1 00:00:04,540 --> 00:00:05,560 ‫Hello and welcome. 2 00:00:05,560 --> 00:00:10,840 ‫In this lecture, we are going to be making some rudimentary calculations here using some variables. 3 00:00:10,840 --> 00:00:18,190 ‫I've got input A and input B and A, plus B when we hit play, then the result will be calculated on 4 00:00:18,190 --> 00:00:20,830 ‫this actor to give us a result of nine. 5 00:00:20,830 --> 00:00:24,940 ‫Let's dive in and see how we can perform these calculations in C++. 6 00:00:25,090 --> 00:00:31,420 ‫So in the last lecture we saw how we could expose some C++ variables into our editor. 7 00:00:31,420 --> 00:00:37,990 ‫We could see the default values that we'd set, but we haven't really explored how to code in C++. 8 00:00:37,990 --> 00:00:45,490 ‫We've really only declared some variables, so how can we go ahead and actually execute some functionality? 9 00:00:45,490 --> 00:00:48,730 ‫Well, this is where the C++ file comes in. 10 00:00:48,730 --> 00:00:53,710 ‫As and as I've said, there's a bit of an analogy here between the C++ file and event graph, because 11 00:00:53,710 --> 00:00:55,970 ‫this is where we put our functionality out. 12 00:00:55,990 --> 00:00:58,870 ‫What should the program do in Blueprint? 13 00:00:58,870 --> 00:01:04,120 ‫Whereas the event graph is where we define where to find functions and variables and what types they 14 00:01:04,120 --> 00:01:04,270 ‫are. 15 00:01:04,270 --> 00:01:07,240 ‫So let's more configuring the class. 16 00:01:07,240 --> 00:01:14,320 ‫So at the same is true in C++, the header file is for configuring and declaring what things are in 17 00:01:14,320 --> 00:01:18,730 ‫the class, and a C++ file is where the actual code lives. 18 00:01:18,970 --> 00:01:23,980 ‫So in this C++ file we can see there are a few things here. 19 00:01:23,980 --> 00:01:28,300 ‫These are the different functions in our C++ class. 20 00:01:28,300 --> 00:01:30,490 ‫They were defined over in the header file. 21 00:01:30,490 --> 00:01:37,630 ‫So you can see that we mention this big in play and tick over here and in the C++ file we show what 22 00:01:37,630 --> 00:01:39,670 ‫code is actually inside them. 23 00:01:39,670 --> 00:01:42,100 ‫So we've got big in play, we've got tick. 24 00:01:42,100 --> 00:01:49,360 ‫And again, we're seeing these curly braces which surround the definition of the code for these functions. 25 00:01:49,750 --> 00:01:51,910 ‫So the one we're interested in is Begin Play. 26 00:01:51,910 --> 00:01:57,790 ‫It's the same as that Begin Play event that we've seen over in Blueprint and the code that we write 27 00:01:57,790 --> 00:02:04,060 ‫within these curly braces after the begin play, that is code that's going to be executed as soon as 28 00:02:04,060 --> 00:02:05,740 ‫the game starts playing. 29 00:02:06,040 --> 00:02:12,190 ‫So one thing that we can do in here is we can access the variables that we've created in our header 30 00:02:12,190 --> 00:02:14,860 ‫file and potentially update them. 31 00:02:14,860 --> 00:02:21,310 ‫So for example, I could take the my INT and I could say I want to update your value. 32 00:02:21,340 --> 00:02:27,670 ‫We do this with the equals sign, so we say my int equals and then we could set it to something like 33 00:02:27,670 --> 00:02:28,990 ‫nine instead. 34 00:02:28,990 --> 00:02:35,590 ‫And then with any instructions in C++, we also end them with a semicolon like. 35 00:02:35,590 --> 00:02:38,110 ‫So notice again my indentation. 36 00:02:38,110 --> 00:02:44,530 ‫Everything within these curly braces is indented one level to show that it is part of the begin play 37 00:02:44,530 --> 00:02:46,600 ‫function definition. 38 00:02:46,750 --> 00:02:53,080 ‫And it's important that you also add your lines of code after the line that says Super Begin Play. 39 00:02:53,350 --> 00:02:56,380 ‫Now you can see that is on line 18 for me. 40 00:02:56,380 --> 00:03:00,910 ‫And again, we can use as many new lines as we want to separate things out and give us a bit of breathing 41 00:03:00,910 --> 00:03:01,420 ‫room. 42 00:03:01,630 --> 00:03:10,210 ‫So what happens if I compile this with live coding and then with that compilation successful, we go 43 00:03:10,210 --> 00:03:11,830 ‫and play well. 44 00:03:11,830 --> 00:03:16,780 ‫We need to select the moving platform actor in the outline as we're playing. 45 00:03:16,780 --> 00:03:24,760 ‫And you can see that the my INT has been updated from its default value to nine and that is because 46 00:03:24,760 --> 00:03:30,880 ‫begin play that begin play function was run and the command that we'd written there that we should set 47 00:03:30,880 --> 00:03:34,960 ‫my int equal to nine was executed. 48 00:03:34,960 --> 00:03:39,040 ‫Now we could use this to create a little bit of a calculator. 49 00:03:39,040 --> 00:03:47,140 ‫So if I were to have two integers in here that we want to add together, I'm going to create a new INT 50 00:03:47,140 --> 00:03:58,120 ‫32 called input A I'm going to set that default to zero and I'm going to make it a new property edit 51 00:03:58,120 --> 00:03:58,930 ‫anywhere. 52 00:03:59,050 --> 00:04:02,140 ‫Then I'm going to have a second one, which is also a new property. 