main.cpp

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    bool ok = false;
    QString arg;
    if(argc > 1 && argv[1]){arg = argv[1]; arg.toInt(&ok,10);}
    int val = ok? arg.toInt() : 40;
    MainWindow w(val);
    w.show();
    return a.exec();
}