#include <QApplication>
#include <QTextEdit>
#include <QString>

int main(int argc, char *argv[])
{
    QString str = "Hello";

    QApplication app(argc, argv);
    QTextEdit *editor = new QTextEdit(str);
//?    QObject::connect(editor, SIGNAL(textChanged()), ...
    editor->show();
    return app.exec();
}