1 00:00:08,940 --> 00:00:12,332 Well, we're moving onto the next module, where we're going 2 00:00:12,332 --> 00:00:15,110 to learn how we can make decisions in our programs. 3 00:00:16,170 --> 00:00:21,405 Here are the learning objectives for the module. 4 00:00:21,405 --> 00:00:30,021 So I said we're going to learn about how we can make decisions in our programs. 5 00:00:30,021 --> 00:00:33,254 So what kinds of decisions do we need to make? 6 00:00:33,254 --> 00:00:34,104 So, here are some examples. 7 00:00:34,104 --> 00:00:35,271 What does our program have to decide to do? 8 00:00:35,271 --> 00:00:36,276 We might decide, based on user input. 9 00:00:36,276 --> 00:00:39,830 Which direction we should move the player's avatar. 10 00:00:39,830 --> 00:00:43,780 So, for example, if they're using wasd, then you want to 11 00:00:43,780 --> 00:00:46,940 move up with w and left with a and so on. 12 00:00:46,940 --> 00:00:52,350 So movement based on user is one of the things we decide about. 13 00:00:53,900 --> 00:00:59,700 Another thing we decide about 14 00:00:59,700 --> 00:01:05,036 is Is the selection control 15 00:01:05,036 --> 00:01:09,214 structure. That's 16 00:01:09,214 --> 00:01:14,164 what it's called because 17 00:01:14,164 --> 00:01:19,114 we're selecting between 18 00:01:19,114 --> 00:01:24,739 multiple courses of action in 19 00:01:24,739 --> 00:01:28,520 our program. Okay. 20 00:01:28,520 --> 00:01:32,949 So we use the selection control structure to detect 21 00:01:32,949 --> 00:01:37,620 collisions and also we use it to resolve collisions. 22 00:01:38,810 --> 00:01:44,440 So the resolution of a collision may be based on a variety of different factors. 23 00:01:44,440 --> 00:01:47,140 Are we wearing enough armor that the rocket 24 00:01:47,140 --> 00:01:51,370 propelled grenade bounces off when the collision occurs? 25 00:01:51,370 --> 00:01:53,581 Or do we not have the level of protection 26 00:01:53,581 --> 00:01:57,039 so that something else happens when that collision occurs. 27 00:01:58,170 --> 00:01:59,164 Okay. 28 00:01:59,164 --> 00:02:01,030 players do stuff in games right? 29 00:02:01,030 --> 00:02:04,072 That's why they are fun to play and based on the 30 00:02:04,072 --> 00:02:08,752 players performance, say whether they are playing a mini game and they 31 00:02:08,752 --> 00:02:12,106 have to have a sort of a minimal bar of performance, 32 00:02:12,106 --> 00:02:16,960 we can use selection to decide whether they get, loot or not. 33 00:02:16,960 --> 00:02:18,310 So we might need to decide that. 34 00:02:20,360 --> 00:02:25,789 Players navigate menus in most games, and so based on their selection of 35 00:02:25,789 --> 00:02:30,640 which menu they want to go to, we might do that as well. 36 00:02:30,640 --> 00:02:32,800 By the way, menus? 37 00:02:33,820 --> 00:02:37,370 People do not get at all excited about writing menus. 38 00:02:37,370 --> 00:02:41,160 And virtually every single game you'll ever play has 'em. 39 00:02:41,160 --> 00:02:45,448 So it's one of the things that you'll end up doing as a game developer that is 40 00:02:45,448 --> 00:02:49,210 not nearly as exciting as some of the other things you do. 41 00:02:49,210 --> 00:02:54,130 You can actually build some interesting menu systems if you choose to do so. 42 00:02:54,130 --> 00:02:55,390 But. 43 00:02:55,390 --> 00:02:57,648 You know, you're going to have to build them. 44 00:02:57,648 --> 00:02:59,968 Just like tutorials, which has nothing to with 45 00:02:59,968 --> 00:03:02,868 the selection control structure but tutorials are another 46 00:03:02,868 --> 00:03:04,608 thing that people tend to not get too 47 00:03:04,608 --> 00:03:08,280 excited about but everyone builds into their games. 48 00:03:08,280 --> 00:03:09,384 And lots more. 49 00:03:09,384 --> 00:03:10,500 There's lots 50 00:03:10,500 --> 00:03:16,800 more stuff that you might need to do in terms of deciding how your game performs. 51 00:03:19,150 --> 00:03:22,842 So you should go take an in-lecture quiz, so that you can tell 52 00:03:22,842 --> 00:03:27,750 me about the statement we're going to look at today for doing that decision making. 