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Working with complex conditions

From: Foundations of Programming: Fundamentals

Video: Working with complex conditions

So I am going to create a condition and then add a little more thought to it. In this JavaScript file, I am starting off by creating a variable called balance, setting it equal to 5000, just to give us something to work with. Then I'm going to write my if statement. The condition, I am going to write here will be if balance is greater than 0, Yes, we know it is, but we are just writing some sample code. Then I need my code block. Now, it's very common that you'll see programmers when they hit the opening curly brace to also then jump a couple of lines, and do the closing curly brace.

Working with complex conditions

So I am going to create a condition and then add a little more thought to it. In this JavaScript file, I am starting off by creating a variable called balance, setting it equal to 5000, just to give us something to work with. Then I'm going to write my if statement. The condition, I am going to write here will be if balance is greater than 0, Yes, we know it is, but we are just writing some sample code. Then I need my code block. Now, it's very common that you'll see programmers when they hit the opening curly brace to also then jump a couple of lines, and do the closing curly brace.

And this just verifies that I have both of them in place and I'll just come back up and start typing the code that's indented inside my code block. So we are just trying to prove a point here. So I'll do something like alert, the balance is positive, and we have a very straightforward condition. But the question is well, what if it's not? What if that was false? I could do another if statement and check balance again, but what I could also do instead is if that's not the case, I am going to add the word else.

Then I'm going to do the opening curly brace for the code block again because I wrote that, do the closing one, and what we have going on is if the condition is true, we'll do whatever is in the first code block. Otherwise or else, we'll do whatever is in the second code block. So I'm going to write a line of code here, closing that with a semicolon. Now, I have introduced a very common error here and it's an error in my thinking, not in the code.

We ask if balance is greater than 0, we're going to output a message saying the balance is positive. Otherwise, we'll output a message saying the balance is negative. Well, what happens if it's 0? In this case, we're going to hit the if statement. If balance is greater than 0, well that would be false. So if our balance is 0, it will give us the balance is negative message. really not what we want, but it's quite a common error to get hit with, particularly when you're dealing with things like positive and negative numbers. So be a bit too exclusive about what you're checking against.

Thinking a bit deeper about it, what I want to ask here is if the balance is greater than or equal to 0. And of course what we are asking there is as far as our program is concerned, what do we care about? Let's say we are dealing with bank balances, where 0 would not count as a negative balance. Now, there is an operator for that. It's just the greater than or equals sign. This is regarded as a single operator. So it's just the two characters next to each other. What we can also do is take this a little bit further.

Inside this first code block that will be executed if the balance is greater than or equal to 0, I could add another if statement. If balance is greater than 10,000, do my opening curly brace for the code block, couple of lines, and then do the closing one. And notice that what I am doing here is trying to make this apparent. I am lining up my closing curly brace with its corresponding if statement, the same way that I would line up the first closing curly brace with its corresponding if statement, and then I would indent any code inside of that.

If I were to save this and then jump over to my container HTML page that will run it, we should get The balance is positive. Click OK. But we do not get this internal if statement because balance is not greater than 10,000. That would be false. So you can create multiple levels of complex conditions inside your code. Now, do be aware, don't nest too deep. JavaScript can handle a thousand levels of If statements if you started to type them, but lots of nested Ifs, say beyond three levels, can get very difficult to read and make sense of just for a human being.

If we do have to have more complex logic, there are other techniques we can use to deal with it, such as working with functions which we're going to get to soon.

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This video is part of

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Foundations of Programming: Fundamentals

61 video lessons · 85367 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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