1 00:00:04,360 --> 00:00:05,860 ‫Hello and welcome this lecture. 2 00:00:05,860 --> 00:00:12,940 ‫We're going to be learning how we can execute a piece of code variable numbers of times so that we can 3 00:00:12,940 --> 00:00:20,050 ‫print out every object that overlaps inside this area, this trigger component. 4 00:00:20,050 --> 00:00:24,400 ‫So you can see here that when we're both, I'm standing inside and there's a gargoyle, too. 5 00:00:24,430 --> 00:00:29,410 ‫It's printing out both the gargoyles name and the player blueprint name. 6 00:00:29,410 --> 00:00:31,360 ‫Let's dive in and see how this is done. 7 00:00:31,930 --> 00:00:38,890 ‫Now, the issue with our code here is that our actors array may have far more than just one actor in 8 00:00:38,890 --> 00:00:39,220 ‫it. 9 00:00:39,220 --> 00:00:44,380 ‫And if we wanted to display all of the actors overlapping or we want to do something with all of those 10 00:00:44,380 --> 00:00:47,680 ‫actors, we need to be able to run through the code. 11 00:00:47,680 --> 00:00:53,740 ‫It would be highly inefficient to write an if statement for the case where we've got two or three or 12 00:00:53,740 --> 00:00:58,840 ‫four or five, etc. And it certainly would never catch every case because we have got a limited amount 13 00:00:58,840 --> 00:01:00,220 ‫of lines in our file. 14 00:01:00,580 --> 00:01:08,230 ‫So the way we deal with this, when we want to repeat a piece of code multiple times, but a number 15 00:01:08,230 --> 00:01:14,530 ‫of times that we don't actually know when we're compiling the code, we need to replace our if statement. 16 00:01:14,770 --> 00:01:20,170 ‫If statement essentially says, should I execute this code or not with something that says, should 17 00:01:20,170 --> 00:01:25,300 ‫I execute this code or should I execute it many times, two times, three times, four times, etc.? 18 00:01:25,450 --> 00:01:29,440 ‫The way we do this is with something called a wild statement. 19 00:01:29,440 --> 00:01:32,440 ‫Now it's built very much like an if statement. 20 00:01:32,440 --> 00:01:41,350 ‫So the while you then put some sort of boolean value inside the parentheses, and then we have some 21 00:01:41,350 --> 00:01:42,430 ‫curly braces. 22 00:01:42,430 --> 00:01:48,340 ‫And inside the curly braces, that block of code that will be keep getting executed again and again 23 00:01:48,340 --> 00:01:54,340 ‫until the condition in our while statement becomes false. 24 00:01:54,340 --> 00:01:55,990 ‫That's why it's called while. 25 00:01:55,990 --> 00:01:59,320 ‫So while this thing is true, executes this code. 26 00:01:59,320 --> 00:02:04,630 ‫So it's a bit like an if statement in that sometimes it might not execute the code at all, but unlike 27 00:02:04,630 --> 00:02:09,940 ‫an if statement that can only execute a piece of code once, the while statement could basically keep 28 00:02:09,940 --> 00:02:14,890 ‫on executing it forever if this boolean never becomes false. 29 00:02:15,460 --> 00:02:22,420 ‫So why is this useful when we could create an int 32 and call it index and start it off at zero? 30 00:02:22,900 --> 00:02:31,390 ‫And then every time we go through the body of this wild loop, we increase the value stored in that 31 00:02:31,390 --> 00:02:31,750 ‫index. 32 00:02:31,750 --> 00:02:36,130 ‫So we could say index equals index plus one. 33 00:02:36,640 --> 00:02:42,520 ‫Now in C++, there is a shorthand to doing this instead of having to do index plus one like this, you 34 00:02:42,520 --> 00:02:49,480 ‫do plus plus index, and that just adds one to whatever is stored in the index variable. 35 00:02:50,110 --> 00:02:50,360 ‫Okay. 36 00:02:50,470 --> 00:02:52,090 ‫So we start off at zero. 37 00:02:52,120 --> 00:02:54,940 ‫We every time we go around, we increase the index. 38 00:02:54,940 --> 00:03:02,620 ‫And what we can do is we can make it so that we only go around this while loop, while our index is 39 00:03:02,620 --> 00:03:05,200 ‫within the bounds of our array. 