1 00:00:00,960 --> 00:00:05,760 So this time around, I want to look at something you may never have heard of before, if you come from 2 00:00:05,760 --> 00:00:10,650 a language like and you've definitely never, never heard of, if you've never done any programming 3 00:00:10,650 --> 00:00:11,010 before. 4 00:00:11,580 --> 00:00:20,190 But it's the concept of pointers and pointers are incredibly useful and they are often a source of some 5 00:00:20,190 --> 00:00:21,810 confusion to people. 6 00:00:22,440 --> 00:00:26,370 But they're not that hurt, particularly Engo, which handles them really, really well. 7 00:00:26,820 --> 00:00:34,770 So we have seen variables already like ver my strength and that is a string and I'm going to store value 8 00:00:34,770 --> 00:00:35,490 in my string. 9 00:00:35,490 --> 00:00:36,870 I call my string. 10 00:00:36,990 --> 00:00:39,780 Has the value of green a color. 11 00:00:40,200 --> 00:00:42,030 OK, so I'm not using it yet. 12 00:00:42,030 --> 00:00:42,660 Still in error. 13 00:00:42,660 --> 00:00:45,780 So let's just print that out so we don't have an error log print line. 14 00:00:47,710 --> 00:00:54,670 My string is set to and then a comma and then the actual value, etc., which is just the variable itself, 15 00:00:55,000 --> 00:00:55,510 no problem. 16 00:00:55,690 --> 00:00:57,610 So if I run that, you know what's going to happen? 17 00:00:57,610 --> 00:00:58,330 It's going to print. 18 00:00:58,330 --> 00:01:02,770 My string is set to green with a capital G and it does. 19 00:01:02,810 --> 00:01:06,330 OK, no surprises so far and nothing about Pointer so far. 20 00:01:06,730 --> 00:01:15,220 Let's come down here and create a new function funk and I'm going to call it change using a pointer, 21 00:01:15,460 --> 00:01:18,120 which is not a great name, but it's exactly what I'm going to do. 22 00:01:18,520 --> 00:01:24,290 It will take one parameter which I'll call S, and it is a type string, but it's not an ordinary string. 23 00:01:24,310 --> 00:01:29,440 It has an asterisk in front of it and it is a type of pointer to a string. 24 00:01:30,230 --> 00:01:32,500 OK, so you can't see that because it's great out. 25 00:01:32,510 --> 00:01:34,330 So let's actually do something here. 26 00:01:35,080 --> 00:01:35,830 New value. 27 00:01:37,060 --> 00:01:41,380 I'm going to create a new variable called New Value and I'm going to call it store that the value of 28 00:01:41,380 --> 00:01:49,270 red with the capital R and I'm going to say my argument, which is s I'm going to say a star in front 29 00:01:49,270 --> 00:01:49,830 of that. 30 00:01:50,200 --> 00:01:53,530 So a pointer to S is given new value. 31 00:01:53,890 --> 00:01:55,030 I've just decided read to it. 32 00:01:55,030 --> 00:01:57,430 I could have just put red here, but I'm just making it light up. 33 00:01:57,880 --> 00:02:02,560 And then after I print that line up here, let me just try to. 34 00:02:03,880 --> 00:02:09,520 Put it like this, I'm going to call that function, I will call change using pointer and I will pass 35 00:02:09,520 --> 00:02:10,080 in. 36 00:02:10,390 --> 00:02:16,930 I can't pass in my mind variable called my string because that'll give me an error, my string. 37 00:02:17,470 --> 00:02:19,180 And it says, oh, look at that, there's an error. 38 00:02:19,180 --> 00:02:19,780 What's the error? 39 00:02:19,810 --> 00:02:26,050 Will the areas that changes in pointer down here, it actually expects to have a pointer to a string. 40 00:02:26,650 --> 00:02:33,160 And if I roll over this, it says cannot use my string type string as type string pointer, little asterisk 41 00:02:33,160 --> 00:02:34,390 and means it's a pointer. 42 00:02:34,400 --> 00:02:37,450 Well, what I need is a reference to that variable. 43 00:02:37,450 --> 00:02:45,790 All a pointer is a pointer is it points to a specific location in memory and gives you a means of getting 44 00:02:45,790 --> 00:02:47,860 that particular location in memory. 45 00:02:48,070 --> 00:02:52,810 Well, as you probably guessed, when you create a variable, you're creating a variable in memory and 46 00:02:52,810 --> 00:02:55,130 you're storing a value at a particular memory location. 47 00:02:55,690 --> 00:03:02,680 So what I need to do is instead of actually passing a parameter as a as an actual variable to this function, 48 00:03:02,890 --> 00:03:05,530 I want to pass a reference to that variable. 49 00:03:05,560 --> 00:03:10,570 I want to point to the location in memory where that variables contents exists. 50 00:03:10,840 --> 00:03:13,750 And I can do that by putting an ampersand in front of it. 51 00:03:14,140 --> 00:03:14,440 Oops. 52 00:03:14,470 --> 00:03:19,810 Get it in the right spot, put an ampersand in front of it and now it actually works. 53 00:03:20,620 --> 00:03:22,060 So I'm going to do one more thing. 54 00:03:22,480 --> 00:03:26,740 I'm going to copy this log print line and then I'll tell you why I'm going to all this trouble. 55 00:03:27,760 --> 00:03:29,230 I'll say after. 