1 00:00:00,480 --> 00:00:01,680 In this exercise, 2 00:00:01,680 --> 00:00:04,590 you are going to be writing a function 3 00:00:04,590 --> 00:00:07,800 that calculates how many cans of paint you need 4 00:00:07,800 --> 00:00:09,990 in order to paint a wall, 5 00:00:09,990 --> 00:00:14,010 given the height and width of the wall. 6 00:00:14,010 --> 00:00:16,440 So what you're going to do is you're going write a function, 7 00:00:16,440 --> 00:00:20,220 and it has to be called paint_calc 8 00:00:20,220 --> 00:00:24,030 because the code on lines 10 to 13 9 00:00:24,030 --> 00:00:26,460 makes sure that we get the inputs, 10 00:00:26,460 --> 00:00:29,130 we work out the coverage of our paint, 11 00:00:29,130 --> 00:00:32,369 and we use your function, paint_calc, 12 00:00:32,369 --> 00:00:36,150 in order to output the printed statement 13 00:00:36,150 --> 00:00:39,840 to tell the user how many cans of paint they need. 14 00:00:39,840 --> 00:00:44,010 The way to work out the area of a wall 15 00:00:44,010 --> 00:00:47,790 is to multiply the height by the width, 16 00:00:47,790 --> 00:00:52,790 and then we divide that number by the coverage of the paint 17 00:00:53,610 --> 00:00:56,940 in order to work out how many number of cans we need. 18 00:00:56,940 --> 00:01:01,230 Now, because the shops don't sell you a fractional can, 19 00:01:01,230 --> 00:01:03,720 and believe me, I've tried to ask for that, 20 00:01:03,720 --> 00:01:06,150 you have to always round upwards, 21 00:01:06,150 --> 00:01:08,010 y ou can't round down. 22 00:01:08,010 --> 00:01:11,010 So even if it was 1.1 cans, 23 00:01:11,010 --> 00:01:13,440 you will need to purchase two cans, 24 00:01:13,440 --> 00:01:18,060 or so says the sales agent at my local home hardware store. 25 00:01:18,060 --> 00:01:20,580 Now, take a look at the instructions, 26 00:01:20,580 --> 00:01:24,390 you'll see that the Example Input and Example Outputs 27 00:01:24,390 --> 00:01:26,640 and the format that they need to be. 28 00:01:26,640 --> 00:01:29,040 In this case, we're saying that the first number 29 00:01:29,040 --> 00:01:33,360 in the Input is the height and the second is the width, 30 00:01:33,360 --> 00:01:35,130 but in reality it doesn't really matter 31 00:01:35,130 --> 00:01:38,160 because area is worked out in either way, 32 00:01:38,160 --> 00:01:39,870 height times width or width times height, 33 00:01:39,870 --> 00:01:41,580 and it doesn't really matter. 34 00:01:41,580 --> 00:01:43,020 But what it does matter 35 00:01:43,020 --> 00:01:46,080 is to figure out how to round up a number, 36 00:01:46,080 --> 00:01:47,460 and I've put a hint 37 00:01:47,460 --> 00:01:49,770 into the instructions from Stack Overflow. 38 00:01:49,770 --> 00:01:52,770 You could also search for your own ways 39 00:01:52,770 --> 00:01:54,720 of figuring this out. 40 00:01:54,720 --> 00:01:57,390 But, have a go at writing the code, 41 00:01:57,390 --> 00:02:00,450 and hit Submit when you think you're ready, 42 00:02:00,450 --> 00:02:03,033 and check it against the pre-made tests. 43 00:02:06,270 --> 00:02:10,229 The first thing we need to do is to define our function. 44 00:02:10,229 --> 00:02:13,980 So in Python, that is the "def keyword", space, 45 00:02:13,980 --> 00:02:15,480 and then the name of the function. 46 00:02:15,480 --> 00:02:19,020 And we said that it has to match the line 47 00:02:19,020 --> 00:02:22,140 that we already created to call the function on line 12. 