1 00:00:02,000 --> 00:00:04,390 Hey everybody top of them muffin to you today. 2 00:00:04,420 --> 00:00:06,660 Mark Price at the slopes dot com. 3 00:00:06,670 --> 00:00:11,230 And today we are going to learn about functions. 4 00:00:11,290 --> 00:00:16,360 Open up your X code 8 and create a new playground. 5 00:00:16,360 --> 00:00:21,430 My playground we're going to call this up town function you 6 00:00:24,340 --> 00:00:33,280 and I'm going to save this where I'm going to save this Iowas 10 course and swift and new folder functions 7 00:00:33,280 --> 00:00:36,140 you can save yours where ever you want. 8 00:00:37,260 --> 00:00:37,820 OK. 9 00:00:38,080 --> 00:00:47,920 So a function is a core component in programming core building block building block in building functional 10 00:00:47,920 --> 00:00:50,710 applications applications that can actually do things. 11 00:00:50,730 --> 00:00:56,020 OK so here's a perfect example of why we need to use a function. 12 00:00:56,080 --> 00:01:00,560 Let's say that I want to get the area of a shape or a rectangle or square. 13 00:01:00,580 --> 00:01:13,360 OK so say bar length equals five bar with equals and say 10 and then bar area equals length times with. 14 00:01:13,360 --> 00:01:15,160 Now you've probably done something similar to this. 15 00:01:15,190 --> 00:01:16,770 Written wrote some variables. 16 00:01:16,770 --> 00:01:17,680 That's math operation. 17 00:01:17,670 --> 00:01:19,110 We now have the area right. 18 00:01:19,570 --> 00:01:21,310 Well this is cool. 19 00:01:21,370 --> 00:01:23,880 Maybe you don't see what's wrong with this. 20 00:01:24,040 --> 00:01:25,980 Well let's do this now. 21 00:01:25,990 --> 00:01:27,230 Now we have a new shape. 22 00:01:27,310 --> 00:01:29,580 So this was shape number one. 23 00:01:30,220 --> 00:01:30,910 All right. 24 00:01:31,220 --> 00:01:31,840 Oh no. 25 00:01:31,870 --> 00:01:33,220 We've got a new shape now. 26 00:01:33,460 --> 00:01:33,850 OK. 27 00:01:33,850 --> 00:01:41,110 It's another rectangle with a different size so now we're going to say OK length two equals six var 28 00:01:41,350 --> 00:01:51,270 with two equals 12 and var area two equals length two times with two. 29 00:01:51,830 --> 00:01:52,220 OK. 30 00:01:52,240 --> 00:01:53,230 Well that's not so bad. 31 00:01:53,410 --> 00:01:58,640 So this is a shape too but oh no. 32 00:01:59,080 --> 00:02:02,980 Now our program requires a third shape shape 3. 33 00:02:03,160 --> 00:02:06,220 And if you're asking me Is it really going to type this out again. 34 00:02:06,220 --> 00:02:13,130 The answer is yes because I want you to see the brutal pain of not working with function Savar length 35 00:02:13,130 --> 00:02:28,330 three equals three are with three equals eight and bar area 3 equals 0 length 3 times with 3 K. 36 00:02:28,540 --> 00:02:30,190 This is lame. 37 00:02:30,190 --> 00:02:31,370 This is really lame. 38 00:02:31,460 --> 00:02:35,020 And anybody who programming can probably realize that this is not the best way. 39 00:02:35,020 --> 00:02:38,320 You don't have to be an advanced programmer to realize something smells wrong. 40 00:02:38,320 --> 00:02:43,720 This is called a code smell a code smells when something looks or smells wrong with your code. 41 00:02:43,960 --> 00:02:46,660 You know maybe don't know what it is but it just doesn't feel right. 42 00:02:46,760 --> 00:02:48,600 Well this violates a principle. 43 00:02:48,610 --> 00:02:51,470 It violates the dry principle which means don't repeat yourself. 44 00:02:51,490 --> 00:02:53,900 And we are definitely repeating ourself here. 45 00:02:54,220 --> 00:03:02,380 So this is how functions can come in handy functions are a way to perform an operation over and over. 46 00:03:02,380 --> 00:03:04,600 You can pass data into it return things. 47 00:03:04,600 --> 00:03:09,730 In fact let's see what our handy dandy internet says about functions. 