# Programming Concepts 2

# 📚 Watch and Read

# Variables

Watch Code.org's programming variables part 1 and programming variables part 2 to recap the concepts of initializing (sometimes referred to as creating, allocating, or declaring) and data types.

Numeric variables shows why there are multiple types of numeric variables.

Strings are another common data type, almost always represented by using quotes, either 'single' or "double", depending on the programming language. An important point is that in most languages

x = 2 means x is an integer while y = "2" means y is a string

2 and "2" might look the same to humans, but to computers they are different.

Boolean variables are incredibly important to programming, allowing us to set things as true or false. Code.org offers a video introduction to boolean expressions.

Later, we'll explore constructs like if statments and loops that use Boolean variables to determine which statement a program should execute next.

# Number Systems

Binary or base 2, a computer's central processing unit (CPU) only understands 1 and 0, called binary. This is because at the lowest level, the CPU of a computer is working with electricity which is either on or off. This is also one reason why you commonly see electrical and computer engineering together at universities.

Converting decimal (base 10) to binary is a common part of most computer science programs. You aren't required to be an expert at number system conversions for this course, but you will see them throughout your programming journey.

Decimal to binary part 1 and decimal to binary part 2 videos are helpful resources for practicing conversions.

# Hexadecimal number system

Hexadecimal is another commonly used number system in computing because it converts to binary very well.

Converting decimal to hexadecimal shows how to convert numbers between the two systems and this series from BBC shows some of the ways hexadecimal is used in modern computing.

# Arrays and other Data Structures

Variables are incredibly useful, but if the only types of variables programmers had at their disposal were numbers, strings, and booleans, we would be limited in what we could accomplish.

If you worked on the Kindle development team at Amazon, you'd have to figure out how to store a book in your code and display it to a reader. You could store every page as a string variable, but that would be very tedious and you would have to know how many pages are in every book so each page could have its variable created -- yuck.

var page1 = 'In the beginning, there was a lot of words on page 1.'
var page2 = 'Then on page 2, some more stuff happened.'
var page3 = 'Finally, things concluded on page 3'
console.log(page1)
console.log(page2)
console.log(page3)

You may be able to see how a 300 page book would be painful with this model. Thankfully, we have more advanced types of variable at our disposal.

There are many data structures, for this class we're going to focus on Arrays, also known as Lists. Code.org has a great series of videos introducing arrays

• Introduction to Lists
• Accessing elements in a list
• Updating and adding elements in a list
• Getting the length of a list

How would you change in the Kindle example above using arrays?

One way is outline below. NOTE: the specific syntax will be different depending on the language.

Create an array and assign it to the variable book

var book = []

Add each page as a string of words to the array.

book.push('In the beginning, there was a lot of words on page 1.')
book.push('Then on page 2, some more stuff happened.')
book.push('Finally, things concluded on page 3')

That doesn't look too different from the example above. If we had a 300 page book, we would still need 300 .push statements to add them all to the book array. The powerful change comes when you try to print.

for (page in book){
    console.log(page)
}

We'll talk about loops in another module. Read the code above as "for each page in the array named book, print that page". This is an amazing savings, because it works for a 1, 100, or 1,000,000 page book. The for loop processes the array the same, without you having to know how many pages.

Complete lessons 21-45 in freeCodeCamp JavaScript course. Links to individual lessons and their corresponding youtube video are below.

1. Declare String Variables 💻 code📺 watch
2. Escaping Literal Quotes in Strings 💻 code📺 watch
3. Quoting Strings with Single Quotes 💻 code📺 watch
4. Escape Sequences in Strings 💻 code📺 watch
5. Concatenating Strings with Plus Operator 💻 code📺 watch
6. Concatenating Strings with the Plus Equals Operator 💻 code📺 watch
7. Constructing Strings with Variables 💻 code📺 watch
8. Appending Variables to Strings 💻 code📺 watch
9. Find the Length of a String 💻 code📺 watch
10. Use Bracket Notation to Find the First Character in a String 💻 code📺 watch
11. Understand String Immutability 💻 code📺 watch
12. Use Bracket Notation to Find the Nth Character in a String 💻 code📺 watch
13. Use Bracket Notation to Find the Last Character in a String 💻 code📺 watch
14. Use Bracket Notation to Find the Nth-to-Last Character in a String 💻 code📺 watch
15. Word Blanks 💻 code📺 watch
16. Store Multiple Values in one Variable using JavaScript Arrays 💻 code📺 watch
17. Nest one Array within Another Array 💻 code📺 watch
18. Access Array Data with Indexes 💻 code📺 watch
19. Modify Array Data With Indexes 💻 code📺 watch
20. Access Multi-Dimensional Arrays With Indexes 💻 code📺 watch
21. Manipulate Arrays With push() 💻 code📺 watch
22. Manipulate Arrays With pop() 💻 code📺 watch
23. Manipulate Arrays With shift() 💻 code📺 watch
24. Manipulate Arrays With unshift() 💻 code📺 watch
25. Shopping List 💻 code📺 watch