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App Dev Worksheet: Debugging

App development lesson 21: Debugging: find the bug line · Set 137 · 40 questions
TalentJR

Developer's tip (Compare with the comment): Read each line and its comment (after //): does the code do exactly that? Actual = run the lines as written. Expected = follow every comment. After the fix, test again.

NameDateTime takenScore ___ / 40
  1. 1.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let coins = 49; // start at 49
    line 2: coins = coins + 6; // add 6
    line 3: coins = coins - 4; // take away 4
    line 4: coins = coins + 2; // double it
    line 5: show(coins); // show it     (a) line 3 (b) line 1 (c) line 2 (d) line 4
  2. 2.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let points = 41; // start at 39
    line 2: points = points - 3; // take away 3
    line 3: points = points + 4; // add 4
    line 4: show(points); // show it
  3. 3.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let score = 32; // start at 32
    line 2: score = score - 1; // take away 1
    line 3: score = score + 4; // add 3
    line 4: show(score); // show it     (a) line 2 (b) line 1 (c) line 3
  4. 4.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let stars = 44; // start at 44
    line 2: stars = stars - 2; // add 2
    line 3: stars = stars + 4; // add 4
    line 4: show(stars); // show it
  5. 5.🐞 What is a bug? (a) a new feature (b) a fast phone (c) a mistake in the code (d) a nice icon
  6. 6.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let score = 50; // start at 50
    line 2: score = score * 2; // double it
    line 3: score = score + 5; // add 3
    line 4: score = score + 4; // add 4
    line 5: show(score); // show it
  7. 7.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let lives = 38; // start at 38
    line 2: lives = lives - 2; // add 2
    line 3: lives = lives + 6; // add 6
    line 4: show(lives); // show it
  8. 8.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let stars = 39; // start at 39
    line 2: stars = stars * 2; // double it
    line 3: stars = stars + 1; // take away 1
    line 4: stars = stars * 2; // double it
    line 5: show(stars); // show it
  9. 9.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let lives = 35; // start at 35
    line 2: lives = lives - 4; // take away 4
    line 3: lives = lives + 4; // take away 4
    line 4: show(lives); // show it
  10. 10.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let stars = 50; // start at 49
    line 2: stars = stars - 1; // take away 1
    line 3: stars = stars - 4; // take away 4
    line 4: show(stars); // show it
  11. 11.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let lives = 51; // start at 50
    line 2: lives = lives * 2; // double it
    line 3: lives = lives * 2; // double it
    line 4: show(lives); // show it
  12. 12.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let stars = 31; // start at 31
    line 2: stars = stars * 2; // double it
    line 3: stars = stars - 5; // take away 2
    line 4: stars = stars * 2; // double it
    line 5: show(stars); // show it
  13. 13.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let score = 30; // start at 30
    line 2: score = score * 2; // double it
    line 3: score = score + 6; // add 6
    line 4: score = score * 3; // double it
    line 5: show(score); // show it
  14. 14.🐞 After fixing a bug you should ___. (a) test it again (b) release at once (c) never test (d) delete the test
  15. 15.🐞 What is a good first step when an app gives a wrong result? (a) buy a new phone (b) find where it goes wrong (c) delete the app (d) add more colours
  16. 16.🐞 A comment in code (after //) is for ___. (a) people reading the code (b) the battery (c) the phone screen (d) the app store
  17. 17.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let points = 44; // start at 44
    line 2: points = points + 2; // take away 2
    line 3: points = points + 2; // add 2
    line 4: show(points); // show it
  18. 18.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let score = 49; // start at 46
    line 2: score = score * 2; // double it
    line 3: score = score * 2; // double it
    line 4: show(score); // show it     (a) line 1 (b) line 2 (c) line 3
  19. 19.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let coins = 34; // start at 33
    line 2: coins = coins * 2; // double it
    line 3: coins = coins * 2; // double it
    line 4: coins = coins + 5; // add 5
    line 5: show(coins); // show it     (a) line 2 (b) line 1 (c) line 4 (d) line 3
  20. 20.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let points = 30; // start at 30
    line 2: points = points - 2; // add 2
    line 3: points = points * 2; // double it
    line 4: show(points); // show it
  21. 21.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let points = 37; // start at 35
    line 2: points = points - 1; // take away 1
    line 3: points = points - 5; // take away 5
    line 4: show(points); // show it     (a) line 3 (b) line 2 (c) line 1
