Arrays

Quick reference

• 00:04 In this video I want to talk about arrays and
• 00:07 arrays are another very fundamental programming concept.
• 00:10 All computer programming languages have arrays, they're very useful,
• 00:14 you're going to use them forever.
• 00:15 So an array is, think of a variable, we said a variable is like a bucket,
• 00:20 you can put things in it, it's like a box.
• 00:22 Well, you generally put one thing at a time in a variable.
• 00:25 In an array it's the same thing, it's a big bucket, but
• 00:28 you can put lots of different things at the same time, as many things as you want.
• 00:32 And then you can pull out each one separately, you can pull them all out,
• 00:35 you could do all kinds of things with them.
• 00:36 So, to create an array, it's just like creating a variable.
• 00:39 We name it, so let's call this first_names.
• 00:43 And then use your assignment operator.
• 00:45 And to create an array we just use these straight brackets.
• 00:49 Now, to put things in there we just type whatever we want, separated by commas.
• 00:56 So we could have John, we could have Bill, we could have Mary,
• 01:02 we could have Tim, whatever you want, as many as you want.
• 01:07 And there you have your array.
• 01:09 So if we put first_names, let's see what happens here if we run this.
• 01:15 We get our nice little list, John, Bill, Mary, and Tim.
• 01:19 So that's actually pretty cool.
• 01:21 Now normally you're not going to want to just print out a list of things in your
• 01:24 array, you're going to want to pull a specific thing out of your array.
• 01:28 And arrays in Ruby, these are numbered indexes so
• 01:32 each of these items corresponds with a number.
• 01:35 And the first item in your array is always zero.
• 01:38 So John is the zeroth thing in our array, it's the zeroth item.
• 01:43 Bill is the first item, Mary is the second, Tim is the third,
• 01:46 and that's confusing for a lot of people.
• 01:48 Even to this day, every once in a while I forget, and
• 01:51 I want the first thing out of here so I type in a 1 and I get Bill.
• 01:55 And then I go, yeah, I forgot, arrays start with zero.
• 01:57 So just burn that into your brain, arrays start with zero.
• 02:00 So to call a specific item out of your array, we stick with this theme of these
• 02:05 straight brackets here and you just type in whatever item you want.
• 02:09 So first_name[0], that should output John.
• 02:12 So we run it, John.
• 02:13 So let's say we want Tim.
• 02:16 Tim is the zero, one, two, third item, so we save this and run it, Tim.
• 02:22 If we asked for the fourth item, we get nothing because there aren't four items.
• 02:27 So you might want the last thing in your array list and
• 02:30 you might not know what that is.
• 02:31 Remember in the last video, we did that length?
• 02:35 You can use that here too.
• 02:36 So if we save this, we see there are four items in our array.
• 02:41 So one, two, three, four, they're named zero, one, two,
• 02:46 three, a little bit confusing there.
• 02:47 So let's say we want the last item,
• 02:51 we can call [first _name.length].
• 02:56 And we know that will return four so we have to do- 1.
• 03:00 Getting a little complicated here.
• 03:02 Now if we run this, misspelled names, see, errors, always errors, so we get Tim.
• 03:08 So what this is doing, it's calling the length and remember our length is four.
• 03:12 But since it starts with zero, we need to subtract one.
• 03:16 So zero, one, two, three, is 4 -1 = 3, so we get Tim.
• 03:23 So just an interesting little thing.
• 03:25 Those are arrays, very, very useful, you'll just use them forever.
• 03:29 Arrays are just one of the most common programming type things.
• 03:33 So in the next video will look at multidimensional arrays.

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