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Understanding strong, weak, and duck-typed languages

From: Foundations of Programming: Fundamentals

Video: Understanding strong, weak, and duck-typed languages

In many programming languages when you create a variable, you don't just give it a name but you must also say exactly what type of information is going to be stored in that variable. You must decide beforehand if it's going to store an integer, meaning a whole number without anything after the decimal point, or perhaps a floating-point number which might have a value after the decimal point or perhaps you need to store a single character, just one letter, or perhaps multiple characters, what's called a string, or is it a Boolean value, and that just means a value that can only be true or false, or it could be even more complex type of data, but you have to choose that data type.

Understanding strong, weak, and duck-typed languages

In many programming languages when you create a variable, you don't just give it a name but you must also say exactly what type of information is going to be stored in that variable. You must decide beforehand if it's going to store an integer, meaning a whole number without anything after the decimal point, or perhaps a floating-point number which might have a value after the decimal point or perhaps you need to store a single character, just one letter, or perhaps multiple characters, what's called a string, or is it a Boolean value, and that just means a value that can only be true or false, or it could be even more complex type of data, but you have to choose that data type.

And once you have chosen it you are not allowed to change it, and that's what's known as a strongly typed language. You can create as many variables as you want but each variable must be of one particular type and that's actually enforced and it can cause your program to crash if you try to put the wrong type in a variable that wasn't designed for it, but in JavaScript we don't do that. JavaScript is what's called a weakly-typed language. We don't make a variable that's only for integers or a variable only for strings.

We just create a generic variable, an empty container, and then we can simply put whatever type of value we want in it. Now if I create this variable without giving it a value, it starts off as what JavaScript calls undefined. However, then I can use the name of the variable and the equal sign, or more formally the assignment operator, to set the value of myVariable = 200. Now if I wanted to, right after this I could use the same format and set it equal to a string. That just means one more characters strung together.

Now we need to use the double quotes here to say where the string begins and where it ends. Inside those double quotes it can contain spaces and special characters. Now in JavaScript you can use either double or single quotes to mark the start and end of a string. But don't mix them. Don't start with a single quote and close with a double quote. Now I tend to use double quotes because that's more common in other languages but you will see both ways. And we can also store what are called Boolean values. Boolean just means a value that's either true or false.

We can use the word true or the word false and written this way, they do not need the quotes around them. JavaScript understands the word true and false written all lowercase. They are considered part of the language. So we can create a variable as undefined, then put a number in it, then put a string in it, then a Boolean. Now that doesn't mean JavaScript doesn't care about the type of data you have. It does. It treats numbers differently from strings and strings differently from Boolean values. But any JavaScript variable can hold any of these values and even more complex ones besides, like arrays and objects and functions, but we'll get into those later on.

Now you might think, well it sounds much easier to be a weakly-typed language where you can put anything anywhere. One issue with a weakly-typed language like this is there is no guarantee that the variable you think you have contains the right kind of data. Most of the time when you're programming, you won't need or want to change the type of data that a variable stores. If you have a variable that you've called high score, well you would expect it to have a number in it, not the word pomegranate or the value true. If you have a variable called firstName you don't want it to contain the value of 74.5. And there is nothing that would prevent that in JavaScript, but in other languages strong typing can have an advantage by providing internal rules that stop a lot of common errors from happening.

Now of course, the point of making any variable is that we are going to use them, we are going to manipulate them, to ask questions of them, but that all begins by knowing how to make them.

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This video is part of

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Foundations of Programming: Fundamentals

61 video lessons · 84610 viewers

Simon Allardice
Author

 
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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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