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PHP is a popular, reliable programming language at the foundation of many smart, data-driven websites. This comprehensive course from Kevin Skoglund helps developers learn the basics of PHP (including variables, logical expressions, loops, and functions), understand how to connect PHP to a MySQL database, and gain experience developing a complete web application with site navigation, form validation, and a password-protected admin area. Kevin also covers the basic CRUD routines for updating a database, debugging techniques, and usable user interfaces. Along the way, he provides practical advice, offers examples of best practices, and demonstrates refactoring techniques to improve existing code.
In this movie, we'll look at For Loops. For loops are very similar to While Loops. They repeat a section of code, until a condition is met. But the syntax used for doing it is very different. Why have both, then? Well, probably because For Loops are the most classic kind of loop that there is, and they're used in many other programming languages. And some people prefer the compact syntax of For Loops. Let's take a look at this syntax now. A For Loop looks very similar at first, except for the expression part. Instead of having one expression in parenthesis, we're going to have three separated by semicolons. And each one's going to perform a different function. Expression 1, is going to be executed the first time only. It's like an initializing statement before the loop starts. Expression 2, is the test expression that's going to be checked at the start of each loop.
Just like the expression that we had in the While Loop. Expression 3, is going to be executed at the end of every loop. Right after the loop finishes, right before it goes back and evaluates expression two again. Perhaps a better way to think of it is as initial test and each. There's the initial value, there's the test that its going to perform each time, and then each time through the last thing that its going to do is execute that each statement. Now, this syntax will work for a single line statement, but just like we saw with the While Loops. I think it's a good practice to always put curly braces around it. And if we have a multi-line statement those curly braces are required, we have to have it.
So, I'm going to suggest that it's the best practice for for you to always use those those curly braces any time you have a For Loop. And then we can tell what's being looped across. It's everything inside those curly braces. Alright, so I haven't really fully explained how initial test that each work can practice. Let's actually go to some code. So that we can try it out, and see how they work. So to start with, I'm going to open up basic.html. And I'll just do save as on this. And we're going to call this one forloops.php. We'll call it loops:for. Right now to begin with, I'm actually going to paste in a while loop, while loop example.
And I want you to see this while loop, because the way that it relates to the for loops, I think will help for loops make a lot more sense to you. So, let's write our for loop now, right below it and let's try to accomplish the exact same thing that the while loop does. So, we're going to have our PHP tags, and then let's start with for, and then we have our initializing statement. Right, that's the first argument. The thing that we're going to do at the beginning is initialize. So, we did some initialization up here, look at this. Count equals 0. We initialized the value count before we did the while. Well, that's exactly what we want to do here.
That's our initialization. Here it was on a separate line. Here it's inside the arguments to the loop. Now, right after that, we need a semicolon, so we have a second statement after that. In the next statement, is going to be the expression of what we do each time through that. And I told you that was exactly like the while loop. So we're just going to copy that, we're going to put that in there. And then, the last we'll remember is something that happens at the end of every loop, right before it goes back again. Well, lets look at our while loop. What are we doing each and every time? We're incrementing, and that's the probably the most common thing it happens in this third expression. You can also decrements it can be count minus minus. Or it can do something much more complicated.
It could divide by two, or multiply by four. All sorts of things can go there. But typically, the most common one is just to simply increment. So, now that we have that, we just need to put our curly braces, and then what are we actually going to loop? What's the business that we want to do each time we go through this loop? Well there it is right there. We're just going to take count and then output it. So, some people like this syntax better. We're doing all the initialization. We're doing the incrimenting. We're doing the testing all in one line. It's all kind of get that business out of the way, right there at the start. And then what's inside our loop is a little bit more isolated. It has nothing to do with the business of looping.
It really is just the thing that we want it to do each time through. So, let's try it, just to make sure that this works. Let's give ourselves a br tag here just, so we can separate that out from the one before it. Let's go to Firefox and instead of while loops, we're now going to open up for loops. And there we go, see it did the exact same thing right underneath it. Now just like we had with while loops, we can do all the same things. You want to watch out for infinite loops and you can have if statements inside here that do conditional operations. So as another example, let's look at the loop that I gave you as a assignment at the end of the while loop section.
Something to do on your own. Let's try those results here. So we'll do br tag, and then I'm going to paste in a for loop. It's going to start out with count equals to one. Count is while it's less than 20, it's going to keep executing. And each time it's going to increment count. Now, just to see the difference. Let's just try it in reverse. Let's say, count is equal to 20 to start with. And as long as count is greater than zero, then were gona keep going. So were going to count down, and then we're going to count down that I need to do minus minus here at the end. You also could do minus equals 1 if you wanted.
That does the exact same thing. Now, here's the, the heart of my loop. If count modulo 2 is equal to 0. That means if I take count and divide it by 2, if there is no remainder, right? If it divides evenly, then it will be equal to zero. Nothing left over, then I'll know that it's an even number. Otherwise it's an odd number. All right, so let's just try that out. Let's go over here to Firefox. Let's reload. There it goes, 20 is even, 19 is odd. All the way down until we get to one is odd. So, hopefully, you see how that works, and you see the relationship between a while loop and a for loop. How they're basically doing the exact same thing? It's just a different syntax and a different way to write it. Use whichever one feels most comfortable to you. They both accomplish exactly the same thing, it's just a matter of personal style and taste.
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