题目：点击按钮改变文字

需要增加一个count属性，并且只需要定义槽，信号函数已经内置好了

//widget.h

#ifndef WIDGET_H
#define WIDGET_H

#include <QWidget>

QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE

class Widget : public QWidget    //窗体对象
{
    Q_OBJECT

public:
    Widget(QWidget *parent = nullptr);
    ~Widget();
    int count;    //计数

public slots:
    void pushBtn(void);    //接收槽

private:
    Ui::Widget *ui;
};
#endif // WIDGET_H

//widget.cpp

#include "widget.h"
#include "ui_widget.h"
#include <QDebug>

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    count=0;    //初始化count

    //绑定信号与接收槽
    connect(ui->pushButton_3,SIGNAL(clicked()),this,SLOT(pushBtn()));
    connect(ui->pushButton_4,SIGNAL(clicked()),this,SLOT(pushBtn()));
}

Widget::~Widget()
{
    delete ui;
}

void Widget::pushBtn()
{
    count++;
//    qDebug()<<"count="<<count;
    QString str=QString("你点击了%1次").arg(count);   // 类似printf
    ui->label->setText(str);

}