WEBVTT 00:01.020 --> 00:08.210 In this lecture I want to go over the fundamental building blocks of all programs variable's most basic 00:08.240 --> 00:15.080 and important things computer can do is to store data for later use in calculations to do this. 00:15.080 --> 00:22.690 We use what is called the variable variable is a container that is used to store information in memory. 00:22.730 --> 00:30.390 They are able to be labeled or named by the programmer in order to be able to be more understandable. 00:30.520 --> 00:33.540 The name of a variable is called an identifier. 00:33.580 --> 00:40.750 You'll be seeing that word a lot when you make mistakes with the compiler just know that an identifier 00:40.750 --> 00:46.930 is what we call something that the programmer has named of course the definition of variable actually 00:46.930 --> 00:48.690 means it can be changed. 00:48.820 --> 00:52.510 And we use the assignment operator to do this. 00:52.590 --> 01:00.480 The last thing we need to know about variables and C++ is that they all have a specific type all variables 01:00.480 --> 01:08.220 are stored somewhere in memory as ones and zeroes are programs usually don't need to know or care about 01:08.220 --> 01:15.070 the exact location of a variable because we can just refer to it by the identifier. 01:15.150 --> 01:22.680 It does need to know however the kind of data that is stored to interpret it properly storing a number 01:22.680 --> 01:25.770 is different than storing say a character. 01:25.830 --> 01:30.980 In fact depending on the type of number it is it might require a different type to. 01:31.010 --> 01:36.420 So let's go through some basic types and write some examples of variables. 01:36.440 --> 01:38.810 So here's our first example. 01:40.040 --> 01:47.140 Rissi int x that's the name of our variable This is our identifier. 01:47.400 --> 01:50.040 And we're going to end it with a semi-colon 01:52.450 --> 01:56.560 so the first part is the type. 01:56.680 --> 02:02.200 This is this entier is the type of our variable. 02:02.200 --> 02:09.340 So it is short for what's called an integer which is and which is a whole number so a number with no 02:09.340 --> 02:12.570 fractional parts no decimal point after it. 02:12.610 --> 02:22.370 So for example it could be something like 10 or 3 but it can't be something like three point one. 02:22.370 --> 02:26.850 Say that's no good. 02:26.900 --> 02:31.580 So the names of all variables have some restrictions. 02:32.770 --> 02:36.090 Our names can only be made up of letters and digits. 02:36.100 --> 02:39.610 But the first character must be a letter. 02:39.680 --> 02:46.170 We can use underscores since they are also considered letters here characters. 02:47.000 --> 02:55.850 So our convention for our variables will be something called camel case so let me show you an example 02:55.850 --> 02:57.210 of camel case. 02:58.860 --> 03:00.440 In case will 03:05.140 --> 03:17.110 so note here that we have each word except for the very first word will be uppercase So the first letter 03:17.110 --> 03:24.160 of every word after the first word is uppercase is what's called camel case and this is going to be 03:24.160 --> 03:31.650 our convention when we make our programs. 03:31.700 --> 03:36.740 So you may wonder why we have a semi-colon after all are variables. 03:37.840 --> 03:47.200 Because in C and C++ the whole line is considered a statement and all statements must end with a semi-colon 03:47.770 --> 03:49.590 in our variable x. 03:49.600 --> 03:50.780 Example here. 03:52.210 --> 03:54.540 The. 03:54.810 --> 04:04.740 This is what's called a declaration which is just an introduction for the compiler so it understands 04:05.070 --> 04:11.880 that there is an identifier that's going to be called X and it's going to be used for later use. 04:11.880 --> 04:17.970 So let's start changing our variables since that's the whole point of very well. 04:18.040 --> 04:23.050 So let's say we have it's the value 10. 04:23.580 --> 04:28.750 Notice how similar this is to our examples we did in the last section. 04:28.860 --> 04:31.380 So we have some variable that we have. 04:31.680 --> 04:45.850 And then this is the assignment signs this equal sign this one equals sign assigns X the value 10 so 04:46.530 --> 04:54.790 note that it doesn't test for equality it's actually like giving it real value so and of course this 04:54.790 --> 04:56.100 is a statement as well. 04:56.130 --> 04:58.290 So always needs a semi-colon. 