>How do I send variables of type date as parameter to RDC for crystal report?

It is not possible to pass values to date parameter fields in the Report Design Component (RDC). The solution involves inserting a formula field in the report from the RDC. You can then use the formula field instead of a parameter field in a Selection Formula for example.

To reference a formula field by name and populate it at runtime:

'assuming that the formula name is "@formula"
For Each crxFormulafield In Report.FormulaFields
If crxFormulafield.FormulaFieldName = "formula"
crxFormulafield.Text = "'11/7/1998'"
Exit

EndFor

or

If you know how the formula is indexed:

Report.FormulaFields.Item(1).Text = "'" & CDate("11/7/1998") & "'"