteLine(random.Length) 
Console.WriteLine(length) 
Console.WriteLine() 
Console.WriteLine() 
Console.ReadLine() 

Dim curStart = 0 
Dim loopCounter = 0 
while(curStart < random.Length) 
    Console.WriteLine(random.Substring(curStart, System.Math.Min(20, length - 20 * loopCounter))) 
    curStart = curStart + 20 
    loopCounter = loopCounter + 1 
End While