[c#] How to use OUTPUT parameter in Stored Procedure

I am new to writing Stored Procedure. So I wrote one with output parameters and want to access the output value, hot to do it.

My Stored Procedure:

ALTER PROCEDURE selQuery
    (
        @id int, @code varchar(50) OUTPUT
    )
AS
    SELECT RecItemCode = @code, RecUsername from Receipt where RecTransaction = @id
    RETURN @code

If trying to set "@code=RecItemCode" getting error as : "A SELECT statement that assigns a value to a variable must not be combined with Data Retrieval operations."

And I am using the Stored Procedure as:

con.Open();
cmd.Parameters.AddWithValue("@id", textBox1.Text);
SqlParameter code = new SqlParameter("@code", SqlDbType.Int);
code.Direction = ParameterDirection.Output;
cmd.Parameters.Add(code);
SqlDataReader sdr = cmd.ExecuteReader();
MessageBox.Show(cmd.Parameters["@code"].Value.ToString()); // getting error
con.Close();

Error : "Object reference not set to an instance of an object." I want to get the value of output parameter. How to get that?

Thanks.

SqlCommand yourCommand = new SqlCommand();
yourCommand.Connection = yourSqlConn;
yourCommand.Parameters.Add("@yourParam");
yourCommand.Parameters["@yourParam"].Direction = ParameterDirection.Output;

// execute your query successfully

int yourResult = yourCommand.Parameters["@yourParam"].Value;

There are a several things you need to address to get it working

1. The name is wrong its not @ouput its @code
2. You need to set the parameter direction to Output.
3. Don't use AddWithValue since its not supposed to have a value just you Add.
4. Use ExecuteNonQuery if you're not returning rows

Try

SqlParameter output = new SqlParameter("@code", SqlDbType.Int);
output.Direction = ParameterDirection.Output;
cmd.Parameters.Add(output);
cmd.ExecuteNonQuery();
MessageBox.Show(output.Value.ToString());

You need to close the connection before you can use the output parameters. Something like this

con.Close();
MessageBox.Show(cmd.Parameters["@code"].Value.ToString());

You need to define the output parameter as an output parameter in the code with the ParameterDirection.Output enumeration. There are numerous examples of this out there, but here's one on MSDN.