ADO.NET Procedures!

/* procedure
alter procedure dbo.UpdateSalary
    @id int,
    @changeSalary decimal(6, 1),
    @salary decimal(6, 1) output
as
begin
    update Users
    set salary=@changeSalary
    where id = @id
end
*/

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

namespace AdoApp
{
    public partial class Form1 : Form
    {
        string connectionString = @"Server=LAB-418-10-PC\STUDENT; Database=vakho; Integrated Security=true;";
        SqlConnection con;

        public Form1()
        {
            InitializeComponent();
            this.con = new SqlConnection(this.connectionString);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                SqlCommand insertCommand = new SqlCommand("INSERT INTO dbo.users (name, surname, birthday, salary) VALUES (@name, @surname, @birthday, @salary)", con);

                SqlParameter name = new SqlParameter("@name", DbType.String);
                SqlParameter surname = new SqlParameter("@surname", DbType.String);
                SqlParameter birthday = new SqlParameter("@birthday", SqlDbType.Date);
                SqlParameter salary = new SqlParameter("@salary", SqlDbType.Decimal);

                insertCommand.Parameters.Add(name).Value = textBox1.Text;
                insertCommand.Parameters.Add(surname).Value = textBox2.Text;
                insertCommand.Parameters.Add(birthday).Value = dateTimePicker1.Value.ToShortDateString();
                insertCommand.Parameters.Add(salary).Value = Convert.ToDecimal(textBox3.Text);

                con.Open();
                insertCommand.ExecuteNonQuery();
            }
            catch (SqlException ex)
            {
                MessageBox.Show(ex.Message, "Sql Error!");
            }
            catch (FormatException ex)
            {
                MessageBox.Show(ex.Message, "Format Error!");
            }
            finally
            {
                con.Close();
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            try
            {
                SqlCommand updateCommand = new SqlCommand("dbo.UpdateSalary @id, @changeSalary, @salary", con);

                SqlParameter id = new SqlParameter("@id", SqlDbType.Int);
                SqlParameter newSalary = new SqlParameter("@changeSalary", SqlDbType.Decimal);
                SqlParameter salary = new SqlParameter("@salary", SqlDbType.Decimal);

                updateCommand.Parameters.Add(id).Value = textBox4.Text;
                updateCommand.Parameters.Add(newSalary).Value = Convert.ToDecimal(textBox3.Text);
                updateCommand.Parameters.Add(salary).Direction = ParameterDirection.Output;

                con.Open();
                updateCommand.ExecuteNonQuery();
                // parameter not showing properly!
                MessageBox.Show(updateCommand.Parameters[updateCommand.Parameters.Count-1].Value.ToString(), "New Salary!");
            }
            catch (SqlException ex)
            {
                MessageBox.Show(ex.Message, "Sql Error!");
            }
            catch (FormatException ex)
            {
                MessageBox.Show(ex.Message, "Format Error!");
            }
            finally
            {
                con.Close();
            }
        }
    }
}