1 00:00:00,240 --> 00:00:03,870 So now that you've learned all about if, elif and else, 2 00:00:04,260 --> 00:00:06,150 as well as nested if statements, 3 00:00:06,330 --> 00:00:11,330 then I've got two code challenges coming up for you. In the first one, in the 4 00:00:12,000 --> 00:00:16,020 code challenge that's called day 3.2 BMI calculator 5 00:00:16,230 --> 00:00:17,100 2.0, 6 00:00:17,730 --> 00:00:22,730 this is going to be an upgraded version of the BMI calculator that you created 7 00:00:23,190 --> 00:00:24,023 yesterday. 8 00:00:24,630 --> 00:00:28,260 Instead of just working out the BMI value of somebody, 9 00:00:28,590 --> 00:00:30,810 we're going to give them an interpretation. 10 00:00:31,650 --> 00:00:34,680 You might've come across a BMI chart that looks like this, 11 00:00:35,280 --> 00:00:40,280 where it divides up people's BMI and tells them whether if the underweight, 12 00:00:41,340 --> 00:00:46,020 normal weight, overweight, et cetera. And this depends on the value of the BMI. 13 00:00:46,230 --> 00:00:50,100 So if the value of the BMI is less than 18.5, 14 00:00:50,490 --> 00:00:54,960 then they are underweight. If they're over 18.5, 15 00:00:54,990 --> 00:00:58,350 but below 25, then they have a normal weight. 16 00:00:58,920 --> 00:01:03,240 So your job is to not only create a BMI calculator, 17 00:01:03,840 --> 00:01:08,670 but also to give them the corresponding interpretation message. 18 00:01:09,330 --> 00:01:10,170 Now it's really, 19 00:01:10,170 --> 00:01:14,820 really important that you use the words here that are highlighted in bold in your 20 00:01:14,820 --> 00:01:18,480 interpretation, that based on a particular height and weight, 21 00:01:18,540 --> 00:01:21,360 you actually give them the correct interpretation. 22 00:01:22,500 --> 00:01:25,680 Pause the video and try to give this challenge a go. 23 00:01:29,370 --> 00:01:31,140 All right. So how did you get on? 24 00:01:31,380 --> 00:01:34,560 There was a little bit of a revision from what you've done previously. 25 00:01:34,920 --> 00:01:38,970 Hopefully you've been able to calculate the BMI without much trouble and then 26 00:01:39,000 --> 00:01:43,800 use what you learned about if, elif and else to provide the user with the 27 00:01:43,800 --> 00:01:47,640 corresponding interpretation for the BMI that they have. 28 00:01:48,480 --> 00:01:52,620 Let's start out by calculating the BMI. And the BMI, 29 00:01:52,680 --> 00:01:55,860 according to this equation is equal to the weight in kilograms 30 00:01:55,860 --> 00:01:59,580 divided by the height squared. So we've got the weight already, 31 00:01:59,790 --> 00:02:04,050 and then we divided by the height to the power of two. 32 00:02:04,800 --> 00:02:09,060 Now, notice how I've already converted these inputs to floats. 33 00:02:09,090 --> 00:02:13,290 So we don't have to do what we did previously when we were calculating the BMI. 34 00:02:14,940 --> 00:02:17,340 Now what the exercise does mention though 35 00:02:17,370 --> 00:02:20,610 is that we should round the result of the nearest whole number. 36 00:02:21,210 --> 00:02:25,590 But you probably remember how to do this right? Using the round function. 37 00:02:25,830 --> 00:02:29,550 So if we wrap the entire equation inside a round function, 38 00:02:29,880 --> 00:02:32,130 then it's going to round it to the nearest whole number. 39 00:02:32,820 --> 00:02:36,600 So if this is what you got stuck on, then head back to your code and just fix it. 40 00:02:37,260 --> 00:02:40,740 Now, once we've calculated the rounded value of BMI, 41 00:02:41,100 --> 00:02:46,100 the next step is to give the user an interpretation message based on their BMI. 42 00:02:47,070 --> 00:02:48,900 So let's start with the first one. 43 00:02:49,140 --> 00:02:53,100 If the BMI is less than 18.5, 44 00:02:53,520 --> 00:02:56,520 well then in this case, they're actually underweight, right? 45 00:02:56,910 --> 00:03:00,880 So it will print something like your BMI is, 46 00:03:01,480 --> 00:03:04,990 and then inside here we'll insert the value of their BMI. 47 00:03:05,500 --> 00:03:09,420 And this of course is using f-strings, so let's add an F to the beginning. 48 00:03:10,030 --> 00:03:15,030 Your BMI is this particular value and you are underweight. 49 00:03:17,380 --> 00:03:17,860 Now, 50 00:03:17,860 --> 00:03:22,860 what if their BMI was between 18.5 and 25? 