int num1=strNum1.toInt(&ok,10); lineEdit_3->setText(QString("%1").arg(sum));

{
   qDebug()<<"TestBtnClicked: "<<bState<<endl;
    qDebug()<<QObject::sender()->objectName();

    QString strNum1=ui->lineEdit->text();
    QString strNum2=ui->lineEdit_2->text();
    bool ok;
    int num1=strNum1.toInt(&ok,10);
    if(!ok)
        return;
    int num2=strNum2.toInt(&ok,10);
    if(!ok)
        return;
    int sum=num1+num2;

    ui->lineEdit_3->setText(QString("%1").arg(sum));


}