48 00:03:09,940 --> 00:03:16,470 Define function in programming in computer science. 49 00:03:16,510 --> 00:03:20,610 Functional Programming is a programming paradigm a style of building the structure and elements of a 50 00:03:20,610 --> 00:03:26,650 computer program that treats computation as the evaluation of mathematical functions and avoids changing 51 00:03:26,650 --> 00:03:28,730 state and mutable data. 52 00:03:28,810 --> 00:03:30,880 So this is functional programming. 53 00:03:30,900 --> 00:03:37,480 It's not functions in general but there actually is some merit to functional programming functional 54 00:03:37,480 --> 00:03:44,380 programming basically means you want to create functions that can repeat operations in a mathematical 55 00:03:44,380 --> 00:03:48,340 sense and don't do a whole bunch of things and manipulate all kinds of data. 56 00:03:48,370 --> 00:03:55,230 They do one thing and they do it well and so that's kind of how you should be designing functions anyway. 57 00:03:56,020 --> 00:03:58,330 But that's not exactly what we're looking for. 58 00:03:58,330 --> 00:04:03,340 Let's go over to Wikipedia and if you're wondering why does Mark Price always pull up documentation 59 00:04:03,350 --> 00:04:06,700 always go to these things because you should not be just copying and pasting code. 60 00:04:06,700 --> 00:04:11,800 I'm going to teach you how to become a programmer and programmers the good programmers always learn 61 00:04:11,980 --> 00:04:15,420 they read the documentation they go underneath the hood and that's what we're going to do here. 62 00:04:15,490 --> 00:04:21,310 And if you don't like it just put me on to x speed and you can listen to me talk really fast just like 63 00:04:21,310 --> 00:04:21,710 this. 64 00:04:21,820 --> 00:04:26,740 OK so let's take a side in a function OK. 65 00:04:27,190 --> 00:04:28,030 And 66 00:04:32,070 --> 00:04:33,540 this is a good one too. 67 00:04:33,540 --> 00:04:38,400 A function is a relation between a set of inputs and a set of permissible outputs with the property 68 00:04:38,640 --> 00:04:41,640 that each input is related to exactly one output. 69 00:04:41,640 --> 00:04:48,210 This is really cool how does the word function it translates into different things in math but it all 70 00:04:48,210 --> 00:04:49,860 makes those very similar. 71 00:04:49,860 --> 00:04:51,540 Look at this diagram right here. 72 00:04:51,600 --> 00:04:58,260 A function takes input and it can also provide output doesn't always have to though and this can be 73 00:04:58,260 --> 00:04:59,880 the same thing in programming. 74 00:05:00,230 --> 00:05:05,430 And I would encourage you to do some more searches on an functional math functional programming. 75 00:05:05,430 --> 00:05:06,870 What is a function. 76 00:05:07,200 --> 00:05:11,400 Really good idea of what's going on and I'm going to show you hands on now. 77 00:05:11,520 --> 00:05:14,990 OK we just took a glance at some of the things that are on the Internet. 78 00:05:14,990 --> 00:05:18,020 It's always fun to do that to start educating yourself. 79 00:05:18,200 --> 00:05:23,140 And so what I want you to do is create a function just like I'm going to do. 80 00:05:23,160 --> 00:05:25,000 Func is how you do it in swift. 81 00:05:26,220 --> 00:05:29,810 And we're going to call this calculate area. 82 00:05:30,410 --> 00:05:33,730 OK so we have a function and it's going to do something. 83 00:05:33,750 --> 00:05:41,640 So what we're going to do is we're going to put in two parameters and we're going to say length of time. 84 00:05:41,810 --> 00:05:45,590 This can just be an int and width of type. 85 00:05:46,050 --> 00:05:47,330 So this is the input. 