1. 08 Deterministic iteration1May 15 08 Deterministic iteration CE00858-1: Fundamental Programming Techniques

2. 08 Deterministic iteration2May 15 Objectives In this session, we will: introduce repetition using a for loop analyse problems involving repetition consider loops within loops implement solutions to problems involving both repetition and selection

3. 08 Deterministic iteration3May 15 Control structures any program only uses: sequence selection repetition so far only written programs using simple sequences each statement performed in order and selections different statements are performed dependent on some condition

4. 08 Deterministic iteration4May 15 Iteration doing the same actions repeatedly while there is more shopping in the basket, put an item on the conveyor belt loop condition action two types of iteration: deterministic – know before hand how many times to repeat non-deterministic – don’t know how many times to repeat

5. Analysis of iteration when faced with a new specification we need to decide whether actions are performed more than once if they are, there will normally be an iteration in the program if a program has an iteration in it, need to consider: what data is used what operations are done once before the loop? how many times is loop repeated? what operations are repeated inside the loop? what operations are done once after the loop? to decide on how many times the loop is executed, need to consider when the loop starts when the loop finishes 05 Simple selection5May 15

6. 08 Deterministic iteration6May 15 Deterministic iteration repeating a known number of times dealing a hand of 7 cards to two players: repeat 7 times deal card to player 1 deal card to player 2 singing 10 green bottles repeat 10 times from 10 down to 1 sing 1 verse also used to count number of repetitions

7. 08 Deterministic iteration7May 15 For statement in Java for (initial statement; condition; increment) { statement; } done once before loop starts tested before starting each repetition of loop: if true, enter loop if false, exit loop done just before end of each repetition braces are needed to block more than one statement

8. 08 Deterministic iteration8May 15 For loop example – Sum problem: input 10 integers calculate the sum and output it

9. 08 Deterministic iteration9May 15 Sum analysis what data is used? num: integer input by user sum: integer total calculated in program what operations are performed? iteration needed to add up several numbers what operations are done once before the loop? create Scanner prompt user for number initialise sum to 0 how many times is loop repeated? loop repeated 10 times what operations are repeated inside the loop? input num add num to sum what operations are done once after the loop? output sum

10. 08 Deterministic iteration10May 15 Sum code //calculate and output sum of 10 integers Scanner myKeyboard = new Scanner(System.in); System.out.print("Enter 10 integers: "); int sum = 0; int num; //sum numbers entered by user for (int i = 0; i < 10; i++) { num = myKeyboard.nextInt(); sum = sum + num; } System.out.println("Sum is: " + sum); loop repeated 10 times statements repeated inside loop Sum.java could also put: for (int i = 1; i <= 10; i++)

11. 08 Deterministic iteration11May 15 Sum loop explanation initially i is set to 0 as i is less than 10, the loop is entered the statements within the loop are executed the next number is entered the number is added to sum the value of i is incremented to 1 (i++) i is now 1 which is still less than 0, the loop is entered this continues until i is not less than 10 when the test will be false the loop terminates

12. 08 Deterministic iteration12May 15 Using counter example – Squares the variable declared in the for statement can be used within the loop problem: to output the squares of numbers from 1 to 10

13. 08 Deterministic iteration13May 15 Squares analysis what data is used? i: integer counter to control number of repetitions, used inside loop what operations are performed? iteration needed to calculate square of several numbers what operations are done once before the loop? none how many times is loop repeated? loop repeated 10 times, i = 1 to 10 what operations are repeated inside the loop? square = i * i output square what operations are done once after the loop? none

14. 08 Deterministic iteration14May 15 Squares code //calculate and output squares for (int i = 1; i <= 10; ++i ) { System.out.println ( i + " squared is " + (i * i)); } Squares.java

15. 08 Deterministic iteration15May 15 Count back example – CountDown the loop counter can start and end at any value problem: count down from a number entered by the user when count down finished, " Lift off " should be output

16. 08 Deterministic iteration16May 15 CountDown analysis what data is used? start: positive integer input by user count: integer counter to control number of repetitions, used inside loop what operations are performed? iteration needed to count down from starting value what operations are done once before the loop? create Scanner prompt user for start input start how many times is loop repeated? loop repeated start times, count = start down to 0 what operations are repeated inside the loop? output count what operations are done after the loop? output "Lift off"

17. 08 Deterministic iteration17May 15 CountDown code //count down for lift off Scanner myKeyboard = new Scanner(System.in); System.out.print("Enter start value for count down: "); int start = myKeyboard.nextInt(); //count back from starting point for (int count = start; count >= 0; count --) { System.out.println(count); } //lift off System.out.println("Lift off!"); CountDown.java

18. 08 Deterministic iteration18May 15 Common mistake 1 problem... for (i = 0; i <= 10; i++) System.out.print("i is: "); System.out.println(i);

