My first attempt to create a calculator as a novice in Qt programming

Chris Kawa

Right, I'm not sure it's a good idea to learn the obsolete stuff first, but anyway...

With the old syntax you can use a QSignalMapper, like @mrjj suggested.
You would create an instance of it as a member variable:

private:
    QSignalMapper buttonMapper;

Then you would add mappings for the buttons (you can use the same loop as for creating them):

for (int i=0; i < 10; ++i) {
   //create the button same as previously
   QPushButton* button = new QPushButton(QString::number(i));
   buttons.push_back(button);

   //create the mapping. When button emits "clicked" the mapper will emit "mapped(int)" signal with the value i we mapped for this button
   buttonMapper.setMapping(button, i);
   connect(button, SIGNAL(clicked(bool)), &buttonMapper, SLOT(map()));
}

Now all is left is to connect the mapper to the original slot:

connect(&buttonMapper, SIGNAL(mapped(int)), this, SLOT(show_number(int)));

PS. I write this stuff out of my head. Sorry for the little errors (the missing * in previous post, I fixed it).

tomy

Thank you. Using the link dear mrjj had suggested, I changed the code this waw.
My_First_Calculator.h:

/#ifndef MY_FIRST_CALCULATOR_H
#define MY_FIRST_CALCULATOR_H
#include <QDialog>
#include <QSignalMapper>
#include <QStringList>

class QPushButton;
class QLineEdit;

class My_First_Calculator : public QDialog
{
    Q_OBJECT
public:
    My_First_Calculator(const QStringList& texts
                        ,QWidget* parent = 0);

signals:
   void clicked(const QString& text);

private:
    QLineEdit* lineEdit;
    QSignalMapper* signalMapper;
    QPushButton* quit;
};

#endif // MY_FIRST_CALCULATOR_H

My_First_Calculator.cpp:

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

My_First_Calculator::My_First_Calculator(const QStringList& texts,
          QWidget* parent = 0) : QDialog(parent)
{
     lineEdit = new QLineEdit;
     quit = new QPushButton(tr("Close"));

     signalMapper = new QSignalMapper(this);
     QGridLayout* gridLayout = new QGridLayout;

     for(int i=0; i<texts.size(); ++i)
     {
         QPushButton* button = new QPushButton(texts[i]);
         connect(button, SIGNAL(clicked(bool)),
                 signalMapper, SLOT(map()));
         signalMapper -> setMapping(button, texts[i]);
         gridLayout -> addWidget(button, i/3, i%3);
     }

     connect(signalMapper, SIGNAL(mapped(QString)), this,
             SIGNAL(clicked(QString)));



     connect(quit, SIGNAL(clicked(bool)), this, SLOT(close()));

     QVBoxLayout* layout = new QVBoxLayout;
     layout -> addWidget(lineEdit);
     layout -> addLayout(gridLayout);
     layout -> addWidget(quit);
     setLayout(layout);
}

And main.cpp:

#include <QApplication>
#include "my_first_calculator.h"

int main(int argc , char* argv[])
{
    QApplication app(argc, argv);
    QStringList texts;
    texts << "0" << "1" << "2" << "3" << "4"
          << "5" << "6" << "7" << "8" << "9";
    My_First_Calculator myCal(texts);
    myCal.show();
    return app.exec();
}

I get the following error. I guess I need to supply an argument for the parent parameter of QDialog when creating myCal instance in main.cpp.

some questions:

1- But do I need to inherit from QDialog in the.h file?
2- Is it a good choice or should I inherit from QWidget?
3- Is the following error related to my guess please?
4- Have I changed my code correctly, according to the example mrjj suggested?

C:\Users\ME\Documents\Qt\My_First_Calculator\my_first_calculator.cpp:5: error: default argument given for parameter 2 of 'My_First_Calculator::My_First_Calculator(const QStringList&, QWidget)' [-fpermissive]
QWidget* parent = 0) : QDialog(parent)*
^

Chris Kawa

QDialog is a specialized case of QWidget. You don't have to subclass it if you don't use its features (which you don't seem to). In this case QWidget would be enough (but change it in both .h and .cpp if you do).
You don't use any of special QDialog features so it doesn't matter.
No, It means you provided a default argument in the constructor implementation in the .cpp file. Default arguments go only in the header:

//the header:
My_First_Calculator(const QStringList& texts ,QWidget* parent = 0);

//the implementation:
My_First_Calculator::My_First_Calculator(const QStringList& texts, QWidget* parent) : QDialog(parent) //no = 0 here

The signal mapper looks to be hooked up correctly, but you don't connect anything to the clicked() signal of your class so nothing will actually happen.

tomy

@Chris-Kawa

you don't connect anything to the clicked() signal of your class so nothing will actually happen.

