The next customization is to add a button to our application. The most common button that is used in any GUI is a push or command button. We push (click on) the button to command the computer to perform some action or answer a decision. Typical push buttons include: OK, Apply, Cancel, Close, Yes, No, and Help. Usually the push button is rectangular with some label on it. It can also have an optional icon associated with it. It is also possible to define a shortcut key combination to the button to which it responds on clicking the key combination.

The button emits a signal when it is activated by any external event, such as a mouse click or by pressing the spacebar, or by a keyboard shortcut. A widget may be associated with this key click event, which is executed on receiving this signal, and it is usually called a slot in Qt. We will learn more about signals and slots in the later chapters. As for now, be informed that a signal will connect to a slot on emission. There can...