WEBVTT 00:00.180 --> 00:00.500 Great. 00:00.540 --> 00:05.700 You now have a basic understanding of variables and functions all along the course. 00:05.700 --> 00:09.720 You will use them extensively and develop a better understanding with time. 00:09.720 --> 00:15.990 But there is one last important thing to understand about variables, and this is the scope of a variable. 00:16.350 --> 00:19.170 Depending on where you declare a variable. 00:19.170 --> 00:25.800 For example, if it's declared here or here, well, it may or may not be accessible from other parts 00:25.800 --> 00:26.880 of the program. 00:26.880 --> 00:29.100 And this is what we call the scope. 00:29.100 --> 00:35.550 So as you can see in this example, I create a variable named number one, and that's outside of any 00:35.550 --> 00:36.240 function. 00:36.420 --> 00:38.340 You can see this is outside of anything. 00:38.340 --> 00:41.970 And then I use number one here in this void set of function. 00:41.970 --> 00:48.450 But now you can see that I also create a variable A, but I create the variable A In the setup function, 00:48.450 --> 00:52.020 I create a variable A between those two curly brackets here. 00:52.620 --> 00:56.940 And let's see what will happen if I try to access this variable. 00:56.940 --> 00:58.230 A in the void loop. 00:58.230 --> 01:07.500 For example, if I do serial print ln with a like this, let's see what's going to happen if I try to 01:07.500 --> 01:08.280 compile. 01:09.220 --> 01:15.310 I'm going to have an error saying that A was not declared in the scope. 01:16.360 --> 01:18.610 What if I try to print number one? 01:19.120 --> 01:23.440 If I print number one, you see that it is going to work. 01:23.800 --> 01:29.950 But if I print a, I get this error not declared in the scope. 01:30.100 --> 01:31.290 So what is the scope? 01:31.300 --> 01:34.330 Basically with C++ and Arduino. 01:34.510 --> 01:37.810 The scope will just be something that's inside curly brackets. 01:38.020 --> 01:44.410 So when you create a new function, you will open and close curly brackets and later on with conditions 01:44.410 --> 01:45.160 and other stuff. 01:45.160 --> 01:48.000 You will also see that we open close curly brackets. 01:48.010 --> 01:55.540 And so when you have this here, it means that whatever is inside those curly brackets is inside a nested 01:55.540 --> 02:01.290 scope, a more nested scope than the global scope, which has no curly brackets by default. 02:01.300 --> 02:08.080 And so when you create a variable here in a more global scope and you use it in a more nested scope, 02:08.080 --> 02:09.220 then it's working. 02:09.430 --> 02:10.990 The variable is accessible. 02:10.990 --> 02:15.610 As you can see here, we have a more nested scope and we can access to number one. 02:15.610 --> 02:23.200 But here you can see I create the variable in this scope, so I can't use it outside of this scope. 02:23.680 --> 02:29.410 And you can see to go from the setup to the loop, we have to go out of the curly brackets and then 02:29.410 --> 02:31.600 we have to go inside another scope. 02:31.600 --> 02:38.230 So another set of curly brackets and that means that the variable A will not be accessible in this scope 02:38.230 --> 02:46.630 here, the variable A when it's created here, it will be accessible only in this scope and if you create 02:46.630 --> 02:47.230 another scope. 02:47.230 --> 02:52.150 So basically, if you have another set of curly brackets like this with conditions and stuff that we're 02:52.150 --> 02:56.650 going to see later, then you can access the variable here, no problem. 02:57.280 --> 03:01.720 But you cannot access it outside of the scope where it is created. 03:01.720 --> 03:09.160 So you cannot go out of the curly brackets and then expect that you can use this variable basically, 03:09.160 --> 03:10.030 that's the rule. 03:10.030 --> 03:16.420 So if you want to have a variable that you can use, for example in both setup and loop, you need to 03:16.420 --> 03:18.220 make it a global variable. 03:18.220 --> 03:23.080 So in the global scope like this, you can see it's not in any curly brackets. 03:23.080 --> 03:27.430 And as you could see with this example, the number one, we can use it actually in the setup and we 03:27.430 --> 03:28.810 can use it in the loop. 03:28.810 --> 03:34.510 But any variable that you create in the setup, you can only use it in the setup and not in the loop. 03:34.930 --> 03:40.450 And there is another thing is you can see that here we have so in this function and in that function 03:40.450 --> 03:46.120 we have a parameter for the function and this parameter for the function here, when you have this for 03:46.150 --> 03:51.730 function, this is also going to be a nested scope and we call that a local variable. 03:52.030 --> 03:58.030 We call that a local variable to the scope, which means that here the number, so the variable int 03:58.030 --> 04:02.380 number is going to be created here when you call the function. 04:02.380 --> 04:07.660 So the value that you pass to the function is going to create a new variable with this value. 04:07.660 --> 04:12.190 And this variable will only exist within the curly brackets here. 04:12.220 --> 04:17.500 After the curly brackets, the variable doesn't exist anymore, so you can't get access to it. 04:17.500 --> 04:22.360 And so that's why you can see that basically we have for example, int number here and we have int number 04:22.360 --> 04:22.810 here. 04:22.810 --> 04:25.750 We have the same name, but that's not a problem. 04:25.750 --> 04:30.340 It's not going to be a collision because of course you cannot create two variables with the same name. 04:30.340 --> 04:34.270 That's going to be a collision issue and you will have an error. 04:34.270 --> 04:40.180 But if the two variables are in the two different scopes, you can see here we have one scope and another 04:40.180 --> 04:42.910 scope because we have different set of curly brackets. 04:42.910 --> 04:47.290 So there is no collision, there is no problem between those scopes. 04:47.290 --> 04:49.480 You can create any variable you want here. 04:49.660 --> 04:53.500 You will not be able to access them in this scope. 04:53.500 --> 04:58.180 So basically what you can do is you can create the same name for the same variables, just like we did 04:58.180 --> 05:00.880 here into number and int number. 05:01.480 --> 05:03.610 And I want you to talk about the scope right now. 05:03.610 --> 05:09.340 I know it's a bit more complex, but I want you to talk about it now just so you can get a starting 05:09.340 --> 05:14.860 of an understanding because that's a very important concept and also because, well, you will probably 05:14.860 --> 05:20.290 have some errors when you start to program and some of those errors are going to be because of the scope. 05:20.290 --> 05:25.720 So when you have an error because of something like the scope, well, you can come back to this lesson 05:25.720 --> 05:27.670 and things will make more sense. 05:27.670 --> 05:31.510 You will understand more and maybe be able to fix your error. 05:31.540 --> 05:31.960 All right. 05:31.960 --> 05:37.570 So to recap on the scope, when you create a variable, pay attention to the scope. 05:37.720 --> 05:45.520 A variable is only accessible in its own scope or in any nested scope inside the scope. 05:46.030 --> 05:50.710 Thus, you could have different variables with the same name in different scopes.