can input parameters be used as output parameters ?

Yes you can dear friend, Take an example of a stored procedure with only one out parameter. In this you can send the input to the stored procedure and set the value of the same parameter in order to return he value.

For E.g.:-

CREATE PROCEDURE GetEmployeeType
   @employeeTypeOrName varchar(80) OUTPUT
AS
BEGIN
   SELECT employeeTypeOrName = EmployeeType
   FROM HumanResources.Employee
   WHERE EmployeeName Like '%employeeTypeOrName%'
END

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