53 00:03:31,860 --> 00:03:38,370 Okay, so this a graphical representation of the if statement. 54 00:03:38,370 --> 00:03:42,716 And this graphical representation is what's called a control 55 00:03:42,716 --> 00:03:46,734 flow graph because it graphs how the control flows through 56 00:03:46,734 --> 00:03:50,342 the program, eh, looks something like a flow chart 57 00:03:50,342 --> 00:03:53,603 for those of you who have heard of such things. 58 00:03:53,603 --> 00:03:57,375 We don't tend to use these things as design mechanisms 59 00:03:57,375 --> 00:04:01,130 anymore, but we do use them to help visualize. 60 00:04:01,130 --> 00:04:03,370 What the program will do. 61 00:04:03,370 --> 00:04:07,374 And so, let's pretend, because we're going to do it soon, 62 00:04:07,374 --> 00:04:12,380 let's pretend that we're going to ask the player for some input. 63 00:04:12,380 --> 00:04:17,310 We're going to ask them a yes or no question, and if they answer yes, we 64 00:04:17,310 --> 00:04:22,428 want to print an appropriate yes message. And so, this is sort 65 00:04:22,428 --> 00:04:27,340 of, a picture of how that flow through the program would work. 66 00:04:27,340 --> 00:04:29,400 We'll ask them the question. 67 00:04:29,400 --> 00:04:33,890 And then we'll check their response. Let's put it in a variable called answer. 68 00:04:33,890 --> 00:04:38,610 And we'll check their response to see if it's equal to Y for yes. 69 00:04:38,610 --> 00:04:41,200 And if it is we'll print that message. 70 00:04:41,200 --> 00:04:42,490 And if it's not we won't. 71 00:04:45,900 --> 00:04:47,880 So those things. 72 00:04:47,880 --> 00:04:54,090 Those edges, if you will, that come out of that top node are called branches. 73 00:04:54,090 --> 00:04:56,826 And so you should take and in-lecture quiz 74 00:04:56,826 --> 00:05:00,250 to tell me about what you understand about branches. 75 00:05:01,450 --> 00:05:06,310 And now you should go do another in-lecture quiz to tell me what you 76 00:05:06,310 --> 00:05:11,390 know about that answer equal equal yes part that we labeled the node with. 77 00:05:15,390 --> 00:05:22,900 So that expression the answer equal equal yes Is called a Boolean expression. 78 00:05:22,900 --> 00:05:27,112 Remember, Boolean variables can have values of true or false 79 00:05:27,112 --> 00:05:31,648 and a Boolean expression is merely an expression that evaluates to 80 00:05:31,648 --> 00:05:34,969 true or false and we use that result, the value it 81 00:05:34,969 --> 00:05:39,091 evaluates to decide whether or not we should do the thing. 82 00:05:39,091 --> 00:05:41,072 The branch, on the true side. 83 00:05:41,072 --> 00:05:44,830 Let's fire up the IDE, I already have a template built. 84 00:05:46,470 --> 00:05:52,710 Notice I remembered to zoom in this time, so we're going to look at some forms of 85 00:05:52,710 --> 00:05:59,620 the if statement and so, the first thing we're going to do is ask for and get. 86 00:05:59,620 --> 00:06:03,280 An input from the user to a yes or no question. 87 00:06:03,280 --> 00:06:05,255 So we know how to ask for, we do a prompt. 88 00:06:05,255 --> 00:06:05,820 [NOISE] 89 00:06:05,820 --> 00:06:11,710 And let's give them something interesting to answer about. 90 00:06:11,710 --> 00:06:15,518 Pick up the shiny thing, and we'll tell 91 00:06:15,518 --> 00:06:19,730 them, they should tell us either yes or no. 92 00:06:21,820 --> 00:06:22,884 So there's our prompt 93 00:06:22,884 --> 00:06:23,164 [NOISE] 94 00:06:23,164 --> 00:06:25,510 and then we're going to read this in. 95 00:06:25,510 --> 00:06:28,749 Now, this is a single character we're trying to 96 00:06:28,749 --> 00:06:32,067 read in so let's call it answer and I've declared 97 00:06:32,067 --> 00:06:37,170 it to be the char data type and of course, I try to do a console dot read line. 98 00:06:40,890 --> 00:06:43,100 And, I get a compilation error that says 99 00:06:43,100 --> 00:06:45,730 I can't implicitly convert a string to a char. 100 00:06:46,840 --> 00:06:51,030 I've specifically chosen to put this into a char for two reasons. 