86 00:05:47,370 --> 00:05:51,150 Just like in that diagram that you saw or something go into the function then it does something and 87 00:05:51,150 --> 00:05:52,220 something can come out. 88 00:05:52,470 --> 00:05:54,320 We're can do that exact same thing here. 89 00:05:54,400 --> 00:06:00,630 OK very similar to what you might do in some paper math and length and width and so what's going to 90 00:06:00,630 --> 00:06:04,620 happen is we're going to pass in the length and passing it with it's going to calculate it and it's 91 00:06:04,620 --> 00:06:07,450 going to return it's going to give us back of value. 92 00:06:07,530 --> 00:06:09,870 So this is the syntax for a function. 93 00:06:09,900 --> 00:06:11,670 You start off with the func keyword. 94 00:06:11,850 --> 00:06:16,260 OK and then you give it a name and then you create parentheses. 95 00:06:16,470 --> 00:06:19,520 OK you don't have to have parameters in. 96 00:06:19,860 --> 00:06:25,930 It can be OK that it's just not doing what I want it to do. 97 00:06:25,980 --> 00:06:31,450 You don't have to print this or stuff in the parentheses it can be empty like that. 98 00:06:32,140 --> 00:06:39,780 But good programming or the functional programming that you want to start gravitating towards takes 99 00:06:39,810 --> 00:06:46,170 inputs and returns output without necessarily modifying what you would call your variables or your properties. 100 00:06:46,260 --> 00:06:50,430 And if this doesn't make any sense to set that's absolutely fine because when you watch this video again 101 00:06:50,670 --> 00:06:53,490 you probably should start making more sense. 102 00:06:53,580 --> 00:06:58,230 So we're going to pass in a length passen with these are parameters which means you can put things in 103 00:06:58,230 --> 00:07:04,860 them and then what we're going to do is we're going to put a dash and then a greater than sign. 104 00:07:04,860 --> 00:07:06,360 Kind of like an arrow right. 105 00:07:06,360 --> 00:07:12,880 This is what you're going to return what data type Do we want to return where we want to return an int. 106 00:07:13,350 --> 00:07:14,760 When we say let. 107 00:07:14,750 --> 00:07:21,180 When a critic constant area equals length times with no that's just a simple math operation right. 108 00:07:21,610 --> 00:07:23,410 Length times with. 109 00:07:23,410 --> 00:07:24,670 But then what we're going to do. 110 00:07:24,670 --> 00:07:27,910 We're going to return the area. 111 00:07:27,910 --> 00:07:29,560 So what does this all mean. 112 00:07:29,560 --> 00:07:32,110 OK what's going on here. 113 00:07:32,290 --> 00:07:37,620 Well you don't know because we haven't put it into action yet so what we're going to do is we're going 114 00:07:37,630 --> 00:07:40,680 to say var actual say let. 115 00:07:41,350 --> 00:07:45,580 Area equals calculate area so we're going to call our function. 116 00:07:45,580 --> 00:07:47,980 Notice how it's appearing here on the autocomplete. 117 00:07:48,010 --> 00:07:49,090 It is appearing it's blue. 118 00:07:49,090 --> 00:07:50,110 It has our parameters in it. 119 00:07:50,110 --> 00:07:57,450 This is great so we're going to say calculate area and we're going to pass in a length and width. 120 00:07:57,460 --> 00:08:07,140 So let's say 5 and then with this for k Kukla air with five and four. 121 00:08:07,200 --> 00:08:10,620 And we already have an area means that it doesn't like that because we already have an area I'm going 122 00:08:10,620 --> 00:08:13,220 to call this new area. 123 00:08:13,410 --> 00:08:14,040 OK. 124 00:08:14,270 --> 00:08:17,310 So let new area calculate area and look at this. 125 00:08:17,340 --> 00:08:21,680 It's giving us the proper result of what is happening here what is going on. 126 00:08:21,870 --> 00:08:26,550 Well let's see if I can show you. 127 00:08:26,550 --> 00:08:29,430 So we're calling a function or passing in a 5. 128 00:08:29,430 --> 00:08:35,970 So the second that we pass it to 5 it's taking that and dropping it here in this bucket and calling 129 00:08:36,060 --> 00:08:39,660 it length so it's taken this value in putting it in a new variable called length. 