QT - make a simple calculator - realize four operations

Realization effect

Realization Add

Realization reduce

Realization ride

Realization except

How to complete ?

On the basis of the previous chapter , Delete +, Change to
This .
choice Editing project , Pictured .

Install the plus sign in the figure below , add to + ,- , * , / arithmetic

Code section

Complete code

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui {
     class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
private slots:
    void calSlot();
};
#endif // MAINWINDOW_H

main.cpp

#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

mainwindow.cpp( Key code )

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    
    ui->setupUi(this);
    QObject::connect(
                //ui Inside calButton object ( Calculate button )
                ui->calButton,
                // Send a signal ( Click the signal )
                SIGNAL(clicked()),
                // Give the current object 
                this,
                // With a slot function calSlot() To connect 
                SLOT(calSlot()));
}

MainWindow::~MainWindow()
{
    
    delete ui;
}
void MainWindow::calSlot()
{
    
    int first=ui->firstLineEdit->text().
            toInt();
    int second=ui->secondLineEdit->text().
            toInt();
    int result;
    if(ui->comboBox->currentIndex()==0){
    //+
        result=first+second;
        ui->resultLineEdit->setText(QString::number(result));
    }
    if(ui->comboBox->currentIndex()==1){
    //-
        result=first-second;
        ui->resultLineEdit->setText(QString::number(result));
    }
    if(ui->comboBox->currentIndex()==2){
    //*
        result=first*second;
        ui->resultLineEdit->setText(QString::number(result));
    }
    if(ui->comboBox->currentIndex()==3){
    // /
        if(second==0)return;
        result=first/second;
        ui->resultLineEdit->setText(QString::number(result));
    }
}