A1-B2-C3

char MainWindow::checkSum(QByteArray &b)
{
    char val = 0x00;
    char i;
    foreach (i, b)
    {
       val ^= i;
    }

    return val;
}

...

 QChar resultCh =  checkSum(output);

        ui->lineEdit->setText(resultCh);
        ui->outputLabel->setText(resultCh);

        printf("%xn", resultCh);
...

ui->lineEdit->setText(QString("%1").arg(resultCh.unicode(), 0, 16));