In most cases, VB Migration Partner can infer the rank (i.e. the number of dimensions) of an array that isn't initialized in its Dim statement, as in this VB6 code:

        Dim arr() As Integer
        ' ...
        ReDim arr(10, 20) As Integer

which is correctly migrated as follows:

        ' VB.NET
        Dim arr(,) As Integer
        ' ...
        ReDim arr(10, 20) As Integer

        // C#
        int[,] arr = null;
        ' ...
        arr = new int[11,21];

In a few cases, however, it isn't possible for VB Migration Partner to infer the array rank. This happens, for example, for functions that return an array. Consider the following VB6 code:

        Sub Test()
            Dim arr() As Integer
            ' ...
            arr = GetArray()
        End Sub

        Function GetArray() As Integer()
            Dim res(3, 5) As Integer
            ' ...
            GetArray = res
        End Function

The converted .NET code has a compilation error in the line that assigns the GetArray return value, because you can't assign a 2-dim array to a vector. In fact, the GetArray method should return a 2-dim array and the arr variable should also be a 2-dim array. You can solve this issue by adding a couple of ArrayRank pragmas in the original VB6 code:

        Sub Test()
            '## arr.ArrayRank 2
            Dim arr() As Integer
            ' ...
            arr = GetArray()
        End Sub

        '## GetArray.ArrayRank 2
        Function GetArray() As Integer()
            Dim res(3, 5) As Integer
            ' ...
            GetArray = res
        End Function

which produces the following .NET code:

        ' VB.NET
        Sub Test()
            Dim arr(,) As Integer
            ' ...
            arr = GetArray()
        End Sub

        Function GetArray() As Integer(,)
            Dim res(3, 5) As Integer
            ' ...
            GetArray = res
        End Function

        // C#
        public void Test()
        {
               int[,] arr = null
            
               //...
               arr = GetArray();
         }
         public int[,]GetArray() 
         {
               int[,] res = new int[4,6];
               // ...
               return res;
          }