Поиск слова заданной длины - Visual Basic .NET

Формулировка задачи:

Возникает исключение на 31 строке, как его исправить, и в целом?

                    Листинг программы
                
 
                            
                        
''Поиск слова заданной длины
''
Imports System.Console
Module Module1
 
    Sub Main()
        Title = "Поиск слов"
        Dim flag As Boolean = False,
        n As Integer = CInt(InputBox("Введите длину слова")),
        a As String() = input("Введите строки слов, ввод завершается пустой строкой"),
        x As Integer()() = cycle(flag, a, n)
        MsgBox(outform(x, n, flag))
        ReadKey()
    End Sub
    Function input(p As String) As String()
        Dim q As String = InputBox(p),
        a As String() = New String(0) {},
        t As Integer = 0
        While q.Length <> 0
            ReDim Preserve a(a.Length + 1)
            a(t) = q
            q = InputBox("Ввести очередную строку")
            t += 1
        End While
        Return a
    End Function
    Function outform(x As Integer()(), n As Integer, flag As Boolean)
        Dim p As String = ""
        If flag Then
            For u As Integer = 0 To x.Length - 1
                p += String.Format("Строка №{0}, индекс от {1} до {2}\n", x(u)(0), x(u)(1) - n + 1, x(u)(1))
            Next
        Else : p = "нет слов заданной длины"
        End If
        Return p
    End Function
    Function cycle(ByRef flag As Boolean, a As String(), n As Integer) As Integer()()
        Dim per As Integer = 0,
        x As Integer()() = New Integer(0)() {}
        For t As Integer = 0 To a.Length - 1
            For m As Integer = 0 To Len(a(t)) - 1
                per += 1
                If a(t)(m) = "," Then
                    If per = n Then
                        ReDim Preserve x(x.Length + 1)
                        x(x.GetUpperBound(0)) = {t, m - 1}
                        flag = True
                    End If
                    per = 0
                End If
                If m = Len(a(t)) - 1 And per = n Then
                    ReDim Preserve x(x.Length + 1)
                    x(x.GetUpperBound(0)) = {t, m}
                    flag = True
                End If
            Next
            per = 0
        Next
        Return x
    End Function
           
End Module

Решение задачи: «Поиск слова заданной длины»

textual
                            Листинг программы 
                        
 
                            
                        
Sub Main()
    Title = "Поиск слов"
    Dim flag As Boolean = False
    Dim n As Integer = CInt(InputBox("Введите длину слова"))
    Dim a As String() = inputStrings("Введите слова, ввод завершается пустой строкой")
    Dim s As String = ""
    If a.Length > 0 Then
        For i = 0 To a.Length - 1
            Dim b() As String = a(i).Split(","c)
            Dim ss As String = outform(b, n)
            If ss.Length > 0 Then s &= "строка " & i.ToString & ": " & ss & vbCrLf
        Next
        If s.Length = 0 Then s = "нет слов заданной длины"
    Else
        s = "нет списка слов"
    End If
    MsgBox(s)
    ReadKey()
End Sub
Function inputStrings(ByVal p As String) As String()
    Dim q As String = InputBox(p)
    Dim a() As String = {}
    Dim t As Integer = 0
    While q.Length <> 0
        ReDim Preserve a(t)
        a(t) = q
        q = InputBox("Ввести очередную строку")
        t += 1
    End While
    Return a
End Function
Function outform(ByVal aa() As String, ByVal n As Integer) As String
    Dim p As String = ""
    For i = 0 To aa.Length - 1
        If aa(i).Length = n Then
            p &= aa(i) & " (" & i.ToString & "), "
        End If
    Next
    Return p.TrimEnd(",", " ")
End Function