Foundations of Programming: Fundamentals
Illustration by Richard Downs

Working with arrays


Foundations of Programming: Fundamentals

with Simon Allardice

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Video: Working with arrays

An array is a collection of values all wrapped up and given a name. Okay, so what does that mean? Well, we already know how to create one variable at a time. We use the word var, we give it a name, and then we can use the equal sign to give that variable a value. That could be a letter, it could be a number, it could be a string, it could be a Boolean, but it's one value. Now an array is the idea of multiple values but all contained in one named variable such as this one.
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  1. 4m 15s
    1. Welcome
      1m 17s
    2. Making the most of this course
      2m 8s
    3. Using the exercise files
  2. 22m 11s
    1. What is programming?
      5m 45s
    2. What is a programming language?
      4m 48s
    3. Writing source code
      5m 34s
    4. Compiled and interpreted languages
      6m 4s
  3. 16m 29s
    1. Why JavaScript?
      4m 45s
    2. Creating your first program in JavaScript
      6m 54s
    3. Requesting input
      4m 50s
  4. 31m 38s
    1. Introduction to variables and data types
      5m 16s
    2. Understanding strong, weak, and duck-typed languages
      3m 51s
    3. Working with numbers
      5m 4s
    4. Using characters and strings
      4m 5s
    5. Working with operators
      4m 47s
    6. Properly using white space
      6m 46s
    7. Adding comments to code for human understanding
      1m 49s
  5. 24m 48s
    1. Building with the if statement
      7m 35s
    2. Working with complex conditions
      4m 9s
    3. Setting comparison operators
      6m 59s
    4. Using the switch statement
      6m 5s
  6. 17m 54s
    1. Breaking your code apart
      4m 1s
    2. Creating and calling functions
      2m 56s
    3. Setting parameters and arguments
      6m 7s
    4. Understanding variable scope
      2m 23s
    5. Splitting code into different files
      2m 27s
  7. 13m 31s
    1. Introduction to iteration
      4m 28s
    2. Writing a while statement
      5m 24s
    3. Creating a for loop
      3m 39s
  8. 19m 28s
    1. Cleaning up with string concatenation
      4m 30s
    2. Finding patterns in strings
      8m 3s
    3. Introduction to regular expressions
      6m 55s
  9. 19m 58s
    1. Working with arrays
      5m 46s
    2. Array behavior
      5m 29s
    3. Iterating through collections
      5m 18s
    4. Collections in other languages
      3m 25s
  10. 10m 50s
    1. Programming style
      5m 55s
    2. Writing pseudocode
      4m 55s
  11. 25m 55s
    1. Input/output and persistence
      3m 6s
    2. Reading and writing from the DOM
      8m 11s
    3. Event driven programming
      7m 47s
    4. Introduction to file I/O
      6m 51s
  12. 24m 25s
    1. Introduction to debugging
      5m 57s
    2. Tracing through a section of code
      7m 5s
    3. Understanding error messages
      3m 21s
    4. Using debuggers
      8m 2s
  13. 14m 16s
    1. Introduction to object-oriented languages
      5m 18s
    2. Using classes and objects
      6m 28s
    3. Reviewing object-oriented languages
      2m 30s
  14. 11m 14s
    1. Memory management across languages
      5m 11s
    2. Introduction to algorithms
      4m 2s
    3. Introduction to multithreading
      2m 1s
  15. 29m 20s
    1. Introduction to languages
      1m 42s
    2. C-based languages
      4m 40s
    3. The Java world
      3m 13s
    4. .NET languages: C# and Visual Basic .NET
      6m 17s
    5. Ruby
      3m 4s
    6. Python
      2m 56s
    7. Objective-C
      4m 3s
    8. Libraries and frameworks
      3m 25s
  16. 1m 2s
    1. Where to go from here
      1m 2s

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Watch the Online Video Course Foundations of Programming: Fundamentals
4h 47m Beginner Sep 22, 2011

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This course provides the core knowledge to begin programming in any language. Simon Allardice uses JavaScript to explore the core syntax of a programming language, and shows how to write and execute your first application and understand what's going on under the hood. The course covers creating small programs to explore conditions, loops, variables, and expressions; working with different kinds of data and seeing how they affect memory; writing modular code; and how to debug, all using different approaches to constructing software applications.

Finally, the course compares how code is written in several different languages, the libraries and frameworks that have grown around them, and the reasons to choose each one.

Topics include:
  • Writing source code
  • Understanding compiled and interpreted languages
  • Requesting input
  • Working with numbers, characters, strings, and operators
  • Writing conditional code
  • Making the code modular
  • Writing loops
  • Finding patterns in strings
  • Working with arrays and collections
  • Adopting a programming style
  • Reading and writing to various locations
  • Debugging
  • Managing memory usage
  • Learning about other languages
Developer Web
Simon Allardice

Working with arrays

An array is a collection of values all wrapped up and given a name. Okay, so what does that mean? Well, we already know how to create one variable at a time. We use the word var, we give it a name, and then we can use the equal sign to give that variable a value. That could be a letter, it could be a number, it could be a string, it could be a Boolean, but it's one value. Now an array is the idea of multiple values but all contained in one named variable such as this one.

