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Setting parameters and arguments

From: Foundations of Programming: Fundamentals

Video: Setting parameters and arguments

So I have a simple function here called addTwoNumbers. It just creates two variables, adds them together, and displays the result. And that's fine, but of course this isn't very useful because it's always adding the same two numbers together, always 5 and 10, no matter how many times we call it. Well, I'd like something a bit more flexible than that. I'd like this function to be able to take in some different information to add different numbers together. And I can do that by defining parameters for this function, to say that whenever we call it, we're going to pass information into it.

Setting parameters and arguments

So I have a simple function here called addTwoNumbers. It just creates two variables, adds them together, and displays the result. And that's fine, but of course this isn't very useful because it's always adding the same two numbers together, always 5 and 10, no matter how many times we call it. Well, I'd like something a bit more flexible than that. I'd like this function to be able to take in some different information to add different numbers together. And I can do that by defining parameters for this function, to say that whenever we call it, we're going to pass information into it.

That's what the parentheses are for after the function name. They allow us to say do we pass one piece of information into this or two or three or a dozen. And all we need to do here is give it the name of what will become two variables. In this case what I could do is remove my variable declaration here, var a and var b, and just say that this function takes in two parameters called a,b. If I wanted three parameters, I could say a,b,c. I can call them whatever I want, whatever is meaningful.

They obey the same rules as variable names, because really what's happening is we will have variables created for us called a and b. That means the first line that I can run here is var result = a + b. Those parameters that were passed into this function will be added together and will display the result. Now of course the flip side of this is if my function expects information passed into it, well, I better pass information into it when I'm calling it. Now I could create two variables and pass in the variable names or in this case, I could just pass in 5,10. Save that.

When this function is called, 5 will be passed in under the name a. 10 will be passed in under the name b. We save it, we run it, and we should have the 15 alert box being popped in. The flexibility of this simply means that I could call this again, passing in different numbers. Save that, run it again. We'll get three alert boxes, 15, 600, and -2316.

When you start working with defining parameters to your functions, you'll often hear the term arguments as well and parameters and arguments can seem a little bit interchangeable. There is a formal definition. When I'm defining a function, here what I'm defining here are a and b. They're my parameters. When I'm calling the function, I'm passing in 5 and 10. These are my arguments. Now often in conversation with other software developers, these terms are almost interchangeable, but they do have a formal meaning.

So if you're interested in what that was, that was it. Now if you think this looks a little strange and you need time to get used to it, well, bear in mind, the very first thing that we did in JavaScript was calling a function, passing in a parameter. When I said alert("Hello, world"), I'm calling the built-in alert function in JavaScript, passing in the string literal "Hello, world" as an argument. But let's take this one a little bit further.

Instead of just passing information into a function, I can also pass information back out of a function. The way that we do that is by using a new keyword called return. If I wanted to create say this result by adding these two numbers together and instead of popping up an alert box I just want to pass that result back to whoever called this function, well, what I'm going to say is return result. Now the question is, well, what does that do? Now as soon as you hit the word return, you're actually going to jump right out of this function.

So one of the things you don't want to do is start say creating new variables after this because you'll never actually get to this line of code. When we call the function, we're going to be executing the first line and then the second line and when this one is executed, return result, we're going to jump back to whoever called this. So it's often the last line of the function, although occasionally you can use return to leave a function early if you need to. The question is what happens? If we say return result, well, what's going to happen now? Well, I'm just going to save this and just run this page and we'll see nothing happening at all.

The function is actually being called three times and it's returning results, it's returning these numbers added together. But the problem is I'm not doing anything with those returned results. What I need to do is something like this. Create a new variable and set it equal to whatever happens when I call the addTwoNumbers function. So in this case, we're going to pass in 5 and 10. They will be added together in the function. That number will be returned, and the result will be stored in the variable called x. I could then pop up an alert box, save that over here, and run it.

We should get one alert box saying 15. As you can see, even if a function returns values, I don't have to do anything with the information that's returned. But most of the time, you'll want to. And again, if this looks a little unusual, this is what we were using very early on when we called the prompt function in JavaScript. Prompt is a built-in JavaScript function. It takes in one argument. In this case, the string that's going to be displayed. And then whatever is returned from that is what we were accepting back into a variable called name.

So both passing information in, passing in arguments to be received as parameters into functions, and returning values is a very core piece of any programming language. It's something you'll be using all the time.

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This video is part of

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

61 video lessons · 88729 viewers

Simon Allardice
Author

 
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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
      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

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