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Looping

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Looping

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  1. Looping Lecture Week 5

  2. Topic • Increment Operator • while loop • for loop • Do …. While loop

  3. Increment Operator • ++ and – are operators that add and subtract 1 • For example number = number + 1; is equivalent to number += 1; or can rewrite as number++; • Or number = number - 1; is equivalent to number -= 1; or can rewrite as number--;

  4. Postfix and Prefix Modes • Examine the difference number = 4; System.out.println (number++); System.out.println (number number=number + 1 Output 4

  5. Postfix and Prefix Modes • Examine the difference number = 4; System.out.println (number++); System.out.println (number); • Output 4 5

  6. Postfix and Prefix Modes • Examine the difference number = 4; System.out.println (++number); • Output 5 number=number + 1 System.out.println (number

  7. What is the value of x and y? a. int x = 1,y; y = x++; // y=x; x=x+1; b. int x = 1, y; y = ++x; // x=x+1; y=x;

  8. while loop • Loop makes a program seem powerful. • Loop is a structure that allows repeated actions. • General format : while (boolean expression) statement; Boolean expression Loop body true false

  9. Example • Print salam 5 times System.out.println(“Assalamu’alaikum”); System.out.println(“Assalamu’alaikum”); System.out.println(“Assalamu’alaikum”); System.out.println(“Assalamu’alaikum”); System.out.println(“Assalamu’alaikum”);

  10. Smarter way int count=1; while (count <=5){ System.out.println(“Assalamu’alaikum”); count++; } Set initial counter no Increase counter Stop? print yes

  11. Check for validity int pinNo = 1234; boolean notValid = true; while ( notValid) { pin = inputDevice.typeInt(); if (pin == pinNo) notValid = false; }

  12. What will happen??? int n = 5; while (n <10){ System.out.println(“Please stop”); n++; }

  13. What will happen??? int n = 5; while (n <10); { System.out.println(“Please stop”); n++; }

  14. do … while loop Structure Do { …. } while (non-stopping criteria) Loop body Boolean expression true false

  15. Example int count=1; while (count <=5){ System.out.println(“Assalamu’alaikum”); count++; } int count=1; do { System.out.println(“Assalamu’alaikum”); count++; } while (count <5);

  16. Example int pinNo = 1234; boolean notValid = true; while ( notValid) { pin = inputDevice.typeInt(); if (pin == pinNo) notValid = false; } int pinNo = 1234; do { pin = inputDevice.typeInt(); } while pin != pinNo;

  17. for loop • structure when definite number of iterations is required. for (start counter; stopping criteria; increment counter) loop body initialization test update Set initial counter no Loop body Increase counter Stop? yes

  18. Example for (int count =1;count <=5;count++) System.out.println(“Assalamu’alaikum”);

  19. write the code to read a selection from a food menu • 1. nasi lemak • 2. roti canai • 3. lontong • 4. nasi dagang • Sila masukkan pilihan anda.

  20. int choice; do { System.out.println(“1.Nasi lemak”); System.out.println(“2.Roti canai”); System.out.println(“3. Lontong”); System.out.println(“4. Nasi dagang”); System.out.println(“Sila masukkan pilihan anda”); choice = inputDevice.nextInt(); } while ((choice <1) II (choice >4));

  21. int choice = 999; while ((choice <1) II (choice >4)) { System.out.println(“1.Nasi lemak”); System.out.println(“2.Roti canai”); System.out.println(“3. Lontong”); System.out.println(“4. Nasi dagang”); System.out.println(“Sila masukkan pilihan anda”); choice = inputDevice.nextInt(); }

  22. Time delay for (int n=1; n < 10000;n++);