title: Input String is not in Correct Format when reading DataTable values
body: <p>I am performing sum of two columns using DataTable, first time converts and perform addition but second time it is giving me Input string is not in correct format
  My code is here:</p>
  
  <pre><code>Dim dt As New DataTable()
  dt.Columns.Add("BillingAmount")
  dt.Columns.Add("RecievedAmount")
  dt.Columns.Add("Balance")
  
  For i As Integer = 0 To mstr_DataTable.Rows.Count - 1
     Dim BillingAmount As Decimal = Decimal.Parse(drw("BillingAmount").ToString()) + Decimal.Parse(mstr_DataTable.Rows(0)("BillAmount").ToString()) 
     '^ I am getting exception here .
     drw("BillingAmount") = BillingAmount.ToString()
     drw("RecievedAmount") = mstr_DataTable.Rows(0)("PaymentAmount").ToString()
     Dim Balance As Decimal = Decimal.Parse(drw("BillingAmount").ToString()) - Decimal.Parse(mstr_DataTable.Rows(0)("PaymentAmount").ToString())
     '^ I am getting exception here .
     drw("Balance") = Balance.ToString()
  Next
  </code></pre>