05:00.530 --> 05:12.010 So if we tried to print out X let's say you x is 05:14.910 --> 05:20.920 print x in it Bill that it's 05:32.360 --> 05:39.260 so there's Council value of x is that right. 05:39.430 --> 05:43.060 So it works exactly the way you think it should. 05:43.060 --> 05:52.550 You know just give you the output of 10 because we signed to be 10 so you may wonder then if we didn't 05:52.550 --> 05:59.700 give it the value 10 what would happen. 05:59.720 --> 06:01.550 So what would it output. 06:01.610 --> 06:09.230 So let's see. 06:09.440 --> 06:19.310 See it's giving me some warnings of saying it's not initialize it doesn't have default value. 06:19.510 --> 06:22.000 Let's ignore all that. 06:22.000 --> 06:25.880 So the value is zero which is kind of interesting. 06:27.730 --> 06:29.800 So I'm assuming then that 06:32.580 --> 06:38.880 gcc or clip's or something gives it a default value at the start. 06:38.880 --> 06:43.020 This isn't always the case for different compilers. 06:43.050 --> 06:47.680 Usually it's just given whatever value that existed before. 06:47.910 --> 06:59.240 So if you made a variable and you didn't assign a default value then wherever that variable is in memory 06:59.630 --> 07:03.970 should have some value associated with it and they'll just print out that value. 07:03.980 --> 07:08.660 Usually it's just some some kind of garbage value that you probably don't want. 07:08.660 --> 07:14.800 So what we should always do when we make a variable is give it some default value. 07:14.830 --> 07:21.680 So here in this case zero now you're never going to have a problem. 07:21.730 --> 07:22.540 Always be 07:27.030 --> 07:28.840 something that we actually care about 07:31.950 --> 07:35.250 so let's take a look at some other built in types. 07:35.250 --> 07:41.540 Let's say we have this is a character type char. 07:41.880 --> 07:49.650 Char c is going to be a here and we can print this out as well. 07:51.700 --> 07:55.310 Now you should give it should print out a worse 07:59.250 --> 08:01.650 see is 08:10.890 --> 08:13.220 so the value of C is right. 08:14.870 --> 08:25.620 So here this char and we call it C remember is the identifier and all char's will always have this kind 08:25.620 --> 08:30.740 of format ever is going to give it some kind of literal value like a. 08:31.020 --> 08:33.770 And always have the single quotes around it. 08:33.780 --> 08:41.810 So if you want to have some specific value for a char c always have these quotes especially if it's 08:41.810 --> 08:45.110 a letter you know it's one of these quotes here. 08:47.900 --> 08:51.200 So let's look at some other ones. 08:51.220 --> 08:56.790 There's also a floating point number. 08:57.240 --> 09:03.180 So let's say pi 3.1 for pi or 8. 09:04.550 --> 09:14.200 It's not exact but now that you know you pi is 09:26.270 --> 09:33.070 so and it prints out 3.1 for so floating point or float. 09:33.070 --> 09:38.430 Here stands for floating point number which is represents real value. 09:38.440 --> 09:45.430 So it has it can be something like three point 1 4 1 5 etc.. 09:47.150 --> 09:56.570 Unlike an int which can only be a whole number like pen and these floating point numbers come with different 09:56.570 --> 10:00.970 precisions precisions get pretty complicated. 10:01.190 --> 10:08.830 But just know that you really need much more precision than floating point type in this course anyway. 10:09.170 --> 10:15.820 So if you want to add more precision say we have something called a double 10:19.200 --> 10:21.990 double pi. 10:22.220 --> 10:47.590 Let's say 1 for 1. 10:47.730 --> 10:51.750 Print this out. 10:51.840 --> 10:55.140 See it prints out the whole thing. 10:55.150 --> 11:04.800 In fact this probably can have this level of precision as well. 11:04.840 --> 11:07.900 So if you really want a lot of precision. 11:07.900 --> 11:13.990 Use a double instead you can have many many more 11:17.510 --> 11:23.720 although guess not for this one but usually it shouldn't really matter too much. 11:26.310 --> 11:30.680 So the amount of precision really will depend on your system. 11:30.960 --> 11:37.380 And we're not really going to worry about it too much in this course but either just know either float 11:37.380 --> 11:40.860 or double or we'll do just fine for what we need. 11:41.860 --> 11:46.370 So we're going to talk more about types in the next lecture.