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Compiled and interpreted languages

From: Foundations of Programming: Fundamentals

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.

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.

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This video is part of

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

61 video lessons · 87935 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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