private void EquationButtonHandler(string expression)
        {
            if (!ValidateStr(mainDisplay) && !ValidateStr(secondNum))
            {
                if (expressionQueue == false)
                {
                    secondNum = mainDisplay;
                    UpdateTextBoxes(firstNum, secondNum, expression);
                }
                else
                {
                    string temp = expression;
                    expression = Equations.GetQueueExpression();
                    secondNum  = mainDisplay;
                    UpdateTextBoxes(firstNum, secondNum, expression);
                    Equations.SetExpression(temp);
                    //expressionQueue = false;
                }
            }
            else if (!ValidateStr(mainDisplay) && ValidateStr(secondNum))
            {
                firstNum            = mainDisplay;
                txtBox_History.Text = Equations.Builder(firstNum, expression);
                if (ValidateStr(secondNum))
                {
                    secondNum = mainDisplay;
                }
                mainDisplay = "";
                Equations.SetExpression(expression);
                expressionQueue = true;
            }
            else if (ValidateStr(mainDisplay))
            {
                Equations.SetExpression(expression);
                expressionQueue = true;
            }

            //if (numSaved == false)
            //{
            //    if (ValidateStr(firstNum)) firstNum = mainDisplay;
            //    txtBox_History.Text = Equations.Builder(firstNum, expression);
            //    numSaved = true;
            //    mainDisplay = "";

            //}
            //else
            //{
            //    if (!ValidateStr(mainDisplay))
            //    {
            //        secondNum = mainDisplay;
            //        txtBox_History.Text = Equations.HistoryBuilder(firstNum, secondNum, expression);
            //        firstNum = txtBox_Equation.Text = Equations.Builder(firstNum, secondNum, expression);
            //        mainDisplay = "";

            //    }

            //}
        }
 private void UpdateTextBoxes(string _firstNum, string _secondNum, string _expression)
 {
     txtBox_History.Text = Equations.HistoryBuilder(_firstNum, _secondNum, _expression);
     firstNum            = txtBox_Equation.Text = Equations.Builder(_firstNum, _secondNum, _expression);
     mainDisplay         = "";
 }