private bool ExistsAlready(List <TeamLeader> inputList, TeamLeader inputTeamLeader)
        {
            bool found = false;
            int  index = 0;

            while (!found && index < inputList.Count)
            {
                if (inputList[index].Name == inputTeamLeader.Name)
                {
                    found = true;
                }

                index++;
            }

            return(found);
        }
        private void addButton_Click(object sender, EventArgs e)
        {
            if (IsInputValid())
            {
                TeamLeader theTeamLeader = new TeamLeader(name, number, shiftNumber, hourlyPayRate, trainingHoursAttended);

                if (!ExistsAlready(teamLeaders, theTeamLeader))
                {
                    teamLeaders.Add(theTeamLeader);
                    teamLeadersListBox.Items.Add(theTeamLeader.Name);
                    ClearAll();
                    nameTextBox.Focus();
                }
                else
                {
                    MessageBox.Show(theTeamLeader.Name + " exists already.");
                    ClearAll();
                    nameTextBox.Focus();
                }
            }
        }