gridview date format

 <asp:boundfield datafield="ModifiedDate" xmlns:asp="#unknown">
                    HeaderText="ModifiedDate" 
                    SortExpression="ModifiedDate" 
                    DataFormatString="{0:d}" />
</asp:boundfield>

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For datagridview in windows application
you can define additional 'virtual' column with expression. but the better approach is use DefaultCellStyle.Format in the DataGridView. an example is here