qt下字符串形式与整型的转换

这里写代码片void MainWindow::calculationSlot(){    int firstNumber=ui->firstLineEdit->text().toInt();                     int secondNumber=ui->secondLineEdit->text().toInt();          //字符串转成整形   int resultNumber=firstNumber+secondNumber;   ui->resultLineEdit->setText(QString::number(resultNumber)); //整形转成字符串}