130 00:08:39,660 --> 00:08:44,250 Actually this is a constant you can't change these values OK once they're set in there and then it's 131 00:08:44,250 --> 00:08:48,160 taking this one and it's passing it in here and giving it a name. 132 00:08:48,240 --> 00:08:51,940 So the values you pass in it gives it a new name puts it in a new constant. 133 00:08:51,960 --> 00:08:56,670 You can use inside of your function and then we take the length and the width and it performs a math 134 00:08:56,670 --> 00:09:02,680 operation and stores the result here in this constant and then using the return keyword. 135 00:09:02,860 --> 00:09:03,640 OK. 136 00:09:03,690 --> 00:09:04,620 We actually return something. 137 00:09:04,620 --> 00:09:09,310 So what happens is this is called and then goes right into here. 138 00:09:09,930 --> 00:09:17,220 OK so we pass in the length we pass in the with it performs an operation here and then it returns that 139 00:09:17,220 --> 00:09:21,840 operation or the value of the operation it returns here into our variable. 140 00:09:21,840 --> 00:09:23,140 So now we can use that. 141 00:09:23,460 --> 00:09:26,040 And this is really really cool. 142 00:09:26,170 --> 00:09:28,110 And why is this cool. 143 00:09:28,470 --> 00:09:32,300 Because we don't have to write all this crazy code now pay. 144 00:09:32,370 --> 00:09:32,950 We don't. 145 00:09:33,030 --> 00:09:36,480 The more you have to write code the more chances you have of screwing up. 146 00:09:36,480 --> 00:09:39,980 So what if I was writing the third area here and actually did a minus sign. 147 00:09:39,990 --> 00:09:41,510 Well that's no longer the area is it. 148 00:09:41,550 --> 00:09:46,040 I just broke our code because I wasn't paying attention maybe a sneeze or whatever. 149 00:09:46,200 --> 00:09:51,660 I had to write more code and it created more possibilities for mistakes. 150 00:09:51,660 --> 00:10:01,450 So now if I want to get three different shapes that let's just call this shape one OK let shaped two 151 00:10:01,910 --> 00:10:07,680 we can just now call the function and all the code inside that program just crash. 152 00:10:07,680 --> 00:10:08,910 But all the code inside 153 00:10:11,580 --> 00:10:12,760 you don't ever have to write again. 154 00:10:12,810 --> 00:10:25,500 And that's the beauty of functions open recent. 155 00:10:25,570 --> 00:10:33,380 Now we go so calculate area and this and we're going to say 6 and 2. 156 00:10:33,850 --> 00:10:35,290 OK. 157 00:10:35,290 --> 00:10:36,180 Cool stuff. 158 00:10:36,190 --> 00:10:45,490 So now we've only written the code once inside and it's been used multiple times. 159 00:10:45,490 --> 00:10:48,690 So you're already starting to see the value of a function. 160 00:10:48,700 --> 00:10:56,320 It lets you take input perform operations mathematical or other operations on that input and returning 161 00:10:56,320 --> 00:10:59,580 the result of that so somebody can use it and this is a nice clean function. 162 00:10:59,980 --> 00:11:04,870 And if we really want to clean things up and save some space we don't even have to store this in a constant 163 00:11:04,870 --> 00:11:05,260 like this. 164 00:11:05,260 --> 00:11:14,710 We can actually just say return length times with like so and it's going to perform the operation and 165 00:11:14,720 --> 00:11:16,910 then it's going to return automatically. 166 00:11:16,960 --> 00:11:18,410 And so we don't have to change anything else. 167 00:11:18,420 --> 00:11:22,780 Behere we just cleaned up a little bit of code and this is more common for simple operations. 168 00:11:22,780 --> 00:11:26,980 If you have multiple multi-line operations you have to do then of course stored in the content like 169 00:11:26,980 --> 00:11:28,150 we had before. 170 00:11:28,150 --> 00:11:32,990 So again you take values you pass it into these parameters here also. 171 00:11:33,010 --> 00:11:33,920 That's the keyword. 