1 00:00:00,060 --> 00:00:02,880 So we're onto our final debugging exercise. 2 00:00:02,970 --> 00:00:07,530 This is debugging Fizzbuzz. Fizzbuzz, if you remember, 3 00:00:07,530 --> 00:00:10,680 is a program that will print Fzzbuzz 4 00:00:11,100 --> 00:00:15,690 if a number is divisible by both three and five. 5 00:00:16,110 --> 00:00:17,370 It will print fizz 6 00:00:17,400 --> 00:00:21,120 if it's only divisible by three, and it will print buzz 7 00:00:21,180 --> 00:00:23,160 if it's only divisible by five. 8 00:00:23,550 --> 00:00:26,640 If it's not divisible by three or five, 9 00:00:26,970 --> 00:00:29,550 then it's just going to print the number. 10 00:00:30,150 --> 00:00:34,950 And our code is going to do this all the way from 1 to 100. 11 00:00:35,430 --> 00:00:40,230 So what should happen by the end of this is in our console when we hit run, 12 00:00:40,590 --> 00:00:45,590 it should start typing one and then it should type two and then three, 13 00:00:45,720 --> 00:00:49,710 it will type fizz. And four, it will type four. Five, 14 00:00:49,710 --> 00:00:51,810 it will type buzz and so on and so forth. 15 00:00:52,140 --> 00:00:55,590 You should remember this from the previous exercise where you actually had to 16 00:00:55,590 --> 00:00:58,830 write all this code. Now, as always, 17 00:00:59,040 --> 00:01:03,060 don't just paste the solution code in. That won't do anything. 18 00:01:03,330 --> 00:01:05,550 You need to work for it to gain knowledge. 19 00:01:06,120 --> 00:01:09,270 So now that you know what the program is supposed to do, 20 00:01:09,930 --> 00:01:14,640 what you are going to do is try to figure out all of the bugs in here and try to 21 00:01:14,670 --> 00:01:19,230 fix all the bugs so that the program runs as it should do. 22 00:01:20,220 --> 00:01:24,690 Pause the video, think about the 10 steps and try to apply it here. 23 00:01:25,140 --> 00:01:28,620 Now, just as a quick note, unlike the previous debugging exercises, 24 00:01:28,860 --> 00:01:32,640 there's more than one bug in this code. So, good luck 25 00:01:32,760 --> 00:01:34,020 and I'll see you on the other side. 26 00:01:38,120 --> 00:01:38,630 All right. 27 00:01:38,630 --> 00:01:39,800 So, as I mentioned, 28 00:01:39,860 --> 00:01:43,490 there's quite a few bugs in here and we're going to fix them one by one. 29 00:01:44,090 --> 00:01:44,630 As always, 30 00:01:44,630 --> 00:01:48,410 the first thing we're gonna do is we're just gonna run the code and see what 31 00:01:48,410 --> 00:01:49,243 happens. 32 00:01:49,430 --> 00:01:53,810 So the first thing you'll notice that's a little bit odd is it's printing 33 00:01:53,840 --> 00:01:56,240 instead of just one, two, three, four, 34 00:01:56,600 --> 00:02:00,260 it's printing it as if it's a list with the square bracket around it. 35 00:02:00,710 --> 00:02:04,730 So let's see if we can identify why. Well in our code, 36 00:02:04,940 --> 00:02:09,320 if none of these if statements are true, then it prints the number. 37 00:02:09,680 --> 00:02:11,690 But in this case it's not just the number. 38 00:02:12,110 --> 00:02:14,900 There seems to be some square brackets around the number, 39 00:02:15,230 --> 00:02:20,230 in which case it's printing a list with that number as the single item inside. 40 00:02:21,710 --> 00:02:24,380 So let's get rid of that and let's run our code again. 41 00:02:24,440 --> 00:02:29,330 That looks a little bit better, a bit cleaner. Now let's take a look at the code. 42 00:02:29,780 --> 00:02:34,100 So we know that when the number is only divisible by three then it should print 43 00:02:34,130 --> 00:02:34,963 fizz, 44 00:02:35,240 --> 00:02:40,240 but three, in this case, is actually printing Fizzbuzz, and five is printing Fizzbuzz 45 00:02:41,960 --> 00:02:46,580 and then three and four, it seems a bit of a mumbo-jumbo. 46 00:02:47,300 --> 00:02:49,130 So, what's actually happening here? 47 00:02:50,060 --> 00:02:53,210 It seems like instead of just printing fizz, 48 00:02:53,480 --> 00:02:56,000 it's printing Fizzbuzz and the number. 49 00:02:56,210 --> 00:02:59,180 So there must be a problem in our checking code. 50 00:02:59,830 --> 00:03:04,780 So let's think about what our code needs to do. When the number is divisible by 51 00:03:04,870 --> 00:03:09,400 both three and five, then instead of the number, it should print Fizzbuzz. 52 00:03:09,760 --> 00:03:12,700 So Fizzbuzz should only be printed 53 00:03:13,120 --> 00:03:18,120 if the number that we're currently checking is divisible by both three and five. 54 00:03:19,630 --> 00:03:21,610 Let's use the print statement to help us. 55 00:03:22,240 --> 00:03:27,240 If we use an f-string and we say that we are currently on number and then we 56 00:03:30,670 --> 00:03:33,730 put the number in here. This way 57 00:03:33,730 --> 00:03:36,820 we'll actually print out the current number we're looping through 58 00:03:37,120 --> 00:03:40,810 and then we can see what's being printed each time. So let's run the code. 59 00:03:41,320 --> 00:03:45,910 And if we scroll to the top, currently on number one it prints one, 60 00:03:45,940 --> 00:03:49,270 currently on number two it prints two, currently on number three 61 00:03:49,270 --> 00:03:53,980 it prints Fizzbuzz, Fizz and three. So that is very, 62 00:03:53,980 --> 00:03:55,510 very strange behavior indeed. 