}// end submitButton_Click

        /// <summary>
        /// Converts the input string to all lowercase letters and removes all spaces. Then checks if
        /// the variables being used have values in their textboxes and that they are correct values. 
        /// If not, the user is alerted. The variables in the string are replaced with their values.
        /// Then, the input string is them converted to postfix format and evaluated.
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void submitButton_Click(object sender, EventArgs e)
        {
            string infix = evaluationBox.Text; // Get the string from the evaluation textbox

            System.Diagnostics.Debug.WriteLine(infix);

            infix = infix.ToLower(); // Converts all upper case characters in the string to lower case
            infix = infix.Replace(" ", string.Empty); // Remove all spaces from the string

            System.Diagnostics.Debug.WriteLine(infix);

            if (variableCheck(ref infix))
            {
                System.Diagnostics.Debug.WriteLine(infix);

                // Replace all variables with their associated values
                infix = replaceVariablesWithValues(infix);

                System.Diagnostics.Debug.WriteLine(infix);

                //CommandFactory factory = new BasicFactory();
                CommandFactory factory = new OptimizedFactory();

                // Parse the user's equation from infix into postfix format
                Parser parser = new Parser();
                List<Command> postfix = parser.infixToPostfix(infix, factory);

                System.Diagnostics.Debug.WriteLine(infix);

                // Evaluate the postfix format equation
                Evaluator evaluator = new Postfix();
                int result = evaluator.evaluatePostfix(postfix);

                lblEqual.Visible = true;
                lblResult.Text = result.ToString();
                
            }// end if
        }// end submitButton_Click