Yes, you are right. Nothing happens.
But I've used the following connect in My_First_Calculator.cpp. Don't you mean this?

connect(signalMapper, SIGNAL(mapped(QString)), this,
           SIGNAL(clicked(QString)));

Chris Kawa

Yes, when signal mapper emits mapped your widget emits clicked and that's it. No one is connected to that signal so nothing happens.
I think what you meant to do is to hook the signal mapper to a show_number slot:

//header
private slots:
    void show_number(const QSring& text);

//cpp
void My_First_Calculator::show_number(const QSring& text)
{
    lineEdit -> setText(text);
}

and connect it like this:

connect(signalMapper, SIGNAL(mapped(QString)), this, SLOT(show_number(QString)));

tomy

@Chris-Kawa
Thank you. It works as is expected now.

I also removed

signals:
  void clicked(const QString& text);

in .h file because I though it was useless.

Another question. (Please excuse me for asking those many questions)
Do I need to essentially inherit from QDialog, that is, can't I remove it this way:

class My_First_Calculator  {
    Q_OBJECT

?

Chris Kawa

can't I remove it this way

No, you can't. You need a window that you can show, You need to be able to put widgets in it, you need a layout etc. All those things are functions of a QWidget (QDialog is a subclass of QWidget).
Look in the main() function. There's myCal.show();. show() is a method of a QWidget. Look in the constructor. There's setLayout(layout);. setLayout() is a method of QWidget. There's also connect(.... connect() is also a method of QWidget. There are more examples but the answer is no, you need to at least inherit from QWidget.

tomy

Thank you very much.
The first step is finished. I will think about the code well to understand every part properly. And think to start a new means to develop it. If I have question I will post them again.
Bye for now.

tomy

Hello guys, I'm back to this thread. :)

I had a very little time for Qt (I'm involving many aspects of CS and scheduled my works :)) using which I went a few steps on the process of developing my fist app the way I mentioned in the first post of this thread.

Anyway, Thanks for your patient and we will go to the game!

The changes I make (just using the experience I have on C++) are as follows:

My_First_Calculator.h

#ifndef MY_FIRST_CALCULATOR_H
#define MY_FIRST_CALCULATOR_H
#include <QDialog>
#include <QSignalMapper>
#include <QStringList>

class QLineEdit;

class My_First_Calculator : public QDialog
{
    Q_OBJECT
public:
    My_First_Calculator(const QStringList& texts
                        ,QWidget* parent = 0);

private slots:
    void show_number(const QString&);
    void reset();

private:
    QLineEdit* lineEdit;
    QSignalMapper* signalMapper;
    QString temp_text;
};

#endif // MY_FIRST_CALCULATOR_H

My_First_Calculator.cpp:

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

My_First_Calculator::My_First_Calculator(const QStringList& texts,
          QWidget* parent) : QDialog(parent)
{
     lineEdit = new QLineEdit;
     QPushButton* quit = new QPushButton(tr("Close"));
     QPushButton* clear = new QPushButton(tr("C"));

     signalMapper = new QSignalMapper(this);
     QGridLayout* gridLayout = new QGridLayout;

     for(int i=0; i<texts.size(); ++i)
      {
         QPushButton* button = new QPushButton(texts[i]);

         connect(button, SIGNAL(clicked(bool)),
                 signalMapper, SLOT(map()));

         signalMapper -> setMapping(button, texts[i]);
         gridLayout -> addWidget(button, i/3, i%3);
      }

     connect(signalMapper, SIGNAL(mapped(QString)), this,
             SLOT(show_number(QString)));

     connect(quit, SIGNAL(clicked(bool)), this, SLOT(close()));
     connect(clear, SIGNAL(clicked(bool)), this, SLOT(reset()));

