I have created one application where i am using two form - 1) planform and 2) statusform
public void sendmailbtn_Click(object sender, EventArgs e)
        {
            planform obj = new planform();
            statusform obj1 = new statusform(); 
            MailMessage mail = new MailMessage();
           
            mail.To.Add(tobox.Text);
            mail.From = new MailAddress(frombox.Text);
	    mail.Subject = DateTime.Now.ToShortDateString() + "-Planned Task Register (PTR)"; // subject
            mail.Body = bodyboxarea.Text;
            mail.CC.Add(new MailAddress(ccbox.Text));
            mail.IsBodyHtml = true;           
            System.Net.Mail.Attachment attachment;
            attachment = new System.Net.Mail.Attachment(filebox.Text);
            mail.Attachments.Add(attachment);
            
            SmtpClient smtp = new SmtpClient();
            smtp.Host = "smtp.gmail.com";
            smtp.Credentials = new System.Net.NetworkCredential("gmailid", "password");
            smtp.EnableSsl = true;
            smtp.Send(mail);
            this.Hide();           
            MessageBox.Show("Mail sent");
        }
it is working fine, currently "subject" will be same for both plan and status but i want subject line should change when i ll click on status form
            for this i have created global variable but still i did'nt get...