Question

    Qt :: WindowFlags flags = 0;

    // Makes the Pomodoro stay on the top of all windows.
    flags |= Qt :: WindowStaysOnTopHint;

    // Removes minimize, maximize, and close buttons.
    flags |= Qt :: WindowTitleHint | Qt :: CustomizeWindowHint;

    window->setWindowFlags (flags);
    window->setWindowTitle ("Failing to plan is planning to fail");

This removes minimize, maximize, and close buttons. The default menu on the left is still there. How to get rid of that?

I want the title bar to be there, but just want the menu to be removed.

Default menu contains: Minimize, Maximize, Move etc options.

EDIT 1:

timer.cpp

#include <QApplication>
#include <QMainWindow>
#include "timer.h"

#include <QPushButton>
#include <QListWidget>
#include <QtGui>
#include <QTreeWidget>
int main(int argc, char *argv[])
{
    QApplication    app (argc, argv);

    // The window on which we will place the timer.
    QMainWindow *window           = new QMainWindow();
    QWidget           *centralWidget = new QWidget (window);

    /* Button widget */
    // Displays a button on the main window.
    QPushButton   *startButton     = new QPushButton("Start", window);
    // Setting the size of the button widget.
    startButton->setFixedSize (245, 25);

    /* Text box */
    // Displays a time interval list on the main window.
    QListWidget *timeIntervalList = new QListWidget (window);
    timeIntervalList->setFixedSize (30, 145);

    QStringList timeIntervals;
    timeIntervals << "1" << "20" << "30" << "40";
    timeIntervalList->addItems (timeIntervals);

    /* LCD widget */
    // Start Counting down from 25 minutes
    lcdDisplay *objLcdDisplay = new lcdDisplay (centralWidget);
    // Setting the size of the LCD widget.
    objLcdDisplay->setFixedSize (245, 140);

    // The clicked time interval should be returned from the list to the timer.
    QObject :: connect (timeIntervalList, SIGNAL (itemClicked (QListWidgetItem *)), objLcdDisplay, SLOT (receiveTimeInterval (QListWidgetItem *)));

    // The timer should start and emit signals when the start button is clicked.
    QObject :: connect (startButton, SIGNAL (clicked ()), objLcdDisplay, SLOT (setTimerConnect ()));

    *************************************************************************
    Qt :: WindowFlags flags = 0;
    // Makes the Pomodoro stay on the top of all windows.
    flags |= Qt :: Window | Qt :: WindowStaysOnTopHint;
    // Removes minimize, maximize, and close buttons.
    flags |= Qt :: WindowTitleHint | Qt :: CustomizeWindowHint;
    window->setWindowFlags (flags);
    *************************************************************************
    window->setWindowTitle   ("Failing to plan is planning to fail");

    QGridLayout *layout = new QGridLayout();
    centralWidget->setLayout(layout);

    //Add Items to QGridLayout Here 
    //Row and Column counts are set Automatically
    layout->addWidget (objLcdDisplay, 0, 1);
    layout->addWidget (startButton, 1, 1);
    layout->addWidget (timeIntervalList, 0, 0);

    window->setCentralWidget (centralWidget);
    window->show();

    return app.exec();
}

Timer.h

#ifndef  LCDNUMBER_H
#define LCDNUMBER_H

#include <QLCDNumber>
#include <QTimer>
#include <QTime>
#include <QListWidget>
#include <QMessageBox>
#include <iostream>

class lcdDisplay : public QLCDNumber
{
    Q_OBJECT  

    public:
        // The QTimer class provides repetitive and single-shot timers.
        QTimer* objTimer;
        // The QTime class provides clock time functions.
        QTime*  objTime;

    public:
        lcdDisplay (QWidget *parentWidget)
        {
            objTimer = new QTimer ();
            // Setting our own time with the specified hours, minutes, and seconds.
            objTime  = new QTime  (0, 0, 0);

            setParent (parentWidget);
        };

        ~ lcdDisplay () {};

    public slots:
        // This slot is called after the timer timeouts (1 second).
        void setDisplay ()
        {
            // TODO
            objTime->setHMS (0, objTime->addSecs (-1).minute (), objTime->addSecs (-1).second ());
            display (objTime->toString ());

            if ((objTime->minute () == 0) && (objTime->second () == 0)) 
            {
                objTimer->stop ();
                QMessageBox msgBox;
                msgBox.setWindowTitle ("Pomodoro");
                msgBox.setText ("Time's up.");
                msgBox.setWindowModality(Qt::ApplicationModal);
                msgBox.exec();
            }
        };

        void receiveTimeInterval (QListWidgetItem *item)
        {
            QString h = item->text();
            objTime->setHMS (0, h.toUInt(), 0);
        }

        void setTimerConnect ()
        {
            // connect (objectA, signalAFromObjectA, objectB, slotAFromObjectB)
            // timeout (): This signal is emitted when the timer times out. The time out period can be specified with `start (int milliseconds)` function.
            QObject :: connect (objTimer, SIGNAL (timeout ()), this, SLOT (setDisplay ()));

            // 1 second has 1000 milliseconds.
            // start (int milliseconds): Starts the timer with a timeout interval of specified milliseconds. this means that after 1 second the timer will emit a signal. TODO placement
            objTimer->start (1000);
        }
};
#endif

Answer 1

This is working for me:

Qt::Window | Qt::WindowTitleHint | Qt::WindowStaysOnTopHint | Qt::CustomizeWindowHint

Sometimes you have to specify these in the constructor of the window for them to take effect. If you assign them later (setWindowFlags), some of the settings may not apply.