The Weird and The Wonderful

private MailMessage BuildMailMessage(...)
{
...

mailMessage.BCC.Add("guys@address.com");

..
}

private void button1_Click(object sender, EventArgs e)
{
    int lefttop = Convert.ToInt16(_1.Text);
    int centertop = Convert.ToInt16(_2.Text);
    int righttop = Convert.ToInt16(_3.Text);
    int leftcenter = Convert.ToInt16(_4.Text);
    int centercenter = Convert.ToInt16(_5.Text);
    int rightcenter = Convert.ToInt16(_6.Text);
    int leftbottom = Convert.ToInt16(_7.Text);
    int centerbottom = Convert.ToInt16(_8.Text);
    int rightbottom = Convert.ToInt16(_9.Text);
    int row1 = lefttop + centertop + righttop;
    int row2 = leftcenter + centercenter + rightcenter;
    int row3 = leftbottom + centerbottom + rightbottom;
    int col1 = lefttop + leftcenter + leftbottom;
    int col2 = centertop + centercenter + centerbottom;
    int col3 = righttop + rightcenter + rightbottom;
    int dia1 = lefttop + centercenter + rightbottom;
    int dia2 = leftbottom + centercenter + righttop;
    if (row1 == row2)
    {
        if (row2 == row3)
        {
            if (row3 == col1)
            {
                if (col1 == col2)
                {
                    if (col2 == col3)
                    {
                        if (col3 == dia1)
                        {
                            if (dia1 == dia2)
                            {
                                MessageBox.Show("Your magic square is correct!");
                            }
                            else
                            {
                                MessageBox.Show("Wrong! Application will restart!");
                                this.Close();
                                Process restart = new Process();
                                restart.StartInfo.FileName = @"path name here";
                                restart.Start();
                            }
                        }
                        else
                        {
                            MessageBox.Show("Wrong! Application will restart!");
                            this.Close();
                            Process restart = new Process();
                            restart.StartInfo.FileName = @"path name here";
                            restart.Start();
                        }
                    }
                    else
                    {
                        MessageBox.Show("Wrong! Application will restart!");
                        this.Close();
                        Process restart = new Process();
                        restart.StartInfo.FileName = @"path name here";
                        restart.Start();
                    }
                }
                else
                {
                    MessageBox.Show("Wrong! Application will restart!");
                    this.Close();
                    Process restart = new Process();
                    restart.StartInfo.FileName = @"path name here";
                    restart.Start();
                }
            }
            else
            {
                MessageBox.Show("Wrong! Application will restart!");
                this.Close();
                Process restart = new Process();
                restart.StartInfo.FileName = @"path name here";
                restart.Start();
            }
        }
        else
        {
            MessageBox.Show("Wrong! Application will restart!");
            this.Close();
            Process restart = new Process();
            restart.StartInfo.FileName = @"path name here";
            restart.Start();
        }
    }
    else
    {
        MessageBox.Show("Wrong! Application will restart!");
        this.Close();
        Process restart = new Process();
        restart.StartInfo.FileName = @"path name here";
        restart.Start();
    }
}

element(n) = address + n * size_of_the_element
//If you consider the first element the first, the computation becomes

element(n) = address + (n-1) * size_of_the_element
//Not a huge difference but it adds an unnecessary subtraction for each access.