2. 2Object-Oriented Program Development Using C++

3. 3 Basic Loop Structures Loops repeat execution of an instruction set Three repetition structures: while, for, do-while Three common elements –Test condition controls repetition –Statement initializes state of test condition –Internal statement terminates loop Syntax variations around placement/type of test

4. 4Object-Oriented Program Development Using C++ Pretest and Posttest Loops Pretest (entrance-controlled) loop –Condition tested before loop statements executed –Examples: while and for statements Posttest (exit-controlled) loop –Termination condition tested at end of loop –Loop guaranteed to execute at least once –Example: do-while Infinite loop: results from improper update of test

5. 5Object-Oriented Program Development Using C++ Figure 6-1 A Pretest Loop

6. 6Object-Oriented Program Development Using C++ Figure 6-2 A Posttest Loop

7. 7Object-Oriented Program Development Using C++ Fixed-Count versus Variable- Condition Loops Fixed-count loop: condition tracks number of repetitions Variable condition loop: test depends on changing variable All C++ repetition structures adaptable to either type

8. 8Object-Oriented Program Development Using C++ while Loops Example of while statement: int count = 1; // initialize count while (count <= 10){ cout << count << endl; count++; // increment count } Loop turns around value of count Termination value: count after increment to 11

9. 9Object-Oriented Program Development Using C++ Figure 6-3 Structure of a while Loop

10. 10Object-Oriented Program Development Using C++ Interactive while Loops while statement promotes interactivity Include interactive prompts and cin statement Sample program –Enters and echo-prints four numbers –Utilizes accumulation statement –Totals input, computes average, outputs result Terminates after fixed count

11. 11Object-Oriented Program Development Using C++ Figure 6-4 Flow of Control for Program 6-5

12. 12Object-Oriented Program Development Using C++ Figure 6-5 Accepting and Adding a Number to a Total

13. 13Object-Oriented Program Development Using C++ Sentinels –Values signal start or end of series –May or may not share data type of input Code fragment: cout << "\nTo stop entering numbers, type in any " << "number greater than 100" << endl; while (number <= MAX_COUNT) number value greater than 100 terminates loop

14. 14Object-Oriented Program Development Using C++ break and continue Statements break statement –Forces exit from repetition or switch statement –Syntax: break; –Most appropriately used in switch statement continue statement –Short circuit to next iteration –Syntax: continue; –Applies to while, do-while, and for structures

15. 15Object-Oriented Program Development Using C++ The null Statement null statement: consists of a semicolon ( ; ) Typical use: repetition structure without loop body Example – for (int count = 1; count <= pow(10,7) ; count++); – Time delay loop requires no explicit action

16. 16Object-Oriented Program Development Using C++ for Loops for loop: while functionality with alternate syntax Syntax template: for (initializing list; expression; altering list){ statement(s); } Three components between parentheses optional Initialization, test, and update conveniently clustered Commas separate additional items added to component

17. 17Object-Oriented Program Development Using C++ Figure 6-7 for Loop Control

18. 18Object-Oriented Program Development Using C++ Figure 6-8 Simplified for Loop Flowchart

19. 19Object-Oriented Program Development Using C++ Nested Loops Nested loops: loops within other control structures –Add dimensionality to data Code fragment for (int i = 1; i <= 10; i++){ // start outer loop for (int j = 1; j <=10; j++){ // start inner loop cout << asterisk << space; } // end inner loop } // end outer loop Inner loop completes 10 x 10 (100) iterations

20. 20Object-Oriented Program Development Using C++ do-while loops –Iterates while condition true –Ends when posttest condition evaluates to false –Loop guaranteed to execute at least once Syntax template: do{ statement(s); }while (expression);

21. 21Object-Oriented Program Development Using C++ Figure 6-10 The do-while Loop Structure

22. 22Object-Oriented Program Development Using C++ Figure 6-11 The do-while Statement's Flow of Control

23. 23Object-Oriented Program Development Using C++ Validity Checks do-while structure well suited to error handling Code fragment: do{ cout << "An invalid grade was just entered\n"; cout << "Please check the grade and re-enter\n"; cin >> grade; }while (grade MAX_GRADE); If loop entered, guaranteed to execute at least once

24. 24Object-Oriented Program Development Using C++ Program Design and Development: UML State Diagrams State diagram: represents object states over time Critical design step: specify events that change state Event –Signal (or stimulus) from one object to another –Example: press button to move elevator Basic notation –Flow line: denotes event –State: rectangle with rounded corners

25. 25Object-Oriented Program Development Using C++ Figure 6-12 The State Model Identifies Operations to Be Included in the Class Diagram

26. 26Object-Oriented Program Development Using C++ Figure 6-13 State Diagram Notation

27. 27Object-Oriented Program Development Using C++ Objects communicate via messages Event attributes –Data values in message –Translate to method arguments Action of event: occurs in zero time (instantaneously) Activity of object: response takes place over time Examples –Action: push door bell (or elevator) button –Activity: chimes sound (or elevator moves to floor) Program Design and Development: UML State Diagrams (continued)

28. 28Object-Oriented Program Development Using C++ Figure 6-15 An Example of an Event Activity

29. 29Object-Oriented Program Development Using C++ Figure 6-16 A State with an Activity

30. 30Object-Oriented Program Development Using C++ Figure 6-18 A State Diagram for an Elevator

31. 31Object-Oriented Program Development Using C++ Applications: Random Numbers and Simulations Many models include statistical/probabilistic elements Computers support models with random numbers Random numbers –Set of numbers whose order cannot be predicted –Pseudorandom numbers: approximate random condition General purpose C++ method: rand ( )

32. 32Object-Oriented Program Development Using C++ Scaling rand ( ) may be adapted to floating-point data rand ( ) may be modified to scale data values –Typical scaled range: 0.0 to 1.0 –Technique Cast return expression to floating-point type Divide result by RAND_MAX (compiler dependent) rand ( ) may be used to return remainders –a + rand( ) % b –a and b represent end-points of interval

33. 33Object-Oriented Program Development Using C++ Simulations –Computer programs imitating scientific experiment –Produce important research results –Avoid overhead associated with experiments Random numbers used extensively in simulations

34. 34Object-Oriented Program Development Using C++ Coin Toss Simulation Hypothesis: head as likely as tail (probability =.5) Coin toss algorithm –Generates random number between 0 and 1 n times –If random number >=.5, increment heads (else tails) Class diagram –Instance variables: heads and tosses –Main methods: flip ( ) and percentages ( ) Results close to projections (difference <.5%)

35. 35Object-Oriented Program Development Using C++ Figure 6-22 A Class Diagram for a CoinToss Class

36. 36Object-Oriented Program Development Using C++ Elevator Simulation State diagram –Action: pressing button –Activity: move to floor (iterative) Class diagram –Two attributes: currentFloor and maxFloor –Four methods request ( ) performs primary service –Evaluates floor request and moves to same –Uses selection and repetition structures Driver enhanced with do-while encasing

37. 37Object-Oriented Program Development Using C++ Figure 6-23 A State Diagram for an Elevator

38. 38Object-Oriented Program Development Using C++ Figure 6-24 A Class Diagram for an Elevator Class

39. 39Object-Oriented Program Development Using C++ Summary Basic repetition structures: while, for, and do-while Basic loop components: initialization, test, termination Interactive I/O improved with repetition structures Nesting: combining structures for complex computation UML state diagram: event driven

40. 40Object-Oriented Program Development Using C++ Summary (continued) Action: associated with event Activity: response associated with object rand ( ) method generates random numbers Random numbers simulate statistical/probabilistic patterns Example simulations: coin toss and elevator movement