C++Part III (not in the textbook)课件.ppt

C++Part III (not in the textbook) Yingcai Xiao 10/01/2008 精品文档 Event-driven Programming (EDP) 精品文档 Programming Paradigms Sequential: Program statements are executed one at a time. The order of execution is predetermined by the programmer. The user has no or little control of the order. Not user friendly. Event-driven: Program idles after initialization, waits for events. When an event is generated by the user, it will be sent to the program to be processed. The event is first send to the event-mapper, which dispatches the event to its handler. The event-handler process the event. The program goes to idle mode again. The order of events is not predetermined by the programmer. The user can select what the program should do next. User friendly. 精品文档 Programming Paradigms Text-based: Users issue commands as texts. Users have to remember the texts of the commands and their format. Not user friendly. GUI-based: Users issue commands by point-and-click on GUI (Graphical User Interface) objects. Users do not have to remember the texts of the commands (but have to remember where the GUI items are). WYSIWYG (What you see is what you get). User friendly. 精品文档 Friendliness of Programming Paradigms Sequential EDP Text least modest GUI no use most EDP: The application continuously waits until interrupted by some input events to respond. The application has an event-handler for each event it wants to handle. The event-handler is invoked when the corresponding event occurs. GUI-EDP: Application waits (idles) until the user generates an event trough an input device (keyboard, mouse, …). The OS dispatches the event to the application who owns the window. The corresponding event handler(s) of the application is invoked to process the event. 精品文档 Text-Based EDP #include iostream using namespace std; int value; // global int main() { // Initialization char s = +; value = 0; while(1) { // event loop cout Please select an operation (+,-,q): \n; cin s; //wait for an ev