This class gives you access to the cells of the crosstab. You may access just one cell, a whole row or column, or - by using the All Property - all cells simultaneously.
// set value and content for all cells
crosstab.Definition.Cells.All.Formula = "Sum(Order_Details.Quantity*Order_Details.UnitPrice)";
crosstab.Definition.Cells.All.Value = "Sum(Order_Details.Quantity*Order_Details.UnitPrice)";
// modify value for the first cell
crosstab.Definition.Cells[0, 0].Formula = "\"First cell\"";