A little calculator problem

[wysota]

Shouldn't you be connecting to the clicked() signal of the "Execute" button then?

[bijan311]

OK, here is the entire code,

#include <QApplication>
#include <QPushButton>
#include <QLabel>
#include <QSpinBox>
#include <QLCDNumber>
#include <QHBoxLayout>
#include <QVBoxLayout>
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QLabel *minus = new QLabel("-");
    QPushButton *equal = new QPushButton("Execute");
    QSpinBox *num1 = new QSpinBox;
    QSpinBox *num2 = new QSpinBox;
    QLCDNumber *show = new QLCDNumber(3);
    int calc1, calc2;
 
    QObject::connect(num1, SIGNAL(valueChanged(calc1)), this, SLOT(setValue(calc1)));
    QObject::connect(num2, SIGNAL(valueChanged(calc2)), this, SLOT(setValue(calc2)));
    QObject::connect(equal, SIGNAL(clicked()), show, SLOT(setValue(calc1-calc2)));
 
    QHBoxLayout *layout = new QHBoxLayout;
    layout->addWidget(num1);
    layout->addWidget(minus);
    layout->addWidget(num2);
    layout->addWidget(show);
    QVBoxLayout *mainLayout = new QVBoxLayout;
    mainLayout->addLayout(layout);
    mainLayout->addWidget(equal);
 
    return app.exec();
}

#include <QApplication>
#include <QPushButton>
#include <QLabel>
#include <QSpinBox>
#include <QLCDNumber>
#include <QHBoxLayout>
#include <QVBoxLayout>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    QLabel *minus = new QLabel("-");
    QPushButton *equal = new QPushButton("Execute");
    QSpinBox *num1 = new QSpinBox;
    QSpinBox *num2 = new QSpinBox;
    QLCDNumber *show = new QLCDNumber(3);
    int calc1, calc2;

    QObject::connect(num1, SIGNAL(valueChanged(calc1)), this, SLOT(setValue(calc1)));
    QObject::connect(num2, SIGNAL(valueChanged(calc2)), this, SLOT(setValue(calc2)));
    QObject::connect(equal, SIGNAL(clicked()), show, SLOT(setValue(calc1-calc2)));

    QHBoxLayout *layout = new QHBoxLayout;
    layout->addWidget(num1);
    layout->addWidget(minus);
    layout->addWidget(num2);
    layout->addWidget(show);
    QVBoxLayout *mainLayout = new QVBoxLayout;
    mainLayout->addLayout(layout);
    mainLayout->addWidget(equal);

    return app.exec();
}

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and here are the errors I receive.

|19|error: invalid use of `this' in non-member function|
|20|error: invalid use of `this' in non-member function|

|19|error: invalid use of `this' in non-member function|
|20|error: invalid use of `this' in non-member function|

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[wysota]

Well, there is no "this" object when you are not inside any objective code so obviously it won't work. Your connect statements still don't make sense anyway. You can't do mathematical operations there and you can't pass variable names there.

Here is something more reasonable:

class Calculator : public QWidget {
  Q_OBJECT
public:
  Calculator(QWidget *parent = 0) : QWidget(parent){
    minus = new QLabel("-");
    equal = new QPushButton("Execute");
    num1 = new QSpinBox;
    num2 = new QSpinBox;
    show = new QLCDNumber(3);
 
    QHBoxLayout *layout = new QHBoxLayout;
    layout->addWidget(num1);
    layout->addWidget(minus);
    layout->addWidget(num2);
    layout->addWidget(show);
    QVBoxLayout *mainLayout = new QVBoxLayout(this);
    mainLayout->addLayout(layout);
    mainLayout->addWidget(equal);
    connect(equal, SIGNAL(clicked()), show, SLOT(calculate()));
  }
public slots:
  void calculate() {
    show->setValue(num1->value()-num2->value());
  }
private:
  QLabel *minus;
  QPushButton *equal;
  QSpinBox *num1;
  QSpinBox *num2;
  QLCDNumber *show;
};
 
#include "main.moc"
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  Calculator w;
  w.show();
  return app.exec();
}

class Calculator : public QWidget {
  Q_OBJECT
public:
  Calculator(QWidget *parent = 0) : QWidget(parent){
    minus = new QLabel("-");
    equal = new QPushButton("Execute");
    num1 = new QSpinBox;
    num2 = new QSpinBox;
    show = new QLCDNumber(3);

    QHBoxLayout *layout = new QHBoxLayout;
    layout->addWidget(num1);
    layout->addWidget(minus);
    layout->addWidget(num2);
    layout->addWidget(show);
    QVBoxLayout *mainLayout = new QVBoxLayout(this);
    mainLayout->addLayout(layout);
    mainLayout->addWidget(equal);
    connect(equal, SIGNAL(clicked()), show, SLOT(calculate()));
  }
public slots:
  void calculate() {
    show->setValue(num1->value()-num2->value());
  }
private:
  QLabel *minus;
  QPushButton *equal;
  QSpinBox *num1;
  QSpinBox *num2;
  QLCDNumber *show;
};

#include "main.moc"

int main(int argc, char **argv){
  QApplication app(argc, argv);
  Calculator w;
  w.show();
  return app.exec();
}

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[bijan311]

now it says

|error: 'class QLCDNumber' has no member named 'setValue'

|error: 'class QLCDNumber' has no member named 'setValue'

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P.S
Sorry this is taking this long, I am a complete beginner.

[Lykurg]

It's because it has to be

show->display(num1->value()-num2->value());

show->display(num1->value()-num2->value());

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. A quick look it the documentation helps in such cases.

[bijan311]

sorry, I didn't post these errors and I thought the others would go away but here are all the errors.

|40|error: `QLCDNumber*calculator::show' is private|
|48|error: within this context|
|48|error: `w.calculator::show' cannot be used as a function|

|40|error: `QLCDNumber*calculator::show' is private|
|48|error: within this context|
|48|error: `w.calculator::show' cannot be used as a function|

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again, sorry if I'm beginning to be a pain.

[wysota]

Call the variable differently. It clashes with the method name (QWidget::show()).

[Lykurg]

Seems to be a name clash, so rename your QLCDNumber to lcdnumber or something else and recompile.

[bijan311]

OK so everything compiled, BUT when it is linking to the .EXE it gives me this error

C:\Program Files\CodeBlocks\MinGW\bin\..\lib\gcc\mingw32\3.4.5\..\..\..\..\include\c++\3.4.5\bits\stl_algobase.h:(.text$_ZN10calculatorD1Ev[calculator::~calculator()]+0xb)||undefined reference to `vtable for calculator'|

C:\Program Files\CodeBlocks\MinGW\bin\..\lib\gcc\mingw32\3.4.5\..\..\..\..\include\c++\3.4.5\bits\stl_algobase.h:(.text$_ZN10calculatorD1Ev[calculator::~calculator()]+0xb)||undefined reference to `vtable for calculator'|

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[wysota]

Did you remember to run qmake after making changes I initially suggested to the code?

[bijan311]

I'm sorry, I don't know how to make a .moc file, I was playing around in the QT command prompt but I can't get a .moc file.

I've treid qmake, qmake -o file, qmake -v.

[squidge]

Run QMake and then rebuild. That'll create your moc files and even run moc on them

[bijan311]

ok i ran qmake in the folder of main.cpp then I pressed rebuild in Code::Blocks and it gave me the same error.