You can't assign a whole dataset to a string: a dataset is (at it's most basic) a group of datatables, which (at their most basic) is a group of data rows, which again ar a group of data cells.
The cells individually can be assigned to a string, but assigning a dataset would not produce anything particularly useful for the user.
Have you considered useing a DataGrid? There is an article which covers that here:
Using ADO.NET for beginners[
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