1 00:00:00,830 --> 00:00:03,240 So we talked about problem solving, 2 00:00:03,240 --> 00:00:07,720 which is a very important skill of any software developer. 3 00:00:07,720 --> 00:00:09,530 Now, another extremely important 4 00:00:09,530 --> 00:00:12,070 developer skill is debugging, 5 00:00:12,070 --> 00:00:15,710 which means to find and fix errors. 6 00:00:15,710 --> 00:00:19,010 So let's finish this section by talking about debugging 7 00:00:19,010 --> 00:00:22,043 to make you ready for the rest of the course ahead. 8 00:00:23,490 --> 00:00:26,270 So first of all, as you might already know, 9 00:00:26,270 --> 00:00:29,790 a software bug is a defect or a problem 10 00:00:29,790 --> 00:00:32,110 in a computer program. 11 00:00:32,110 --> 00:00:36,270 So basically, any unexpected or unintended behavior 12 00:00:36,270 --> 00:00:39,340 of a program is called a bug. 13 00:00:39,340 --> 00:00:43,370 And the actual term bug was coined in the 1940s 14 00:00:43,370 --> 00:00:46,580 when this real bug was causing an error 15 00:00:46,580 --> 00:00:47,923 in Harvard's computer. 16 00:00:48,780 --> 00:00:52,150 Now, there are many reasons for bugs in programs, 17 00:00:52,150 --> 00:00:54,550 but what matters here is that bugs 18 00:00:54,550 --> 00:00:58,640 are a completely normal part of software development, 19 00:00:58,640 --> 00:01:00,280 because we are humans, 20 00:01:00,280 --> 00:01:02,950 and humans make mistakes. 21 00:01:02,950 --> 00:01:06,870 In fact, every complex application contains bugs, 22 00:01:06,870 --> 00:01:09,940 which sometimes go undiscovered for years 23 00:01:09,940 --> 00:01:13,790 and can cause security holes or other problems. 24 00:01:13,790 --> 00:01:17,300 So really, don't feel bad if you introduce bugs 25 00:01:17,300 --> 00:01:18,560 in your own count. 26 00:01:18,560 --> 00:01:21,893 We all do it, even the most expert programmers. 27 00:01:22,780 --> 00:01:27,300 Now luckily, not all bugs cause huge security holes. 28 00:01:27,300 --> 00:01:30,090 In fact, many bugs are quite small 29 00:01:30,090 --> 00:01:32,200 and simple to discover. 30 00:01:32,200 --> 00:01:34,600 So let's see a simple example. 31 00:01:34,600 --> 00:01:37,240 Remember in our previous example, 32 00:01:37,240 --> 00:01:40,030 the goal was to reverse whatever was passed 33 00:01:40,030 --> 00:01:41,690 into the function. 34 00:01:41,690 --> 00:01:45,170 So let's say we finished writing the reverse function, 35 00:01:45,170 --> 00:01:49,400 and call it with this array and get this result. 36 00:01:49,400 --> 00:01:52,840 But clearly something is wrong here, right? 37 00:01:52,840 --> 00:01:55,970 The return value looks scrambled, 38 00:01:55,970 --> 00:01:58,370 but not reversed at all. 39 00:01:58,370 --> 00:02:01,310 So this means that we must have a bug somewhere 40 00:02:01,310 --> 00:02:04,490 in our reverse function, okay? 41 00:02:04,490 --> 00:02:07,840 To fix this, we use a process called debugging, 42 00:02:07,840 --> 00:02:10,800 which is essentially finding, fixing, 43 00:02:10,800 --> 00:02:12,760 and then preventing bugs. 44 00:02:12,760 --> 00:02:14,453 So let's see how that works. 45 00:02:15,690 --> 00:02:19,160 So the first step is to actually become aware 46 00:02:19,160 --> 00:02:21,310 that there is some kind of bug, 47 00:02:21,310 --> 00:02:24,220 because as I said, in a large application, 48 00:02:24,220 --> 00:02:28,130 bugs can actually go undiscovered for years. 49 00:02:28,130 --> 00:02:30,450 Now, discovering bugs usually happens 50 00:02:30,450 --> 00:02:34,580 during development using automated testing software 51 00:02:34,580 --> 00:02:37,570 or user reports during production. 