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Foundations of Programming: Fundamentals

Building with the if statement


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Foundations of Programming: Fundamentals

with Simon Allardice

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.
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  1. 4m 14s
    1. Welcome
      1m 16s
    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 49s
    1. Building with the if statement
      7m 35s
    2. Working with complex conditions
      4m 10s
    3. Setting comparison operators
      6m 59s
    4. Using the switch statement
      6m 5s
  6. 17m 56s
    1. Breaking your code apart
      4m 1s
    2. Creating and calling functions
      2m 57s
    3. Setting parameters and arguments
      6m 7s
    4. Understanding variable scope
      2m 23s
    5. Splitting code into different files
      2m 28s
  7. 13m 32s
    1. Introduction to iteration
      4m 28s
    2. Writing a while statement
      5m 24s
    3. Creating a for loop
      3m 40s
  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 59s
    1. Working with arrays
      5m 47s
    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 26s
    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 3s
  13. 14m 17s
    1. Introduction to object-oriented languages
      5m 18s
    2. Using classes and objects
      6m 29s
    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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Foundations of Programming: Fundamentals
4h 47m Beginner Sep 22, 2011

Viewers: in countries Watching now:

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
Subjects:
Developer Web Programming Foundations
Author:
Simon Allardice

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.

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