1. Programming Methodology (1)

2. Iteration

3. Learning objectives • explain the term iteration; • repeat a section of code with a for loop; • repeat a section of code with a while loop; • repeat a section of code with a do...while loop; • select the most appropriate loop for a particular task; • explain the term input validation and write simple validation routines.

4. When to use a loop?

5. Display a square of stars (five by five) on the screen as follows: REPEAT 5 times { } System.out.println("*****"); System.out.println("*****"); System.out.println("*****"); System.out.println("*****"); System.out.println("*****"); * * * * * * * * * * * * * * * * * * * * * * * * * System.out.println("*****");

6. The ‘for’ loop

7. int i; for ( ; ; ) { } i = 1 i <= 5 i++ start counter test counter change counter // instruction(s) to be repeated go here System.out.println(“*****”);

8. Variable Scope

9. public static void main (String [] args) { } int x; x = 10; if ( /* some test */) { } int y; y = x+1; System.out.print(x); System.out.print(y); System.out.print(y);

10. i 6 5 4 3 2 1 int i; for ( ; ; ) { } i = 1 int i = 1 i <= 5 i++ System.out.println(“*****”); ***** ***** RUN ***** ***** *****

11. Different ways of using the loop counter

12. for ( ; ; ) { } int i = 1 i <= 5 i ++ System.out.println(“*****”); ***** ***** ***** *****

13. for ( ; ; ) { } int i = 1 i <= 5 i = i + 2 System.out.println(“*****”); ***** ***** ***** *****

14. for ( ; ; ) { } int i = 1 i <= 10 i = i + 2 System.out.println(“*****”); ***** ***** ***** *****

15. i 11 9 7 5 3 1 for ( ; ; ) { } int i = 1 i <= 10 i = i + 2 System.out.println(“*****”); ***** ***** RUN ***** ***** *****

16. i 10 2 3 4 5 6 7 8 9 1 0 for ( ; ; ) { } int i = 10 i >= 1 i-- start counter test counter change counter // instruction(s) to be repeated go here System.out.println( i ); 10 9 8 RUN 7 6 5 4 3 2 1

17. The body of the loop

18. for ( ; ; ) { } int i = 1 i <= 3 i ++ System.out.println(“First line”); *****

19. for ( ; ; ) { } int i = 1 i <= 3 i ++ System.out.println(“First line”); System.out.println(“Second line”); ***** First line Second line First line Second line First line Second line

20. for ( ; ; ) { } int i = 10 i >= 1 i -- System.out.println( i ); ***** 10 9 8 7 6 5 4 3 2 1

21. for ( ; ; ) { } int i = 10 i >= 1 i -- if ( i > 5 ) { System.out.println( i ); } 10 9 8 7 6

22. Nested loops

23. for (int i = 1; i <= 5; i++) { System.out.println("*****"); }

24. for (int i = 1; i <= 5; i++) { System.out.print("*"); System.out.print("*"); System.out.print("*"); System.out.print("*"); System.out.print("*"); System.out.println( ); }

25. for (int i = 1; i <= 5; i++) { for (int j = 1; j <= 5; j++) { } System.out.print("*"); System.out.println( ); }

26. Allowing the user to fix the size of the square * * * * * * * * * * * * * * * * * * * * * * * * *

27. Allowing the user to fix the size of the square * * * * * * * * *

28. for (int i = 1; i <= 5 ; i++) { for (int j = 1; j <= 5 ; j++) { System.out.print("*"); } System.out.println( ); } System.out.println("Size of square?"); num = sc.nextInt(); num; i++) num; j++)

29. Running the program Size of square? 8 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *

30. Running the program Size of square? 3 * * * * * * * * *

31. Non-fixed repetitions

32. The ‘while’ loop

33. 3422

34. Error!

35. 7343

36. Error!

37. 1234

38. CASH

39. System.out.print(“Enter PIN: ”); pin = sc.nextInt( ); while ( ) { } */ test goes here */ pin != 1234 System.out.print(“Invalid PIN, please re-enter: ”); pin = sc.nextInt( ); System.out.println(“Correct PIN, have some money! ”); Enter PIN: 1234 5555 Correct PIN, have some money! Invalid PIN, please re-enter: RUN 4321 Invalid PIN, please re-enter: 1234 Correct PIN, have some money!

40. Input Validation

41. import java.util.*; public class DisplayResult { public static void main(String[] args) { int mark; Scanner sc = new Scanner (System.in); System.out.println("What exam mark did you get?"); mark = sc.nextInt(); if (mark >= 40) { System.out.println("Congratulations, you passed"); } else { System.out.println("I‘m sorry, but you failed"); } System.out.println("Good luck with your other exams"); } } CHECK MARK HERE

42. System.out.println("What exam mark did you get?"); mark = sc.nextInt( ); || while ( ) { } mark < 0 mark > 100 CHECK MARK HERE System.out.println(“Invalid mark: please re-enter“); mark = sc.nextInt( ); if (mark >= 40) { System.out.println("Congratulations, you passed"); } else { System.out.println("I‘m sorry, but you failed"); } System.out.println("Good luck with your other exams");

43. Sample Program Run What exam mark did you get? 101 Invalid mark: please re-enter -10 Invalid mark: please re-enter 10 I'm sorry, but you failed Good luck with your other exams

44. The ‘do…while’ loop

45. // some code here do { } while ( /*test goes here*/ ) // some code here ; // some code goes here

46. import java.util.*; public class FindCost4 { public static void main(String[] args ) { double price, tax; Scanner sc = new Scanner(System.in); char reply; do { } // code for rest of program here System.out.print (“Enter another product (y/n)?: ”); reply = sc.next().charAt(0); ? || } } while ( ); reply == ‘y’ reply == ‘Y’

47. Sample Program Run *** Product Price Check *** Enter initial price: 50 Enter tax rate: 10 Cost after tax = 55.0 Enter another product (y/n)?: y *** Product Price Check *** Enter initial price: 70 Enter tax rate: 5 Cost after tax = 73.5 Enter another product (y/n)?: n

48. Menu Driven Programs

49. *** Product Price Check *** [1] Enter Price [2] Enter tax [3] Calculate Cost [4] Quit Enter choice [1-4]: 1 Enter initial price: 12.5

50. *** Product Price Check *** [1] Enter Price [2] Enter tax [3] Calculate Cost [4] Quit Enter choice [1-4]: 1 Enter initial price: 100