You will be required to have JavaScript programming language. Finally, to use the Git repository of this book, the user needs to install Git.

The code files of this chapter can be found on GitHub:
https://github.com/PacktPublishing/Lua-Quick-Start-Guide/tree/master/Chapter02

Check out the following video to see the code in action:
http://bit.ly/2LDVPd0

Variables are labels that provide a descriptive name for some data that a program can read or modify. You can literally think of a variable as a label.

For example, let's assume there are a number of jars containing different colored jam. How do you know what flavor a specific jar contains? Hopefully, there is a label on the jar that is descriptive of its content.

The labels on the jar can change over time. For example, a jar might contain strawberry jam, but after that's gone it might be filled with peach jam. When the contents of the jar changes, a different label can be used to describe what's in it. Variables work in a similar fashion.

To create a variable, you need to do two...

In Lua, any time you see --, the rest of that line is considered a comment. Comments are there to help you read and understand code, but they are never executed. This example demonstrates how comments are used:

foo = "bar"
-- print (foo)
-- The above statement never prints
-- because it is commented out.

In the last section, you were introduced to the concepts of a variable and a value. This section explores the concept of what a value is. Every value has a data type, which intuitively describes what kind of data the value holds. Lua supports eight basic value types:

• nil: The absence of data. This type represents literal nothingness. If a certain piece of data is invalid or unknown, nil is usually the best way to represent that it is invalid or unknown.
• Boolean: A value of true or false. A Boolean value is binary and can only ever be in one of two states, true or false.
• number: A number can represent any real number: 0, -1, 5, or even decimals such as 3.14159265359.
• string: A string is an array of characters. When declaring a string literal, it must be "enclosed within quotation marks."
• function: A function is some code that is referred to by a name and...

A string is an array of characters. Strings can represent words, sentences, or even whole books. In this section, we will cover how to perform the following string operations:

• How to get the length of a string
• How to concatenate two strings into a single new string
• The coercion of other types into strings
• String escape characters

Additionally, this section will cover how to read input from the console. You already know how to print information to the console; applications will become much more interactive once you can also read input from the console.

A string literal must be written between quotes. The following line of code demonstrates a string literal. This example does not do anything since...

Like many other programming languages, Lua implements the concept of scope for anything that can be named (like a variable). A scope defines where in the program a variable can be used. Scopes are limited to the chunks they appear in. A chunk is just a section of code. Some languages call chunks blocks because they are represented by blocks of code.

Every Lua file that is executed is a chunk. This chunk can contain other, smaller chunks. Think of it as a hierarchical relationship. Such a relationship could be visualized as follows:

You can create a local chunk in a file by using the do keyword. The chunk ends with the end keyword. The following bit of code demonstrates how to create a local chunk in a file:

-- main file chunk is anywhere in the file

do
  -- local chunk
end

do
  -- a different local chunk
end

As mentioned earlier, scope refers to visibility. A chunk can access...

A function is essentially a named chunk of code. Unlike other chunks, the contents of a function are not automatically executed when the file is loaded. When a file is first loaded, functions are simply defined. Once a function has been defined, you can execute the function by calling it. Because a function is a named chunk, you can call a function as many times as you want. The same scope rules apply to functions as to do/end blocks.

A function declaration starts with the function keyword. After the function keyword, you provide the function name. The name of the function follows the same naming rules as the name of a variable...

Operators such as addition +, string concatenation .., and even the assignment operator = have been used throughout this book. Let's take some time to cover in detail what operators are and how they work. Operators fall into one of the following categories:

• Arithmetic operators do math.
• Relational operators always return a Boolean value: true or false. Relational operators are used to compare the relationship between two things, for example, by checking whether one number is smaller than another number.
• Logical operators express complex relations such as and/or. For example, logical operations can be used to check whether a number is less than seven AND greater than two.
• Misc operators: All other operators, such as assignment, fall into this category.

Operators can be unary or binary. A unary operation works on only one operand. For example, the minus sign (...

Control structures are used to make decisions in code; they control the path of code based on a Boolean value. Lua provides the if statement for this purpose. An if statement is followed by a Boolean condition, which in turn is followed by a then/end chunk. The chunk is only executed when the Boolean condition evaluates to true.

The most basic syntax of an if statement is as follows:

A logical control structure always starts with an if statement. As described previously, an if statement consists of the if keyword, a Boolean expression, and a then/end chunk. The then/end chunk is only executed when the Boolean condition evaluates to true. The following code sample demonstrates the basic use of an if statement...

A chunk of code can be repeated multiple times by using a loop. Lua provides three types of loop, the while, repeat, and for loops. Each loop type will be covered in depth, but the rest of the book will mainly use the for loop.

Syntactically, a while loop starts with the while keyword, followed by a Boolean condition and a do/end chunk. The loop will keep executing the chunk of code so long as the Boolean condition evaluates to true:

x = 10 -- Initialize a "control" variable

while x > 0 do -- Boolean condition: x > 0
    print ("hello, world")

    x = x - 1 -- Decrement the "control" variable
end

This chapter covered a lot of topics, such as variables, data types, functions, operators, code blocks, scope, and code flow. All of these concepts are the basic building blocks of Lua. These concepts are very important to programming, so you may need to come back to this chapter.

In Chapter 3, Tables and Objects, we will cover tables and objects. An alternate syntax of the for loop will be covered that can be used to easily iterate over tables or arrays.