We have a variable called myArray with multiple values in it. It's a great way to keep data together that belongs together, to keep dozens, hundreds, or even thousands of pieces of information together without having to name every single individual piece as an individual variable. But before we make one, here are a couple of concepts. See if all we have is one name for this entire array, how do we get individual pieces in or out? Well in an array each individual value, often referred to as an element, has a number, an index that identifies where it is in the array.

Arrays have an internal order. Tey don't shuffle their values around randomly. So the first slot has an index of 0, the second slot or second position has an index of 1, third slot is 2, and so on. So I have got an array with seven elements in it here but there is no minimum or maximum size. You can make arrays as big as you need them. You are simply limited by the amount of memory you have available. In JavaScript, like most languages these days, arrays are zero-based and that means the first position, the first element in the array, is considered to be at position 0, not position 1.

In some languages like older versions of Visual Basic used 1-based arrays but 0-based arrays are far more common. So we can use that number, that index to either set that value or to get to that value. So I need to use both the name of the array and the index of the element to access any one part of the array. So let's make one. In JavaScript, we can make the variable the same way we always do it, but we need to tell JavaScript this is an array.

There is actually a few ways to do it, but this is the easiest one. We'll use the word var and I'm going to call my variable multipleValues. You can call it whatever you like. Then we will use the equal sign and then what we are going to use is this opening square bracket and closing square bracket, and this is the indicator that we're dealing with an array, not a single value. When you see those square brackets in JavaScript, it's a pretty good sign you have got an array somewhere. So this line and these characters here simply create a single variable called multipleValues that you can put a bunch of stuff inside.

Well how do you do that, how do I get to the individual elements of that array? I use these square brackets again. So if I want this array to hold multiple values we need to be able to say which element of the array are we trying to get to? So we use the index. So here is an example. I use the name of the variable but instead of just saying equals, I am using those square brackets again. I'm saying here I want the element at position 0 to be set to the value 50 and I want the element at position 1 to be set to the value 60.

I can say I want the element of position 2 to be able to the word "Hello" and notice that what I can do in this array is I can put in a number, I can put in a string, I could also put in a Boolean, I can actually put anything in there. It doesn't matter what kind of data you're putting in at the different slots in the array, but all of them are accessed using that index and that's whether you are setting these values or whether you're getting these values. It's always a 0-based index.

Now what we can then do is use the same format to get to the contents of the array. So for example, if I want to write an alert message with whatever is at the second position I use the square brackets. I use the same way to access them and to set them and it writes out the word "Hello" in this case. So if this is the way that we write arrays. It's okay, it's not too bad, but it would be nice if there was something a little quicker, and in fact there is. There is a shorthand method for doing it.

So instead of doing it over several statements like this, we can use those square brackets and combine all this stuff onto one line. We can just load this array up with the initial values. In this case, 50, 60, "Hello", and it will automatically create an array and put them in that position 0, position 1, position 2. You could then come along and add position 3, position 4, and so on but it's always a 0-based index. Now arrays are found in every language, and as we will see there are other ways of grouping values together.

Sometimes you might not want a 0-based index but perhaps a letter-based index or some other way of accessing the elements of the array. And we can do that too. But these arrays are the classic way to get started with what we are often referred to as collections in a programming language, and this time the buzz word really is straightforward. A collection in a programming language is simply multiple values grouped together in some way, and there are often slightly different ways of creating them across languages but the overall concept is the same.

Find answers to the most frequently asked questions about Foundations of Programming: Fundamentals .

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Q: Using TextEdit with Mac OS 10.9 Mavericks? 
A: If you're using the built-in TextEdit program in Mavericks to write your first examples and your code doesn't seem to be working, here's one reason why: by default, "smart quotes" are now turned on in TextEdit Preferences.
This is where TextEdit will automatically change pairs of double quotes to "smart quotes" - where the opening and closing quote are different, like a 66 and 99.
While this is fine for human eyes, programming languages don't want this - when writing code, they need to be the plain, generic straight-up-and-down quotes.
So make sure that in TextEdit > Preferences, that "Smart quotes" are unchecked.
Important! Whenever you make a change to TextEdit preferences, make sure to then completely quit out of the program (Command-Q or using TextEdit > Quit TextEdit) and then re-open it, as changes won't take effect on documents you already have open.
However, we're not finished - just because you've changed the preferences, it does **not** change any *existing* smart quotes back to "regular" quotes - it just doesn't add new ones - so make sure to go through your files for any time you wrote quotes and TextEdit may have changed them to smart quotes - look in both the JavaScript, and your HTML too, and compare to the downloadable exercise files if necessary.
If that sounds like a bit of a chore, I recommend just downloading a code editor like Sublime Text ( or TextMate ( and using that instead of TextEdit - it's only a matter of time before you'd move away from TextEdit anyway - we only used it in the course because it was built-in and a quick way to get started, but it's now become more of a inconvenience than it was before.
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