172 00:11:34,120 --> 00:11:34,770 OK. 173 00:11:34,930 --> 00:11:37,180 Write this down if you're new to programming write this down. 174 00:11:37,180 --> 00:11:39,640 These are parameters also known as arguments. 175 00:11:39,640 --> 00:11:42,140 Some nice people use those terms interchangeably. 176 00:11:42,250 --> 00:11:48,280 Also another thing to write down functions are called functions in some languages and methods in other 177 00:11:48,280 --> 00:11:48,920 languages. 178 00:11:48,930 --> 00:11:52,100 OK very important you might write that keyword down as well too. 179 00:11:52,330 --> 00:11:57,310 Over here on the right hand side is the return statement and executing that return statement the return 180 00:11:57,310 --> 00:11:58,060 type. 181 00:11:58,060 --> 00:12:00,870 OK this is where you specify the return type. 182 00:12:01,120 --> 00:12:04,780 And this is the type here dash greater then sign like an arrow. 183 00:12:05,170 --> 00:12:11,110 And then if you are returning something you must use the return keyword to return a value of that type. 184 00:12:11,110 --> 00:12:17,690 Notice how we couldn't return a string if we wanted to I couldn't say hey you let's try that. 185 00:12:19,690 --> 00:12:24,820 Cannot convert return expression of type string to return type and it must be an integer. 186 00:12:25,030 --> 00:12:26,700 OK this is no bueno. 187 00:12:26,830 --> 00:12:27,630 No good. 188 00:12:28,020 --> 00:12:28,540 OK. 189 00:12:30,320 --> 00:12:36,280 And so we've already saved ourselves some errors by using a function here which is pretty cool and you've 190 00:12:36,280 --> 00:12:40,600 just learned really the core features of a function of what you would use it for and these are used 191 00:12:40,600 --> 00:12:41,950 for everything. 192 00:12:41,950 --> 00:12:43,180 Anything you can think of. 193 00:12:43,180 --> 00:12:46,370 For instance let's talk about bank accounts. 194 00:12:46,720 --> 00:12:59,750 So let's say var say bank account balance equals five hundred zero zero which is a double. 195 00:13:00,300 --> 00:13:01,160 OK. 196 00:13:01,210 --> 00:13:07,020 And then what we do is we say var what you want to. 197 00:13:07,080 --> 00:13:08,600 What do we want to buy something cool. 198 00:13:08,620 --> 00:13:09,240 So yeah. 199 00:13:09,250 --> 00:13:16,870 So the other day get this the day Reebok announces the release of you know the alien Stomper shoes the 200 00:13:16,870 --> 00:13:22,960 shoes that Sigourney Weaver wore in the alien aliens movie. 201 00:13:22,960 --> 00:13:23,490 OK. 202 00:13:23,500 --> 00:13:25,050 And also the Android war of them. 203 00:13:25,480 --> 00:13:27,790 You know 30 years later they're rereleased in the shoes right. 204 00:13:27,790 --> 00:13:29,450 I was all excited ready for it. 205 00:13:29,530 --> 00:13:32,460 Went on the one onto the Web site the second and went live. 206 00:13:32,500 --> 00:13:34,940 And then guess what happened because there's only 2000 shoes. 207 00:13:35,230 --> 00:13:38,270 A bunch of nerds that should have been me because I'm a nerd. 208 00:13:38,370 --> 00:13:43,150 Many nerds with their bots bought up every shoe and then sold them on eBay for like 10 times the amount 209 00:13:43,150 --> 00:13:43,770 of money. 210 00:13:44,230 --> 00:13:45,990 That's all irrelevant. 211 00:13:46,000 --> 00:13:48,700 So my point is that's what we're going to buy today is 212 00:13:52,770 --> 00:14:00,070 you know we're going to buy Sigourney Weaver Alien Stomper shoes. 213 00:14:00,070 --> 00:14:03,610 OK you got $350 now. 214 00:14:03,670 --> 00:14:05,310 She's OK. 215 00:14:05,330 --> 00:14:07,240 So we want to buy these items right. 