sorry about that i pasted the wrong code

void Settings::setData(int data)
{
 printf("BLAH BLAH BLAH %d\n", data);
 ui->lineEdit->setText(QString::number(data));
}

this is the code im using but has the same effect and nothing happens
never mind i was just being really thick i should have done this in my MainWindow.cpp

 dlg->show();

however i cant seem to get the line Edit to work

Because setText expects a QString as you can clearly see in the documentation: https://doc.qt.io/qt-6/qlineedit.html#text-prop
So, convert the int to QString: https://doc.qt.io/qt-6/qstring.html#number-1

MainWindow.cpp

void MainWindow::on_actionSettings_triggered()
{
 qDebug() << "Settings";
 Settings *dlg = new Settings();
     connect(this, SIGNAL(sendData(int)), dlg, SLOT(setData(int)));
     emit sendData(35);
 settings.show();
}

Settings.cpp

void Settings::setData(int data)
{
 printf("BLAH BLAH BLAH %d\n", data);
ui->lineEdit->setText(data);
}

my printf function does show that data is 35 however i cant seem to get the line Edit to work

Thank you

connect(MainWindow,SIGNAL(SendData(int)),Settings,SLOT(getData(int)));

At a guess, from your Settings.cpp extract void Settings::getData() it looks like Settings is a class name. For signal/slot you must connect instances (presumably MainWindow is one?), what is your Settings instance's variable?

Next, given you have declared the getData() slot as private in Settings.h obviously you are not going to be able to access it on a Settings instance anyway, only from within Settings class. If you want to connect() to it from the outside world/on an instance don't make it private, that is what private is there to prevent!

You should not be using SIGNAL/SLOT() macros for connect(), they are old-style from many years ago. You should be using new style, the error messages may be more helpful.