How display multiple values in QLabel in Qcreator - qt

Question

I am developing calculator using Qt SDK I want to get values from the calculator buttons in to one Qlabel. I have designed GUI using design view I tried to get values using following code.
void MainWindow::on_three_button_clicked(){
ui->label->setText("3");
}
but then Only I can get one button value at a time
please help me on this...

Answer 1

You can have one QString variable to store current pressed value. Here I am considering your class variable defined as QString myEnteredNum. Then you can use it as below code:
void MainWindow::on_three_button_clicked(){
myEnteredNum.append("3"); // This method you can add in each number slot
ui->label->setText(myEnteredNum);
}
I hope this helps you.

Answer 2

There are two general approaches to this. You can append the digits directly to a number, and bind the label to the number. The m_first label below is updated that way. You can also append the digits directly to the label. The m_second label is updated so.
#include <QtWidgets>
class Window : public QWidget {
Q_OBJECT
Q_PROPERTY(double number MEMBER m_number WRITE setNumber NOTIFY numberChanged)
double m_number;
QGridLayout m_grid;
QLabel m_first, m_second;
QPushButton m_digits[10], m_clear;
public:
Window(QWidget * parent = 0) : QWidget(parent),
m_grid(this), m_clear("C") {
m_grid.addWidget(&m_first, 0, 0, 1, 3);
m_grid.addWidget(&m_second, 1, 0, 1, 3);
m_grid.addWidget(&m_clear, 5, 2);
for (int i = 0; i < 9; ++i) {
m_digits[i].setText(QString::number(i));
if (i > 0) m_grid.addWidget(m_digits + i, 2 + (i-1)/3, (i-1)%3);
else m_grid.addWidget(m_digits + i, 5, 1);
QObject::connect(m_digits + i, &QPushButton::clicked, [i, this]{
// Add the digit to the number
setNumber(m_number * 10.0 + i);
// Add the digit to the label
m_second.setText(m_second.text().append(QString::number(i)));
});
}
QObject::connect(&m_clear, &QPushButton::clicked, [this]{
setNumber(0);
m_second.setText("0");
});
QObject::connect(this, &Window::numberChanged,
&m_second, &QLabel::setNum);
emit m_clear.clicked(); // initialize everything
}
Q_SIGNAL void numberChanged(double);
void setNumber(double n) { m_number = n; emit numberChanged(n); }
};
int main(int argc, char ** argv) {
QApplication app(argc, argv);
Window window;
window.show();
return app.exec();
}
#include "main.moc"
Finally, a calculator is stateful and, to avoid common mistakes, you could use a QStateMachine to make this fact explicit, and to adjust the behavior of the calculator depending on which state it's in.