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Foundations of Programming: Fundamentals

Requesting input


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Foundations of Programming: Fundamentals

with Simon Allardice

Video: Requesting input

Computer programs are all about input and output. From the earliest programs where you might feed a stack of punch cards in one end to get a printout on the other end, where these days the input might be click the button, or move the mouse or even wave your hand in the air, and the output could be change what's displayed on the screen, or cause the game controller to vibrate. The different languages favor different kinds of input and output. JavaScript is all about the webpage. It doesn't read files on your hard drive.
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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

Requesting input

Computer programs are all about input and output. From the earliest programs where you might feed a stack of punch cards in one end to get a printout on the other end, where these days the input might be click the button, or move the mouse or even wave your hand in the air, and the output could be change what's displayed on the screen, or cause the game controller to vibrate. The different languages favor different kinds of input and output. JavaScript is all about the webpage. It doesn't read files on your hard drive.

It doesn't talk directly to your printer. It's interested primarily in what's on the webpage and what you might interact with on the webpage. Now we've already got some output going on. We've got an alert box. That might not be impressive output, but it is output. It's our computer program causing something to happen on the screen, so let's get something into our program. So I have a folder with two files in it. It's the same setup as last time. In fact, it's an identical container.html file that is only there to point to script.js, a JavaScript file which I'm going to Open up in my text editor and as you can see is currently empty.

I'm going to add two lines here, two JavaScript statements, and then explain what they are doing. So the first line, var name = prompt, all of this written in lowercase, open parentheses, open double quotes, the phrase, What is your name, question mark, close double quote, close parentheses, semicolon, and then on the next line alert and inside the parentheses we have "Hello, " then a plus sign, and then the word name and of course we're closing both of these lines with the semicolon.

I'm going to just save this JavaScript, and because the container.html page is already pointing to it if I double- click that HTML page to open up in the web browser we should immediately load in and run that JavaScript, and indeed what we get is a prompt. Depending on the browser this may look a little different, but it should be asking, What is your name?, and giving a place to type in and I'll say it's Simon. Click OK and then I get the message Hello, Simon. Now because I'm using a fairly recent version of Firefox it's also detecting that this page is popped up two alert boxes and it's asking me, do I want to prevent this page from doing that? Well, no I don't.

That's fine. It's all I was expecting to do right now. Again, very simple code, but what's it actually doing here? Well we have two JavaScript statements, but the first statement is doing two things. It's using the JavaScript prompt command to ask for a name and then it's going to store that name in a variable. This is a container, a bucket that can hold some data, and that's simply so we can use it on the next line. And if we don't tell our program some way of remembering it we won't have anyway to use it on the next line.

Now usually our code will just start at line 1 and move through all the different statements as quickly as possible, but what's actually happening is when we call prompt in JavaScript, it's not just What is your name? It's What is your name? and wait for our response. So we've actually paused at this line while somebody types in an answer into this dialog box that's popped open. And only when somebody type something in and clicks OK, do we actually come back. What's happening is the value that they typed will be stored in a variable called name.

Now whether that was five seconds later or five minutes later, we have paused to that point and then we run the next line of code. And that's going to combine the Hello, space, with whatever they typed in using this plus sign to combine these two parts of the message, and then pop-up another dialog box. If I open up this webpage to load it again, there is nothing to actually ensure that somebody types a name here. I could type in a number and click OK and it will just combine that message.

It could have been a number. It could have been a sentence. It could have been nothing at all. If I want to run that code again, I could either close and reopen it or I could click the button in the browser to reload the current page and we'll effectively run the script again. I could even leave that completely blank and click OK. Now here it doesn't matter, but if our program, if our code, was expecting something very specific to work with like a birth date or an amount or an email address, the wrong kind of input could cause it to crash.

Because again programs are all about input and output. There is an old phrase called G-I-G-O, GIGO for Garbage In, Garbage Out, whatever you're asking for, and whatever you get better make sense. Later on we'll see how to do some checking on our input.

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