51 00:03:23,680 --> 00:03:28,000 Well, because we've already checked that their BMI is less than 18.5, 52 00:03:28,420 --> 00:03:32,950 then if this is false because it's jumped to the next level, 53 00:03:33,280 --> 00:03:34,990 then we don't actually have to check this. 54 00:03:35,290 --> 00:03:39,940 All we have to do is check that it's still below 25. And to do that, 55 00:03:39,940 --> 00:03:41,170 we're going to use an Elif. 56 00:03:41,710 --> 00:03:46,710 So elif BMI is less than 25, well then in this case, 57 00:03:47,260 --> 00:03:51,130 we're going to print you bmi 58 00:03:51,160 --> 00:03:55,810 is this particular value, and you have a normal 59 00:03:55,810 --> 00:04:00,580 weight. If this is a little bit mysterious to you, 60 00:04:00,760 --> 00:04:05,200 why it is that I'm not checking that their BMI is over 18.5, 61 00:04:05,230 --> 00:04:10,120 but below 25 and I'm simply just checking that it's less than 25, 62 00:04:10,390 --> 00:04:13,930 then I recommend having a play around with the code as it is right now, 63 00:04:14,350 --> 00:04:17,350 and trying out some different values for BMI. 64 00:04:17,560 --> 00:04:21,190 Just change this to say 18, 65 00:04:21,190 --> 00:04:26,050 and then try maybe something like 22 so that it's caught by each of these 66 00:04:26,050 --> 00:04:29,950 conditions. And then you'll soon realize that this 67 00:04:30,130 --> 00:04:34,930 if, elif, else is an entire group of statements, 68 00:04:35,320 --> 00:04:39,940 and it's going to check this one first and only if this fails, 69 00:04:39,970 --> 00:04:43,090 when it's false, does it go and check the next one. 70 00:04:43,570 --> 00:04:48,570 So then this is only going to be printed when their BMI is over 18.5, 71 00:04:49,450 --> 00:04:53,170 but below 25. And once you're comfortable with this, 72 00:04:53,230 --> 00:04:55,810 then the rest of the statements should be pretty easy. 73 00:04:58,920 --> 00:04:59,753 All right, 74 00:05:00,030 --> 00:05:00,240 Now, 75 00:05:00,240 --> 00:05:05,240 once we've reached here and their BMI is not less than 35 and we want to catch the 76 00:05:07,650 --> 00:05:10,770 remaining cases where the BMI is over 35, 77 00:05:11,220 --> 00:05:14,160 then all we have to do is add an else statement. 78 00:05:17,520 --> 00:05:18,960 That's all we have to do. 79 00:05:19,380 --> 00:05:23,730 We've managed to check for those people that have BMI less than 18.5. 80 00:05:24,120 --> 00:05:28,230 If it's not less 18.5, well, is it less than 25? 81 00:05:28,650 --> 00:05:33,450 So this will print when the BMI is greater than 18.5, 82 00:05:33,480 --> 00:05:37,920 but less than 25. And we've done that for all of these separate statements. 83 00:05:40,200 --> 00:05:42,150 If you struggled with this code, 84 00:05:42,210 --> 00:05:46,590 then I recommend having a look back at the previous lesson where we talked more 85 00:05:46,590 --> 00:05:50,760 in detail in terms of if, elif and else. 86 00:05:51,810 --> 00:05:53,670 If you struggled with this challenge, 87 00:05:53,730 --> 00:05:58,730 then have a go at pasting the code that's in the solution into the Thonny code 88 00:05:58,760 --> 00:06:03,140 editor. And instead of having the BMI being a workout value, 89 00:06:03,470 --> 00:06:07,640 just set it to some different numbers. So for example, if we start out testing, 90 00:06:07,910 --> 00:06:10,220 if the BMI is equal to 18, 91 00:06:10,550 --> 00:06:15,470 which of these will it fall into, then we can click on the debug step into each 92 00:06:15,470 --> 00:06:18,980 of these. And you can see that when it evaluates this condition, 93 00:06:19,010 --> 00:06:22,100 is the BMI less than 18.5, well, 94 00:06:22,130 --> 00:06:26,300 18 is less than 18.5. So this is true. 95 00:06:26,720 --> 00:06:30,260 And in that case, it's going to execute this line of code. 96 00:06:30,680 --> 00:06:34,220 So it is going to print out your BMI is 18, you are underweight. 97 00:06:34,760 --> 00:06:38,330 And then it's done. That's the end of the code. Now, 98 00:06:38,360 --> 00:06:43,280 if we change this to say 22 however, and we click on debug, 99 00:06:43,940 --> 00:06:48,830 then it's going to evaluate the first condition, is 22 less than 18.5 and 100 00:06:49,070 --> 00:06:50,540 that's going to be false. 101 00:06:50,780 --> 00:06:54,230 So then it skips to the next elif that it can find 102 00:06:54,740 --> 00:06:59,300 and it checks whether if the BMI 22 is less than 25. 103 00:06:59,660 --> 00:07:02,750 So now it's going to execute this print statements. 104 00:07:03,710 --> 00:07:04,970 Have a play around with that 105 00:07:05,150 --> 00:07:08,690 if it's still a little bit mysterious to you and hopefully, 106 00:07:08,690 --> 00:07:09,680 once you're done there, 107 00:07:09,890 --> 00:07:12,800 then you'll be ready to move on to the next code challenge 108 00:07:12,860 --> 00:07:17,150 which is a little bit more challenging. For all of that and more, 109 00:07:17,330 --> 00:07:17,900 I'll see you there.