Datatable add int column to extisting table

I have got a datatable with several rows. I want to add a column of type int.
If I do following I get an error: 'dataType' argument cannot be null.
Parameter name: dataType

 ds.Tables[0].Columns.Add("NewId", System.Type.GetType("System.Int"));

After I have created the column I will loop through the rows in the table and fill values in the new column. How can I add this new int column?Start Free Trial