WEBVTT 00:00.380 --> 00:09.380 In this lecture I want to go over a very important concept called scope scope is the region of program 00:09.380 --> 00:13.280 that you can access and use variables. 00:13.730 --> 00:21.450 So far we've had our variables only in our main function like this x variable rate here. 00:22.010 --> 00:30.230 So X it can only be used in this main function it can't use anywhere else in the program so I couldn't 00:30.230 --> 00:41.460 have X being used in this other function that I called func x is x here. 00:42.390 --> 00:48.140 And all so c the compiler is complaining to me. 00:48.140 --> 00:54.170 So symbol X could not be resolved right. 00:54.430 --> 01:03.310 So it doesn't understand what this symbol x is because X is local only to this main function can't use 01:03.310 --> 01:05.770 X anywhere else. 01:06.230 --> 01:06.500 Can. 01:06.770 --> 01:10.250 So this is called a local scope. 01:10.280 --> 01:14.080 So X has only local scope it's local to me. 01:14.090 --> 01:20.190 Only so we saw another example of this in fact with the for loop. 01:20.190 --> 01:29.670 So we had our FOR loop in we declare the inside for loop and we say I'm less than you know some number 01:29.770 --> 01:38.480 say and then I plus plus and I said we couldn't do something like this. 01:38.610 --> 01:43.500 Can't say I is this 01:45.750 --> 01:56.660 is I Andel because I is local to only the for loop. 01:56.690 --> 02:04.300 It's not you can't use I anywhere else sides inside this for. 02:04.430 --> 02:13.240 And so it's local it's for live only just like x' local only to the main function. 02:13.240 --> 02:26.150 Now we could have X be outside of the main function like this we could declare it in or define it up 02:26.150 --> 02:29.340 here and then. 02:29.360 --> 02:31.350 So let's just get rid of this. 02:31.700 --> 02:33.170 Then we could have 02:35.680 --> 02:41.800 the X being used in this function here. 02:42.050 --> 02:49.840 And all a year is to distinguish it. 02:50.120 --> 02:53.120 It run it and it says X equals 5. 02:53.120 --> 02:54.420 That's this one right here. 02:54.430 --> 02:55.420 So this line. 02:55.550 --> 02:57.620 And then it says phunk X is 5. 02:57.620 --> 03:00.380 So it actually did work. 03:00.410 --> 03:07.700 So when you declare or define a variable outside of any function. 03:07.700 --> 03:17.640 So here we have it above main and this phunk This is called global scope. 03:17.890 --> 03:21.400 So it's global to the entire program. 03:22.530 --> 03:28.580 And you may be asking why not just use global scope for all variables. 03:28.590 --> 03:32.070 Well this is usually a bad idea. 03:33.080 --> 03:42.670 In if a function modifies a global variable x here and you're not aware or you forgot maybe you wrote 03:42.670 --> 03:45.090 it a little while ago and you can't remember. 03:45.250 --> 03:48.310 You might get some very strange results. 03:48.340 --> 03:57.200 You don't usually want variables being modified without us understanding why it's being modified and 03:57.330 --> 04:02.160 all variables really make things harder and it's hard to reason about. 04:02.200 --> 04:10.030 So we're never going to be using global variables in any of our programs and I suggest you don't use 04:10.030 --> 04:14.510 it either in the C really understand how things really work. 04:14.590 --> 04:20.780 So these will be seeing some other examples of scope in some upcoming lectures.