1 00:00:01,050 --> 00:00:06,360 Hello and welcome to a new lesson today, we're going to talk about variables and types. 2 00:00:06,960 --> 00:00:10,050 So the first thing that we need to talk about is a. 3 00:00:11,250 --> 00:00:15,540 Variable is a container that we use to store of value. 4 00:00:15,870 --> 00:00:18,600 We can name our variable whatever we want. 5 00:00:18,600 --> 00:00:25,590 But there are some rules to keep in mind that you must follow when we create the variable. 6 00:00:26,250 --> 00:00:35,490 And the first thing that we need to decide is what type of data we will actually host in our variable, 7 00:00:35,910 --> 00:00:40,530 because that will dictate what type of variable we need to create. 8 00:00:40,560 --> 00:00:48,870 So for example, if we want to create a variable that will just hold a whole number, we would make 9 00:00:48,870 --> 00:00:53,940 it a type and which is an integer, and we'll get to that in just a little bit. 10 00:00:54,420 --> 00:01:03,150 But your method thing that I want to say about variables is that the variable gets assigned a memory 11 00:01:03,150 --> 00:01:07,140 address where the value will be stored at. 12 00:01:07,710 --> 00:01:17,880 So to store a value in a variable, we will need to use the equals sign, also called an assignment 13 00:01:17,880 --> 00:01:18,810 operator. 14 00:01:19,170 --> 00:01:28,050 So I sort of drew this to demonstrate how a variable gets stored in memory. 15 00:01:28,230 --> 00:01:32,490 So let's pretend that this is our computers memory. 16 00:01:33,060 --> 00:01:44,640 And you can see that we are creating a new variable here called value, which is of type IND, so that 17 00:01:44,850 --> 00:01:52,440 the thing that happens here is that one memory address gets assigned to that variable. 18 00:01:53,590 --> 00:01:58,450 Or the variable gets assigned to a memory address that already exists. 19 00:01:59,050 --> 00:02:07,330 And now we are trying to sort of value 10 inside of that variable. 20 00:02:07,660 --> 00:02:17,500 What will happen is, as you can see, 10 will be stored exactly that memory address that the variable 21 00:02:17,500 --> 00:02:18,950 gets mapped with. 22 00:02:19,360 --> 00:02:27,700 So the computer will just go there to that memory whenever you call the value name. 23 00:02:29,320 --> 00:02:33,090 So naming a variable is very important. 24 00:02:33,100 --> 00:02:39,910 And here as well, there are a few rules to keep in mind when you create variables. 25 00:02:41,110 --> 00:02:49,810 A very important one is that you cannot use anything other than a letter or an underscore for the first 26 00:02:49,810 --> 00:02:51,880 character of the variable name. 27 00:02:52,660 --> 00:03:01,870 And then after that first character, you can use any number, any combinations of numbers or letters. 28 00:03:02,860 --> 00:03:05,650 Uppercase and lowercase will be different. 29 00:03:05,650 --> 00:03:14,350 So if you create a variable that's called value and it's all lowercase, it won't be the same as creating 30 00:03:14,650 --> 00:03:21,370 a variable called value that starts with a capital V. But everything else is lowercase. 31 00:03:21,580 --> 00:03:29,890 So that's a very important thing that you must keep in mind, and you should always call your variable 32 00:03:29,890 --> 00:03:31,360 a meaningful name. 33 00:03:32,260 --> 00:03:39,820 It has to be related with what the variable is doing if you need to count the number of times a certain 34 00:03:39,820 --> 00:03:40,690 thing happens. 35 00:03:40,960 --> 00:03:48,250 You can call your variable count, for example, or number of times those are both meaningful names. 36 00:03:49,270 --> 00:03:56,260 So that makes it easier for you also to realize what you are doing in your code, and that makes the 37 00:03:56,260 --> 00:04:00,100 code more readable in case other people need to read your code. 38 00:04:01,270 --> 00:04:12,790 Now, you cannot use any words that the C++ language reserves for syntax, for example, and using include 39 00:04:13,870 --> 00:04:15,640 words like that are reserved. 40 00:04:16,090 --> 00:04:20,320 So the programmer cannot use them to name variables. 41 00:04:23,050 --> 00:04:34,330 When it comes to creating a variable, you must create all your variables before using, name them in 42 00:04:34,330 --> 00:04:35,650 the program. 43 00:04:36,220 --> 00:04:43,750 Otherwise, the program won't know what the word is unless you tell it explicitly beforehand. 44 00:04:44,290 --> 00:04:54,400 So there are two ways of declaring variables you can define without initializing, and you can define 45 00:04:54,400 --> 00:05:01,060 and initialize and what that means if you define a variable without initialization. 46 00:05:01,390 --> 00:05:06,820 You basically are just putting aside memory for that variable. 47 00:05:07,240 --> 00:05:15,520 You haven't decided on a type of data that you will store in your variable, but you don't have yet 48 00:05:15,520 --> 00:05:18,370 a value to put in there. 49 00:05:18,790 --> 00:05:28,340 So in this case, you will just do something like this and value that puts aside the memory for it. 50 00:05:28,360 --> 00:05:37,180 The variable exists, but you don't really have anything meaningful there yet, as you have to assign 51 00:05:37,180 --> 00:05:44,410 a value like this using the assignment operator that we previously talked about. 52 00:05:44,860 --> 00:05:53,890 So one thing that I do want to mention if you do create a variable like this, a value may still exist 53 00:05:55,600 --> 00:05:58,660 when you created that is called garbage. 