GAS-AdvCalc.gs

function doGet() {
  var app = UiApp.createApplication().setTitle("The Math Machine");
  app.setStyleAttribute('background', 'black');
  var formPanel = app.createFormPanel();
  var verticalPanel = app.createVerticalPanel();
  var label1 = app.createLabel("First Number: ").setStyleAttribute('color', 'white');
  var textBox1 = app.createTextBox().setName('textBoxResult1');
  var label2 = app.createLabel("Second Number: ").setStyleAttribute('color', 'white');
  var textBox2 = app.createTextBox().setName('textBoxResult2');
  var lb = app.createListBox().setName('lb1').addItem('Addition').addItem('Subtraction').addItem('Multiplication');
  var submitButton = app.createSubmitButton("Perform the Operation");
  verticalPanel.add(label1).add(textBox1).add(label2).add(textBox2).add(lb).add(submitButton);
  formPanel.add(verticalPanel);
  app.add(formPanel);
  return app;
}

function doPost(e) {
  var app = UiApp.getActiveApplication();
  var operator = "";
  var numFinal = 0;

  switch(e.parameter.lb1)
  {
    case 'Addition':
      operator = " + ";
      numFinal = e.parameter.textBoxResult1 * 1 + e.parameter.textBoxResult2 * 1
      break;
    case 'Subtraction':
      operator = " - ";
      numFinal = e.parameter.textBoxResult1 * 1 - e.parameter.textBoxResult2 * 1      
      break;
    case 'Multiplication':
      operator = " x ";
      numFinal = e.parameter.textBoxResult1 * 1 * e.parameter.textBoxResult2 * 1
      break;
  }

  var label1 = app.createLabel(e.parameter.textBoxResult1 + operator + e.parameter.textBoxResult2 + " = " + numFinal)
    .setStyleAttribute('color', 'white').setStyleAttribute('fontSize', '500%');

  app.add(label1);
  return app;
}