1 00:00:00,480 --> 00:00:02,910 All right, this is the final debugging exercise 2 00:00:02,910 --> 00:00:07,910 for today, and it is to debug our FizzBuzz program. 3 00:00:08,640 --> 00:00:10,290 Read the code carefully, 4 00:00:10,290 --> 00:00:13,650 see if you can spot any problems first time. 5 00:00:13,650 --> 00:00:17,220 If you can't, run the code and see what errors you get 6 00:00:17,220 --> 00:00:20,340 or submit the code and see which tests don't pass 7 00:00:20,340 --> 00:00:21,390 in order to give you a hint 8 00:00:21,390 --> 00:00:24,600 as to where the program might be going wrong. 9 00:00:24,600 --> 00:00:27,060 Now, if you can't remember how the FizzBuzz program 10 00:00:27,060 --> 00:00:28,470 is supposed to work, 11 00:00:28,470 --> 00:00:30,930 take a look inside the Description box 12 00:00:30,930 --> 00:00:33,660 where we've got a detailed description to remind you 13 00:00:33,660 --> 00:00:35,460 of how it's meant to work. 14 00:00:35,460 --> 00:00:38,310 Remember that in this debugging problem, 15 00:00:38,310 --> 00:00:41,310 I've actually put in quite a few bugs. 16 00:00:41,310 --> 00:00:44,550 You could call it a bug fest, 17 00:00:44,550 --> 00:00:48,480 so have fun squishing bugs, and see if you can figure out 18 00:00:48,480 --> 00:00:51,003 and find all the bugs and fix the code. 19 00:00:54,000 --> 00:00:55,380 Okay, I was a little bit mean 20 00:00:55,380 --> 00:00:57,600 and I maybe put in quite a few bugs in there 21 00:00:57,600 --> 00:00:58,830 for you to find, 22 00:00:58,830 --> 00:01:02,130 but it's good getting debugging practice, 23 00:01:02,130 --> 00:01:04,620 and this is the last debugging practice of the day. 24 00:01:04,620 --> 00:01:07,950 So take a look at line 4. 25 00:01:07,950 --> 00:01:10,920 The original code, we had: 26 00:01:10,920 --> 00:01:13,980 if number % 3 == 0 27 00:01:13,980 --> 00:01:16,920 or number % 5 == 0, 28 00:01:16,920 --> 00:01:18,300 and what this is going to do 29 00:01:18,300 --> 00:01:20,280 is it's going to check when the number 30 00:01:20,280 --> 00:01:23,610 is divisible by 3 or divisible by 5. 31 00:01:23,610 --> 00:01:24,780 It's not going to check 32 00:01:24,780 --> 00:01:27,750 when both of these conditions are True. 33 00:01:27,750 --> 00:01:29,370 And in order to do that, 34 00:01:29,370 --> 00:01:31,050 we have to fix this line of code 35 00:01:31,050 --> 00:01:33,480 and change "or" to "and", 36 00:01:33,480 --> 00:01:36,440 that way we know when we need to print "FizzBuzz". 37 00:01:37,440 --> 00:01:39,750 The next two bugs are pretty much related. 38 00:01:39,750 --> 00:01:41,310 I had to put them both in, 39 00:01:41,310 --> 00:01:43,860 otherwise it would look a bit suspicious. 40 00:01:43,860 --> 00:01:47,790 And the problem here is we have two if statements: 41 00:01:47,790 --> 00:01:52,790 if number % 3 == 0 and if number % 5 == 0. 42 00:01:53,700 --> 00:01:57,150 Now the problem with this is not only is it inefficient, 43 00:01:57,150 --> 00:02:01,260 it means that even if the first line, line 6, was True, 44 00:02:01,260 --> 00:02:05,100 it's going to continue checking every single if statement. 45 00:02:05,100 --> 00:02:07,260 Whereas if we have an elif statement, 46 00:02:07,260 --> 00:02:11,730 then at any point, it could end the if, elif, else loop 47 00:02:11,730 --> 00:02:13,530 once it finds one of them to be true, 48 00:02:13,530 --> 00:02:15,450 so that's an early exit option 49 00:02:15,450 --> 00:02:17,580 and it's more efficient in most cases. 