40 00:03:05,200 --> 00:03:11,440 ‫So we can say that the index must be less than the actors dot num. 41 00:03:11,440 --> 00:03:13,210 ‫So that is the size of the array. 42 00:03:13,210 --> 00:03:19,570 ‫Remember that when we've got five items in array, the last item in the array is index four. 43 00:03:19,870 --> 00:03:28,450 ‫And so we can see that this will be true when the index is valid, when index four is less than five. 44 00:03:28,450 --> 00:03:34,540 ‫But as soon as our index goes past the end of the array, when it gets to index five, then the actor 45 00:03:34,540 --> 00:03:37,390 ‫number is going to be not no longer. 46 00:03:37,390 --> 00:03:39,220 ‫It's five is no longer less than five. 47 00:03:39,220 --> 00:03:45,220 ‫So the while loop will stop executing and continue with the rest of the function. 48 00:03:45,700 --> 00:03:53,110 ‫So what that means is we could now take the code that we had above and rewrite it. 49 00:03:53,290 --> 00:03:58,270 ‫Let's take it, copy it, cut it out and stick it in here in our wild loop. 50 00:03:58,270 --> 00:04:03,520 ‫But before we increase the index, most importantly, because what we're going to do is replace this 51 00:04:03,520 --> 00:04:08,560 ‫zero where we were getting actor zero, we're going to replace it with actor index. 52 00:04:08,800 --> 00:04:10,210 ‫So let's follow this through. 53 00:04:10,240 --> 00:04:11,950 ‫How would this work? 54 00:04:12,580 --> 00:04:15,910 ‫Let's remove our if statement because that's confusing matters a little bit. 55 00:04:15,910 --> 00:04:20,230 ‫So we start off the value in the variable index is going to be zero. 56 00:04:20,530 --> 00:04:23,470 ‫Now imagine we have two actors to keep things simple. 57 00:04:23,680 --> 00:04:27,070 ‫Is zero less than two? 58 00:04:27,100 --> 00:04:27,760 ‫Yes. 59 00:04:27,760 --> 00:04:28,570 ‫Yes, it is. 60 00:04:28,570 --> 00:04:37,510 ‫So we go in and we get actor zero, we get its name and we log it out and then we increase the value 61 00:04:37,510 --> 00:04:38,680 ‫in index by one. 62 00:04:38,680 --> 00:04:40,840 ‫So it goes from being zero to being one. 63 00:04:41,320 --> 00:04:47,320 ‫Now we go back to evaluate the while loop condition and we say is one less than two? 64 00:04:47,320 --> 00:04:48,190 ‫Yes it is. 65 00:04:48,190 --> 00:04:55,540 ‫We can then go in and get actor one and then we're going to get its name and print its name. 66 00:04:55,540 --> 00:05:02,380 ‫Then we increase the index again to index two and we ask the question again in the wild loop, saying 67 00:05:02,380 --> 00:05:03,760 ‫is two less than. 68 00:05:04,240 --> 00:05:05,890 ‫Well, that answer is no. 69 00:05:05,890 --> 00:05:12,070 ‫So we skip over the body of the while loop and we go on and execute the rest of the code. 70 00:05:12,430 --> 00:05:15,120 ‫So that's basically what we want to achieve. 71 00:05:15,130 --> 00:05:22,990 ‫We want to print out the name of each actor in the array, and that's what this piece of code is going 72 00:05:22,990 --> 00:05:23,590 ‫to do. 73 00:05:23,620 --> 00:05:26,370 ‫Let's go ahead and compile it and check that I'm right. 74 00:05:26,380 --> 00:05:33,010 ‫If we go ahead and hit play and step into the box, you can see that we were overlapping just the BP 75 00:05:33,010 --> 00:05:33,610 ‫player. 76 00:05:33,730 --> 00:05:36,270 ‫What if we go and get our gargoyle? 77 00:05:36,280 --> 00:05:41,070 ‫If we stick only it into the bounce, you can see that we get overlapping the gargoyle. 78 00:05:41,080 --> 00:05:43,250 ‫But what if I step in as well? 79 00:05:43,270 --> 00:05:49,600 ‫Now you can see it's printing both that we're overlapping the player and the gargoyle all in the same 80 00:05:49,600 --> 00:05:50,080 ‫frame. 81 00:05:50,080 --> 00:05:56,770 ‫So our while loop is working, it's executing a piece of code multiple times when there are multiple 82 00:05:56,770 --> 00:05:58,520 ‫actors in the array. 