  22. 22.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let coins = 48; // start at 48
    line 2: coins = coins + 2; // add 2
    line 3: coins = coins + 2; // double it
    line 4: show(coins); // show it
  23. 23.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let points = 39; // start at 37
    line 2: points = points * 2; // double it
    line 3: points = points * 2; // double it
    line 4: show(points); // show it     (a) line 2 (b) line 1 (c) line 3
  24. 24.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let lives = 41; // start at 41
    line 2: lives = lives + 6; // add 6
    line 3: lives = lives - 2; // add 2
    line 4: show(lives); // show it
  25. 25.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let score = 50; // start at 50
    line 2: score = score + 4; // add 4
    line 3: score = score + 2; // double it
    line 4: score = score * 2; // double it
    line 5: show(score); // show it
  26. 26.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let score = 51; // start at 48
    line 2: score = score + 6; // add 6
    line 3: score = score * 2; // double it
    line 4: show(score); // show it     (a) line 2 (b) line 3 (c) line 1
  27. 27.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let points = 33; // start at 33
    line 2: points = points + 2; // add 2
    line 3: points = points * 2; // double it
    line 4: points = points + 7; // add 4
    line 5: show(points); // show it
  28. 28.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let points = 40; // start at 40
    line 2: points = points + 1; // take away 1
    line 3: points = points - 1; // take away 1
    line 4: show(points); // show it
  29. 29.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let score = 48; // start at 47
    line 2: score = score * 2; // double it
    line 3: score = score - 2; // take away 2
    line 4: show(score); // show it
  30. 30.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let stars = 36; // start at 33
    line 2: stars = stars + 6; // add 6
    line 3: stars = stars - 4; // take away 4
    line 4: show(stars); // show it
  31. 31.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let stars = 48; // start at 48
    line 2: stars = stars + 2; // double it
    line 3: stars = stars * 2; // double it
    line 4: show(stars); // show it
  32. 32.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let lives = 42; // start at 39
    line 2: lives = lives * 2; // double it
    line 3: lives = lives * 2; // double it
    line 4: lives = lives - 4; // take away 4
    line 5: show(lives); // show it     (a) line 3 (b) line 2 (c) line 1 (d) line 4
  33. 33.🐞 Finding and fixing bugs is called ___. (a) designing (b) decorating (c) downloading (d) debugging
  34. 34.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let coins = 41; // start at 38
    line 2: coins = coins - 5; // take away 5
    line 3: coins = coins - 1; // take away 1
    line 4: coins = coins * 2; // double it
    line 5: show(coins); // show it
  35. 35.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let coins = 39; // start at 39
    line 2: coins = coins + 2; // double it
    line 3: coins = coins + 5; // add 5
    line 4: show(coins); // show it
  36. 36.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let points = 37; // start at 37
    line 2: points = points - 3; // take away 3
    line 3: points = points + 7; // add 4
    line 4: show(points); // show it     (a) line 1 (b) line 2 (c) line 3
  37. 37.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let coins = 52; // start at 49
    line 2: coins = coins + 6; // add 6
    line 3: coins = coins + 3; // add 3
    line 4: coins = coins * 2; // double it
    line 5: show(coins); // show it
  38. 38.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let stars = 31; // start at 31
    line 2: stars = stars - 4; // take away 3
    line 3: stars = stars + 5; // add 5
    line 4: show(stars); // show it     (a) line 3 (b) line 1 (c) line 2
  39. 39.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let lives = 41; // start at 41
    line 2: lives = lives + 2; // double it
    line 3: lives = lives * 2; // double it
    line 4: show(lives); // show it
  40. 40.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let points = 49; // start at 46
    line 2: points = points + 6; // add 6
    line 3: points = points * 2; // double it
    line 4: points = points * 2; // double it
    line 5: show(points); // show it

Answer key

  1. line 4
  2. 40
  3. line 3
  4. 46
  5. a mistake in the code
  6. 107
  7. 42
  8. 158
  9. 35
  10. 44
  11. 204
  12. 120
  13. 132
  14. test it again
  15. find where it goes wrong
  16. people reading the code
  17. 48
  18. line 1
  19. line 1
  20. 56
  21. line 1
  22. 52
  23. line 1
  24. 49
  25. 112
  26. line 1
  27. 77
  28. 40
  29. 92
  30. 35
  31. 192
  32. line 1
  33. debugging
  34. 64
  35. 46
  36. line 3
  37. 122
  38. line 2
  39. 164
  40. 220

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