Please, read my comment to the question first.
The way you're trying to achieve that is wrong!
Instead creating "dynamic query" to call sp in it, call stored procedure directly!
Have a look here:
How to: Create and Execute an SQL Statement that Returns a Single Value[
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When you open above link, on the left side of window, you'll find many usefull links about executing queries.
I must warn you about SQL Injection:
How To: Protect From SQL Injection in ASP.NET[
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If you would like to display data using sp, please see:
Walkthrough: Displaying Data Using a Stored Procedure in the GridView Web Server Control[
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