53 00:04:02,140 --> 00:04:05,560 ‫And just to make it easier, I'm going to copy the whole lot. 54 00:04:05,770 --> 00:04:11,620 ‫I'm going to have a second one, which I'm going to call Input B, and then I'm going to have a third 55 00:04:11,620 --> 00:04:17,020 ‫one, which again, I'm just going to copy called a plus B. 56 00:04:17,020 --> 00:04:23,800 ‫Now, what we want to do here is take the value that's in A, the value that's in B and add them together 57 00:04:23,800 --> 00:04:28,720 ‫and put them in a plus B well, we can do this by going back to the C++ file. 58 00:04:28,750 --> 00:04:33,850 ‫I'm going to add a new line underneath where I set my INT equal to nine. 59 00:04:34,030 --> 00:04:46,270 ‫And I'm going to say that a plus B is equal to input A plus input B and again, notice the variable 60 00:04:46,270 --> 00:04:48,400 ‫names are all without spaces. 61 00:04:48,400 --> 00:04:53,350 ‫I've put spaces around my plus symbol to make it easier to read, and then I need to finish off the 62 00:04:53,350 --> 00:04:55,360 ‫line with a semicolon. 63 00:04:55,360 --> 00:05:03,340 ‫So if I go back into the editor and I recompile using live coding, I should see in my moving platform 64 00:05:03,340 --> 00:05:03,670 ‫active. 65 00:05:03,850 --> 00:05:10,540 ‫Charles Payne that we've got an input A and input B and an A plus B, so I can put some numbers into 66 00:05:10,540 --> 00:05:17,470 ‫A and B, and that will actually update the values inside my class so I can put four and I can put five 67 00:05:17,470 --> 00:05:18,130 ‫in here. 68 00:05:18,250 --> 00:05:25,120 ‫And then when I hit play, my instruction to calculate the sum of those two will be executed. 69 00:05:25,120 --> 00:05:30,190 ‫And if I go and look at the details pane for the moving platform, you can see that the value in A plus 70 00:05:30,220 --> 00:05:33,850 ‫B has been set to nine, the sum of four and five. 71 00:05:33,940 --> 00:05:36,700 ‫So I'd like to challenge you to add two floats together. 72 00:05:36,700 --> 00:05:38,680 ‫We've just done it with 30 twos. 73 00:05:38,710 --> 00:05:39,910 ‫Now let's try with the float. 74 00:05:39,910 --> 00:05:43,240 ‫So add three new float variables to your header file. 75 00:05:43,240 --> 00:05:48,940 ‫Call them something like input, float a, input float B and a plus B float. 76 00:05:48,940 --> 00:05:53,110 ‫Again, we're having to use different names because you can't have multiple variables with the same 77 00:05:53,110 --> 00:05:58,330 ‫name, even if there are different types and then add them together in big play so that you get the 78 00:05:58,330 --> 00:06:02,920 ‫result in a plus b float pause video and have a go. 79 00:06:07,320 --> 00:06:07,680 ‫Okay. 80 00:06:07,680 --> 00:06:10,290 ‫So this is going to be fairly straightforward. 81 00:06:10,320 --> 00:06:11,910 ‫Almost copying and pasting here. 82 00:06:11,910 --> 00:06:16,530 ‫I'm going to take the three variables that I've got that were in 32. 83 00:06:16,620 --> 00:06:19,680 ‫I'm going to paste a copy of these. 84 00:06:19,710 --> 00:06:24,600 ‫I'm going to have input, a float, and I'm going to change its type to float as well. 85 00:06:24,630 --> 00:06:29,280 ‫The input B I'm going to change the float and have the output be a float as well. 86 00:06:29,670 --> 00:06:36,970 ‫And then I'm going to have the type for a plus B, be a float and have it called a plus B float, which 87 00:06:36,970 --> 00:06:40,200 ‫is just going to make it easy to see the difference between all of these. 88 00:06:40,200 --> 00:06:41,790 ‫Let's go back into the editor. 89 00:06:41,790 --> 00:06:47,490 ‫Stop playing, hit the live coding button and that's recompiled it. 90 00:06:47,490 --> 00:06:49,590 ‫But I haven't actually put the code in Begin Play yet. 91 00:06:49,590 --> 00:06:56,850 ‫So let's go back into Visual Studio code, go to the C++ file and this is where we need to have a new 92 00:06:56,850 --> 00:07:03,990 ‫line at the end of the begin playback before the curly brace where we've got a plus B float is equal 93 00:07:03,990 --> 00:07:11,550 ‫to input A float plus input B float and then a semicolon at the end of the line. 94 00:07:11,550 --> 00:07:17,190 ‫And that will be executed after the other two lines are executed at the beginning of play. 95 00:07:17,190 --> 00:07:24,270 ‫So we'll hit the live coding button, close the terminal down and hit play, then select the actor in 96 00:07:24,270 --> 00:07:24,780 ‫the outline. 97 00:07:24,780 --> 00:07:30,450 ‫I have a look in the details pane and well, we haven't added anything into the inputs, so let's have 98 00:07:30,450 --> 00:07:31,320 ‫something in there. 99 00:07:31,320 --> 00:07:39,420 ‫For starters, maybe I will have six and I'll put 7.3 in the A and B floats. 100 00:07:39,420 --> 00:07:44,910 ‫Then I'm going to go ahead and hit play, select the actor, have a look in the details pane. 101 00:07:44,910 --> 00:07:50,280 ‫And sure enough, we've got the result of 13.3 in the result variable. 102 00:07:50,370 --> 00:07:50,970 ‫Great stuff. 103 00:07:50,970 --> 00:07:58,860 ‫So in this lecture we have used the C++ file and begin play function to execute some of our own C++ 104 00:07:58,860 --> 00:07:59,310 ‫code. 105 00:07:59,310 --> 00:08:00,810 ‫I'll see you in the next one.