SQL Returning Output Parameter values from Stored Procedure

This is the stored procedure

ALTER PROCEDURE [dbo].[Usp_purging_updateretentionmth]
@newMonth     INT,
@currentMonth INT OUTPUT

AS

  BEGIN

      SET nocount ON;

      UPDATE tbl_purgingmonth
      SET    currentstatus = 'Archive'
      WHERE  currentstatus = 'Active'

      INSERT INTO tbl_purgingmonth
      VALUES ( @newMonth, Getdate(), system_user, 'Active' )

      SET @currentMonth = @newMonth

  END 

To retrieve output value, you must use this code
command.Parameters["@currentMonth"].Value

   1:                  // Add the input parameter and set its properties.

   2:                  SqlParameter pNewMonth = new SqlParameter();

   3:                  pNewMonth.ParameterName = "@newMonth";

   4:                  pNewMonth.SqlDbType = SqlDbType.Int;

   5:                  pNewMonth.Direction = ParameterDirection.Input;

   6:                  pNewMonth.Value = newMonth;

   7:   

   8:                  // Add the output parameter and set its properties.

   9:                  SqlParameter pCurrentMonth = new SqlParameter();

  10:                  pCurrentMonth.ParameterName = "@currentMonth";

  11:                  pCurrentMonth.SqlDbType = SqlDbType.Int;

  12:                  pCurrentMonth.Direction = ParameterDirection.Output;

  13:   

  14:                  //Add the parameter to the Parameters collection. 

  15:                  command.Parameters.Add(pNewMonth);

  16:                  command.Parameters.Add(pCurrentMonth);

  17:   

  18:                  command.ExecuteScalar();

  19:   

  20:                  mth = Convert.ToInt32(command.Parameters["@currentMonth"].Value);