WEBVTT 0 00:00.050 --> 00:00.560 Hey, guys. 1 00:00.560 --> 00:03.560 Welcome back to 100 Days of Code. 2 00:03.680 --> 00:10.610 Today we're going to look at Debugging, the process of removing bugs from your code. 3 00:10.670 --> 00:15.710 If you've managed to get to this point you've probably written quite a bit of code already. 4 00:15.860 --> 00:22.610 And I will bet that you've probably made some mistakes, some typos, some errors, and some bugs. 5 00:22.640 --> 00:30.260 So in this lesson, I want to talk about some techniques and tips for how to find bugs and how to get 6 00:30.260 --> 00:32.020 rid of them from your code. 7 00:32.290 --> 00:37.780 Now, the first documented bug was actually found by this lady, Grace Hopper. 8 00:37.900 --> 00:44.320 She was probably one of the first programmers and one of the pioneers of the job that we're undertaking 9 00:44.320 --> 00:45.220 right now. 10 00:45.400 --> 00:51.310 Now, in her notes, you'll find a moth that's been taped to the notebook. 11 00:51.370 --> 00:57.160 And this was found in a relay that was preventing her code from running properly. 12 00:57.200 --> 01:03.770 and this was pretty much the first actual case of a bug that's been found in a computer. 13 01:04.010 --> 01:10.430 Even though we're not dealing with moths these days anymore, we're still going to end up finding bits 14 01:10.430 --> 01:16.100 of things in our code that prevent the code from doing the things that we want it to. 15 01:16.130 --> 01:23.740 The important thing to remember is don't feel down when you've created a bug because everyone gets bugs. 16 01:23.740 --> 01:27.850 And when I say gets bugs, I mean we create them, right? 17 01:28.090 --> 01:34.240 So once you've gotten over this next, I want to talk about some of the tips and techniques that you 18 01:34.240 --> 01:39.430 should follow on how to quickly be able to identify and remove these bugs. 19 01:39.460 --> 01:42.910 So the first step is to describe the problem. 20 01:42.910 --> 01:50.010 If the problem is messy and it's not well understood in your head, then it's almost impossible to debug 21 01:50.010 --> 01:50.250 it. 22 01:50.250 --> 01:54.450 So untangle the problem and try to make sense of what's going on. 23 01:54.990 --> 02:00.780 Now, in this block of code, we're going to practice describing the problem to help us solve this debugging 24 02:00.780 --> 02:01.500 problem. 25 02:01.530 --> 02:07.260 Now if you take a look at this function, you can see that at some point in the function, we're supposed 26 02:07.260 --> 02:09.720 to print this line out into the console. 27 02:09.990 --> 02:14.610 But if we go ahead and hit Run you can see that nothing gets printed. 28 02:14.790 --> 02:16.930 So what's going on here? 29 02:17.140 --> 02:22.600 I want you to take a look at this function and describe the actual problem. 30 02:22.630 --> 02:24.670 What is the for loop doing? 31 02:24.670 --> 02:26.560 When is the function meant to print? 32 02:26.560 --> 02:27.520 You got it. 33 02:27.520 --> 02:30.670 What assumptions are you making about the value of i? 34 02:31.360 --> 02:36.250 So pause the video, read the function and have a go at describing the problem. 35 02:38.110 --> 02:38.800 All right. 36 02:38.800 --> 02:46.650 So what we've got here is we've got a function that loops through all the numbers between 1 and 20, 37 02:46.650 --> 02:50.760 and then once that number reaches 20, it's supposed to print, 38 02:50.760 --> 02:51.660 "You got it", 39 02:51.660 --> 02:58.740 but the problem is that when i reaches 20, it doesn't print this line into the console. 40 02:59.160 --> 03:05.490 So now that we've described the problem, and we understand what's going on, let's see if we can solve 41 03:05.490 --> 03:05.790 it. 42 03:06.450 --> 03:12.060 If we think about this problem when i reaches 20, it doesn't print out this line. 43 03:12.060 --> 03:13.890 There's an assumption in there, right? 44 03:13.890 --> 03:18.390 The assumption is that i will definitely reach 20. 45 03:18.510 --> 03:27.480 But if you think back to how the range function works, the stop or the upper bound is actually omitted. 46 03:27.480 --> 03:33.990 So when you write range 4, it actually produces a number from 0 up to 3. 47 03:34.540 --> 03:43.930 And in our case, when we write 1, 20, it actually goes from 1 all the way up to 19, but not including 48 03:43.960 --> 03:44.920 20. 49 03:44.950 --> 03:53.920 The problem here is that i actually never reaches 20, so this assumption is completely false. 50 03:54.310 --> 04:00.040 Pause the video and see if you can fix the code so that this line actually gets printed. 51 04:01.280 --> 04:01.760 All right. 52 04:01.760 --> 04:06.110 So all we need to do is change this to 21 instead of 20, 53 04:06.110 --> 04:10.220 and now when we hit run you can see it actually works, 54 04:10.220 --> 04:12.530 and we manage to debug this problem. 55 04:12.620 --> 04:18.590 Always when you come across a problem in your code, try to describe it so that you really understand 56 04:18.590 --> 04:26.600 what the issue is, and then test your assumptions and see which of those assumptions is actually false.