216 00:14:07,610 --> 00:14:15,350 So you know we could write out some logic here that says you know if you have enough money buy the shoes 217 00:14:15,380 --> 00:14:18,480 and then do another item but what if we had a function that could just purchase an item. 218 00:14:18,580 --> 00:14:19,210 OK. 219 00:14:19,370 --> 00:14:20,540 So let's do that now. 220 00:14:20,720 --> 00:14:24,520 Funk where you say purchase item. 221 00:14:25,610 --> 00:14:26,470 OK. 222 00:14:26,570 --> 00:14:37,200 And what we're going to do purchase item we're going to pass in the current balance type double. 223 00:14:37,310 --> 00:14:41,010 And the item price of type double. 224 00:14:41,260 --> 00:14:42,190 Okay. 225 00:14:42,470 --> 00:14:45,930 And I'll come back to the return statement later. 226 00:14:46,410 --> 00:14:55,090 What we're going to do is say if item price is less than or equal to current balance. 227 00:14:55,590 --> 00:14:55,880 Okay 228 00:14:59,880 --> 00:15:01,220 that's what I'm looking for. 229 00:15:01,220 --> 00:15:03,460 Well we're going to we're going to return. 230 00:15:03,890 --> 00:15:07,250 We're going to return the new balance that you have because you just purchased the items. 231 00:15:07,250 --> 00:15:09,210 Maybe we'll print something too just for fun. 232 00:15:09,230 --> 00:15:14,990 But anyway this is generic It doesn't matter if it's Sigourney Weaver Alien shoes or if it's you know 233 00:15:15,380 --> 00:15:19,310 Teletubbies limited edition lunchpail box. 234 00:15:19,310 --> 00:15:20,370 OK. 235 00:15:20,760 --> 00:15:22,850 From Nineteen ninety eight. 236 00:15:22,890 --> 00:15:29,870 And anyway if item price is less than or equal to current balance you guys are like Do you even hear 237 00:15:29,870 --> 00:15:31,230 the words come out of your mouth Mark. 238 00:15:31,340 --> 00:15:31,700 No. 239 00:15:31,700 --> 00:15:33,880 The answer is No I just say whatever's there. 240 00:15:34,220 --> 00:15:42,590 So now what we can do is return if the prices aren't equal to current balance we can return current 241 00:15:42,590 --> 00:15:47,270 balance minus item price returned the New Balance. 242 00:15:47,280 --> 00:15:47,960 Okay. 243 00:15:48,310 --> 00:15:50,910 And then let's make a return statement. 244 00:15:50,990 --> 00:15:53,620 We're going to make this type double OK. 245 00:15:55,040 --> 00:16:00,900 Like so and then what we do is we're going to say if you can't. 246 00:16:01,040 --> 00:16:07,150 So if it's not less than or equal to then we're going to just return the current balance as it is. 247 00:16:07,170 --> 00:16:08,670 OK. 248 00:16:08,910 --> 00:16:20,500 And what we can do here is say print purchased item for and we can use string interpolation which is 249 00:16:20,500 --> 00:16:22,170 a key word you should have memorized. 250 00:16:22,490 --> 00:16:28,480 Purchased item for item price and we can even put a little dollar sign in front of it. 251 00:16:28,490 --> 00:16:30,390 That's kind of cool I like that. 252 00:16:30,650 --> 00:16:33,290 And otherwise here 253 00:16:36,350 --> 00:16:37,840 you are broke. 254 00:16:40,660 --> 00:16:44,570 You should learn how to save money. 255 00:16:45,140 --> 00:16:46,250 OK. 256 00:16:46,930 --> 00:16:49,720 And so this is cool. 257 00:16:49,720 --> 00:16:56,860 Now what we can do is we can call that function we can say purchase items so purchase item and we can 258 00:16:56,860 --> 00:17:03,160 pass in the narratives we want our current balance so we're going to call it we're going to pass and 259 00:17:03,160 --> 00:17:06,640 bank account balance and then also wants the price of the item. 260 00:17:06,650 --> 00:17:09,810 So this is Sigourney Weaver Alien Stomper shoes. 261 00:17:09,910 --> 00:17:10,650 OK. 262 00:17:11,050 --> 00:17:11,870 And so. 263 00:17:11,980 --> 00:17:19,300 And it's always going to return to us our current balance and now we can say let New Balance equals 264 00:17:19,600 --> 00:17:27,250 not to be confused with the shoe new balance because clearly we're buying Reebok's Reebok so purchased 265 00:17:27,250 --> 00:17:29,380 item for $350. 266 00:17:29,380 --> 00:17:30,870 And notice how the balance is now changed. 