19. 08 Deterministic iteration19May 15 Common mistake 2 problem... for (i = 0; i <= 10; i++); { System.out.print("i is: "); System.out.println(i); }

20. 08 Deterministic iteration20May 15 Common mistake 3 problem... for (i = 0; i >= 10; i++) { System.out.print("i is: "); System.out.println(i); }

21. 08 Deterministic iteration21May 15 Common mistake 4 problem... for (i = 0; i >= 10; i--) { System.out.print("i is: "); System.out.println(i); }

22. 08 Deterministic iteration22May 15 Nested loops example – BlockOfFlats iteration within an iteration inner loop completed each time outer loop executes problem: output address of each flat in a block: four floors, each containing 3 flats output as a table

23. 08 Deterministic iteration23May 15 BlockOfFlats analysis what data is used? floor: integer counter to count 4 floors, used inside loop flat: integer counter to count 3 flats, used inside loop what operations are performed? iteration needed as there are 4 floors nested iteration needed as there are 3 flats on each floor what operations are done once before loop to process floors? none how many times is loop to process floors repeated? loop repeated 4 times, floor = 4 down to 1 as we deal with top floor first what operations are repeated inside loop to process floors? process flats on floor – needs to be expanded output newline what operations are done once after loop to process floors? none

24. 08 Deterministic iteration24May 15 process flats on floor analysis: how many times is loop to process flats repeated? loop repeated 3 times, flat = 1 to 3 what operations are repeated inside loop to process flats? output floor and flat number

25. 08 Deterministic iteration25May 15 BlockOfFlats //process floors for (int floor = 4; floor >= 1; floor--) { //process flats on floor for (int flat = 1; flat <= 3; flat++) { System.out.println("Floor: " + floor + ", flat: " + flat); } System.out.println(); } BlockOfFlats.java

26. 08 Deterministic iteration26May 15 Sequence of loops example – Triangle problem: output triangle of stars: **** *** ** *

27. 08 Deterministic iteration27May 15 Triangle analysis RowPatternSpacesStars 1****04 2-***13 3--**22 4---*31 General case:row – 15 - row

28. 08 Deterministic iteration28May 15 Triangle analysis continued what data is used? row: integer loop counter to count 4 rows, used inside loop space: integer loop counter to count number of spaces on row, used inside loop star: integer loop counter to count number of stars on row, used inside loop what operations are performed? iteration needed as there are 4 rows nested iteration as there are several spaces on each row followed by second nested iteration as there are several stars on each row what operations are done once before row loop? none how many times is row loop repeated? loop repeated 4 times, row = 1 to 4 what operations are repeated inside row loop? process spaces on row – needs to be expanded process stars on row – needs to be expanded output newline what operations are done once after row loop? none

29. 08 Deterministic iteration29May 15 process spaces on row analysis: how many times is spaces loop repeated? loop repeated row – 1 times, space = 1 to row - 1 what operations are done inside spaces loop? output single space process stars on row analysis: how many times is stars loop repeated? loop repeated 5 – row times, star = 1 to 5 - row what operations are done inside the stars loop? output single star

30. 08 Deterministic iteration30May 15 Triangle code //process rows for (int row = 1; row <= 4; row++) { //process spaces on row for (int space = 1; space <= row - 1; space++) { System.out.print(" "); } //process stars on row for (int star = 1; star <= 5 - row; star++) { System.out.print("*"); } System.out.println(); } Triangle.java

31. 08 Deterministic iteration31May 15 Selection in iteration example - Smallest can also perform tests within iteration problem: read in 10 integers output smallest number read in

32. 08 Deterministic iteration32May 15 Smallest analysis what data is used? num: integer input by user smallest: integer to hold smallest value, determined in program what operations are performed? iteration needed to find smallest of 10 integers input nested selection needed as smallest number needs to be stored what operations are done once before loop? create Scanner prompt user for input read first number and store in smallest how many times is loop repeated? 9 times as first integer read outside loop, i = 1 to 9 what operations are repeated inside the loop? read number check if smallest number – needs to be expanded what operations are done once after the loop? output smallest

33. 08 Deterministic iteration33May 15 check if smallest number: what operations are done if num less than smallest? store num in smallest what operations are done if num not less than smallest? none

34. 08 Deterministic iteration34May 15 Smallest code //output smallest number in a list of 10 Scanner myKeyboard = new Scanner(System.in); System.out.println("Enter 10 integers: "); int smallest = myKeyboard.nextInt(); for (int i = 1; i < 10; i++) { int num = myKeyboard.nextInt(); if (num < smallest) { smallest = num; } //output smallest System.out.println("Smallest number: " + smallest); Smallest.java

35. 08 Deterministic iteration35May 15 Summary In this session we have: covered the for loop and how it is used when the number of repetitions is known in advance analysed problems involving deterministic iteration implemented the for loop seen how loops can contain nested loops and other control structures In the next session we will: consider non-deterministic iteration