48 00:02:22,140 --> 00:02:24,200 So it has to be called paint_calc. 49 00:02:25,350 --> 00:02:27,240 And then we have a set of parentheses () 50 00:02:27,240 --> 00:02:30,990 where we can put the inputs to our function. 51 00:02:30,990 --> 00:02:35,430 In this case, it's height, width, and the coverage. 52 00:02:35,430 --> 00:02:38,610 Now, we haven't put any inputs into our function just yet 53 00:02:38,610 --> 00:02:42,450 because remember, our function is a multi-use tool. 54 00:02:42,450 --> 00:02:45,000 It's something that we can use again and again 55 00:02:45,000 --> 00:02:47,190 by putting in different inputs. 56 00:02:47,190 --> 00:02:51,180 So for example, the function len() can take any list, 57 00:02:51,180 --> 00:02:54,600 and it will work out the length of the list 58 00:02:54,600 --> 00:02:57,120 or how many items are in the list. 59 00:02:57,120 --> 00:02:59,220 So the inputs can always change, 60 00:02:59,220 --> 00:03:00,840 but we define in our function 61 00:03:00,840 --> 00:03:03,870 how we want to work with those inputs. 62 00:03:03,870 --> 00:03:07,950 After our definition for our function name and inputs, 63 00:03:07,950 --> 00:03:10,950 we create the actual body of the function. 64 00:03:10,950 --> 00:03:14,580 And we do that by indenting into the function. 65 00:03:14,580 --> 00:03:16,620 The first thing we do is we calculate 66 00:03:16,620 --> 00:03:17,940 the number of cans we need 67 00:03:17,940 --> 00:03:21,180 by multiplying the height by the width to work out the area, 68 00:03:21,180 --> 00:03:23,580 putting a parenthesis around this, 69 00:03:23,580 --> 00:03:28,290 and then we divide it by the coverage of the paint. 70 00:03:28,290 --> 00:03:32,670 This is going to be a decimal number in many cases, 71 00:03:32,670 --> 00:03:35,280 so we have another line on line 5 72 00:03:35,280 --> 00:03:37,980 where we round up the cans. 73 00:03:37,980 --> 00:03:42,980 In order to round it up, we use the math module 74 00:03:43,980 --> 00:03:48,390 and we use the math.ceil() method. 75 00:03:48,390 --> 00:03:51,450 This is going to go to the ceiling of the number, 76 00:03:51,450 --> 00:03:53,340 which basically means rounding it up 77 00:03:53,340 --> 00:03:55,320 to the nearest whole number. 78 00:03:55,320 --> 00:03:57,270 And we pass our number of cans 79 00:03:57,270 --> 00:03:59,610 as the input into this function, 80 00:03:59,610 --> 00:04:04,560 and then we calculate it and store it inside round_up_cans. 81 00:04:04,560 --> 00:04:06,810 And then finally, we print out the message, 82 00:04:06,810 --> 00:04:09,960 You'll need round_up_cans cans of paint, 83 00:04:09,960 --> 00:04:14,310 inserting our number of cans of paint rounded up 84 00:04:14,310 --> 00:04:16,380 into that print statement. 85 00:04:16,380 --> 00:04:19,050 And the way that our function is going to work 86 00:04:19,050 --> 00:04:23,520 is we've already defined our function on lines 3 to 6, 87 00:04:23,520 --> 00:04:25,500 and then on line 12, 88 00:04:25,500 --> 00:04:29,220 we actually call the function, passing in actual values. 89 00:04:29,220 --> 00:04:32,820 So in this case, the first input as the height, 90 00:04:32,820 --> 00:04:34,980 the second input as the width, 91 00:04:34,980 --> 00:04:38,733 and the coverage as whatever is defined on line 11. 92 00:04:39,660 --> 00:04:41,910 And when that line of code is run, 93 00:04:41,910 --> 00:04:46,143 then we get our output printed into the output area.