I need some exercises for each chapter

tomy

According to the advice of some the nice and professional guys of this forum, I started to read the book C++ GUI Programming using Qt-4 2nd Edition as the entrance way to the world of Qt.

OK, I started to read the book and I'm now about to begin chapter 3. I have followed the codes and forms of designer for each example in the book and have run them correctly on my Windows machine so far. But the book has some defect; it doesn't provide any drill of exercises!
Without exercises, I cannot be sure I've learnt the contents correctly. And can't convince myself that I will be able to write a real application throughout passing the book.

What I have seen in the other technical books is that each chapter includes some drill and exercises and the end of itself. This is what I need.

What is/are your suggestion(s) please?

? Offline

Hi! Here is your first exercise: Make a desktop calculator like this:

:-)

koahnig

@tomy

I guess you have to live with what is available. Since there is no really big change from Qt 4 to Qt 5, there is no Qt 5 book available. Therefore, someone recommended a book describing details for Qt 4. In the past people used examples either from the book directly or the official Qt examples for getting experience with the programming.

Therefore, you can use Qt 5 examples or Qt 4 examples and the book you have as a reference.

The examples are typically quite detailed and for a lot of people enough to learn Qt. A book is merely another method to deepen some details respectively to have way of description.

tomy

@Wieland
Thank you for your suggestion but isn't this too advanced for a novice that has just learned the first two-chapter of that book (page 58 of the book)?
If not, OK, I'm interested in it, but may you guide me on the process until end?

Since it was the first practical example (out of the book) for me, I designed a form by Qt Designer using Dialog Without Buttons template. And I designed the form in its basic style by putting only some widgets as follows:

alt text

Then I wrote a calculator.h file like this:

#ifndef CALCULATOR_H
#define CALCULATOR_H

#include <QDialog>
#include "ui_calculator.h"

class Calculator : public QDialog, public Ui::Calculator
{
   Q_OBJECT
public:
   Calculator(QWidget* parent = 0);
};

#endif // CALCULATOR_H

Then, a calculator.cpp this way:

#include <QtWidgets>
#include "calculator.h"

Calculator::Calculator(QWidget *parent)
    : QDialog(parent)
{
    setupUi(this);
}

And finally the main.cpp this way:

#include <QApplication>
#include "calculator.h"
int main(int argc, char* argv[])
{
    QApplication app(argc, argv);
    Calculator* dialog = new Calculator;
    dialog -> show();
    return app.exec();
}

Please note that this kind of exercise is new for me as a newcomer to Qt! So I thought it was better to develop the app step-by-step.

I used qmake and run the code but got these two errors:

1- C:\Users\Me\Documents\Qt\Calculator\calculator.h:8: error: expected class-name before '{' token
{
^
2- C:\Users\Me\Documents\Qt\Calculator\calculator.cpp:7: error: 'setupUi' was not declared in this scope
setupUi(this);
^

And as the final question of this reply! Would what I did be the same as yours if you were me to have this exercise please?

jsulm

@tomy You should not derive your class from Ui::Calculator, instead add a pointer to your class:

class Calculator : public QDialog
{
   Q_OBJECT
public:
   Calculator(QWidget* parent = 0);
private:
    Ui::Calculator *ui;
};

You should create a form via "New file or project/Qt designer Form Class" and check how it works. This way it is easier to get started.

tomy

@jsulm said in I need some exercises for each chapter:

@tomy You should not derive your class from Ui::Calculator, instead add a pointer to your class:

Thanks for your reply but what I wrote was according to the method of examples of the book!

class Calculator : public QDialog
{
   Q_OBJECT
public:
   Calculator(QWidget* parent = 0);
private:
    Ui::Calculator *ui;
};
You should create a form via "New file or project/Qt designer Form Class" and check how it works. This way it is easier to get started.

OK, I re-start from there this time, but how to get it worked?

jsulm

@tomy Can you show the content of ui_calculator.h?

tomy

@jsulm said in I need some exercises for each chapter:

ui_calculator.h

Yes, that's it:

/********************************************************************************
** Form generated from reading UI file 'calculator.ui'
**
** Created by: Qt User Interface Compiler version 5.5.1
**
** WARNING! All changes made in this file will be lost when recompiling UI file!
********************************************************************************/

#ifndef UI_CALCULATOR_H
#define UI_CALCULATOR_H

#include <QtCore/QVariant>
#include <QtWidgets/QAction>
#include <QtWidgets/QApplication>
#include <QtWidgets/QButtonGroup>
#include <QtWidgets/QDialog>
#include <QtWidgets/QHeaderView>
#include <QtWidgets/QLineEdit>
#include <QtWidgets/QPushButton>

