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Our exploration in the PHP programming language is going to begin with an exploration of the different structures or types that we can use while writing PHP. And the first of those that we're going to look at are variables. Now, if you've done programming before, then you're familiar with what a variable is. But if you haven't, then let me start by explaining that a variable is a symbolic representation of a value. You can think of it as a symbol that refers to something and that's going to make a lot more sense once we actually start using them. But as it's name suggests, it can change over time or vary. It has a variable value because it can point to different values. Now, in PHP, there's some rules about the kinds of names that we can give to variables.
They need to start with a dollar sign, that needs to be followed by either letter or an underscore, they can contain letters, numbers, underscores or dashes. They cannot contain any spaces and they are case sensitive. It makes a difference whether we use an upper case letter or a lowercase letter. So let me give you some examples of some variable names and then we can talk about them. So I could have item, which is just $item, and that could be a symbol that then points to an item. So maybe it's just number five, right? Item points to number five. I could also have Item with an uppercase I.
Either one is perfectly fine, but they are different. If I have two of them, if I'm using both of them, and I have item lower case pointing to the number 3, and Item upper case pointing to the number 5. Then depending on whether I use upper case or lower case will determine which one I get back. So you want to make sure that you're consistent with your capitalization. We can also have myVariable with a capital V. That is often referred to as camelCase, because those upper case letters in the middle are like the humps in a camel. So, some developers like that format. Then there's the underscore between words, so this_variable. There's also a dash, this-variable.
That's perfectly valid. You can put numbers in it. So product3, that's perfectly valid to have a third product named that way. You can put underscores in front of it. Remember, the first character has to either be a letter or an underscore, so you could have _book. You could even have multiple underscores, $__bookPage. Now, all of these are valid. Any of these will absolutely work. But I want to steer you towards some and away from others. The first one is I think we should not use the hyphenated version of this, and the main reason why is that, that hyphen looks like a minus sign, and it looks like we're subtracting this minus variable.
And when we start working with variables and we start working with addition and subtraction, that could be confusing for us. So let's avoid confusion and stay away from that. The second one is this multiple underscores. Stay away from that as well, because it makes it hard to tell whether you've got one or two underscores. I once worked on a project where another programmer had written their variable names using underscores. And sometimes they had one underscore, sometimes they had two, sometimes they had three, and it had significance to them. There was a reason why they were using one, two, or three, but it was really kind of lost on me as to what the meaning was behind these, and it was hard to read to tell whether it was one or two or three.
The last one is not quite as evil, but I want to steer you away from it and that is this single underscore at the beginning. The reason it's not evil is that PHP is going to use it itself. And we're going to see that. We're going to see that PHP has some special variables. They're named with this underscore at the beginning, and some developers use this underscore for special cases. They want to denote the fact that a variable has certain access privileges, that certain people can or can't access things by putting that underscore in front of it. Because it has this special meaning both to PHP and to other developers. Let's stay away from it for general use.
Let's go with the other ones. , ow the one that I'm going to use most often and the one that I prefer is the fourth one in this list, this_variable. And that's what you're going to see me using throughout this title. But you can use whichever one you feel most comfortable with. Now, you can't just use any single name that you want. PHP actually has some words that are reserved, words that you're not allowed to use for different things, and it's a good idea to take a review of this list, and then stay away from those words as much as possible. Sometimes, it's not a problem to use it for a variable name, but it might be a problem to use it in other contexts. It's basically just names with special meaning to PHP that we don't want to use. Now, let's try using some variables.
Before we do that though, let's open up our site's folder. Let's get all the way inside that site's folder and let's create a new directory inside here. So File > New Folder, and I'm going to call this sandbox. I find that it's very helpful to have a sandbox where we can put all of our miscellaneous files, like the ones that we've been working with here. So I'm going to grab basic.html, helloworld, my_phpinfo. I'm going to put all of those inside my sandbox. This index value, HTML file, I don't actually need anymore, and I can just throw that away. So, all of my files now are inside my sandbox and this is going to be a little place where I can try experiments out, certainly, while I'm learning PHP. But even after I'm actually developing, I can just jump back to my sandbox, try some things out, see if things work the way I expect, and then switch back to my application to apply what I learned.
I do this all the time. So it's really helpful to have this kind of PHP Sandbox. Let's now open up our basic.html file, and let's just do a Save As on that. And let's save that in our sandbox, as variables.php. Just make sure that ended up in our sandbox. You see there it is. And notice that it ends in .php. So now, we're ready to put in some PHP code. Just give myself a little room here and we'll change the name to variables. Okay, so we're ready to write some variables inside our PHP code and to start out with, let's just do a simple assignment, variable1.
That's the name of our variable, var1 and then we're just going to say it's equal to the number 10. That's it. We've now made that symbolic pointing from the variable to the number 10. Variable 1 now points to 10, and if we talk about variable 1, we're talking about 10. So if we then, in the next line say echo var1, it's going to echo back 10, right? Let's save it and just try it. Go back to Firefox, and instead of HelloWorld, now, we want, variables.
Nope, I forgot I have to put sandbox in front of that, because I've now moved everything to the sandbox. There we are. So there's the number 10. See how that works? It didn't output the actual string, var1. var1 is a variable that points to 10, and of course, this value can vary. We're just going to take these two lines, and let's paste it. And now, let's say it's equal to 100, right? Let's Save it, and before I output it, I'm just going to also echo a br tag in between them. I can echo HTML just like I can anything else and it will output that br tag in between the two of those.
Let's try reloading the page. Now, we got 10 and 100, so var1 the first time points to 1 thing. The second time it points to something else, because I changed its value. It varied. Notice, also, that it's case sensitive. If I had said that this was equal to, I was going to echo back var 1 with a capital V. I save it. It comes up and it says oops, we have a problem here, I don't see that Var1 with a capital V has been initialized, and I get a warning message. This is what a notice looks like in PHP. So var1 here is different from Var1 with a capital V there.
Now, variables don't only point to number, they can point to other things as well. Also, for example, we could have var2 is going to be equal to hello world. And then echo var2. Save that. Come back here, reload the page, and you can see that now the outputs Hello world. So variables can point to anything really. It's just a symbolic representation of something larger, and it gives you a sort of handle, an easy way to work with this larger thing.
And just refer to it by this symbolic name. We'll continue working with variables and text like Hello world in the next movie, when we talk about the data type called Strings .
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