56 00:03:31,880 --> 00:03:38,030 Phone call, after I'm calling this function, my string is set to some value, so what do you think 57 00:03:38,030 --> 00:03:44,120 is going to happen here, bearing in mind that this function we created returns nothing and that the 58 00:03:44,120 --> 00:03:49,980 variable, my string up here exists only in the scope of the main function. 59 00:03:50,540 --> 00:03:56,330 So according to what I told you about SCOP, I really should not be able to effect this variable, my 60 00:03:56,330 --> 00:03:57,860 string down here. 61 00:03:57,860 --> 00:04:01,540 And I'm actually not trying to address that variable by name down here. 62 00:04:02,000 --> 00:04:07,160 And since this function returns, nothing, and I'm just calling it, I'm apparently not storing anything 63 00:04:07,160 --> 00:04:07,840 back in here. 64 00:04:07,850 --> 00:04:14,150 So what do you think might happen is to start the program, find the main function great, create a 65 00:04:14,150 --> 00:04:20,660 variable called my string store the value GREENAN It printed out my string is set to green and then 66 00:04:20,660 --> 00:04:23,240 I call this function that returns nothing. 67 00:04:24,020 --> 00:04:27,380 And then I print that again after function called my string is set to. 68 00:04:27,380 --> 00:04:28,640 You might think it would be green. 69 00:04:28,670 --> 00:04:31,700 Obviously it's not or it wouldn't be spending all this time talking about it. 70 00:04:32,060 --> 00:04:33,620 But look at what I am going to do. 71 00:04:33,620 --> 00:04:34,460 First of all, let's run it. 72 00:04:34,460 --> 00:04:35,240 So I'll run it. 73 00:04:36,200 --> 00:04:36,950 Look at the output. 74 00:04:37,820 --> 00:04:40,340 My string is set to green after function. 75 00:04:40,340 --> 00:04:42,370 Call my string set to read. 76 00:04:42,680 --> 00:04:46,100 So all I did in here was I took the pointer. 77 00:04:46,310 --> 00:04:51,590 So here I said pass a reference to this variable, to this function. 78 00:04:52,060 --> 00:04:54,770 Then this function says, OK, I'm now storing. 79 00:04:54,770 --> 00:04:58,520 The value of that is nothing more than a reference to this variable in memory. 80 00:04:58,520 --> 00:05:08,760 And if I come in here, you show this input logged print line and I say X is set to and I just print 81 00:05:08,760 --> 00:05:09,260 s out. 82 00:05:10,100 --> 00:05:10,880 What's it going to print? 83 00:05:11,120 --> 00:05:12,140 Well, let's see what it does. 84 00:05:13,520 --> 00:05:19,710 Go Roumain Go s is set to and then we have this hexadecimal number. 85 00:05:20,360 --> 00:05:21,460 Well what the heck is that. 86 00:05:21,590 --> 00:05:27,080 That is nothing more than pointing to a specific location on my computer in my computer's ram. 87 00:05:27,080 --> 00:05:31,310 It's memory and saying X is set to whatever you find at this memory address. 88 00:05:31,880 --> 00:05:38,120 So now that I have that memory address, I'm creating the new string called New Value, storing the 89 00:05:38,120 --> 00:05:38,870 value of reading it. 90 00:05:38,880 --> 00:05:45,110 I'm saying go to that memory address that you received up here and change its contents from whatever 91 00:05:45,110 --> 00:05:47,120 they happen to be to this value. 92 00:05:47,790 --> 00:05:54,710 So what I've effectively done is changed a locally scoped variable, a function, a variable that scope 93 00:05:54,710 --> 00:05:55,760 to the main function. 94 00:05:56,060 --> 00:06:01,840 I changed its value by passing a reference or a pointer to that variable, to some function. 95 00:06:02,180 --> 00:06:03,300 So that's what pointers are. 96 00:06:03,740 --> 00:06:09,830 So when you need to get the reference to a variable, you put an ampersand in front of it. 97 00:06:10,070 --> 00:06:14,300 When you need to refer to an actual pointer, you put an asterisk in front of it. 98 00:06:14,780 --> 00:06:17,510 Now, this will become very useful to us as time goes on. 99 00:06:17,840 --> 00:06:21,890 I'm only introducing it to you now because you may never have heard of pointers before and you're going 100 00:06:21,890 --> 00:06:24,050 to have to at some point in the not too distant future. 101 00:06:24,350 --> 00:06:29,540 They're a little confusing at first, but the thing to remember is a reference to a variable. 102 00:06:29,690 --> 00:06:36,110 Put an ampersand in front of it to actually create a pointer type, put it, put an asterisk in front 103 00:06:36,110 --> 00:06:36,290 of it. 104 00:06:36,290 --> 00:06:42,350 So ampersands for reference asterisks for the actual pointer itself when you're pointing to a location 105 00:06:42,350 --> 00:06:42,800 in memory. 106 00:06:42,920 --> 00:06:43,330 All right. 107 00:06:43,610 --> 00:06:44,930 So just keep that in mind. 108 00:06:45,530 --> 00:06:48,560 The best way to learn these things is to actually use them. 109 00:06:48,560 --> 00:06:52,490 And when we start using this, it will make more sense if it doesn't make sense to you now.