// Contribuido por Nuno Anes


--------------------------------- VC++ .NET -------------------------------------------------------------

bool IsValidContrib (String *contrib)
{
      String            *s;
      char              c;
      int               checkDigit;
 
      s = contrib;
 
      if (s->Length == 9)
      {
            c = s->get_Chars (0);
 
            if (c == '1' || c == '2' || c == '5' || c == '6' || c == '8' || c == '9')  //digitos iniciais válidos
            {
                  checkDigit = (c - '0') * 9;
 
                  for (int i = 2 ; i <= 8 ; i++)
                        checkDigit += (s->get_Chars (i - 1) - '0') * (10 - i);
 
                  checkDigit = 11 - (checkDigit % 11);
 
                  if (checkDigit >= 10)
                        checkDigit = 0;
 
                  if (checkDigit == (s->get_Chars (8) - '0'))
                        return true;
            }
      }
 
      return false;
}

 
--------------------------------------- VB .NET -------------------------------------------------------------

 
Public Function IsValidContrib(ByVal contrib As String) As Boolean
 
        Dim s As String = contrib
        Dim c As Char
        Dim i, checkDigit As Integer
 
        If (s.Length = 9) Then
            c = s.Chars(0)
            If (c.Equals("1"c) Or c.Equals("2"c) Or c.Equals("5"c) Or c.Equals("6"c) Or c.Equals("8"c) Or c.Equals("9"c)) Then
                checkDigit = Val(c) * 9
                For i = 2 To 8
                    checkDigit += Val(s.Chars(i - 1)) * (10 - i)
                Next
                checkDigit = 11 - (checkDigit Mod 11)
                If (checkDigit >= 10) Then checkDigit = 0
                If (checkDigit = Val(s.Chars(8))) Then Return True
            End If
        End If
 
        Return False
 
End Function