267 00:17:30,880 --> 00:17:32,110 Now we're we're being smart. 268 00:17:32,110 --> 00:17:35,870 We're working with functions we're putting in input it's returning things. 269 00:17:36,220 --> 00:17:41,590 And now you know that's our new balance right there are we could well we could have done is instead 270 00:17:41,590 --> 00:17:46,240 of just saying New Balance we could have just said bank account balance we can override it. 271 00:17:46,240 --> 00:17:52,810 Now equals purchased item and then it again remember this is returning something. 272 00:17:52,810 --> 00:17:56,680 OK let me just show you again in case you forgot. 273 00:17:56,800 --> 00:18:02,990 So this return statement right here is returning a value and that's coming in right here. 274 00:18:03,280 --> 00:18:04,410 Okay. 275 00:18:04,570 --> 00:18:10,510 Also keep in mind whenever you call return that is the end that is the end of that function nothing 276 00:18:10,510 --> 00:18:11,790 else will be called after return. 277 00:18:11,800 --> 00:18:14,710 So if it gets here nothing else is going to be called after it. 278 00:18:14,830 --> 00:18:18,300 So if I write code here you know like a print statement you know. 279 00:18:18,490 --> 00:18:20,400 Hello Nurse. 280 00:18:20,400 --> 00:18:21,390 All right. 281 00:18:21,400 --> 00:18:27,130 That is never ever ever ever ever going to be called and he even gives me a warning code after return 282 00:18:27,160 --> 00:18:28,440 will never be executed. 283 00:18:28,590 --> 00:18:33,320 OK return statements and your function. 284 00:18:33,370 --> 00:18:33,880 OK. 285 00:18:34,150 --> 00:18:35,830 So now now we're being smart you know. 286 00:18:35,830 --> 00:18:37,450 And so now we can buy whatever we want. 287 00:18:37,450 --> 00:18:48,400 You know we could save our you know retro lunch box you know equals you know $40. 288 00:18:48,400 --> 00:18:49,230 All right. 289 00:18:49,600 --> 00:18:55,810 So now we have to do is save bank account balance equals purchase item pass in the current bank account 290 00:18:55,810 --> 00:19:01,770 balance and then the item price is you know the retro lunchbox and boom. 291 00:19:02,030 --> 00:19:02,450 OK. 292 00:19:02,500 --> 00:19:05,780 Our bank account balance has now been updated and it's $110. 293 00:19:06,040 --> 00:19:08,050 And we bought we bought her item. 294 00:19:08,050 --> 00:19:10,120 See how it's reusing the code. 295 00:19:10,150 --> 00:19:12,670 We don't have to rewrite things over and over and over again. 296 00:19:12,820 --> 00:19:15,950 That is the beauty of working with functions. 297 00:19:16,020 --> 00:19:20,490 OK now one more thing I want to show you. 298 00:19:20,590 --> 00:19:26,080 This is a little more on the advance side but I just think it be good to know is that you know how I 299 00:19:26,080 --> 00:19:27,450 said these are constants right. 300 00:19:27,470 --> 00:19:33,420 You can not modify these values for instance I cannot say current balance equals zero. 301 00:19:33,700 --> 00:19:35,370 Let's see what happens if I do that. 302 00:19:35,460 --> 00:19:39,490 He yells at us can assign value to current balance is a letter or constant. 303 00:19:39,490 --> 00:19:45,340 Well what if I may not recommend doing it for the specific function function but what if I didn't want 304 00:19:45,340 --> 00:19:46,780 to pass in the current balance. 305 00:19:46,780 --> 00:19:52,840 OK what if or what if I didn't want to return the new balance because it just sounds silly. 306 00:19:53,020 --> 00:19:57,790 I'm purchasing that item why you give me the new balance seems a little bit silly so well we can do 307 00:19:58,600 --> 00:20:01,490 is return the or remove the return statement. 308 00:20:01,960 --> 00:20:02,600 OK. 309 00:20:02,680 --> 00:20:09,700 So instead of returning this here and returning this here what we can do is we can use a keyword here 310 00:20:09,880 --> 00:20:11,550 called in out. 311 00:20:11,970 --> 00:20:18,090 OK current balance in out what it's going to do is it's actually going to modify the original variable. 