What are event driven programs used in?

Answer 1

set counter K to 0

repeat

{

if a number has been entered (from the keyboard)

{

store in A[K] and increment K

if K equals 2 print A[0]+A[1] and reset K to 0

}

}

Answer 2

Event-driven programs are typically used in graphical user interfaces (GUI) and multi-tasking/multi-threaded environments. The operating system maintains a message queue containing events generated by all active applications and services. Every message has an ID denoting the target application, along with the ID of the event itself plus any data that is relevant to the event. When an application is idle, it enters an idle loop which repeatedly checks the first message on the queue. If the application ID matches, the message is dequeued and processed. If the ID does not match, the idle loop terminates.

Since every application is given an allocated time-slice of the CPU according to its priority, so long as the applications are idle during their allotted time then all messages will be processed fairly rapidly. However, if an application is busy and the first message in the queue is intended for it, that message will effectively block all other messages to all other applications. The operating system will appear sluggish because messages are being enqueued all the time but the busy application is preventing them from being processed. To prevent this, programmers must periodically yield control to the system during an intensive process to allow messages to be enqueued, and then enter idle mode to process any pending messages. Once it has dealt with those messages it can continue the intensive process until the next yield point.

Since events can be posted from one application to another, applications must be prepared to deal with them. For instance, if the user chooses to shut down the system, every application will be notified that it must close. But if the application is running an intensive operation then it will not be possible to close the application until that process has been aborted gracefully.

There are various ways of dealing with this, but generally the application will override the idle loop in order to filter messages. That is, the override will dequeue messages but will not process them unless certain conditions are satisfied. This is known as "eating" events. If the event is an instruction to close the application but a process is still running, then the idle loop will store the event and set an abort flag that the process can check at each yield point, allowing it to terminate gracefully. When the idle loop determines there is no running process but the abort flag has been set, it will reset the abort flag and repost the event it stored which can then be dealt with normally.

Answer 3

Event driven programming is where code gets executed when the user fires a given event. An event can be when a user clicks a button in a program. When the button gets clicked some code will be executed, that would not be executed if the user had not clicked the button.

Have a good day! RandomGeek