QT_BEGIN_NAMESPACE

class Ui_Dialog
{
public:
    QLineEdit *lineEdit;
    QPushButton *oneButton;
    QPushButton *twoButton;
    QPushButton *equalButton;
    QPushButton *quitButton;
    QPushButton *plusButton;
    QPushButton *menusButton;

    void setupUi(QDialog *Dialog)
    {
        if (Dialog->objectName().isEmpty())
            Dialog->setObjectName(QStringLiteral("Dialog"));
        Dialog->resize(400, 300);
        lineEdit = new QLineEdit(Dialog);
        lineEdit->setObjectName(QStringLiteral("lineEdit"));
        lineEdit->setGeometry(QRect(220, 100, 113, 20));
        oneButton = new QPushButton(Dialog);
        oneButton->setObjectName(QStringLiteral("oneButton"));
        oneButton->setGeometry(QRect(40, 90, 75, 23));
        twoButton = new QPushButton(Dialog);
        twoButton->setObjectName(QStringLiteral("twoButton"));
        twoButton->setGeometry(QRect(40, 160, 75, 23));
        equalButton = new QPushButton(Dialog);
        equalButton->setObjectName(QStringLiteral("equalButton"));
        equalButton->setGeometry(QRect(240, 130, 75, 23));
        quitButton = new QPushButton(Dialog);
        quitButton->setObjectName(QStringLiteral("quitButton"));
        quitButton->setGeometry(QRect(240, 190, 75, 23));
        plusButton = new QPushButton(Dialog);
        plusButton->setObjectName(QStringLiteral("plusButton"));
        plusButton->setGeometry(QRect(160, 130, 31, 21));
        menusButton = new QPushButton(Dialog);
        menusButton->setObjectName(QStringLiteral("menusButton"));
        menusButton->setGeometry(QRect(120, 130, 31, 21));

        retranslateUi(Dialog);
        QObject::connect(equalButton, SIGNAL(clicked()), Dialog, SLOT(accept()));
        QObject::connect(quitButton, SIGNAL(clicked()), Dialog, SLOT(reject()));
        QObject::connect(oneButton, SIGNAL(clicked()), lineEdit, SLOT(paste()));
        QObject::connect(menusButton, SIGNAL(clicked()), lineEdit, SLOT(paste()));
        QObject::connect(twoButton, SIGNAL(clicked()), lineEdit, SLOT(paste()));
        QObject::connect(plusButton, SIGNAL(clicked()), lineEdit, SLOT(paste()));

        QMetaObject::connectSlotsByName(Dialog);
    } // setupUi

    void retranslateUi(QDialog *Dialog)
    {
        Dialog->setWindowTitle(QApplication::translate("Dialog", "Calculator", 0));
        oneButton->setText(QApplication::translate("Dialog", "1", 0));
        twoButton->setText(QApplication::translate("Dialog", "2", 0));
        equalButton->setText(QApplication::translate("Dialog", "=", 0));
        quitButton->setText(QApplication::translate("Dialog", "Quit", 0));
        plusButton->setText(QApplication::translate("Dialog", "+", 0));
        menusButton->setText(QApplication::translate("Dialog", "-", 0));
    } // retranslateUi

};

namespace Ui {
    class Dialog: public Ui_Dialog {};
} // namespace Ui

QT_END_NAMESPACE

#endif // UI_CALCULATOR_H

tomy

Thank you guys. Apparently I will get no help here. I pose the issue on another thread.

jsulm

@tomy The name of your UI class is Dialog not Calculator, so change to:

class Calculator : public QDialog, public Ui::Dialog

see here from ui_calculator.h:

namespace Ui {
    class Dialog: public Ui_Dialog {};
}

"Apparently I will get no help here" - you should be more patient. People here are volunteers.

tomy

@jsulm
Yeah, you are right. Thank you for the answer. :)

On the process of developing the app step-by-step, I made these changes.
The .uifile:

alt text

My main.cpp:

#include <QApplication>
#include <QDialog>

#include "ui_Calculator.h"

int main(int argc, char* argv[])
{
    QApplication app(argc, argv);

    Ui::Calculator ui;
    QDialog* dialog = new QDialog;
    ui.setupUi(dialog);
    dialog -> show();

    return app.exec();
}

The .h file:

#ifndef CALCULATOR_H
#define CALCULATOR_H

#include<QDialog>
#include "ui_Calculator.h"

class Calculator : public QDialog, public Ui::Calculator
{
    Q_OBJECT

public:
    Calculator(QWidget* parent = 0);
private slots:
   void on_lineEdit_textChanged();
};

#endif // CALCULATOR_H

The .cpp file:

#include <QtWidgets>
#include "calculator.h"

Calculator::Calculator(QWidget *parent)
    :QDialog(parent)
{
    setupUi(this);

    connect(oneButton,SIGNAL(clicked(bool)), lineEdit, SLOT(setText("1")));
    connect(twoButton,SIGNAL(clicked(bool)), lineEdit, SLOT(setText("2")));
    connect(addButton,SIGNAL(clicked(bool)), lineEdit, SLOT(setText("+")));
}

void Calculator::on_lineEdit_textChanged() { // I will add some code here
}

My problems:
The program runs without errors but there is a red line under each lines of the connect.
And when I run the app and click on 1, 2 or + button, they will not be shown in lineEdit!
What are the reasons please?

mrjj

Hi
The reason it do not work is that you say

connect(twoButton,SIGNAL(clicked(bool)), lineEdit, SLOT(setText("2")));

The signal should go to a slot with same signature, meaning it should take same parameters
and you cannot give it "fixed" ones like "2" as it would need to store it for later then and it cannot.
so
connect(twoButton,SIGNAL(clicked(bool)), this/"Calculator"/, SLOT(myslot(bool)));

in myslot could do

void Calculator::myslot(bool) {
lineEdit->setText("2");
}

tomy

Thanks but it didn't work!