312 00:20:18,220 --> 00:20:21,320 Okay I'm going to get rid of these 2 x we don't need to assign a new value anywhere. 313 00:20:21,530 --> 00:20:28,030 Okay purchase item and we'll come back to those in a second so we can use the in out keyword which will 314 00:20:28,060 --> 00:20:33,460 allow us to modify the bank account balance directly which is kind of cool. 315 00:20:33,460 --> 00:20:34,760 Now you want to use it sparingly. 316 00:20:34,780 --> 00:20:36,980 But I'm just showing you you can use this. 317 00:20:37,090 --> 00:20:43,450 And so what we can do is we can put the same math we had before except just adjust the existing parameter 318 00:20:43,450 --> 00:20:43,750 here. 319 00:20:43,750 --> 00:20:48,280 Remember how it was a constant we couldn't change it but now we can and that's done by putting the in 320 00:20:48,280 --> 00:20:49,930 out before the type right there. 321 00:20:49,930 --> 00:20:56,190 So now we can say current balance equals current balance minus item price. 322 00:20:56,410 --> 00:20:57,920 Okay. 323 00:20:58,000 --> 00:21:01,890 And so it allows us to modify the variable directly. 324 00:21:02,050 --> 00:21:03,350 Pretty awesome right then right here. 325 00:21:03,370 --> 00:21:04,890 We don't have to do anything except print. 326 00:21:04,890 --> 00:21:06,960 We don't have to return any things is great. 327 00:21:06,970 --> 00:21:10,840 And then over here we can reduce our functions or purchase item. 328 00:21:10,840 --> 00:21:17,770 And what we're going to do is we're going to pass in the bank account balance or the the bank account 329 00:21:17,770 --> 00:21:24,130 balance current balance is what is going on here. 330 00:21:24,440 --> 00:21:32,370 No silly it's being silly bank account balance and item price is going to be the Sigourney Weaver issue 331 00:21:32,370 --> 00:21:33,150 right. 332 00:21:33,680 --> 00:21:34,320 Pretty cool right. 333 00:21:34,320 --> 00:21:37,570 And so all you do is you put that ampersand symbol here. 334 00:21:38,000 --> 00:21:43,040 When you're when you're doing it now when you're doing it out OK put the ampersand symbol before the 335 00:21:43,040 --> 00:21:46,240 variable you pass in and that lets you modify the variable directly. 336 00:21:46,340 --> 00:21:47,880 So we didn't even have to return anything. 337 00:21:47,900 --> 00:21:50,910 So it just whatever you put in here it modifies this directly. 338 00:21:51,040 --> 00:21:51,290 OK. 339 00:21:51,290 --> 00:21:53,060 Again there is use cases for. 340 00:21:53,060 --> 00:21:56,750 I don't recommend using this all the time but I want to show you that it's in your toolbelt of things 341 00:21:56,750 --> 00:21:57,960 that you can do. 342 00:21:58,340 --> 00:22:03,940 And otherwise you know you probably want to go back the way we had it which is just fine and that's 343 00:22:04,040 --> 00:22:04,860 functions. 344 00:22:05,090 --> 00:22:09,330 Creating something that's reusable that performs an operation over and over again. 345 00:22:09,460 --> 00:22:14,150 It's it's something that you're going to use every single day and it's going to take a while to get 346 00:22:14,150 --> 00:22:14,840 this down. 347 00:22:14,840 --> 00:22:18,100 I know that if you especially if you're new to programming and it's fine. 348 00:22:18,230 --> 00:22:22,700 Just keep practicing you'll get better with it and that's it functions. 349 00:22:24,920 --> 00:22:28,000 I'm trying to think of anything else I could say about it but I doubt it. 350 00:22:28,070 --> 00:22:30,880 Ninety nine point nine percent of everything you'll do every single day. 351 00:22:31,040 --> 00:22:31,630 We just did. 352 00:22:31,770 --> 00:22:32,260 So that's it. 353 00:22:32,260 --> 00:22:35,390 Mark Price of slopes dot com. 354 00:22:35,390 --> 00:22:36,560 See you next time.