QPushButton继承至QObject，查看一下QObject的函数sender()；
比如：
connect(btn, SIGNAL(click()), this, SLOT(chang()));
chang()
{
QPushButton *btn = (QPushButton*)sender();
for(int i = 0; i <= 9; i++)
{
if(btn->text().toInt() == i)lineEdit->setText(lineEdit->text() + btn->text());
}
}
即可。（sender（）函数，可以取得发送信号的对象，返回值是QObject）