     QVBoxLayout* layout = new QVBoxLayout;
     layout -> addWidget(lineEdit);
     layout -> addLayout(gridLayout);
     layout -> addWidget(quit);
     layout -> addWidget(clear);
     setLayout(layout);
}

//****************************

void My_First_Calculator::show_number(const QString& text)
{
    if(text == "C")
        temp_text.clear();
    else  temp_text.append(text);
    lineEdit -> setText(temp_text);
}

//*****************************************

void My_First_Calculator::reset()
{
    emit show_number("C");
}

main.cpp:

#include <QApplication>
#include "my_first_calculator.h"

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

    QStringList texts;
    texts << "0" << "1" << "2" << "3" << "4"
          << "5" << "6" << "7" << "8" << "9";

    My_First_Calculator myCal(texts);
    myCal.show();

    return app.exec();
}

At any given time, I try to add some more features to the app. but now two questions:)

1- Is there any weak part in the code that should be replaced?
2- Apparently since I didn't use the Designer for it, I can't change the form my mouse! Is it true? If so, what nifty means is there to change the shape of the form? I mean buttons, sizes, or whatsoever?

ThankX!

mrjj

Hi
All is debatable but my points would be :
You are using good variable names but Im not crazy with underscores.
Seen code where used a lot and it very hard to read.
Not issue here but now its mentioned.
Also , choose a style for variable naming and use it all over.
QLineEdit* lineEdit; <<< qt style
QSignalMapper* signalMapper; << qt style
QString temp_text; << other style

Also
void My_First_Calculator::reset()
why send a "c" to show_number to reset?
Why not directly

void My_First_Calculator::reset()
{
temp_text.clear();
lineEdit -> setText("");
}

2- Apparently since I didn't use the Designer
Well if you do not use UI files, then you just adjust from code.
with resize or setGeometry.
However, for app like yours, one would use layout to make it auto scale the buttons to any size if dialog is resized.
http://doc.qt.io/qt-5/layout.html

tomy

@mrjj said in My first attempt to create a calculator as a novice in Qt programming:

Hi
All is debatable but my points would be :
You are using good variable names but Im not crazy with underscores.
Seen code where used a lot and it very hard to read.

Hi. :)

You are right. It's hard for reading. I will put enough white spaces and comments when it is finished. :)
And what do you mean by "not crazy with underscore" please? (not a native speaker. :( )

Not issue here but now its mentioned.
Also , choose a style for variable naming and use it all over.
QLineEdit* lineEdit; <<< qt style
QSignalMapper* signalMapper; << qt style
QString temp_text; << other style

How to choose a style please?

Also
void My_First_Calculator::reset()
why send a "c" to show_number to reset?
Why not directly

void My_First_Calculator::reset()
{
temp_text.clear();
lineEdit -> setText("");
}

Yeah, very handy, thanks. I applied it. :)

2- Apparently since I didn't use the Designer
Well if you do not use UI files, then you just adjust from code.
with resize or setGeometry.
However, for app like yours, one would use layout to make it auto scale the buttons to any size if dialog is resized.
http://doc.qt.io/qt-5/layout.html

Apparently, in my form until here, using only HBoxLayout, VBoxLayout, and GridLayout are fine. Do you not agree?

mrjj

Hi :)

And what do you mean by "not crazy with underscore" please? (not a native speaker. :( )

Means, I don't like so much. ( reading it )

How to choose a style please?

Well, Thats is mostly what you like. Sometimes in teams , we must agree but if you are
working solo then just choose one and stick to it.
Its mostly about if you write it like
SomeName
someName
somename
some_name

so the important part is just to name it the same way each time and not mixing it.

Apparently, in my form until here, using only HBoxLayout, VBoxLayout, and GridLayout are fine. Do you not agree?
Those are fine and should make it scale all when you resize the window.

tomy

@mrjj said in My first attempt to create a calculator as a novice in Qt programming:

Hi :)

And what do you mean by "not crazy with underscore" please? (not a native speaker. :( )

Means, I don't like so much. ( reading it )

How to choose a style please?

Well, Thats is mostly what you like. Sometimes in teams , we must agree but if you are
working solo then just choose one and stick to it.
Its mostly about if you write it like
SomeName
someName
somename
some_name

so the important part is just to name it the same way each time and not mixing it.

