WEBVTT 00:00.170 --> 00:06.410 So let's get started by creating a first PHP file inside which we're going to learn about the expressions 00:06.410 --> 00:08.660 and the basics of variables. 00:08.660 --> 00:10.490 You can just call it expressions. 00:10.820 --> 00:19.010 PHP and then as said previously, every PHP file it needs to have this opening PHP tag. 00:19.040 --> 00:25.550 This is a requirement for this file to be actually considered as PHP code. 00:26.690 --> 00:31.520 So the first thing you should learn is how do you output something on the screen. 00:31.520 --> 00:38.300 This is done by using the echo statement, which is followed by a string that should go on the screen. 00:38.300 --> 00:47.570 So I can say welcome to PHP and then make sure that I add a new line using the special character slash 00:47.570 --> 00:48.260 n. 00:48.470 --> 00:50.900 And remember about the semicolon. 00:50.900 --> 00:53.630 Now how do you run this PHP script? 00:53.660 --> 00:58.850 Well, we can just run it in the command line using PHP expression. 00:59.120 --> 00:59.870 PHP. 00:59.870 --> 01:01.940 And here is our output. 01:03.790 --> 01:11.650 So, as we already know in PHP, anything that will return a value is an expression, and in expression 01:11.650 --> 01:17.770 you can just mix raw values, variables, function calls and operators. 01:18.370 --> 01:20.770 So here you've got different examples. 01:20.770 --> 01:29.680 And this page is complex on purpose as that's actually a resource you can download under this video. 01:29.710 --> 01:33.790 Maybe you'd like to print it or just keep it as a reference. 01:33.790 --> 01:43.720 And then with expressions we will also use operators like arithmetic logical comparison and the string 01:43.720 --> 01:45.100 concatenation. 01:45.670 --> 01:52.180 So let's jump back to the code editor and see more examples of expressions in practice. 01:53.860 --> 01:58.990 So in this example here we've directly have put something on the screen. 01:58.990 --> 02:08.730 But sometimes you either have more complex expressions or you just need to do a little more work before 02:08.730 --> 02:11.220 you are ready to output the results. 02:11.220 --> 02:15.510 And in such cases, variables are very helpful. 02:15.540 --> 02:23.100 Let me begin by defining a variable that will be called name and it will contain a string. 02:23.130 --> 02:23.970 Alice. 02:24.000 --> 02:28.440 Now let's take a closer look at variables. 02:30.120 --> 02:38.100 So variables among other things, which we're going to talk about later, are used to store the results 02:38.100 --> 02:38.910 of running. 02:38.910 --> 02:40.320 Expressions. 02:40.830 --> 02:48.180 And variables are defined by using the dollar character followed by the variable name. 02:48.180 --> 02:52.920 Now there are rules for what's the valid variable name. 02:52.920 --> 02:56.160 So as I said it needs to start with a dollar. 02:56.190 --> 03:01.020 Then the second character needs to be a letter or underscore. 03:01.020 --> 03:08.250 And only the third and subsequent characters can be letters, numbers, or an underscore. 03:08.280 --> 03:16.310 You need to keep in mind that variable names are case sensitive, so lowercase variable is not the same 03:16.310 --> 03:19.370 as capitalized variable. 03:19.400 --> 03:23.840 Then there are some conventions on variable naming. 03:23.840 --> 03:28.640 You should either use camel case or snake case. 03:29.420 --> 03:35.120 So here are some examples of valid and invalid variable names. 03:35.120 --> 03:41.750 And also keep in mind not to use PHP reserved words for the variable names. 03:43.670 --> 03:50.840 So here we have assigned the value of Alice string to a name variable. 03:50.840 --> 03:54.290 So this is an assignment expression. 03:54.290 --> 04:00.710 Yes I said expression, which means that this together returns a value. 04:00.710 --> 04:05.240 And we can check that by running the echo statement. 04:05.450 --> 04:12.790 If I rerun this script now we see both welcome to PHP and the text Alice. 04:12.790 --> 04:20.800 So assignment is also an expression and it will return whatever was assigned to a variable. 04:23.110 --> 04:23.380 Okay. 04:23.380 --> 04:26.320 So let's create a more complex expression. 04:26.320 --> 04:34.270 So as we see on this board we have simple expressions like numbers just variables or arithmetic operations. 04:34.270 --> 04:40.480 But also we can create complex expressions mixing all of those together. 04:40.570 --> 04:42.760 So take a look at the operators. 04:42.760 --> 04:47.860 The one that's interesting for us in this case is the concatenation operator. 04:47.860 --> 04:49.330 That's just a dot. 04:49.330 --> 04:54.310 So it would let us put a couple of strings together. 04:54.940 --> 04:56.800 Let's see what can we do with this. 04:56.800 --> 05:01.510 So I can output the text saying hello. 05:01.780 --> 05:07.630 And then I use dot and I put the value of the name variable. 05:07.630 --> 05:13.120 And then also I add an exclamation mark and new line character. 05:13.840 --> 05:16.060 So let's rerun this script. 