101 00:06:51,030 --> 00:06:52,944 First of all, the character is the 102 00:06:52,944 --> 00:06:56,112 right choice, right, they're picking something with 103 00:06:56,112 --> 00:07:01,560 the single character so we should in fact store it in the single character variable. 104 00:07:01,560 --> 00:07:06,074 The other reason I've decided to do it this way is because I wanted to show 105 00:07:06,074 --> 00:07:08,516 you that at this point after this call to 106 00:07:08,516 --> 00:07:13,580 Console.ReadLine we know we're holding a string of characters. 107 00:07:13,580 --> 00:07:14,810 A string in fact. 108 00:07:14,810 --> 00:07:16,720 A string object. 109 00:07:16,720 --> 00:07:19,494 And we also know that we can access particular 110 00:07:19,494 --> 00:07:24,080 characters in that string by indexing using the square brackets. 111 00:07:24,080 --> 00:07:26,950 So I wanted to show you that we can take this 112 00:07:26,950 --> 00:07:31,214 call to the method, and then add at the end, square bracket, 113 00:07:31,214 --> 00:07:36,544 zero, square bracket, and that will take that string object that the method 114 00:07:36,544 --> 00:07:42,670 returns, and index into it to extract the 0th character in the string. 115 00:07:42,670 --> 00:07:46,130 So now we're holding the answer, let's add that. 116 00:07:46,130 --> 00:07:47,995 Extra blank line that I like so much. 117 00:07:47,995 --> 00:07:48,475 [NOISE] 118 00:07:48,475 --> 00:07:51,163 And let's run it now before we add 119 00:07:51,163 --> 00:07:56,000 the if statement to make sure that's working properly. 120 00:07:56,000 --> 00:07:58,020 Pick up the shiny thing, yes or no. 121 00:07:58,020 --> 00:08:01,330 You'll notice that I can type a whole long thing here. 122 00:08:01,330 --> 00:08:06,020 And, it's just going to extract the d from the very beginning. 123 00:08:06,020 --> 00:08:09,540 We'll learn later that there are other ways that we could take care of this, 124 00:08:09,540 --> 00:08:11,190 but for now we're going to focus on the 125 00:08:11,190 --> 00:08:13,380 if statement so we're going to let that happen. 126 00:08:15,470 --> 00:08:19,940 And that's the read line, press any key to continue so I have. 127 00:08:19,940 --> 00:08:24,080 So, let's print an appropriate message. Let's print a message for the yes. 128 00:08:24,080 --> 00:08:29,705 So, this looks much like the control flow graph where 129 00:08:29,705 --> 00:08:35,260 Boolean expression between the parentheses here. 130 00:08:37,190 --> 00:08:40,702 So, if in fact the. Character that they, 131 00:08:40,702 --> 00:08:43,354 the first character of the string they enter is 132 00:08:43,354 --> 00:08:46,485 in fact a lower case y, then we'll print something. 133 00:08:46,485 --> 00:08:47,945 [NOISE] 134 00:08:49,113 --> 00:08:55,860 you have the shiny object. 135 00:08:59,780 --> 00:09:02,040 So, now let's test our code. 136 00:09:02,040 --> 00:09:05,510 So we're going to try it with, we want to go down the true branch. 137 00:09:05,510 --> 00:09:09,114 So we'll make sure we enter a lowercase y, and we want to go down 138 00:09:09,114 --> 00:09:11,698 the false branch from that picture which will 139 00:09:11,698 --> 00:09:14,160 imprint any message at all at this point. 140 00:09:16,000 --> 00:09:19,724 Okay, so let's run it, and I'll just enter 141 00:09:19,724 --> 00:09:24,260 y, and I get that you have the shiny object. 142 00:09:24,260 --> 00:09:24,892 I'll run 143 00:09:24,892 --> 00:09:28,369 it again, and enter anything other than y, like h. 144 00:09:29,750 --> 00:09:31,080 And I don't get that message. 145 00:09:31,080 --> 00:09:33,520 So that was the false branch. 146 00:09:33,520 --> 00:09:36,636 The only thing you might notice is that if I run 147 00:09:36,636 --> 00:09:40,100 this and I enter capital Y instead of lower case y. 148 00:09:40,100 --> 00:09:41,430 Because I've got caps lock on. 149 00:09:41,430 --> 00:09:45,790 Because cruise control for cool. Oh I don't get a message. 150 00:09:45,790 --> 00:09:47,740 And it feels like I should. 