Apparently, in my form until here, using only HBoxLayout, VBoxLayout, and GridLayout are fine. Do you not agree?
Those are fine and should make it scale all when you resize the window.

Thank you :)

I put some other widgets as well, like another lineEdit for the results and so on.
Now I come across two other questions. :)

1- Assume I have a button like this:

QPushButton* two = new QPushButton(tr("2"))

How do I send that string ("2") to the show_number(const QString& text) so that it will be shown by the lineEdit in the form when running the program? I mean without using a signalMapper? Apparently I can't use parameters in connect to send for that function. :(

2- Consider I want to store the contents the lineEdit into a vector of char (so that I will be able to calculate the contents later). How to do it lease?

EDITED!

jsulm

@tomy

In the slot:

QString s = reinterpret_cast<QPushButton*>(sender())->text();

Why? If user enters number 123, why do you want to store this number in a vector like ['1', '2', '3']? It is actually a vector of strings. For that you can split the string, see http://doc.qt.io/qt-5/qstring.html#split

tomy

@jsulm said in My first attempt to create a calculator as a novice in Qt programming:

@tomy

In the slot:
QString s = reinterpret_cast<QPushButton*>(sender())->text();
Why? If user enters number 123, why do you want to store this number in a vector like ['1', '2', '3']? It is actually a vector of strings. For that you can split the string, see http://doc.qt.io/qt-5/qstring.html#split

Because the user types something like "123+256" so it con't be seemingly stored as a (vector of) int.

Guys, I think the program is much more complicated than these items. The app should be able to separate the operands from operators. And also it should be able to observe the priority of the operators, for example:
2+3*4 to be 14 not 20.

What methods would you generally use for each step?

I'm thinking of two tools: first the Dijkstra's algorithm to make the statement a Reverse Polish Notation and then use a stack for calculating. Do you agree?

jsulm

@tomy said in My first attempt to create a calculator as a novice in Qt programming:

Because the user types something like "123+256" so it con't be seemingly stored as a (vector of) int.

But it can be stored as a vector of strings: ["123", "+", "256"] - that's what I said.
Vector of char would be: ['1', '2', '3', '+', '2', '5, '6']

tomy

@jsulm said in My first attempt to create a calculator as a novice in Qt programming:

@tomy said in My first attempt to create a calculator as a novice in Qt programming:

Because the user types something like "123+256" so it con't be seemingly stored as a (vector of) int.

But it can be stored as a vector of strings: ["123", "+", "256"] - that's what I said.
Vector of char would be: ['1', '2', '3', '+', '2', '5, '6']

Buttons send each number as a string; "1", "3", "+" and so on. When the user types "123+256" a string containing "123+256" will be shown on lineEdit. Hence, I should somehow parse to make operators and operands detached. That was why (at the time) I thought of a vector of chars.
But anyway, I'm thinking of a good algorithm to cover expressions like this, that is when we input all of this line once, it makes a correct result:
2+30-12/3+(4^8-1)+sqrt(65)*2.12

tomy

Hi all,

It's done. :) :) :)
The app is finished and it works fine. Please download it from here:
http://www.4shared.com/file/H5brsoaPce/My_First_Calculator.html

It needs only a few .dll files for to be run.

I have some question please:
1- How to change the title of the window from "My_First_Calculator" to "A Qt Calculator!"?
2- I want to design the buttons better from the size, position end etc. How can I do this?
3- Is it possible to make it appear like a professional app?

kshegunov

@tomy said in My first attempt to create a calculator as a novice in Qt programming:

But anyway, I'm thinking of a good algorithm to cover expressions like this, that is when we input all of this line once, it makes a correct result:

Reverse polish notation is what you're probably searching for. See here.

VRonin

This is a infix to postfix conversion for the 4 basic operations and parenthesis I wrote some time ago. it works just for integers but it's a start. once you have the string in postfix (i.e. reverse polish) the calculation is very easy

Edit

Ignore my sh*ty code, see http://rosettacode.org/wiki/Parsing/Shunting-yard_algorithm#C for an idea of converting infix to postfix. thanks @kshegunov for talking some sense into me