Dynamic TSQL Statement with Dynamic Parameters

Question

I'm trying to utilize a dynamic TSQL Statement where I can have various parameters passed of differing kinds, e.g. In some cases parameter 1 would be an int, other cases it may be a datetime, or varchar, etc.
I'm going to keep  a table of with certain key SQL Statements, and then parameters in another column so this can be resusable.
Here is my code:
Case 1
Declare @FromDate as DATE='2013-10-01'
Declare @ToDate as DATE='2013-10-31'
Declare @FamilyMember as nvarchar(2)='20'
DECLARE @retval int
DECLARE @sSQL nvarchar(500);
DECLARE @ParmDefinition nvarchar(500);
DECLARE @tablename nvarchar(50)
--Select Convert(nvarchar(15), @FromDate,126)
SELECT @sSQL = N'select count(distinct id) as AggregateCount from [Table] where familyMember = @FamilyMember
and DateStamp between @FromDate and @ToDate';
SET @ParmDefinition = N'@retvalOUT int OUTPUT';
EXEC sp_executesql @sSQL, @ParmDefinition, @retvalOUT=@retval OUTPUT;
Case 2
Declare @FromDate as DATE='2013-10-01'
Declare @ToDate as DATE='2013-10-31'
Declare @Id as int=3510021
DECLARE @retval int
DECLARE @sSQL nvarchar(500);
DECLARE @ParmDefinition nvarchar(500);
DECLARE @tablename nvarchar(50)
--Select Convert(nvarchar(15), @FromDate,126)
SELECT @sSQL = N'select count(distinct id) as AggregateCount from [Table] where Id=@Id
and DateStamp between @FromDate and @ToDate';
SET @ParmDefinition = N'@retvalOUT int OUTPUT';
EXEC sp_executesql @sSQL, @ParmDefinition, @retvalOUT=@retval OUTPUT;
John

Answer 1

The following is an example I found, but I am receiving a Message "Must declare the scalar variable @StudentNumber"
Alter Procedure [dbo].[spInsertStudentDoc2]
@StudentNumber integer
AS
Begin
DECLARE @P_StudentNumber integer
DECLARE @ParameterList nvarchar(max)
DECLARE @SQLSnippit as nvarchar(max)
SET @ParameterList = N'@P_StudentNumber integer'
SET @SQLSnippit = N'Select Count(*) from dbo.student where patid=@StudentNumber'
PRINT @SqlSnippit -- debug & test
Exec SP_EXECUTESQL @SqlSnippit, @ParameterList, @P_StudentNumber=@StudentNumber
End
John