151 00:09:47,740 --> 00:09:50,260 Right, so there are a variety of ways that we can do this. 152 00:09:50,260 --> 00:09:52,816 We can make sure that the time we get to the if 153 00:09:52,816 --> 00:09:55,656 statement, we've capitalized or lower cased 154 00:09:55,656 --> 00:09:58,283 whatever character they entered, but I'd 155 00:09:58,283 --> 00:10:03,040 rather actually build a more complicated Boolean expression here, to show you 156 00:10:03,040 --> 00:10:08,070 how that works, so we're checking if answer equals lower case y here. 157 00:10:08,070 --> 00:10:15,792 And we learned that we have this or, Boolean operator, so we can check if it's 158 00:10:15,792 --> 00:10:18,860 lowercase y or, uppercase y. 159 00:10:18,860 --> 00:10:22,657 And so that way when I Ctrl+F5, we'll try all three again. 160 00:10:22,657 --> 00:10:25,080 Y still works the way it should've. 161 00:10:26,340 --> 00:10:30,276 H still works the way it should've, but now when 162 00:10:30,276 --> 00:10:34,590 I enter a capital I, I get that message again. 163 00:10:34,590 --> 00:10:37,983 So, we've looked at the first former variant 164 00:10:37,983 --> 00:10:40,854 of an if statement where we just have the 165 00:10:40,854 --> 00:10:44,640 if clause, or the if block, this part right here. 166 00:10:45,810 --> 00:10:49,050 And we've built a, not really complicated but 167 00:10:49,050 --> 00:10:53,870 more complicated than just testing one thing, Boolean expression. 168 00:10:54,980 --> 00:10:59,944 So let's go back to the slides and look at 169 00:10:59,944 --> 00:11:05,359 another form where in fact, if they say no. 170 00:11:06,990 --> 00:11:09,770 We can do something else. 171 00:11:09,770 --> 00:11:16,080 So at this point we have both a Print yes message along the true branch. 172 00:11:16,080 --> 00:11:19,020 And a Print no message along the false branch. 173 00:11:19,020 --> 00:11:21,396 So this is a pictorial representation of an 174 00:11:21,396 --> 00:11:24,320 If statement that has an Else clause in it. 175 00:11:24,320 --> 00:11:26,500 So now we add the code for that. 176 00:11:28,040 --> 00:11:30,590 And we add the code, by saying else. 177 00:11:39,080 --> 00:11:42,248 And we'll write now, whoops, sorry 178 00:11:42,248 --> 00:11:42,958 [LAUGH]. 179 00:11:42,958 --> 00:11:48,590 Something really compelling, you don't have the shiny object. 180 00:11:52,350 --> 00:11:56,460 So now we have an if statement that will do this part. 181 00:11:57,540 --> 00:12:00,350 If the Boolean expression of that leads to true. 182 00:12:00,350 --> 00:12:04,390 And if the Boolean expression of that leads to false it will go do this part. 183 00:12:04,390 --> 00:12:09,726 So when we Ctrl+F5, I'll test y again. And 184 00:12:09,726 --> 00:12:16,840 I'll test n. Oh, good that's what it should have done. 185 00:12:16,840 --> 00:12:20,530 However, you might also realize that if we enter 186 00:12:20,530 --> 00:12:25,140 H, we still get, you don't have the shiny object. 187 00:12:25,140 --> 00:12:28,936 And that maybe acceptable for what we're writing right now, 188 00:12:28,936 --> 00:12:32,878 however, lets actually be, we're tired, we're tired of the 189 00:12:32,878 --> 00:12:34,922 use of being a dork and so we want to 190 00:12:34,922 --> 00:12:38,320 be a little abusive if they don't pick yes or no. 191 00:12:38,320 --> 00:12:41,946 other than being mean to the you, player, there's a good 192 00:12:41,946 --> 00:12:46,780 reason for this because it lets me show you one more piece of the if statement. 