How to resize window with pushbutton

[jpn]

You cannot put parameter values into the connect statement. You are only allowed to put possible parameter types, and in this case the parameter types must match. For further details, see Signals and Slots.

What you need is most likely a custom slot. Connect the button's clicked() signal to that slot and do the resizing there. Again, for details, see the link above.

Only widgets are resizable. See QWidget::resize(). You cannot resize QApplication as it's nothing visible.