← Debugging: find the bug line lesson New set →

App Dev Worksheet: Debugging

App development lesson 21: Debugging: find the bug line · Set 307 · 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.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let score = 39; // start at 39
    line 2: score = score - 2; // add 2
    line 3: score = score + 2; // add 2
    line 4: show(score); // show it
  2. 2.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let lives = 47; // start at 47
    line 2: lives = lives - 2; // add 2
    line 3: lives = lives * 2; // double it
    line 4: show(lives); // show it     (a) line 2 (b) line 1 (c) line 3
  3. 3.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let points = 31; // start at 31
    line 2: points = points - 3; // take away 3
    line 3: points = points - 2; // take away 2
    line 4: points = points * 3; // double it
    line 5: show(points); // show it     (a) line 3 (b) line 2 (c) line 4 (d) line 1
  4. 4.🐞 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 34
    line 2: lives = lives - 3; // take away 2
    line 3: lives = lives + 6; // add 6
    line 4: show(lives); // show it
  5. 5.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let lives = 37; // start at 37
    line 2: lives = lives - 5; // add 5
    line 3: lives = lives + 3; // add 3
    line 4: show(lives); // show it
  6. 6.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let coins = 35; // start at 34
    line 2: coins = coins * 2; // double it
    line 3: coins = coins + 6; // add 6
    line 4: show(coins); // show it
  7. 7.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let points = 43; // start at 43
    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
  8. 8.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let coins = 45; // start at 44
    line 2: coins = coins - 1; // take away 1
    line 3: coins = coins - 1; // take away 1
    line 4: show(coins); // show it
  9. 9.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let score = 43; // start at 43
    line 2: score = score * 2; // double it
    line 3: score = score + 1; // take away 1
    line 4: score = score + 3; // add 3
    line 5: show(score); // 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 lives = 41; // start at 38
    line 2: lives = lives - 1; // take away 1
    line 3: lives = lives * 2; // double it
    line 4: lives = lives * 2; // double it
    line 5: show(lives); // show it
  11. 11.🐞 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 + 8; // add 6
    line 4: stars = stars * 2; // double it
    line 5: show(stars); // show it
  12. 12.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let points = 38; // start at 38
    line 2: points = points + 2; // add 2
    line 3: points = points + 5; // take away 5
    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 = 47; // start at 47
    line 2: coins = coins - 3; // add 3
    line 3: coins = coins - 3; // take away 3
    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 stars = 48; // start at 48
    line 2: stars = stars + 3; // add 3
    line 3: stars = stars - 6; // add 6
    line 4: stars = stars + 3; // add 3
    line 5: show(stars); // show it
  15. 15.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let score = 38; // start at 38
    line 2: score = score * 3; // double it
    line 3: score = score - 1; // take away 1
    line 4: score = score + 5; // add 5
    line 5: show(score); // show it
  16. 16.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let lives = 46; // start at 46
    line 2: lives = lives + 1; // take away 1
    line 3: lives = lives * 2; // double it
    line 4: lives = lives + 2; // add 2
    line 5: show(lives); // show it     (a) line 4 (b) line 3 (c) line 1 (d) line 2
  17. 17.🐞 After fixing a bug you should ___. (a) delete the test (b) release at once (c) never test (d) test it again
  18. 18.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let points = 40; // start at 40
    line 2: points = points - 2; // take away 1
    line 3: points = points + 5; // add 5
    line 4: show(points); // show it     (a) line 2 (b) line 3 (c) line 1
  19. 19.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let points = 50; // start at 50
    line 2: points = points + 5; // take away 5
    line 3: points = points - 3; // take away 3
    line 4: show(points); // show it
  20. 20.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let stars = 42; // start at 41
    line 2: stars = stars + 5; // add 5
    line 3: stars = stars * 2; // double it
    line 4: stars = stars * 2; // double it
    line 5: show(stars); // show it
  21. 21.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let coins = 48; // start at 48
    line 2: coins = coins * 2; // double it
    line 3: coins = coins + 2; // double it
    line 4: show(coins); // show it     (a) line 3 (b) line 2 (c) line 1