193 00:12:48,230 --> 00:12:52,390 So let's actually say that we want the else to be 194 00:12:52,390 --> 00:12:56,980 something mean. You are a noob. 195 00:12:59,030 --> 00:13:05,498 And here we want to print the no message. What 196 00:13:05,498 --> 00:13:11,897 we can do is we can add an else if, 197 00:13:11,897 --> 00:13:13,082 [SOUND] 198 00:13:13,082 --> 00:13:23,036 and I will check both lowercase n, and uppercase N 199 00:13:23,036 --> 00:13:24,221 [NOISE] 200 00:13:24,221 --> 00:13:26,201 like so. 201 00:13:26,201 --> 00:13:27,196 [NOISE] 202 00:13:27,196 --> 00:13:34,559 And here's where we'll write, you don't 203 00:13:34,559 --> 00:13:42,430 have the shiny object. So thinking about how this will work. 204 00:13:42,430 --> 00:13:47,650 What happens is when we're running this code we get to this point right here. 205 00:13:47,650 --> 00:13:52,607 And we check the Boolean expression. If this Boolean expression 206 00:13:52,607 --> 00:13:58,869 evaluates to true it will print this line. And then it goes all the way down here. 207 00:13:59,970 --> 00:14:04,760 So it goes all the way past this very last curly brace. 208 00:14:04,760 --> 00:14:11,000 If this evaluates to a false, it goes down and checks at this one. 209 00:14:11,000 --> 00:14:14,192 And if this one evaluates to a true, it does this, 210 00:14:14,192 --> 00:14:17,729 and then comes all the way past the whole if statement. 211 00:14:19,120 --> 00:14:22,927 If neither this nor this evaluated to true, it'll come 212 00:14:22,927 --> 00:14:25,970 to the else and tell the user they are a noob. 213 00:14:27,800 --> 00:14:28,550 Let's try it. 214 00:14:30,050 --> 00:14:33,506 I pressed F5 and I crashed it because I just 215 00:14:33,506 --> 00:14:37,226 hit Enter because the user is in fact a moron. 216 00:14:37,226 --> 00:14:42,455 So let me do Ctrl+F5, we'll check yes. Yes, works fine. 217 00:14:42,455 --> 00:14:43,590 [SOUND] 218 00:14:43,590 --> 00:14:49,038 We'll check both lowercase 219 00:14:49,038 --> 00:14:53,980 n, oh, dear. It says, we're a noob. 220 00:14:56,130 --> 00:14:59,580 So now we have this debugging thing. Right? 221 00:14:59,580 --> 00:15:03,009 We have to go look at this Boolean expression and say, what's going wrong? 222 00:15:04,200 --> 00:15:08,432 And if we look at this Boolean expression we can see that 223 00:15:08,432 --> 00:15:13,308 in my frenzy of typing, I said for this Boolean expression, if 224 00:15:13,308 --> 00:15:16,804 the answer is, this is an and not an or, I said 225 00:15:16,804 --> 00:15:21,220 if the answer is both lower case and uppercase n, and that 226 00:15:21,220 --> 00:15:26,389 is, in fact, impossible. So, this should have been an or. 227 00:15:27,490 --> 00:15:30,946 See, even in a well-polished well-prepared lecture, there 228 00:15:30,946 --> 00:15:34,330 can be mistakes, just like programming happens in general. 229 00:15:35,390 --> 00:15:36,410 That's why we're testing it. 230 00:15:37,440 --> 00:15:41,598 Okay, so, I'll try the lower case n, you don't have the shiny 231 00:15:41,598 --> 00:15:46,295 object, I'll try the upper case N, you don't have the shiny object and 232 00:15:46,295 --> 00:15:48,759 finally I'll try my, my favorite not 233 00:15:48,759 --> 00:15:52,040 search for something, I'll try my favorite h. 234 00:15:53,100 --> 00:15:55,490 And, I am, in fact, a noob. 235 00:15:58,470 --> 00:16:02,089 So, that's it for the sort of different variance of the 236 00:16:02,089 --> 00:16:06,890 if statement, we looked at three different ways we could use this. 237 00:16:06,890 --> 00:16:09,463 We looked at and if that just has a true 238 00:16:09,463 --> 00:16:12,949 branch and nothing on the false branch We looked at 239 00:16:12,949 --> 00:16:16,684 the if else, which has both true and false branches, 240 00:16:16,684 --> 00:16:20,370 and then we looked at adding else ifs, as well. 241 00:16:20,370 --> 00:16:23,475 In case we have a more complicated sequence of Boolean 242 00:16:23,475 --> 00:16:25,420 expressions that we want to test. 243 00:16:26,610 --> 00:16:30,106 You should know, once we start adding else ifs, we can 244 00:16:30,106 --> 00:16:33,720 add as many else ifs if we want, as we want. 245 00:16:33,720 --> 00:16:38,208 And, the else part is in fact, option, we can just have if, 246 00:16:38,208 --> 00:16:43,910 else, if and that's it and it will be exactly as you'd expect. 247 00:16:43,910 --> 00:16:45,950 Next time, we're going to look. 248 00:16:45,950 --> 00:16:48,710 So that's it for today, next time we're going 249 00:16:48,710 --> 00:16:53,690 to look at another statement in C# that we can use to make decisions in our programs.