05:16.060 --> 05:17.050 And there we have it. 05:17.080 --> 05:18.580 Hello, Alice. 05:20.770 --> 05:28.810 So as you can see in this example, I can say that that's the first time when we can see that we are 05:28.810 --> 05:31.210 already doing something useful. 05:31.240 --> 05:39.790 So you can easily imagine that if we have assigned a value to this variable called name, we can also 05:39.790 --> 05:44.530 get an input from the user and then set the value of that variable. 05:44.530 --> 05:53.140 And then once someone enters his or hers name, we can welcome him with this let's say personalized 05:53.140 --> 05:54.250 message. 05:54.370 --> 05:54.820 Okay. 05:54.850 --> 05:57.220 So let's continue with expressions. 05:57.250 --> 06:01.420 This time let's do an arithmetic operation. 06:01.420 --> 06:04.060 So let's calculate something. 06:04.060 --> 06:07.420 First let me create a new variable called pizzas. 06:07.420 --> 06:09.280 And we will have three. 06:09.370 --> 06:13.720 Then let's create another one slices per pizza. 06:13.840 --> 06:15.850 That's typically eight. 06:15.880 --> 06:23.820 Now let's do an arithmetic operation so we can multiply, divide, add or subtract or calculate the 06:23.820 --> 06:24.810 modulo. 06:24.810 --> 06:30.000 So let's calculate the total amount of slices. 06:30.210 --> 06:39.150 This would be multiplying pizzas by the slices per pizza. 06:39.780 --> 06:41.940 And let's echo that. 06:42.720 --> 06:45.930 We can say total pizza slices. 06:45.930 --> 06:48.690 And now we concatenate. 06:49.800 --> 06:54.690 So we use the dot operator and we output the total slices. 06:54.690 --> 06:59.010 And again we concatenate that with the new line character. 07:00.510 --> 07:02.730 And now let me run this. 07:02.760 --> 07:03.780 There we have it. 07:03.810 --> 07:05.820 Total pizza slices 24. 07:05.850 --> 07:07.440 That was expected. 07:08.190 --> 07:11.340 Now at this point let me quickly mention the data types. 07:11.340 --> 07:16.110 So I'm going to go on data types in detail a little bit later. 07:16.110 --> 07:21.230 For now let me just explain This line right here. 07:21.230 --> 07:29.990 So we can see that we have total slices variable which is a result of multiplying three times eight. 07:30.020 --> 07:38.090 Yet we concatenate the string and a number and we get the proper output which is a string. 07:38.090 --> 07:47.450 So what happened here is called the type coercion, which is implicitly casting one of the data type 07:47.450 --> 07:48.320 to the other. 07:48.320 --> 07:50.630 So everything makes sense. 07:50.630 --> 07:59.060 So in case of a string concatenation the sensible output is to produce a string. 07:59.060 --> 08:05.240 That's why this number was implicitly casted to a string in PHP. 08:05.240 --> 08:13.370 But as I said we're gonna talk about data types and typecasting later on okay. 08:13.370 --> 08:14.840 So let's see another example. 08:14.840 --> 08:21.950 Let's define a variable and call that is hungry and initialize it with true. 08:21.950 --> 08:29.830 So this would be of data type boolean which basically can hold one of two values either true or false. 08:29.830 --> 08:33.850 So Boolean values are very commonly used. 08:34.210 --> 08:39.820 They are always the result of for example the comparison expressions. 08:40.870 --> 08:44.260 And in this case we will just set it to true. 08:44.260 --> 08:52.420 And what I would like to do is to output different text depending on whether someone is hungry or not. 08:53.110 --> 08:58.780 So let's always echo hungry with a question mark. 08:58.780 --> 09:03.340 And then we're going to use something called ternary operator. 09:03.340 --> 09:05.830 So it's super simple thing. 09:05.860 --> 09:13.150 First you add an expression on the left side, then a question mark and a colon. 09:13.900 --> 09:18.790 And this would return either something on the left side of the colon. 09:18.790 --> 09:26.520 If this expression is true, or the right side after the colon if this expression is false. 09:26.550 --> 09:37.230 Ternary operator is something you will commonly use, so I'd like to return the text yes, or alternatively 09:37.230 --> 09:38.130 the text. 09:38.160 --> 09:38.850 No. 09:38.850 --> 09:40.560 Let's run this. 09:40.590 --> 09:46.620 Or maybe let's also follow up with a new line character. 09:47.640 --> 09:51.180 Now let's run it and we have it. 09:51.210 --> 09:51.750 Hungary. 09:51.780 --> 09:52.740 Yes. 09:53.040 --> 09:57.450 Now let's change this value to false and rerun the script. 09:57.450 --> 10:00.660 And now the Hungary displays the text. 10:00.690 --> 10:01.560 No. 10:02.400 --> 10:03.660 Let's summarize. 10:03.660 --> 10:04.740 So you've learned. 10:04.740 --> 10:08.760 How can you output something on the screen, how to define a variable. 10:08.760 --> 10:17.340 And then couple of operators like concatenation arithmetic operators or an often used ternary operator 10:17.910 --> 10:18.960 Ethz. 10:19.170 --> 10:26.910 Then we've also heard a little bit about different data types like Boolean numbers strings, and the 10:26.910 --> 10:28.440 type coercion.