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# Looping

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### Looping

1. 1. loops executing code over and over again Thursday, September 24, 2009
2. 2. Thursday, September 24, 2009
3. 3. for loop loop a speciﬁed number of times; the only loop you need to know http://www.w3schools.com/jS/js_loop_for.asp Thursday, September 24, 2009
4. 4. for (var i=0; i < 5; i++) { // some code to run } Thursday, September 24, 2009
5. 5. before any loops for (var i=0; i < 5; i++) { // some code to run } Thursday, September 24, 2009
6. 6. before each loop for (var i=0; i < 5; i++) { // some code to run } Thursday, September 24, 2009
7. 7. after each loop for (var i=0; i < 5; i++) { // some code to run } Thursday, September 24, 2009
8. 8. for (var i=0; 0 < 5; i++) { // i would be 0 } Thursday, September 24, 2009
9. 9. for (var i=0; 1 < 5; i++) { // i would be 1 } Thursday, September 24, 2009
10. 10. for (var i=0; 2 < 5; i++) { // i would be 2 } Thursday, September 24, 2009
11. 11. for (var i=0; 3 < 5; i++) { // i would be 3 } Thursday, September 24, 2009
12. 12. for (var i=0; 4 < 5; i++) { // i would be 4 } Thursday, September 24, 2009
13. 13. for (var i=0; 5 < 5; i++) { // condition false so this // would never happen } Thursday, September 24, 2009
14. 14. for (var i=0; 5 < 5; i++) { // condition false so this // would never happen } Thursday, September 24, 2009
15. 15. var colors = ['red', 'green', 'blue']; for(var i=0; i < colors.length; i++) { colors[i]; } Thursday, September 24, 2009
16. 16. var colors = ['red', 'green', 'blue']; for(var i=0, length=colors.length; i < length; i++) { colors[i]; } Thursday, September 24, 2009
17. 17. var colors = ['red', 'green', 'blue']; var length = colors.length; for(var i=0; i < length; i++) { colors[i]; } Thursday, September 24, 2009
18. 18. while loop loop while a condition is true http://www.w3schools.com/JS/js_loop_while.asp Thursday, September 24, 2009
19. 19. var i = 0; while (i < 5) { // some code to run i++; } Thursday, September 24, 2009
20. 20. var i = 0; before each loop while (i < 5) { // some code to run i++; } Thursday, September 24, 2009
21. 21. var i = 0; while (0 < 5) { // i would be 0 i++; // i would be 1 } Thursday, September 24, 2009
22. 22. var i = 0; while (1 < 5) { // i would be 1 i++; // i would be 2 } Thursday, September 24, 2009
23. 23. var i = 0; while (2 < 5) { // i would be 2 i++; // i would be 3 } Thursday, September 24, 2009
24. 24. var i = 0; while (3 < 5) { // i would be 3 i++; // i would be 4 } Thursday, September 24, 2009
25. 25. var i = 0; while (4 < 5) { // i would be 4 i++; // i would be 5 } Thursday, September 24, 2009
26. 26. var i = 0; while (5 < 5) { // condition is false so // this would never happen i++; } Thursday, September 24, 2009
27. 27. var i = 0; while (5 < 5) { // condition is false so // this would never happen i++; } Thursday, September 24, 2009
28. 28. for..in loop loop through the properties of an object http://www.w3schools.com/jS/js_loop_for_in.asp Thursday, September 24, 2009
29. 29. for (property in object) { // some code here } Thursday, September 24, 2009
30. 30. var person = { name: 'John Nunemaker', age: 27, married: true, cat_owner: 'unfortunately' }; for (property in person) { property; person[property]; } Thursday, September 24, 2009
31. 31. var person = { name: 'John Nunemaker', age: 27, married: true, cat_owner: 'unfortunately' }; for (property in person) { property; // ‘name’ person[property]; // ‘John Nunemaker’ } Thursday, September 24, 2009
32. 32. var person = { name: 'John Nunemaker', age: 27, married: true, cat_owner: 'unfortunately' }; for (property in person) { property; // ‘age’ person[property]; // 27 } Thursday, September 24, 2009
33. 33. var person = { name: 'John Nunemaker', age: 27, married: true, cat_owner: 'unfortunately' }; for (property in person) { property; // ‘married’ person[property]; // true } Thursday, September 24, 2009
34. 34. var person = { name: 'John Nunemaker', age: 27, married: true, cat_owner: 'unfortunately' }; for (property in person) { property; // ‘cat_owner’ person[property]; // ‘unfortunately’ } Thursday, September 24, 2009
35. 35. break break the current loop and continue with code after loop if any http://www.w3schools.com/jS/js_break.asp Thursday, September 24, 2009
36. 36. think “stop looping right now” Thursday, September 24, 2009
37. 37. for (var i=0; i < 5; i++) { if (i === 2) { break; } i; } Thursday, September 24, 2009
38. 38. for (var i=0; 0 < 5; i++) { if (0 === 2) { // false break; } i; // 0 } Thursday, September 24, 2009
39. 39. for (var i=0; 0 < 5; i++) { if (0 === 2) { // false break; } i; // 0 } Thursday, September 24, 2009
40. 40. for (var i=0; 1 < 5; i++) { if (1 === 2) { // false break; } i; // 1 } Thursday, September 24, 2009
41. 41. for (var i=0; 1 < 5; i++) { if (1 === 2) { // false break; } i; // 1 } Thursday, September 24, 2009
42. 42. for (var i=0; 2 < 5; i++) { if (2 === 2) { // true break; // breaks out of loop } i; // never gets here } Thursday, September 24, 2009
43. 43. for (var i=0; 2 < 5; i++) { if (2 === 2) { // true break; // breaks out of loop } i; // never gets here } Thursday, September 24, 2009
44. 44. most common use is switch statement, but good to know it works elsewhere Thursday, September 24, 2009
45. 45. continue break the current loop and continue with the next value http://www.w3schools.com/jS/js_break.asp Thursday, September 24, 2009
46. 46. think “skip current loop” Thursday, September 24, 2009
47. 47. for (var i=0; i < 3; i++) { if (i === 1) { continue; } i; // comment } Thursday, September 24, 2009
48. 48. for (var i=0; 0 < 3; i++) { if (0 === 1) { // false continue; } i; // 0 } Thursday, September 24, 2009
49. 49. for (var i=0; 0 < 3; i++) { if (0 === 1) { // false continue; } i; // 0 } Thursday, September 24, 2009
50. 50. for (var i=0; 1 < 3; i++) { if (1 === 1) { // true continue; } i; // never gets here } Thursday, September 24, 2009
51. 51. for (var i=0; 1 < 3; i++) { if (1 === 1) { // true continue; } i; // never gets here } Thursday, September 24, 2009
52. 52. for (var i=0; 2 < 3; i++) { if (2 === 1) { // false continue; } i; // 2 } Thursday, September 24, 2009
53. 53. for (var i=0; 2 < 3; i++) { if (2 === 1) { // false continue; } i; // 2 } Thursday, September 24, 2009
54. 54. for (var i=0; 3 < 3; i++) { // never gets here if (i === 1) { continue; } i; } Thursday, September 24, 2009
55. 55. for (var i=0; 3 < 3; i++) { // never gets here if (i === 1) { continue; } i; } Thursday, September 24, 2009
56. 56. assignment04 http://teaching.johnnunemaker.com/capp-30550/sessions/looping/ Thursday, September 24, 2009