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App Dev Worksheet: Debugging

App development lesson 21: Debugging: find the bug line · Set 62 · 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 = 39; // start at 39
    line 2: coins = coins * 2; // double it
    line 3: coins = coins + 7; // add 5
    line 4: coins = coins + 3; // add 3
    line 5: show(coins); // show it     (a) line 3 (b) line 1 (c) line 4 (d) line 2
  2. 2.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let score = 42; // start at 42
    line 2: score = score * 2; // double it
    line 3: score = score - 5; // take away 5
    line 4: score = score + 7; // add 5
    line 5: show(score); // show it
  3. 3.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let score = 35; // start at 35
    line 2: score = score - 2; // take away 2
    line 3: score = score - 2; // add 2
    line 4: show(score); // show it
  4. 4.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let stars = 50; // start at 50
    line 2: stars = stars * 2; // double it
    line 3: stars = stars + 6; // add 6
    line 4: stars = stars * 3; // double it
    line 5: show(stars); // show it     (a) line 3 (b) line 2 (c) line 1 (d) line 4
  5. 5.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let points = 45; // start at 45
    line 2: points = points * 3; // double it
    line 3: points = points * 2; // double it
    line 4: points = points - 2; // take away 2
    line 5: show(points); // show it
  6. 6.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let lives = 38; // start at 35
    line 2: lives = lives + 3; // add 3
    line 3: lives = lives * 2; // double it
    line 4: lives = lives * 2; // double it
    line 5: show(lives); // show it
  7. 7.🐞 A comment in code (after //) is for ___. (a) the phone screen (b) the battery (c) the app store (d) people reading the code
  8. 8.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let stars = 45; // start at 44
    line 2: stars = stars + 6; // add 6
    line 3: stars = stars + 2; // add 2
    line 4: stars = stars + 5; // add 5
    line 5: show(stars); // show it     (a) line 3 (b) line 4 (c) line 1 (d) line 2
  9. 9.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let score = 35; // start at 33
    line 2: score = score - 1; // take away 1
    line 3: score = score - 5; // take away 5
    line 4: show(score); // show it     (a) line 2 (b) line 1 (c) line 3
  10. 10.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let score = 37; // start at 37
    line 2: score = score * 2; // double it
    line 3: score = score + 5; // take away 5
    line 4: score = score - 1; // take away 1
    line 5: show(score); // show it
  11. 11.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let stars = 34; // start at 33
    line 2: stars = stars * 2; // double it
    line 3: stars = stars - 4; // take away 4
    line 4: stars = stars - 3; // take away 3
    line 5: show(stars); // show it
  12. 12.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let points = 31; // start at 30
    line 2: points = points - 1; // take away 1
    line 3: points = points * 2; // double it
    line 4: show(points); // show it
  13. 13.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let coins = 44; // start at 42
    line 2: coins = coins - 5; // take away 5
    line 3: coins = coins + 4; // add 4
    line 4: show(coins); // show it     (a) line 3 (b) line 1 (c) line 2
  14. 14.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let score = 49; // start at 47
    line 2: score = score + 3; // add 3
    line 3: score = score + 6; // add 6
    line 4: show(score); // show it
  15. 15.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let lives = 41; // start at 38
    line 2: lives = lives + 2; // add 2
    line 3: lives = lives - 4; // take away 4
    line 4: show(lives); // show it
  16. 16.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let coins = 47; // start at 47
    line 2: coins = coins - 6; // take away 5
    line 3: coins = coins - 2; // take away 2
    line 4: show(coins); // show it
  17. 17.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let lives = 34; // start at 31
    line 2: lives = lives - 5; // take away 5
    line 3: lives = lives + 2; // add 2
    line 4: show(lives); // show it
  18. 18.🐞 After fixing a bug you should ___. (a) never test (b) test it again (c) release at once (d) delete the test
  19. 19.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let lives = 42; // start at 42
    line 2: lives = lives * 2; // double it
    line 3: lives = lives + 4; // add 4
    line 4: lives = lives * 3; // double it
    line 5: show(lives); // show it     (a) line 1 (b) line 3 (c) line 4 (d) line 2
  20. 20.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let stars = 37; // start at 37
    line 2: stars = stars + 3; // add 3
    line 3: stars = stars * 2; // double it
    line 4: stars = stars * 3; // double it
    line 5: show(stars); // show it     (a) line 2 (b) line 3 (c) line 1 (d) line 4
  21. 21.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let coins = 39; // start at 39
    line 2: coins = coins * 2; // double it
    line 3: coins = coins * 2; // double it
    line 4: coins = coins + 2; // double it
