Array.copy method in vb.net - vb.net

Question

Public Shared Function EncryptRSA(ByVal infilename As String, ByVal outfilename As String, ByVal pubkey As String) As String
Dim buffer2 As Byte()
Dim buffer3 As Byte()
Dim provider As New RSACryptoServiceProvider
provider.FromXmlString(File.ReadAllText(pubkey))
Dim sourceArray As Byte() = File.ReadAllBytes(infilename)
Dim num As Integer = (sourceArray.Length / &H3A)
Dim stream As FileStream = File.Create(outfilename)
Dim num2 As Integer = 0
For num2 = 0 To num - 1
buffer2 = New Byte(&H3A - 1) {}
Array.Copy(sourceArray, (num2 * &H3A), buffer2, 0, &H3A)
buffer3 = provider.Encrypt(buffer2, True)
stream.Write(buffer3, 0, buffer3.Length)
Next num2
If ((sourceArray.Length Mod &H3A) <> 0) Then
buffer2 = New Byte((sourceArray.Length Mod &H3A) - 1) {}
Array.Copy(sourceArray, ((sourceArray.Length / &H3A) * &H3A), buffer2, 0, (sourceArray.Length Mod &H3A))
buffer3 = provider.Encrypt(buffer2, True)
stream.Write(buffer3, 0, buffer3.Length)
End If
stream.Close()
Return File.ReadAllText(outfilename)
End Function
Error 1 Overload resolution failed because no accessible 'Copy' can be called without a narrowing conversion:
'Public Shared Sub Copy(sourceArray As System.Array, sourceIndex As Long, destinationArray As System.Array, destinationIndex As Long, length As Long)': Argument matching parameter 'sourceIndex' narrows from 'Double' to 'Long'.
'Public Shared Sub Copy(sourceArray As System.Array, sourceIndex As Integer, destinationArray As System.Array, destinationIndex As Integer, length As Integer)': Argument matching parameter 'sourceIndex' narrows from 'Double' to 'Integer'. C:\Users\user\AppData\Local\Temporary Projects\WindowsApplication1\Crypto.vb 52 13 WindowsApplication1

Answer 1

You have this line:
Array.Copy(sourceArray, ((sourceArray.Length / &H3A) * &H3A), buffer2, 0, (sourceArray.Length Mod &H3A))
What the compiler wants to tell you is that you provided a double value for sourceIndex but it expected a long value. double cannot be cast to long implicitly because long cannot represent all possible values of double.
So do the conversion explicitly:
Array.Copy(sourceArray, CLng((sourceArray.Length / &H3A) * &H3A), buffer2, 0, (sourceArray.Length Mod &H3A))