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We've seen the basics of working with strings. Now I want us to take a look at some functions that we can use with strings. We haven't looked at a lot of functions yet. So far we've really just looked at the PHP info function and Echo. Those are really the two main functions that we've seen. So we're going to start diving into the world of functions. And before we do, I just want to remind you that the php.net website has some excellent documentation for functions. And it will tell you all of the different functions that are predefined in PHP, it'll tell you how to use them, has good user submitted tips for you, all of that's there. And you can browse through those if you're looking for something, you're not quite sure what it is. Or if you know the name of the function you can just type it into the search bar at the top and it will return the documentation for it directly. Alright.
Let's take a look at a few. So lets start by opening up our strings.php that we were just working on before. And we'll just do save as on that real quick. And make this string_functions.php. That's what we're going to call it string function and lets take everything out between all these PHP tags here. There we go. Now I have a nice space to to drop in my code. I'm going to start by just pasting in some text, so you don't have to watch me create it. You can pause the movie if you want to copy some of this down. I've got a string that I'm assigning to the variable first. The string is, The quick brown fox.
And I've got another string, jumped over the lazy dog with a space at the beginning, that I'm assigning to second. So we've seen how we assigned variables to strings, like we're doing there. And we've also seen concatenation. We've seen how we can just concatenate these before. I want to show you another way to do concatenation real quick. We're going to do concatenation and assignment at the same time. So let's say we have third, it's going to be another variable. And third is going to be equal to first. And then, on a new line it's going to be third is equal to concatenated equal to second.
Alright, do you see what it's doing there? So it says, alright, first of all third points to the same thing as first does. You're going to get that same string and bring it into third. Now in the next slide, I'm going to tell third that it should add on the second string to the end, because you can concatenate it to what's already there. It's like appending it to the end. The values of first and second haven't changed. Those values are exactly the same still. But third now has the complete phrase in it. This is going to be a very handy way to write your code if you're trying to build up a string over time. We'll definitely use it when we start working with MySQL later on. And, of course, I could then say echo $third.
Alright. So now that we have our third string, let's take a look at some functions. I'm just going to drop down here a little bit. Let's put in a br tag and instead of opening PHP tags again I'm going to paste in more text here. This includes some HTML as well as PHP tags calling some functions. So these are the string functions that we're going to be learning. The first function that I want us to look at is stringtolower. So strtolower, that's the name of the function. And functions often take something as an argument.
They take something as input into the function, and then they return output to you. So the input in this case, is going to be inside the parentheses, and it's going to be our variable third, which is equal to The quick brown fox jumped over the lazy dog. So that whole phrase is being sent in to string to lower. And you can guess what string to lower does, it lower-cases it. So it then returns a lowercase value, and then, echo, another function, echoes it back. So we're calling one function, on the results of another function. The argument to echo is the results of string to lower.
Now we have the same thing here with string to upper, raising it to uppercase. ucfirst is going to make the first letter uppercase, and ucwords will make the words all uppercased. So let's just try that out, so we can see what it does. Let's save it. Let's go back to Firefox. And instead of strings, we're now going to be loading up string_functions. (SOUND) So there it is. So you see here's the original phrase that we echoed the first time. Here's the lower case version, the upper case, the upper case first only. Everything else stayed lower cased and upper case words for each one gets upper cased.
So, make sure that you understand that idea before we go on. Let's just do a few more here. I'll just put a br tag and we're going to do length string, len, strlen is going to tell us the length of the string. Trim, I'm going to use a different phrase here, just to illustrate it. What trim does is it removes the leading or trailing white space. Right? That's spaces. No matter how many there are, it gets removed. So I've got A being concatenated with a trimmed version of B C D, followed by E. Alright? So there should normally, if there was no trim here, it would be A space B space C space D space E.
But the trim is going to take out those spaces. We'll see that in a second. Find, which uses strstr. That's the function name. The way you can remember that is that you're finding a string within a string. That's why it's called strstr. So inside the string that $third points to, we're going to look for Brown. We'll see what that returns. And then replace by string is going to replace quick with super-fast inside third. So it takes three arguments, right? So we now have some that takes two arguments. Another one that takes three arguments. The order of those arguments is important and it's something that you have to look up or know already from the way the function works. And you can look those up on the PHP.net website if you forget them. The way that string replace works is it wants the thing you're looking for, the thing you're replacing it with, and then the item we're searching inside of. They call it the haystack often.
We're searching for a needle in a haystack, well the haystack is third and the needle we're looking for is quick. We're looking for quick inside third and we're going to replace it with super-fast. So let's try those real quick and see what those look like. Go back, just hit Reload. So the length of it is 45 characters long, that's how many letters and spaces there are in there. Notice here that the spaces got trimmed out of b c d, so that there is no space now between a b and d e. Find, did find the word brown. Notice what it returned to us. It returned everything after that in the string.
So, it found it and the result, what it returned back, was not just the word itself, it was everything that follows. That's the behavior of find. Again, the documentation will tell us that that's the way it behaves. And we might want to slightly modify that or account for that in our code to handle it, if we were looking for something like we want the word that follows brown, well we then have to apply a few more functions to it, so that we could get the word fox from that. Replace by string, you can see that it put the super-fast brown fox, so it did exactly what we would've expected.
Okay. Let's look at one last set, br. (SOUND) And we're going to look at repeating str underscore repeat, we'll repeat a string. It's going to repeat third two times, echo substring substr, that's going to make a substring from third, starting at the fifth position to the tenth position of the string. And string position is going to tell us the position of brown, tells us where brown is located. Or we can find a character, where is the character z located, it will return a number to us telling us where that's located.
These positions can be really helpful for trying to parse out, we're trying to find where something is and then make a substring from it. Then you can see how we can use a combination of tell me what the position is or find it for me and then make a substring starting at this position going until whatever position is, you know, at the ending position. Let's try those out real quick. Let's go back, and you see repeat, the quick brown fox jumped over the lazy dog, the quick brown fox jumped over the lazy dog, make substring, you can see where it grabbed, it grabbed from the fifth character going forward. Notice that the fifth character is 1, 2, 3, 4, 5, right? So that's where it started from the UIC.
And then, find position of brown as in the tenth position, and then find character. We were looking for z. It works the same way that find did, right? When we were up here, it found brown and returned everything after it, returning z returns everything from z going forward from there. So these are your first set of functions. This is the way that PHP is going to work. We're going to be able to manipulate all sorts of things by using different functions, and these are the string functions. These are not the only ones. There are a lot more and I don't expect that you will have memorized all of these.
You're going to be looking them up for a while, so they become second nature to you. You're going to have to make yourself some notes. Keep yourself a little chart, maybe jot down the ones, you know, that you use most often. So that there is a handy reference or just keep the PHP.net website open, so that you can quickly go and search and look up, how you use each of these. I've been using PHP a long time and I'm still constantly looking up, the usage of these and the order of the arguments and that kind of thing. Now we've explored strings and string functions. We're ready to move on and look at integers.
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