52 00:02:37,570 --> 00:02:40,500 And bugs that are identified during production 53 00:02:40,500 --> 00:02:42,080 are the worst bugs, 54 00:02:42,080 --> 00:02:44,620 because it means that they went undiscovered 55 00:02:44,620 --> 00:02:46,830 during development and are now affecting 56 00:02:46,830 --> 00:02:49,730 real users of our application. 57 00:02:49,730 --> 00:02:51,900 So that's why it's really important 58 00:02:51,900 --> 00:02:53,950 to identify bugs early, 59 00:02:53,950 --> 00:02:57,150 for example, using automated tests. 60 00:02:57,150 --> 00:02:59,460 Now, while identifying the bug, 61 00:02:59,460 --> 00:03:02,150 sometimes we also need to take into consideration 62 00:03:02,150 --> 00:03:04,850 the context in which the bug happened. 63 00:03:04,850 --> 00:03:07,570 For example, certain bugs might only happen 64 00:03:07,570 --> 00:03:08,960 in a certain browser, 65 00:03:08,960 --> 00:03:11,983 or only for certain users, for some reason. 66 00:03:12,930 --> 00:03:15,660 Next, once we know there is a bug, 67 00:03:15,660 --> 00:03:19,290 we need to go into our code and find the bug. 68 00:03:19,290 --> 00:03:22,650 We need to isolate where exactly it's happening, 69 00:03:22,650 --> 00:03:25,310 and we can do that using the developer console 70 00:03:25,310 --> 00:03:26,363 that we already know. 71 00:03:27,210 --> 00:03:29,490 However, that only works for small bugs 72 00:03:29,490 --> 00:03:32,430 and simple code where we have a good idea 73 00:03:32,430 --> 00:03:35,010 where the bug might be located. 74 00:03:35,010 --> 00:03:36,800 But if the code is more complex 75 00:03:36,800 --> 00:03:40,060 and we have no idea where the bug might be, 76 00:03:40,060 --> 00:03:42,920 then we need to use a debugger software. 77 00:03:42,920 --> 00:03:45,570 And I will show you how that works in the next video 78 00:03:45,570 --> 00:03:47,830 because it's really important for developer 79 00:03:47,830 --> 00:03:49,823 to be able to use a debugger. 80 00:03:50,740 --> 00:03:54,270 Anyway, once we know where the bug is located, 81 00:03:54,270 --> 00:03:58,800 we can finally fix it so we can correct the bug. 82 00:03:58,800 --> 00:04:01,790 And this is probably the easiest part. 83 00:04:01,790 --> 00:04:03,960 So essentially, all we need to do 84 00:04:03,960 --> 00:04:08,320 is to replace the existing, so the wrong solution, 85 00:04:08,320 --> 00:04:12,620 with a new correct solution that actually works. 86 00:04:12,620 --> 00:04:15,670 As a final step, we should then prevent this bug 87 00:04:15,670 --> 00:04:19,030 from ever happening again in our code base. 88 00:04:19,030 --> 00:04:21,630 For example, we can search our project 89 00:04:21,630 --> 00:04:24,280 for the same bug in similar code, 90 00:04:24,280 --> 00:04:26,580 like in a similar function. 91 00:04:26,580 --> 00:04:29,250 It's totally possible that we did the same mistake 92 00:04:29,250 --> 00:04:30,900 twice in our code, 93 00:04:30,900 --> 00:04:32,200 and if that's the case, 94 00:04:32,200 --> 00:04:35,010 we must fix the bug everywhere. 95 00:04:35,010 --> 00:04:37,710 A more advanced way of preventing bugs 96 00:04:37,710 --> 00:04:40,980 is to write tests using testing software. 97 00:04:40,980 --> 00:04:43,360 And I might add a bonus section on testing 98 00:04:43,360 --> 00:04:45,530 to the course at some point 99 00:04:45,530 --> 00:04:47,790 because this is actually an important part 100 00:04:47,790 --> 00:04:49,780 of software development. 101 00:04:49,780 --> 00:04:51,610 Okay, and that's it. 102 00:04:51,610 --> 00:04:55,170 That's a broad overview of debugging in programming. 103 00:04:55,170 --> 00:04:57,830 And we really just scratched the surface here, 104 00:04:57,830 --> 00:05:00,640 because you're still at the beginning of the journey. 105 00:05:00,640 --> 00:05:02,653 And so this is just an introduction. 106 00:05:03,510 --> 00:05:06,983 Anyway, let's now fix some bugs in the next video.