63 00:03:55,510 --> 00:04:00,510 It seems like lots of things are true in our if statement. What's happening? Well, 64 00:04:03,610 --> 00:04:05,800 if number is equal to three, 65 00:04:06,460 --> 00:04:09,220 then it seems to be printing Fizzbuzz, 66 00:04:09,580 --> 00:04:14,410 which means if we walk backwards, this if statement must have been true. 67 00:04:14,950 --> 00:04:18,820 Now three divided by three should have zero as the remainder, 68 00:04:18,820 --> 00:04:22,720 so this should be true. But this can't be true, 69 00:04:22,720 --> 00:04:27,720 so this must be false. And it should only print Fizzbuzz if it's divisible by 70 00:04:28,990 --> 00:04:32,590 both three and five. So instead of an or, 71 00:04:32,890 --> 00:04:34,570 this really needs to be an 'and'. 72 00:04:34,900 --> 00:04:39,850 So let's hit run again and see what happens this time. Currently on number three, 73 00:04:39,850 --> 00:04:44,050 it prints Fizz and three. So that's again, 74 00:04:44,080 --> 00:04:47,920 a bit of a problem. So we fixed the Fizzbuzz parts. 75 00:04:48,100 --> 00:04:51,430 It is now printing Fizzbuzz correctly. Namely, 76 00:04:51,460 --> 00:04:56,290 when it's on number 15. But why is it still printing the number? 77 00:04:57,190 --> 00:05:02,190 The number should only be printed if none of the others are true. 78 00:05:03,970 --> 00:05:08,970 But instead, it seems to be printing Fizz and then also printing the number. 79 00:05:10,540 --> 00:05:12,910 What's the reason here? Well, 80 00:05:12,940 --> 00:05:17,800 notice how we've got an else statement here that triggers the printing of the 81 00:05:17,800 --> 00:05:22,570 number. Now, an else is paired with an if. So in this case, 82 00:05:22,570 --> 00:05:27,190 what's happening is it's checking if the number is not divisible by five, 83 00:05:27,520 --> 00:05:31,780 then print the number. That's not what we want. And in fact, 84 00:05:31,900 --> 00:05:33,460 if you look at the print statements, 85 00:05:33,700 --> 00:05:37,870 you can see that only when the number is divisible by five 86 00:05:38,140 --> 00:05:41,590 does it not print the number. When it's divisible by three, 87 00:05:41,860 --> 00:05:45,700 it's still printing the number. This is not what we want. 88 00:05:45,730 --> 00:05:50,650 What we want is for this to be checked, and if that's not true, 89 00:05:50,950 --> 00:05:54,610 then check the next thing. And if that is not true, then the next thing. 90 00:05:54,910 --> 00:05:59,300 And finally, if all three of these are not true, then print the number. 91 00:06:00,080 --> 00:06:05,080 So what we actually need instead of a whole bunch of ifs is actually some else 92 00:06:05,810 --> 00:06:06,560 ifs. 93 00:06:06,560 --> 00:06:11,560 So let's replace those two ifs with some elifs and now let's run our code. 94 00:06:13,570 --> 00:06:17,620 So currently on number one, two, three, 95 00:06:17,680 --> 00:06:22,600 so three now prints Fizz, five prints Buzz, nine prints 96 00:06:22,600 --> 00:06:26,770 Fizz, 10 prints Buzz and 15 prints Fizzbuzz. 97 00:06:27,130 --> 00:06:30,550 So I think we've actually managed to fix all of our code. 98 00:06:30,910 --> 00:06:33,880 So I think we should be able to remove our print statement now. 99 00:06:34,300 --> 00:06:39,300 And indeed we've managed to successfully solve all of the debugging problems 100 00:06:39,550 --> 00:06:43,090 here. Now did you manage to get all that right? Don't worry 101 00:06:43,090 --> 00:06:45,700 if you have to struggle a little bit. In the future, 102 00:06:45,730 --> 00:06:49,540 you're going to be making a lot more bugs and you're going to be repeating this 103 00:06:49,540 --> 00:06:52,060 process of using the 10 steps 104 00:06:52,270 --> 00:06:57,270 to try and identify the problems and fix the code and make it free of bugs. 105 00:06:58,330 --> 00:07:00,970 So hope you had a fun and jam packed day. 106 00:07:01,390 --> 00:07:05,710 Now this might be a good time to revisit some code that you've given up on a 107 00:07:05,710 --> 00:07:08,650 long time ago or projects that you've started 108 00:07:08,680 --> 00:07:12,700 but you've stopped because you ran into bugs. And then review them, 109 00:07:12,760 --> 00:07:17,760 use what you learned today and try to fix the bugs and get your code working. 110 00:07:18,790 --> 00:07:21,790 Now tomorrow, I've got a big day for you coming up. 111 00:07:22,090 --> 00:07:26,500 We're going to spend the whole day creating a big project and we're going to be 112 00:07:26,500 --> 00:07:29,950 making the Higher-Lower game. So I'm looking forward to it, 113 00:07:30,220 --> 00:07:33,730 I hope you are too. So get a good night's rest and I'll see you tomorrow.