setVisible, -> token, problems

[Salazaar]

Understood. Assuming, what do I have to change in this Dialog->setWindowTitle to make it no-errormaking program?

[high_flyer]

Define a QDialog pointer instead of Dialog.

Allthough the above is the answer to your question, it will not solve your problem, which is knowing and understanding C++ rules and syntax.
As long as you wont master that, you will have these problems all the time.

[Salazaar]

Define a QDialog pointer instead of Dialog.

I don't understand, Dialog is a pointer of QDIalog

[high_flyer]

Not in your code.

[Salazaar]

void setupUi (QDialog * Dialog)

[high_flyer]

yes, but I already told you, its not in the scope of your code.
You would have understood that if you knew C++ rules.
We can't teach you C++.
First learn C++, then code Qt.