    line 5: show(coins); // show it     (a) line 2 (b) line 1 (c) line 3 (d) line 4
  22. 22.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let coins = 31; // start at 31
    line 2: coins = coins + 2; // double it
    line 3: coins = coins + 3; // add 3
    line 4: show(coins); // show it
  23. 23.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let lives = 43; // start at 43
    line 2: lives = lives - 2; // take away 2
    line 3: lives = lives * 2; // double it
    line 4: lives = lives - 2; // take away 1
    line 5: show(lives); // show it     (a) line 4 (b) line 1 (c) line 3 (d) line 2
  24. 24.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let lives = 30; // start at 30
    line 2: lives = lives + 6; // add 6
    line 3: lives = lives * 3; // double it
    line 4: lives = lives * 2; // double it
    line 5: show(lives); // show it
  25. 25.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let coins = 43; // start at 42
    line 2: coins = coins - 3; // take away 3
    line 3: coins = coins * 2; // double it
    line 4: coins = coins - 1; // take away 1
    line 5: show(coins); // show it     (a) line 4 (b) line 3 (c) line 2 (d) line 1
  26. 26.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let lives = 48; // start at 48
    line 2: lives = lives * 2; // double it
    line 3: lives = lives + 4; // add 2
    line 4: show(lives); // show it
  27. 27.🐞 What is a bug? (a) a fast phone (b) a nice icon (c) a mistake in the code (d) a new feature
  28. 28.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let stars = 37; // start at 37
    line 2: stars = stars * 2; // double it
    line 3: stars = stars * 2; // double it
    line 4: stars = stars - 6; // take away 3
    line 5: show(stars); // 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 lives = 45; // start at 45
    line 2: lives = lives * 2; // double it
    line 3: lives = lives - 6; // add 6
    line 4: lives = lives * 2; // double it
    line 5: show(lives); // show it
  30. 30.🐞 What is a good first step when an app gives a wrong result? (a) buy a new phone (b) delete the app (c) add more colours (d) find where it goes wrong
  31. 31.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let coins = 46; // start at 44
    line 2: coins = coins + 4; // add 4
    line 3: coins = coins - 1; // take away 1
    line 4: coins = coins - 3; // take away 3
    line 5: show(coins); // show it
  32. 32.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let stars = 41; // start at 41
    line 2: stars = stars + 3; // add 3
    line 3: stars = stars - 5; // take away 5
    line 4: stars = stars * 3; // double it
    line 5: show(stars); // show it     (a) line 3 (b) line 2 (c) line 1 (d) line 4
  33. 33.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let score = 30; // start at 30
    line 2: score = score + 6; // add 6
    line 3: score = score - 4; // add 4
    line 4: show(score); // show it
  34. 34.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let lives = 47; // start at 46
    line 2: lives = lives + 4; // add 4
    line 3: lives = lives * 2; // double it
    line 4: lives = lives * 2; // double it
    line 5: show(lives); // show it     (a) line 4 (b) line 1 (c) line 2 (d) line 3
  35. 35.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let score = 47; // start at 47
    line 2: score = score * 3; // double it
    line 3: score = score + 3; // add 3
    line 4: score = score * 2; // double it
    line 5: show(score); // show it
  36. 36.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let score = 42; // start at 42
    line 2: score = score + 3; // add 3
    line 3: score = score + 4; // add 3
    line 4: show(score); // show it
  37. 37.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let score = 39; // start at 38
    line 2: score = score - 5; // take away 5
    line 3: score = score + 5; // add 5
    line 4: score = score + 5; // add 5
    line 5: show(score); // show it     (a) line 1 (b) line 3 (c) line 2 (d) line 4
  38. 38.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let score = 47; // start at 47
    line 2: score = score + 2; // double it
    line 3: score = score + 5; // add 5
    line 4: show(score); // show it
  39. 39.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let score = 50; // start at 50
    line 2: score = score * 3; // double it
    line 3: score = score + 4; // add 4
    line 4: score = score + 2; // add 2
    line 5: show(score); // show it     (a) line 1 (b) line 4 (c) line 3 (d) line 2
  40. 40.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let points = 41; // start at 41
    line 2: points = points * 3; // double it
    line 3: points = points + 4; // add 4
    line 4: show(points); // show it

Answer key

  1. line 3
  2. 84
  3. 35
  4. line 4
  5. 268
  6. 152
  7. people reading the code
  8. line 1
  9. line 1
  10. 68
  11. 61
  12. 60
  13. line 1
  14. 58
  15. 39
  16. 39
  17. 28
  18. test it again
  19. line 4
  20. line 4
  21. line 4
  22. 36
  23. line 4
  24. 216
  25. line 1
  26. 100
  27. a mistake in the code
  28. 145
  29. 192
  30. find where it goes wrong
  31. 44
  32. line 4
  33. 32
  34. line 1
  35. 288
  36. 49
  37. line 1
  38. 99
  39. line 2
  40. 127

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