没有加入弹出窗口

#ifndef MAINWINDOW_H
#define MAINWINDOW_H#include <QMainWindow>namespace Ui {
class MainWindow;
}class MainWindow : public QMainWindow
{Q_OBJECTpublic:explicit MainWindow(QWidget *parent = 0);~MainWindow();private slots:void on_pushButton_clicked();private:Ui::MainWindow *ui;
};#endif // MAINWINDOW_H

#include "mainwindow.h"
#include "ui_mainwindow.h"MainWindow::MainWindow(QWidget *parent) :QMainWindow(parent),ui(new Ui::MainWindow)
{ui->setupUi(this);QObject::connect(ui->pushButton,SIGNAL(clicked()),this,SLOT(on_pushButton_clicked()));
}MainWindow::~MainWindow()
{delete ui;}void MainWindow::on_pushButton_clicked()
{int first = ui->first->text().toInt();int second = ui->second->text().toInt();int result;switch (ui->comboBox->currentIndex()) {case 0:result = first + second;break;case 1:result = first - second;break;case 2:result = first * second;break;case 3:if(second < 0)return;result = first / second;break;default:break;}
//    int first = ui->first->text().toInt();
//    int second = ui->second->text().toInt();
//    int sum = first + second;ui->sum->setText(QString::number(result));}