50 00:02:17,580 --> 00:02:19,890 Now, there's another crucial downfall 51 00:02:19,890 --> 00:02:23,520 to just using if statements in this code 52 00:02:23,520 --> 00:02:28,520 in the sense that if it's meant to be FizzBuzz, 53 00:02:28,620 --> 00:02:30,030 it should print FizzBuzz, 54 00:02:30,030 --> 00:02:31,950 it should not print Fizz 55 00:02:31,950 --> 00:02:35,970 because it's divisible by 3 and Buzz and FizzBuzz. 56 00:02:35,970 --> 00:02:38,310 That will mess up our structure 57 00:02:38,310 --> 00:02:40,680 of our answer pretty dramatically. 58 00:02:40,680 --> 00:02:44,430 So in this case, it should only print Fizz 59 00:02:44,430 --> 00:02:48,540 when the first condition on line 6 is False, 60 00:02:48,540 --> 00:02:51,930 and then it falls into the next condition to check, 61 00:02:51,930 --> 00:02:54,720 well, if it's not divisible by 3 and 5, 62 00:02:54,720 --> 00:02:57,540 is it divisible by 3 alone? 63 00:02:57,540 --> 00:02:59,370 And then if that's False as well, 64 00:02:59,370 --> 00:03:00,450 then we go and check, well 65 00:03:00,450 --> 00:03:03,390 is it divisible by 5 alone, 66 00:03:03,390 --> 00:03:05,430 in which case it should print Buzz. 67 00:03:05,430 --> 00:03:08,220 The flow of a conditional statement 68 00:03:08,220 --> 00:03:11,070 is very important thing to wrap your head around, 69 00:03:11,070 --> 00:03:14,940 and this is a good example of where it is crucial 70 00:03:14,940 --> 00:03:16,803 to use elif instead of if. 71 00:03:18,300 --> 00:03:21,210 Now the final bug is just a bit of a naughty one from me. 72 00:03:21,210 --> 00:03:23,370 Instead of printing out a number, 73 00:03:23,370 --> 00:03:26,040 if we wrap some square brackets around that number, 74 00:03:26,040 --> 00:03:29,730 we print out a list containing our number, 75 00:03:29,730 --> 00:03:31,950 which is not what we are checking against, 76 00:03:31,950 --> 00:03:34,230 that's not what we want. 77 00:03:34,230 --> 00:03:36,030 In order to fix this, it's pretty simple, 78 00:03:36,030 --> 00:03:38,010 just remove the square brackets [ ]. 79 00:03:38,010 --> 00:03:40,020 Now, a lot of this involves being sensitive 80 00:03:40,020 --> 00:03:42,810 to how code looks, and the more code you read, 81 00:03:42,810 --> 00:03:44,610 the better you get at debugging, 82 00:03:44,610 --> 00:03:47,460 it's not one of those skills that we're born with for sure. 83 00:03:47,460 --> 00:03:51,870 And if Hollywood movies portray hackers as typing away, 84 00:03:51,870 --> 00:03:53,040 that is not the truth, 85 00:03:53,040 --> 00:03:54,750 most of the time we are debugging, 86 00:03:54,750 --> 00:03:56,760 we are staring deep into space 87 00:03:56,760 --> 00:03:58,830 and trying to figure out what it is 88 00:03:58,830 --> 00:04:00,450 that we've written that is causing 89 00:04:00,450 --> 00:04:02,970 this catastrophic failure of our code. 90 00:04:02,970 --> 00:04:04,500 So don't be disheartened, 91 00:04:04,500 --> 00:04:07,710 this is an important skill to hone and to build, 92 00:04:07,710 --> 00:04:10,440 and this is just one step towards that. 93 00:04:10,440 --> 00:04:11,673 Failure is your friend.