  22. 22.🐞 A comment in code (after //) is for ___. (a) people reading the code (b) the phone screen (c) the app store (d) the battery
  23. 23.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let points = 50; // start at 50
    line 2: points = points * 2; // double it
    line 3: points = points + 2; // double it
    line 4: show(points); // show it
  24. 24.🐞 What is a bug? (a) a new feature (b) a nice icon (c) a fast phone (d) a mistake in the code
  25. 25.🐞 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; // add 2
    line 3: score = score - 2; // add 2
    line 4: show(score); // show it
  26. 26.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let lives = 48; // start at 47
    line 2: lives = lives * 2; // double it
    line 3: lives = lives * 2; // double it
    line 4: lives = lives * 2; // double it
    line 5: show(lives); // show it
  27. 27.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let score = 30; // start at 30
    line 2: score = score * 2; // double it
    line 3: score = score + 2; // double it
    line 4: show(score); // show it
  28. 28.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let points = 46; // start at 43
    line 2: points = points + 3; // add 3
    line 3: points = points * 2; // double it
    line 4: show(points); // show it
  29. 29.🐞 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
  30. 30.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let score = 42; // start at 42
    line 2: score = score - 3; // add 3
    line 3: score = score * 2; // double it
    line 4: show(score); // show it     (a) line 1 (b) line 3 (c) line 2
  31. 31.🐞 This code has a bug. What number SHOULD it show, if every line did what its comment says?
    line 1: let lives = 31; // start at 31
    line 2: lives = lives + 3; // add 3
    line 3: lives = lives + 6; // add 6
    line 4: lives = lives + 7; // add 5
    line 5: show(lives); // show it
  32. 32.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let coins = 30; // start at 30
    line 2: coins = coins - 4; // take away 4
    line 3: coins = coins - 4; // add 4
    line 4: show(coins); // show it     (a) line 3 (b) line 2 (c) line 1
  33. 33.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let lives = 47; // start at 47
    line 2: lives = lives * 2; // double it
    line 3: lives = lives + 2; // double it
    line 4: show(lives); // show it
  34. 34.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let score = 51; // start at 49
    line 2: score = score * 2; // double it
    line 3: score = score - 1; // take away 1
    line 4: score = score * 2; // double it
    line 5: show(score); // show it
  35. 35.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let lives = 49; // start at 49
    line 2: lives = lives * 3; // double it
    line 3: lives = lives - 4; // take away 4
    line 4: lives = lives * 2; // double it
    line 5: show(lives); // show it     (a) line 2 (b) line 1 (c) line 3 (d) line 4
  36. 36.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let lives = 38; // start at 38
    line 2: lives = lives * 2; // double it
    line 3: lives = lives + 2; // double it
    line 4: show(lives); // show it
  37. 37.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let points = 46; // start at 46
    line 2: points = points - 2; // take away 1
    line 3: points = points - 2; // take away 2
    line 4: points = points * 2; // double it
    line 5: show(points); // show it     (a) line 4 (b) line 2 (c) line 3 (d) line 1
  38. 38.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let lives = 46; // start at 46
    line 2: lives = lives + 4; // take away 4
    line 3: lives = lives + 6; // add 6
    line 4: show(lives); // show it
  39. 39.🐞 Each comment says what its line SHOULD do. Which line has the bug?
    line 1: let coins = 41; // start at 41
    line 2: coins = coins - 3; // take away 3
    line 3: coins = coins + 2; // double it
    line 4: show(coins); // show it     (a) line 1 (b) line 2 (c) line 3
  40. 40.🐞 This code has a bug. What number does it ACTUALLY show?
    line 1: let coins = 49; // start at 49
    line 2: coins = coins + 5; // add 5
    line 3: coins = coins + 2; // take away 2
    line 4: coins = coins - 1; // take away 1
    line 5: show(coins); // show it

Answer key

  1. 39
  2. line 2
  3. line 4
  4. 38
  5. 35
  6. 76
  7. line 3
  8. 42
  9. 90
  10. 148
  11. 172
  12. 45
  13. line 2
  14. 48
  15. 118
  16. line 2
  17. test it again
  18. line 2
  19. 42
  20. 184
  21. line 3
  22. people reading the code
  23. 102
  24. a mistake in the code
  25. 54
  26. 384
  27. 62
  28. 92
  29. find where it goes wrong
  30. line 2
  31. 45
  32. line 3
  33. 96
  34. 202
  35. line 2
  36. 78
  37. line 2
  38. 56
  39. line 3
  40. 55

Free app development lessons, practice and worksheets at talentjr.in/app-development-for-students