Easy-to-follow video tutorials help you learn software, creative, and business skills.Become a member

Building with the if statement

From: Foundations of Programming: Fundamentals

Video: Building with the if statement

We've written a few lines of code, but so far, what's been happening is this. We start at the first statement, we execute it, we move onto the next, we execute it, we move on as fast as the computer can fully execute each line. Now it might pause if we're prompting for information from the user, but as soon as we come back, we move on again, top to bottom, each line in order, no exceptions, and it's kind of dumb really. You see beyond the most simple Hello World level programs, we need our code to be smarter than this.

Building with the if statement

We've written a few lines of code, but so far, what's been happening is this. We start at the first statement, we execute it, we move onto the next, we execute it, we move on as fast as the computer can fully execute each line. Now it might pause if we're prompting for information from the user, but as soon as we come back, we move on again, top to bottom, each line in order, no exceptions, and it's kind of dumb really. You see beyond the most simple Hello World level programs, we need our code to be smarter than this.

We need to start asking questions. If the bank balance is positive, calculate interest; if it's negative, charge a penalty. If they check the checkbox on the form, add them to the mailing list; if they didn't, then don't. If the position of the missile image is the same as the position of the spaceship image, then show the explosion image. We need to have code that sometimes runs, and sometimes doesn't depending on the conditions of the program at that time. This is conditional code. We begin with the classic if statement, which is found in every programming language.

The if statement is written in JavaScript and is identical to this in other C-based languages using this format. Now, I've put a few spaces in here and a few line breaks just to make it clearer, but we are using the word if, then we've got a pair of parentheses, an opening and closing one, and then an opening and closing curly brace. And the general format is if some condition is true, then do whatever code goes between the opening and closing curly braces. Now, a quick aside for folks who are brand-new to programming.

Bear in mind that in programming languages, we are very picky about the symbols we use and about what we call them. So just to be really specific here, when I say parentheses, I mean these; when I say brackets, and I'll usually say square brackets; I mean these ones and when I say braces, and I'll try and say curly braces, I mean these ones. They do serve similar purposes, they are mocking where something starts and where it finishes, but they are not interchangeable. Now, unlike things like say a semicolon or an equals sign, when you see parentheses, brackets, or braces, they are always found in pairs.

If you have an opening one, you will need a closing one. It may be several lines later, but it needs to be there. So let's go back to the if statement. So in our case, the parentheses are used to mock out whatever our condition is and the curly braces are used to mark out what we are going to do if that's true which could be one JavaScript statement, could be a dozen of them, could be 100 of them. Okay, so what do we mean by condition? Well, we don't use the word condition. We are going to have something like if a is less than 50. We are actually asking a question, what is the condition? We want to check to see if something is true, a less than 50, or b greater than 20.

Now here is the thing. Whatever is inside these parentheses must evaluate, must break down, as being either true or false. So if I am checking here if the variable b is greater than 20, I don't care what it is. I don't care if that's 21 or 25 million, or 20.000000001. All I want to know is, is this true or is this false? All conditions must boil down to simply true or false.

Now, one of the things that's very common in JavaScript is you want to check quality. That's the condition that you're asking. Well, to check a quality in JavaScript, to ask if something is equal to something else, like in other C-based languages, we don't use the single equals sign. We use the double equals sign and no spaces between them. This is asking if C is equal to the number 99. That's the condition. Is that true or is that false? Now, heads up, even for programmers, JavaScript has another way of checking a quality.

The triple equals sign. This is an unusual one and we'll come back and talk about this later, but realize for now that with all C-based languages, C, C++, C#, Java, JavaScript and many others, if you're in a condition, if you're asking if something is equal to something else, you will never use a single equals sign. As we saw with variables, when you see a single equals sign, that's an assignment. It's a command. It sets a value, not checks a value. We can also check inequality, that something is not equal to something else, which is the != written together as one operator.

So in this case, if d is not equal to 100, is that true or is that false? Now, when you have several statements surrounded by curly braces, that's referred to as a code block and this is all that these curly braces are doing. They are grouping a section of code together; they don't have any other meaning than that. And as you'll see, blocks can be nested inside each other if you need to. Now, what you'll also see is the code inside a code block is indented. Our alert statement is about three spaces in from the if.

It doesn't have to be. Again, white space is insignificant. It just makes it much easier to read. So here is an example. On the first two lines I am creating a couple of variables, variable a = 5, variable b = 10. Then I am checking if a is less than b, we open the code block and we're going to execute this line if that is true. Just pop up an alert, yes, a is less than b, and then we have a second if statement. if a is equal to b. Again, this must be either true or false.

If it's true, we'll run that second alert message. I am going to go and execute the HTML page that contains our JavaScript and we'll get the alert box, yes, a is less than b. But we will not get the second alert message because this will evaluate as false. a is not equal to the value of b. Now, one thing to notice here. You do not have a semicolon after the closing curly brace. You will occasionally see that in say JavaScript you might read on the web, but you won't see it for an if statement.

In fact, it's much rarer. A quick word about these curly braces. When you're reading other people's code, you're likely to see them in a couple of different styles, and you might be wondering, well, what's the difference between the two? The most common way that you will see it in C-based languages and in JavaScript particularly is that the opening curly brace would be on the same line as the keyword. So we've got this word if here and then we have the opening curly brace on the same line. Then we have our code indented inside the block, and then on a following line we have the closing curly brace to say this code block starts here and it ends here.