54 00:05:59,110 --> 00:06:11,200 It's either the data that already existed in that memory address previously or C++ just generates something 55 00:06:11,200 --> 00:06:13,000 at the moment of creation. 56 00:06:13,180 --> 00:06:17,770 So just be mindful of that when you use your variables. 57 00:06:17,770 --> 00:06:26,320 If you have defined the dam but you have an initialize them, the desired values that you're trying 58 00:06:26,320 --> 00:06:29,740 to use will not yet be there. 59 00:06:31,330 --> 00:06:38,200 Now, in defining a variable with initialization, that means that you will create the variable and 60 00:06:38,200 --> 00:06:45,430 assign it a value that you want it, you want it to have when it starts existing. 61 00:06:45,730 --> 00:06:51,910 For example, this or this or this statement. 62 00:06:51,940 --> 00:06:53,320 These are all the same. 63 00:06:53,320 --> 00:06:55,360 You only need to use one of them. 64 00:06:56,020 --> 00:06:58,510 But all these statements do the same thing. 65 00:06:59,380 --> 00:07:01,930 They create a value variable. 66 00:07:03,090 --> 00:07:11,030 And they put in a value 10 inside of it, and the type of variable will be in it. 67 00:07:11,830 --> 00:07:22,800 So a big advantage when doing this is that you know exactly what value gets to be stored in your variable 68 00:07:22,800 --> 00:07:25,170 and you can just use it right away. 69 00:07:26,340 --> 00:07:34,710 So another thing that I want to touch on is the scope of a variable, so scope refers to the program 70 00:07:34,710 --> 00:07:37,620 area that has access to your variable. 71 00:07:38,280 --> 00:07:47,370 Like I said before, if you create a variable, you can use it afterwards, which in C++ is basically 72 00:07:47,370 --> 00:07:53,730 in an in the lines below your variable definition. 73 00:07:56,070 --> 00:07:58,800 So be mindful of that. 74 00:07:59,850 --> 00:08:03,060 Define your variables before you use them. 75 00:08:03,810 --> 00:08:11,340 I think that's enough talking about the scope right now, but we will touch on scope in a later lecture. 76 00:08:12,480 --> 00:08:22,020 So the variable types we do have two main types of variable near our normal variables. 77 00:08:22,920 --> 00:08:25,560 The ones that you can change. 78 00:08:25,560 --> 00:08:30,510 The value that gets stored in them over and over again as many times as you want. 79 00:08:30,990 --> 00:08:40,530 And there are something called constant variables where you create the variable and the value will not 80 00:08:40,530 --> 00:08:45,120 change for the entire duration of the program. 81 00:08:45,420 --> 00:08:46,740 It stays the same. 82 00:08:47,460 --> 00:08:57,030 So for you to create a constant variable, you just need to put the constant word in in front of your 83 00:08:57,030 --> 00:08:58,530 variable definition. 84 00:08:58,530 --> 00:09:05,370 Like this, whether you, well, actually like with the constant variables, you have to initialize 85 00:09:05,370 --> 00:09:13,020 them at the moment of creation because you can't create them and change them afterwards, since they 86 00:09:13,020 --> 00:09:14,610 are not changeable. 87 00:09:16,520 --> 00:09:23,990 So here we are talking about data types and data types. 88 00:09:25,610 --> 00:09:34,340 Exist in C++, because that's just how they exist in real life, actually, because you can't add oranges 89 00:09:34,340 --> 00:09:36,860 and apples together, they are different things. 90 00:09:37,220 --> 00:09:46,790 So that's why we have types and the purpose of the type is to tell the variable what type of data they 91 00:09:46,790 --> 00:09:47,540 can hold. 92 00:09:47,900 --> 00:09:58,070 So a variable of a type is reserved space in memory, and each type occupies a different memory size. 93 00:09:59,000 --> 00:10:06,140 So your type will dictate how much memory your variable will occupy in memory. 94 00:10:07,530 --> 00:10:16,740 So when talking about data types, we have two different kinds, we have primitive data types, the 95 00:10:16,740 --> 00:10:24,510 ones that are built in, and you can already use you, you start writing your program and you can use 96 00:10:24,510 --> 00:10:28,830 them right away and you have non primitive data types. 97 00:10:29,160 --> 00:10:35,520 We're only going to give examples of the non primitive data types, but we're going to talk about primitive 98 00:10:35,520 --> 00:10:37,350 data types a little longer. 99 00:10:38,010 --> 00:10:48,510 So here you can see all the primitive data types and you have Boolean character, integer floating point 100 00:10:48,510 --> 00:10:49,980 and double floating point. 101 00:10:51,700 --> 00:10:55,120 And you can see the sizes that these. 102 00:10:57,320 --> 00:11:03,080 Data types occupy in most computer systems. 103 00:11:05,540 --> 00:11:15,650 So non primitive data types, like I said before, some examples of it would be strings, drug classes, 104 00:11:15,650 --> 00:11:22,130 unions, enemies and there is these are basically. 105 00:11:23,100 --> 00:11:27,000 Programmer defined for the most part. 106 00:11:27,150 --> 00:11:29,940 So you get to create these later on. 107 00:11:30,570 --> 00:11:39,540 So we're going to start talking about the Boolean data type, and this is a very simple one. 108 00:11:39,900 --> 00:11:44,250 So the Boolean will be either true or false. 109 00:11:44,460 --> 00:11:48,360 It occupies one bite of memory. 110 00:11:48,600 --> 00:11:50,700 And the key word for it is bool. 111 00:11:51,570 --> 00:12:01,200 So here you can see an example of a bool variable that has been defined and initialized.