83 00:05:58,540 --> 00:06:04,570 ‫Now, because this pattern is so common that we have some sort of index and we increase it every time 84 00:06:04,570 --> 00:06:09,340 ‫we go through the loop, there's actually some shorthand for this in C++. 85 00:06:09,340 --> 00:06:18,310 ‫And if you type four in your Visual Studio code, then there is a snippet for a four loop here that 86 00:06:18,310 --> 00:06:23,890 ‫you can expand and you can see that this is a general structure. 87 00:06:23,890 --> 00:06:25,420 ‫It's got something called a size T here. 88 00:06:25,420 --> 00:06:29,470 ‫We can just replace that with INT 32 for our purposes. 89 00:06:29,620 --> 00:06:35,980 ‫And essentially what this is saying is there are three statements inside the parentheses of the for 90 00:06:35,980 --> 00:06:36,390 ‫loop. 91 00:06:36,400 --> 00:06:43,240 ‫The first one is equivalent to where we set up our index variable before our while loop. 92 00:06:43,780 --> 00:06:49,120 ‫The second one is the condition which is equivalent to what we put inside our wild loop. 93 00:06:49,510 --> 00:06:54,670 ‫And you can see we could replace the count with actors dot num. 94 00:06:54,670 --> 00:07:01,240 ‫And then the last bit is the basically the plus plus whether you put it before or after, the index 95 00:07:01,240 --> 00:07:07,240 ‫is not too important, but you can see that this is increasing the value in the index. 96 00:07:07,240 --> 00:07:11,080 ‫So it's equivalent to the line that we put at the end of our wild loop. 97 00:07:11,470 --> 00:07:17,980 ‫So this just brings together all in one line what we were having to spread out across multiple using 98 00:07:17,980 --> 00:07:18,910 ‫our wild loop. 99 00:07:18,910 --> 00:07:20,380 ‫So here's a simple challenge for you. 100 00:07:20,380 --> 00:07:23,470 ‫Convert your wild loop to a for loop. 101 00:07:23,470 --> 00:07:30,220 ‫You're going to copy over the body of the code, change the index from that name index to I. 102 00:07:30,250 --> 00:07:36,550 ‫We typically use the abbreviation in for loops of I just an abbreviation for index really and compile 103 00:07:36,550 --> 00:07:38,020 ‫and test pause video. 104 00:07:38,020 --> 00:07:38,800 ‫Now have a go. 105 00:07:41,860 --> 00:07:42,180 ‫Okay. 106 00:07:42,190 --> 00:07:42,760 ‫Welcome back. 107 00:07:42,760 --> 00:07:44,710 ‫So this should be fairly straightforward. 108 00:07:44,710 --> 00:07:47,050 ‫We don't want the index plus plus in here. 109 00:07:47,050 --> 00:07:53,530 ‫So we're going to cut the rest out, channel change over where we are indexing the actors array with 110 00:07:53,530 --> 00:07:54,370 ‫the index variable. 111 00:07:54,370 --> 00:07:58,450 ‫We're going to change that to IE the variable that's available only within this for loop. 112 00:07:58,450 --> 00:08:04,750 ‫That's another advantage by the way of the full loop syntax is that the IE variable is only available 113 00:08:04,990 --> 00:08:10,210 ‫only available within the for loop, whereas when we declared it here in the Y loop, it's available 114 00:08:10,210 --> 00:08:16,990 ‫outside, which kind of pollutes the indexes we can use later on so we can delete that wild loop. 115 00:08:16,990 --> 00:08:23,230 ‫And you can see that the for loop is a lot more condensed and you will get used to the slightly strange 116 00:08:23,230 --> 00:08:25,390 ‫syntax that it has. 117 00:08:25,390 --> 00:08:30,670 ‫Let's go ahead and compile and just check that it does indeed do the same job. 118 00:08:30,670 --> 00:08:38,050 ‫If I go and grab my gargoyle and come up to the overlapping actors, you can see that indeed is printing 119 00:08:38,050 --> 00:08:42,100 ‫both of our actors when we're both overlapping in the alcove. 120 00:08:42,130 --> 00:08:42,850 ‫Great stuff. 121 00:08:42,850 --> 00:08:49,840 ‫So in this lecture we've seen a new programming idea, the idea of loops, and we've particularly come 122 00:08:49,840 --> 00:08:53,230 ‫across the while loop and the for loop. 123 00:08:53,230 --> 00:08:54,910 ‫I'll see you in the next lecture.