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Arrays are a common feature in many programming languages. Arrays are going to be extremely useful for helping us to keep information organized. So, what is an array? An array is an ordered, integer-indexed collection of objects. That's a fancy way of saying that we can take objects, like strings and integers and put them into a group and then keep their position in that group in the same order, so that we can refer to those objects by their positions. We can tell the array, give me back the first object, give me the fifth object, and so on, because the objects are going to be indexed according to what position they hold in the array.
One good way to think about arrays is that they're like those expanding file folders that you can buy to put your bills in. You might put your electric bills in the first pocket and your phone bills in the second pocket, your mortgage payments in the third pocket, and so on. You have a preset order and you can put things in pockets and take them out again. Put this paper into the third pocket. Show me the paper that's in the fifth pocket. That's the way that arrays work. Now there's no limits to how many pockets your array can have. At least none that you're going to need to worry about. And a pocket contained anything that a variable can contain. A string, a number, even another array.
In fact, a pocket can be just plain empty and an array can be assigned to a variable, which makes it easy for us to reference a large collection of information by using a single, simple variable name. Let's try and example. Let's create a new page for ourselves. We'll open up basic.html, do Save As, and let's call this arrays.php. I'll change the title to be Arrays and let's create our first PHP tags here. Now, the first array that I'm going to create, I'm going to assign to the variable: numbers. Now the way that you define an array is array() and that's it. We now have defined an empty array and assigned it to numbers. There's no objects inside this array, it's just empty. We can put a series of objects in our array and separate them by using commas. For example, I'll put in some numbers.
4,8,15,16,23,42. So now, I have an array that consists of numbers. And those numbers are always going to stay in the order that I've put them there. They're going to stay in that exact order. And that way, I can refer to them by position, when I want to get them back out. So let's try that. Let's see how we retrieve something from an array. We'll use echo. We're going to reference the variable numbers because that's what's pointing to our array. It references it. And then we're going to use square brackets.
And inside those square brackets, we're going to provide the index that we want it to return. In this case, the index will be the position that's returned what's in position one. Put our semicolon at the end, and let's bring that up in our browser an take a look. Go back to Firefox and instead of floats, let's bring up arrays. So there it is. It returned an object to us, and the object that it returned was 8. Now, wait a minute. If you go back and you look, 8 is what we would've expected was in the second pocket. And that brings up a very important point about arrays that we must always keep in mind.
Arrays are numbered starting from zero. The first pocket is indexed as zero. The second pocket is indexed as one. It'll take some getting used to if you haven't worked with arrays before but that's how arrays work in almost every single programming language, not just in PHP. So if we change our index to be zero and then we go back and we reload our page. We'll get back the first item, which is 4. So, the first item is indexed with 0. You really want to make sure you drill this idea in your head. First pocket in array, the first item in array, the first value, is always going to be referred to by using the index 0.
And as I said, an array can contain lots of different types of objects. So, for example, we can have a mixed type object. We'll call it mixed, and inside there, we'll have an array. And in that array, let's put the number 6, the word fox, followed by the word dog, followed by another array. Then in that array we'll put x and y and z. So you see how that works? It doesn't matter what kind of objects we put in there. It can be integers, it can be strings, it can even be other arrays. Any valid type in PHP can go inside an array.
So lets now echo back one of those values. Lets do echo from mixed. And let's ask it for what's in number 2. So let's put some BR tags in here just to clean this up a bit; put one up here as well. And let's also ask it, before we go back and reload the page, for what is in pocket number 3. Now, we know what number 2 should be, right? because we know that they start counting at 0, so you can go down the numbers and say, 0, 1, 2, and figure out what's going to be in this second position, the second index. Let's bring that up in a browser and take a look and see if you were right. And it returned dog to us.