I even wanted to use the myslot function in a better way, like this:

#include <QtWidgets>
#include "calculator.h"

Calculator::Calculator(QWidget *parent)
    :QDialog(parent)
{
    setupUi(this);

    connect(oneButton,SIGNAL(clicked(bool)), lineEdit, SLOT(myslot("1")));
    connect(twoButton,SIGNAL(clicked(bool)), lineEdit, SLOT(myslot("2")));
    connect(addButton,SIGNAL(clicked(bool)), lineEdit, SLOT(myslot("+")));
}

void Calculator::on_lineEdit_textChanged() {// I will add some code here
}

void Calculator::myslot(const QString& str){
    lineEdit -> setText(str);
}

But this one too didn't work. That is, when I run the app, clicking the 1, 2, + write nothing in the lineEdit.

PS: In the Calculator.h:

...
private slots:
   void on_lineEdit_textChanged();
   void myslot(const QString&);
};

PS2: The red lines under the connects exist still!

mrjj

PS2: The red lines under the connects exist still!

Well
connect(oneButton,SIGNAL(clicked(bool)), lineEdit, SLOT(myslot("1")));

Cannot work. Its not valid and will never work.
You cannot use it like that. "1" is not used, not valid and it do not work like this.
please read
http://doc.qt.io/qt-5/signalsandslots.html

Please note:
connect return true and false , so please do

qDebug () << "one:" << connect(oneButton,SIGNAL(clicked(bool)), lineEdit, SLOT(setText("1")));

You will see it says "one:false" and wont accept it.

You might want to look into
http://doc.qt.io/qt-5/qsignalmapper.html#details

tomy

I read the first link until "Advanced Signal & Slot ..." part but couldn't find the reason. According to C++ conventions what I wrote seems quite right. And if you think it's not in Qt, speak about the reason please.

connect(oneButton,SIGNAL(clicked(bool)), lineEdit, SLOT(myslot(bool)));

&

void Calculator::myslot(){
    lineEdit -> setText("1");
}

also show nothing in lineEdit!

mrjj

Hi

According to C++ conventions what I wrote seems quite right:

connect(oneButton,SIGNAL(clicked(bool)), lineEdit, SLOT(setText("1")));
This is wrong for the SLOT macro.

The new code you show is correct.
connect(oneButton,SIGNAL(clicked(bool)), lineEdit, SLOT(myslot(bool))); << no "1" just the type

void Calculator::myslot(bool){
lineEdit -> setText("1"); // correct. for normal Qt , it would be ui->lineEdit->setText.
}

jsulm

@tomy You should check what connect(...) returns. My guess is that the connection fails because in the connect you have:

SLOT(myslot(bool))

but your slot does not have any parameter:

void Calculator::myslot()

So, connect(...) cannot find slot myslot(bool)

tomy

Thanks to all.
@jsulm
So apparently you disagree with mrjj. I write what he says but the code shows nothing. I think your assumption is correct because myslot() has no parameters.

Now the question is this: How to connect the buttons (1, 2 & +) to a slot so that, that slot prints out the values of these buttons onto the lineEdit please?

Based on what I'd learned form C++ I thought the code below would work for that purpose:

in the Calculator.h:

...
private slots:
   void myslot(const QString&);
};

And in Calculator.cpp:

...
connect(oneButton,SIGNAL(clicked(bool)), lineEdit, SLOT(myslot("1")));
 connect(twoButton,SIGNAL(clicked(bool)), lineEdit, SLOT(myslot("2")));
 connect(addButton,SIGNAL(clicked(bool)), lineEdit, SLOT(myslot("+")));
}

void Calculator::myslot(const QString& str){
 lineEdit -> setText(str);
}

But this does not work. I have a good experience in C++ but I'm a novice in Qt.
Now what would be your solution for that purpose please?

jsulm

@tomy Where did I disagree with @mrjj?
You should read more carefully what I wrote.
The problem with your code is that you provide a wrong slot signature in connect. Again:

SLOT(myslot(bool))

there is no such slot! Your slot has this signature (no bool parameter):

void Calculator::myslot()

So, either change

SLOT(myslot(bool))
to
SLOT(myslot())

or

void Calculator::myslot()
to
void Calculator::myslot(bool)

tomy

@jsulm

OK & thanks a bunch but still it doesn't work!