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Lua Quick Start Guide
Lua Quick Start Guide

Lua Quick Start Guide

The easiest way to learn Lua programming

$32.99
By Gabor Szauer
Full star icon Full star icon Full star icon Half star icon Empty star icon
3.6 (7 Ratings)
Pages 202
Published in Jul 2018
Product Type Paperback
Edition 1st Edition
ISBN 9781789343229
Lua Quick Start Guide

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Lua Quick Start Guide

Chapter 2. Working with Lua

In Chapter 1, Introduction to Lua, you learned how to set up Lua and Visual Studio Code. At the end of the chapter, we created a simple Hello World application. In this chapter, you will learn the basics of Lua programming. Topics such as variables, function data types, and loops are all going to be covered. By the end of this chapter, you should be familiar enough with Lua as a language to put together some simple programs.

Note

If this is your first time programming, the syntax of Lua can get overwhelming fast. Many resources can be found on the official Lua site at https://www.lua.org/. For a quick example of Lua, check out http://tylerneylon.com/a/learn-lua/.

By the end of this chapter, you will will have a solid understanding of the following:

  • Using variables
  • Data types
  • Working with functions
  • Operators
  • Code blocks
  • Variable scope
  • Code flow

Technical requirements


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


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.

Creating variables

To create a variable, you need to do two things:

  • Declare the variable
  • Assign a value (data) to the variable

As an example, let's make a variable, foo, and assign it the value bar. The code to do this would be:

foo = "bar"

That single line of code declares a variable and assigns a string value to the variable. If you break it into several...

Comments


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.

Basic types


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 can be executed any time.
  • table: A table contains information using key-value pairs. Tables will be covered in depth in Chapter 3...

String types


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.

String literals

A string literal must be written between quotes. The following line of code demonstrates a string literal. This example does not do anything since the literal is a value that is never assigned to a variable:

"hello, world"

Without being assigned to a variable, this string can't be printed. String literals don't have to be assigned to a variable to be useful; they can be passed directly to a function such as print. The following...

Scope


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 any variables declared in its parent chunk, but none of the variables available in any child chunks. To demonstrate...

Functions


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.

Note

Read more about functions online at https://www.lua.org/pil/5.html.

Defining a function

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

After the name of your function, you have to provide a list of parameters. Parameters are variable names enclosed in parentheses (). The list of parameters may be empty if a function needs no parameters, in which case only opening and closing parentheses are given—...

Operators


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 (-) is the unary negation operator. It returns the negative value of a number:

x = -7 -- negation operator applied to the constant...

Control structures


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:

if

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:

print ("Enter your name")
name = io.read()

if #name <= 3 then
    print ("that's a short name, " .. name)
end

elseif

You might want to make a more complicated decision than a simple if statement allows. For example, you may want to do one thing if the length of a...

Loops


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.

while loops

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

Infinite loops

One of the dangers of loops is an infinite loop. You get into an infinite loop when the condition of the loop never evaluates to false. Because the condition keeps being true, the loop goes on forever. The following code snippet demonstrates a simple infinite loop:

while true do
    print ("forever")
end

A more real-life example of an infinite loop would look like...

Summary


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 3Tables 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.

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Key Benefits

The easiest way to learn Lua coding
Use the Lua standard libraries and debug Lua code
Embed Lua as a scripting language using the Lua C API

What You Will Learn

Who Is This Book For?

This book is for developers who want to get up and running with Lua. This book is ideal for programmers who want to learn to embed Lua in their own applications, as well as for beginner programmers who have never coded before.

Book Description

Lua is a small, powerful and extendable scripting/programming language that can be used for learning to program, and writing games and applications, or as an embedded scripting language. There are many popular commercial projects that allow you to modify or extend them through Lua scripting, and this book will get you ready for that. This book is the easiest way to learn Lua. It introduces you to the basics of Lua and helps you to understand the problems it solves. You will work with the basic language features, the libraries Lua provides, and powerful topics such as object-oriented programming. Every aspect of programming in Lua, variables, data types, functions, tables, arrays and objects, is covered in sufficient detail for you to get started. You will also find out about Lua's module system and how to interface with the operating system. After reading this book, you will be ready to use Lua as a programming language to write code that can interface with the operating system, automate tasks, make playable games, and much more. This book is a solid starting point for those who want to learn Lua in order to move onto other technologies such as Love2D or Roblox. A quick start guide is a focused, shorter title that provides a faster paced introduction to a technology. It is designed for people who don't need all the details at this point in their learning curve. This presentation has been streamlined to concentrate on the things you really need to know.
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Table of Contents

(8 Chapters)
Introduction to Lua Chevron down icon Chevron up icon
Working with Lua Chevron down icon Chevron up icon
Tables and Objects Chevron down icon Chevron up icon
Lua Libraries Chevron down icon Chevron up icon
Debugging Lua Chevron down icon Chevron up icon
Embedding Lua Chevron down icon Chevron up icon
Lua Bridge Chevron down icon Chevron up icon
Next Steps Chevron down icon Chevron up icon

Customer reviews

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3.6
(7 Ratings)
5 star 42.9%
4 star 14.3%
3 star 14.3%
2 star 14.3%
1 star 14.3%
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Shannon Nov 03, 2019
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5
It covers the basic run through of the Lua code and that is just what I needed.
Amazon Verified review Amazon
Edward Beck Dec 12, 2021
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5
Nice book easy to follow.
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Rufinity Feb 25, 2021
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5
Still learning. Very informational
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William Aug 04, 2022
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4
The author does a reasonable job of showcasing the language to help someone get started in LUA quickly. I am using it to help teach a beginner how to program. The languag and style is down to earth and should be accessible to most people. NOTE- This book does not teach the art of programming, it is literally just a quick-start for LUA. If you want a book that teaches the art of programming using LUA you should look elsewhere.
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Objective Living Feb 07, 2020
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3
This book is a pithy, bull in a china shop approach to teaching Lua. If you have a small project and just need the basics then this book will probably serve you well enough. If you really want to dig in, skip it entirely. 'Programming in Lua' by Roberto lerusalimschy (one of Lua's authors) is a much more thorough and well written guide to the language.A couple examples of things that frustrated me about this book are making statements like "scopes are limited to their chunks" and then showing examples where you declare variables as local. In actuality, most variables are global by default and thus have global scope unless you explicitly declare it as local. If you are coming from most other languages, you understand scope to be local by default and stating that scopes are limited to their chunks is, in my opinion, misleading or at least not well explained. I also found that he would frequently introduce something and then just not bother to explain it. For example, 'w = 7 and 1 -- value is 1'. Why? Why isn't it "false" instead of a number. In some ways Lua seems to go out of its way to not follow conventions held in common by many other languages. More explanation of the what and why would be really helpful.The book is less than 200 pages and is uses decently large font and lots of white space which makes everything very readable but does so by sacrificing detail. So, as I said, it's probably a decent intro for a small personal or school project but if you really want to dig in, I'd put that $30 into something more substantial. ~$18 seems like a decent price point for this book. I felt $30 is much too high for what it is.
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