pre testing and post testing loops C++

1. Repetition (Looping Concept)

2. After studying this chapter you will be able to: O BJECTIVES  Understand the basic components of a loop: initialization, control expression, and update.  Understand and use pretest, post-test, and count-controlled loops.  Differentiate between event-controlled and counter-controlled loops.  Write loops in C++ using while , for , and do...while loops.  Understand the limitations and use of break and continue statements in loops.

3. Concept of a Loop

5. Figure : The concept of a loop

6. Pretest and Post-Test Loops

8. Pretest Loop In each iteration, the loop control expression is tested first. If it is true, the loop action(s) is executed; if it is false, the loop is terminated. Post-test Loop In each iteration, the loop action(s) are executed. Next, the loop control expression is tested. If it is true, a new iteration is started; otherwise, the loop terminates. Note:

9. Figure : Pretest and post-test loops “ WHILE” test at the top…. “WHILE” test at the bottom CONDITION CONDITION

10. Figure : Two different strategies for starting exercise CONDITION CONDITION False True

11. Figure : Minimum number of iterations in two loops It is important that you understand this critical difference between the two basic types…

12. Initialization and Updating

13. Figure : Loop initialization and updating The initialization may optionally be part of the loop structure.

14. Figure : Initialization and updating for exercise

15. Event-Controlled and Counter-Controlled Loops

16. Figure : Event-controlled loop concept

17. Figure : Counter-controlled loop concept

18. Loops in C++

20. Figure : The while statement while the expression is true, do …..

21. Figure : Compound while statement

22. Figure : for statement The for is just a special case of a while loop.

23. The for loop is constructed in this way… for ( initialization statement(s) , while test expression , update statement(s) )‏ { body of loop… }

24. A for loop is used when your loop is to be executed a known number of times. You can do the same thing with a while loop, but the for loop is easier to read and more natural for counting loops. Note:

25. Figure : Compound for statement

26. Figure : Comparing for and while loops

27. In C/C++ the for loop counter is almost always initialized to a ZERO . So, if you want to do something 5 times, the for loop would be coded like this… for (int i = 0; i < 5; i++)‏ { do something… } It is also legal to have the test expression limit be a variable, as in: for (int i = 0; i < Num; i++)‏

28. Figure : Format of the do…while statement

29. Pre-test and post-test loops

31. The End