However, you might also see them written so they align with each other like this format. If a is equal to b, here is where our block opens, here is the code we are going to execute, here is where our block closes. This is more common in languages like Pascal and C#. Now, programmers can get religious about brace styles. JavaScript doesn't care. It doesn't change the meaning of the code. This is regarded like everything else as insignificant white space. But most commonly, the sample JavaScript you're likely to find online or download or see in books, you will see it written this way and it does become very comfortable once you just get used to the general format.

Show transcript

This video is part of

Image for Foundations of Programming: Fundamentals
Foundations of Programming: Fundamentals

61 video lessons · 100089 viewers

Simon Allardice
Author

 
Expand all | Collapse all
  1. 4m 15s
    1. Welcome
      1m 17s
    2. Making the most of this course
      2m 8s
    3. Using the exercise files
      50s
  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

Start learning today

Get unlimited access to all courses for just $25/month.

Become a member
Sometimes @lynda teaches me how to use a program and sometimes Lynda.com changes my life forever. @JosefShutter
@lynda lynda.com is an absolute life saver when it comes to learning todays software. Definitely recommend it! #higherlearning @Michael_Caraway
@lynda The best thing online! Your database of courses is great! To the mark and very helpful. Thanks! @ru22more
Got to create something yesterday I never thought I could do. #thanks @lynda @Ngventurella
I really do love @lynda as a learning platform. Never stop learning and developing, it’s probably our greatest gift as a species! @soundslikedavid
@lynda just subscribed to lynda.com all I can say its brilliant join now trust me @ButchSamurai
@lynda is an awesome resource. The membership is priceless if you take advantage of it. @diabetic_techie
One of the best decision I made this year. Buy a 1yr subscription to @lynda @cybercaptive
guys lynda.com (@lynda) is the best. So far I’ve learned Java, principles of OO programming, and now learning about MS project @lucasmitchell
Signed back up to @lynda dot com. I’ve missed it!! Proper geeking out right now! #timetolearn #geek @JayGodbold
Share a link to this course

What are exercise files?

Exercise files are the same files the author uses in the course. Save time by downloading the author's files instead of setting up your own files, and learn by following along with the instructor.

Can I take this course without the exercise files?

Yes! If you decide you would like the exercise files later, you can upgrade to a premium account any time.

Become a member Download sample files See plans and pricing

Please wait... please wait ...
Upgrade to get access to exercise files.

Exercise files video

How to use exercise files.

Learn by watching, listening, and doing, Exercise files are the same files the author uses in the course, so you can download them and follow along Premium memberships include access to all exercise files in the library.


Exercise files

Exercise files video

How to use exercise files.

For additional information on downloading and using exercise files, watch our instructional video or read the instructions in the FAQ .

This course includes free exercise files, so you can practice while you watch the course. To access all the exercise files in our library, become a Premium Member.

Join now Already a member? Log in

Are you sure you want to mark all the videos in this course as unwatched?

This will not affect your course history, your reports, or your certificates of completion for this course.


Mark all as unwatched Cancel

Congratulations

You have completed Foundations of Programming: Fundamentals.

Return to your organization's learning portal to continue training, or close this page.


OK
Become a member to add this course to a playlist

Join today and get unlimited access to the entire library of video courses—and create as many playlists as you like.

Get started

Already a member ?

Become a member to like this course.

Join today and get unlimited access to the entire library of video courses.

Get started

Already a member?

Exercise files

Learn by watching, listening, and doing! Exercise files are the same files the author uses in the course, so you can download them and follow along. Exercise files are available with all Premium memberships. Learn more

Get started

Already a Premium member?

Exercise files video

How to use exercise files.

Ask a question

Thanks for contacting us.
You’ll hear from our Customer Service team within 24 hours.

Please enter the text shown below:

The classic layout automatically defaults to the latest Flash Player.

To choose a different player, hold the cursor over your name at the top right of any lynda.com page and choose Site preferences from the dropdown menu.

Continue to classic layout Stay on new layout
Exercise files

Access exercise files from a button right under the course name.

Mark videos as unwatched

Remove icons showing you already watched videos if you want to start over.

Control your viewing experience

Make the video wide, narrow, full-screen, or pop the player out of the page into its own window.

Interactive transcripts

Click on text in the transcript to jump to that spot in the video. As the video plays, the relevant spot in the transcript will be highlighted.

Learn more, save more. Upgrade today!

Get our Annual Premium Membership at our best savings yet.

Upgrade to our Annual Premium Membership today and get even more value from your lynda.com subscription:

“In a way, I feel like you are rooting for me. Like you are really invested in my experience, and want me to get as much out of these courses as possible this is the best place to start on your journey to learning new material.”— Nadine H.

Thanks for signing up.

We’ll send you a confirmation email shortly.


Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

Keep up with news, tips, and latest courses with emails from lynda.com.

Sign up and receive emails about lynda.com and our online training library:

Here’s our privacy policy with more details about how we handle your information.

   
submit Lightbox submit clicked
Terms and conditions of use

We've updated our terms and conditions (now called terms of service).Go
Review and accept our updated terms of service.