WEBVTT

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Hey, I'm super, super amped because now we're going to be getting into some of the meaty stuff when

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it comes to URLs.

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The first thing I want to say is that URLs can understand hexadecimal values.

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"What does that mean,

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Clyde?"

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Well, it just means that any character typed into a URL can be replaced with hexadecimal encoding for

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that character.

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For example, if we type "googl%65.com", then that can be used to get to google.com because

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65 is the hex encoding for the letter e.

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In other words, when you type that into the browser, the browser is going to swap the %65

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for the character "e" and it's going to send it on.

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What 🙄?

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I know.

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That's so weird, right?

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Don't believe me?

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Let's hop on to the browser and let me quickly show you.

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So let me prove to you that a URL can understand both hex and ASCII characters.

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They kind of go hand-in-hand.

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You've got hex on the one hand and you've got Ascii on the other hand.

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And although they're two separate things, the URL understands both Hex and ASCII. 

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Good girls.

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Let me make this screen a bit bigger, and let's just type in the address bar

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Google...

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but now instead of writing "e", I want to write %65 as I just said in the lecture.

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And if we do that, and I hit return, the browser automatically converts that hex value into a character,

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an ASCII character, to be specific.

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Got it?

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Let's jump back to the lecture.

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There you go.

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You saw it in action.

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I'm not making these things up. But most people will just move on from here,

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right?

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And I don't want to. I want us to understand Hex. But what is Hex,

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you may be thinking?

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And that is a very good question.

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It's very, very important to understand the fundamentals before you start getting more advanced in

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your programming career. And don't get intimidated because hexadecimal is just a way of writing values.

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In fact, it's no different from the one we use every day, and that is the decimal system.

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Decimal is base ten and it's great for us humans. And it was designed that way because we've got 10 fingers,

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so it makes sense that it's base ten with decimal - we can use ten unique digits to represent large

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values or small values.

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And I bet you can already tell me what those ten unique digits are.

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Can you?

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That's right.

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0 to 9.

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It's very unique, it's base 10 because there are 10 unique values and they can be combined to represent

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huge numbers and teeny weeny little values.

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Okay,

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got it?

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So, similar to decimal, hex just combines digits to create large and small numbers.

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Well then, how is it different to decimal?

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Well, hex doesn't use a set of only 10 digits.

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Hex is more powerful.

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Hex uses a set of 16 unique digits.

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What digits does it use?

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Well, it uses 0 to 9, just like our fingers, just like decimal.

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And that represents 10 unique digits, ten unique values.

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But over and above decimal, hex also uses the letters A to F, which represents another six unique digits.

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So, you combine that and we've got Hex, which is base 16.

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"Okay, Clyde it's base 16,

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but what does that really mean?

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Like, I still don't get it."

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Well, that's okay.

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Let me try and show you in a slightly different way.

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Let me pick this stone up, throw it at the screen ... and let's just start from a blank slate.

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Let's say we've got a decimal system and a hex system, right?

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And we want to represent 16 unique values.

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Well, how can we do that with decimal?

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Well, very simply, we can just represent 16 unique values from writing the number zero all the way

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through up to 15.

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That represents 16 unique values, right?

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And those last six digits, these are repeated digits.

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It's just another one.

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It's just another two, three, four and a five with an extra 1 or 0 placed somewhere.

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We've used all those digits before in the first ten digits, and that's why this is known as base ten.

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We don't ever use more than ten unique digits.

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What about Hex?

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Hex, as we just said, is base 16 and it uses the characters A through to F as well.

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But you'll notice now that these are not repeated digits, are they?

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They are six brand new digits.

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And this is why Hex is known as base 16.

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Okay, cool.

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That makes sense.

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But how do we count in Hex?

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Well, counting in hex is very similar to how we count in decimal.

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Once a digit becomes greater than F, remember, that's the last character in hex,

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you start at zero again and increment the digit to the left by one ... heh?

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(sound: well, this is awkward)

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Confused 😕?

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Don't be.

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Don't be.

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It really isn't that bad.

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Let me show you.

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So here we've got two tables, decimal and hex. With decimal,

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let's count up to 7.

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How do we do that in Hex?

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Well, it's got exactly the same digits, right?

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So, nothing changes.

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This is how we count in Hex.

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Let's now count from 8 to 15.

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How is that going to work in Hex? Already, 

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I'm sure you can figure it out.

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We've got 8 and 9, which is exactly the same as decimal.

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And then as we just said, we then get A through to F. All is good and well.

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But now how do we do say 16 for example?

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How would that work?

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Well, it's not that difficult.

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16 in decimals, just the characters or the digits

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1 and 6. 

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With Hex, we start all over again, but we increment the left digit by one.

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So here we actually literally have a 1, and then we start from scratch, which the first digit in hex

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is 0.

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So what that means is if we want to represent the number 17, keeping the left digit the same, and we

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just keep incrementing by one.

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Pretty straightforward, and we just keep going on and on.

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"I'm starting to understand it, but how do I know if a certain number I see on a screen is Hex ... or should

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it be decimal?

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Like, how do I know what it is?

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How do I know what characters are represented to me on a screen when I'm looking at it?"

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That's a very, very good question. And let me pose it in another way.

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Say we have these characters on the screen.

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Am I wanting a drink ...

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or am I am trying to represent the decimal number

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74007760487749?

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Well, to avoid confusing situations like this, you'll often see a hexadecimal number prefix.

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And that prefix is kind of like a clue to us, or to software, that we are talking hex numbers.

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And what's really confusing is that we don't only have one prefix, different softwares use different

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prefixes.

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I know it's so irritating, but let me just give you an example of a few of the most popular ones I

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could think of.

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Firstly, and you'll definitely know this one, we've got the hash symbol and this is also just a hex

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prefix. And these are just color references in HTML.

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If you've coded any web page, you would have used these a ton.

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Okay.

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What about another type?

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0x. 0x is a common prefix in UNIX and C-based programming languages. And we get a whole bunch more.

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Literally, we get tons. We get &#D which represents a Unicode character,

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\x, 0h etc etc etc. 

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I don't want to get into that

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now.

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The most important one that we have to concentrate on now, is one relating to forms, because this course

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is all about forms.

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And sometimes when we're dealing with forms you have to deal with URLs.

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So what is that prefix?

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Well, that prefix is the percentage sign.

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The percentage sign is used in URLs to express different characters in Hex.

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I hope this is starting to make sense.

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Don't worry if you not quite sure how it looks in the URL.

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We're going to be looking at examples shortly. But just taking a step back, there are many different

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numeral systems out there.

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We know that binary is the language of computers.

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Binary uses two digits - ones and zeros - to represent unique values.

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We just looked at another numeral system.

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We looked at decimal and we looked at hex.

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And hex is often used in programming.

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I don't know why, it's just the way it is.

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And the community of URLs, the web, they decided that URLs should be based in hexadecimal.

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So if there's nothing else you've learned in this lecture other than this, then that's okay because

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it is such a good thing to know that URLs are based in hexadecimal.

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That's why we could replace the %65 with the letter "e", for example, the browser did that

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automatically.

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It can speak one in the same language.

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But anyway, now that I've introduced you to Hex, I think we can move on.

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We can start getting into more complex topics.