[CS61C FA20] Lecture 04.4 - C Intro: Pointers, Arrays, Strings: Function Pointer Example — Transcript

Full transcript

1. 0:00and welcome back now let's look at a
2. 0:02function pointer example to actually see
3. 0:05how we would do that with c this is the
4. 0:08only slide we're going to show
5. 0:10for this lecture so let's actually jump
6. 0:12in
7. 0:13let's go here and grab the pen and
8. 0:17what does this do so we define two very
9. 0:20simple functions
10. 0:22x10 which is times 10 and times two if
11. 0:24you look at this all they do is return
12. 0:26double the input or 10 times the input
13. 0:28very easy okay
14. 0:30i declare print array is just a simple
15. 0:32thing that's just going to print the
16. 0:33array nothing special here
17. 0:34and here is mutate map okay what i want
18. 0:37to write is map
19. 0:38the simple higher function of map takes
20. 0:40a function and a list and it's going to
21. 0:42return a new list with that function
22. 0:44applied to every element of it but
23. 0:46actually mutate map is easier because i
24. 0:47haven't really told you how to
25. 0:48make new space of things dynamically so
26. 0:50that'll be later so we're going to have
27. 0:52to actually change
28. 0:53the input okay but same idea so
29. 0:57here is mutated map it takes the array
30. 0:59it takes the size i mentioned before in
31. 1:01earlier lecture you have to pass in the
32. 1:02array and the size to it
33. 1:03and here look at this this is the way
34. 1:06you declare to say
35. 1:07i'm going to receive a fp is going to be
36. 1:10a function pointer
37. 1:12that's going to return an int take an
38. 1:14int take an int
39. 1:16and return an it that's that's the you
40. 1:18know these that's the
41. 1:19x2 or x10 okay that's it nothing else is
42. 1:22magical
43. 1:23so here's the code here's the main i
44. 1:25make an array first three digits of pi
45. 1:27three one four and it's three
46. 1:29of the three three numbers in here i
47. 1:31print the array
48. 1:32there's my three one four i call mutate
49. 1:35map watch this address of x10
50. 1:39i pass in a pointer to x text 10.
51. 1:42x2 times 2 i pass in the double that's
52. 1:45the double function
53. 1:47what does it do it mutates a
54. 1:50and now it prints it out print array
55. 1:52prints it out 628
56. 1:54that's pretty cool i pass in the 10
57. 1:57times function
58. 1:58and i print the array and there's 60 20
59. 2:0080. this simple piece of code is how you
60. 2:03would use
61. 2:03a function pointer yourself now you can
62. 2:05think of writing really general
63. 2:06procedures that don't just use
64. 2:08that consume data but actually consume
65. 2:10other functions too and are more general
66. 2:11pretty cool
67. 2:12we'll see the next video