I don't know what a "structured diagram" is. But what you drew is called a "flowchart".
Treat an event structure as a decision point where the code holds waiting for one of any number of events to happen. A diamond with more than just a true and false output.
Yes it seems correct
Agreed, however it could be written so that you did not require 4 controls. Imagine how many controls will be needed if they need to implement more operations.
I want to know if the following Flowchart is correct. You find below the Program (VI).
What happens when Division button changes or summation button changes. Either of those go to a step to do a calculation. But then what? Program stops dead? It doesn't go to the Stop node. Does it return to the event structure? (I imagine yours is like most event structures that they are in a while loop.) In which case you need some leaders take you back to the top where your event case decisions start.