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Foundations of Programming: Fundamentals
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Compiled and interpreted languages


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Foundations of Programming: Fundamentals

with Simon Allardice

Video: Compiled and interpreted languages

So we need to get our source code converted into machine code somehow before it can run and there are two main ways of doing this: what's called compiling the source code and what's called interpreting the source code. Now luckily, this is not a big decision you have to worry about. Most languages you'll deal with will naturally fall into one or the other, but it is worth knowing the difference. So let's have a simple scenario. Let's say it's just you and me. You have your computer and I have my computer and you're going to write a program that you want me to run.
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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

Compiled and interpreted languages

So we need to get our source code converted into machine code somehow before it can run and there are two main ways of doing this: what's called compiling the source code and what's called interpreting the source code. Now luckily, this is not a big decision you have to worry about. Most languages you'll deal with will naturally fall into one or the other, but it is worth knowing the difference. So let's have a simple scenario. Let's say it's just you and me. You have your computer and I have my computer and you're going to write a program that you want me to run.

Now, with a compiled language, what happens is you write your source code and then you have a program called a compiler that will go through that source code and create a separate file that contains the machine code, and you just give me that file. This end result is sometimes referred to as an executable or an executable file because I can directly execute it. I can now just run your program. You keep your source code and I never see it. Now, with an interpreted language on the other hand, you don't compile your source code beforehand. You just give me a copy of it.

So I'll need my machine to interpret it whenever I want to run your program. Now, interpreter is different to a compiler. It does this on-the-fly. We can think of it as going through your source code line by line and processing it on the spot. It does not save it as a separate machine code file. Now, you've used interpreted languages even if you don't know it. Whenever you've looked at a webpage with JavaScript, which if you've surfed the web for more than two minutes in your lifetime you have, this is what's been happening.

The JavaScript has been sent to you over the web along with a bunch of other files like webpages and images and it's been sent as source code onto your machine, and your web browser has just interpreted that JavaScript so it can run that code. So which one is best? Well, they both have their good and their bad points. Benefits of compiled code. Once it's compiled, it's immediately ready to run and you could send it to 100 or 1,000 or 100,000 different people. It's ready to go. It can be optimized for a CPU, so it can actually be faster and you don't have to send your source code to everybody, which might be a good thing.

However, the downsides are if I compile it on a PC, that executable file won't work on a Mac. In fact, it often needs to be compiled separately for different kinds of CPU even on the same platform, and when you're writing code to compile is an extra step that you have to take every time you want to test your program. Now, with interpreted code, the big benefits are I don't really care what kind of machine is on the other end, because we don't provide machine code. We just send the source code and we let the other side take care of it.

So it can be more portable and more flexible across platforms. It's also a little easier when testing because you just write your source code and then run it, letting the interpreter take care of converting it. There is no in-between compile step. It can be easier to debug when things go wrong because you always have access to all the source code. However, it has its down sides too, because everyone who needs to run that program on their machine has to have an interpreter for that language on their machine. It also can be slower because you have to interpret it every time the program is run, and the source code is effectively public because you're sending it to everyone who needs to run that program.

Now, because there are good things about compiled languages and good things about interpreted languages, there is also a third way of doing this which is a bit of both. Instead of the compiled model where all the work is done upfront but can be a little bit inflexible or the interpreted model where all the work is done on the receiving end but can be a little bit slower, we kind of do half-and-half. Upfront, we compile it part of the way to what's called an intermediate language, which takes it as far along the way to machine code as it can get while still being portable often across platforms.

You then distribute this, sending it to the people who need to run it, and each person who runs it takes it the last step to take it to machine code on their computers. This is sometimes referred to as Just-In-Time or JIT compilation. Now, this intermediate language sometimes also goes by the name of bytecode. So this process has to happen somehow. It's just how much of it happens on your machine and how much of it happens on mine. Now, while theoretically all computer languages could use any of these methods, the normal usage of any one language tends to be one or the other.

So for example, C, C++, and Objective-C, these are typically found as compiled languages, so you need a compiler. Now the compiler can be downloaded for free but they're often built into integrated development environment applications. Now, languages like PHP and JavaScript and indeed most languages with the word script at the end are usually interpreted, and languages like Java, C#, VB.NET, and Python use this intermediate hybrid approach.

Now, whether a language is compiled or interpreted or somewhere in-between is rarely a reason by itself to choose a language, but it can be something that you take into account. If one main priority of your program is absolute maximum speed running on one single platform, you'll probably look at a compiled language. If you're more interested in easily moving your code across multiple platforms, you're probably more interested in an interpreted one. But more usually, you're driven more by what you need to do.

You need to build iPhone apps or Windows desktop apps or dynamic website, or, in our case, just learn the fundamentals of programming, and you let that decision drive the language choice and the language choice will determine whether you are compiled, interpreted, or somewhere in the middle.

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 (www.sublimetext.com) or TextMate (www.macromates.com) 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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