Now, notice here, we got a notice, array to string conversion is what's happening, and it returned to us Array. So when we ask for the third item, they came back and said it's an array. That's what I see there. I see an array. And it used array to string conversion to try and give us an output for that, rather than ouput the entire array. Now, if we wanted to see the entire array, we can do that. Let's just try this real quick. Echo, let's look at the array itself. See what that gives us? That comes back and gives us array as well.
(SOUND) Instead, it's really helpful when you're working with arrays to use print_r. That stands for print-readable. And that's a nice way for debugging to see what's inside of our arrays. Now, it's not something we would ever want to show to our users. It's really just for our purposes. With, with our array, hopefully, we've pulled the data out of the array that we want. And we're not going to run into this problem. But let's just do print r on mixed, and see what that gives us back. You see? That's gives us something that's readable now.
It shows us this is an array. And here's what that array contains. And you can see the indexes in front of each one. This is index 0, this is index 1, and so on. Even nicer is if you put the pre tags around it for the HTML. (SOUND) And now, look at that. Now, they're indented and everything. It makes it nice and easy for us to follow and see what's inside that array. Now, what if we wanted to get a value out of this array? Right? So, we're basically looking inside one array, and then from that, pulling another value out of that array.
We can do that. Let's just go up here and copy this line. We'll bring it down here. And after we get back, the nested array which is in position 3, then we'll just going to ask for what's in position 1 right after it. Square bracket followed by square bracket. Let's go take a look. There it is, it returned Y to us. See how that works. I'm just going to get rid of these warnings up here by just commenting these lines out. So we don't hit those anymore. Now what about adding things to our array.
Alright now we were able to pull things out of the array but we want to be able to assign values into it. We don't want to have to redefine the whole array each time. We can put things into pockets by simply saying mixed, and we'll say at position two equals cat. That's it, that's all there is to it. You just say alright, at position 2, set this value, put that in there. It's just a simple assignment operator. Let's do another one. I'll just copy this line and let's say that at position 4, we're going to put mouse.
Now wait a minute, there is no position 4. Position 3 was this item here. So position 4, it's okay to refer to it. It's going to put an item in that fourth position for us. So let's go ahead and take a look and while we're at it, let's move our print the array down to the bottom. And that will allow us to just see everything that's in there. So here it is. See cat up here? And mouse, down here in the fourth position? There's also another way. If you don't know how long something is and you just want it to go to the end, you can just make it be blank.
Let's do horse. And that will put it at the end. It's appending it to the end. Whatever the last index is, this is going to add it to the end of it. Take a look at that, and so there it is, it put horse in the fifth position. So the power of arrays, is that a set of information can be referenced by a single variable. Imagine if we have one thousand email addresses. We wouldn't want to create one thousand variables for those, instead we can assign all of them to an array, and then use one easy to reference variable to pull up each email address by its index. The other thing that's powerful about arrays is that they keep their information in the same order unless we change it. Whatever we put in the first pocket stays in the first pocket. So, arrays are good for keeping ordered lists.
We can sort those 1000 email addresses and then they'll be kept in that order for us by the array. You can imagine how arrays are going to stop helping us when we start pulling records and data out of our database. We can retrieve 50 customer records sorted alphabetically by last name and store them in the array. And they'll stay sorted in that array by last name. The one last thing that I want to mention to you, is that PHP 5.4, which most of you are probably running, 5.4 or later, has a short array syntax. Instead of writing out the word array, we can just use square brackets to define it.
So an array can be equal to 1,2,3. This doesn't work in 5.3 or earlier. So because of that, I'm going to stick with the long notation, so that anyone taking this training who happens to be using an earlier version won't get stuck. But if I were writing PHP for myself, well, I would definitely use this shorter notation. So it's up to you which one you want to use. Array with the parentheses around it is probably going to start becoming rarer over time. But right now the square bracket is a little bit new. So you aren't going to see it in a lot of older code, especially if they still need to support older versions of PHP.
But you should be able to see it in both forms and recognize it as an array.
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