#### Overview of this book

Ruby is a powerful, general-purpose programming language that can be applied to any task. Whether you are an experienced developer who wants to learn a new language or you are new to programming, this book is your comprehensive Ruby coding guide. Starting with the foundational principles, such as syntax, and scaling up to advanced topics such as big data analysis, this book will give you all of the tools you need to be a professional Ruby developer. A few of the key topics are: object-oriented programming, built-in Ruby methods, core programming skills, and an introduction to the Ruby on Rails and Sinatra web frameworks. You will also build 10 practical Ruby programs. Created by an experienced Ruby developer, this book has been written to ensure it focuses on the skills you will need to be a professional Ruby developer. After you have read this book, you will be ready to start building real-world Ruby projects.
Preface
Free Chapter
Introduction to the Ruby Programming Language
Ruby Variables
Ruby Strings
Working with Numbers in Ruby
Ruby Iterators and Loops
Ruby Collections
Ruby Conditionals
Working with the Filesystem in Ruby
Error Handling in Ruby
Regular Expressions in Ruby
Searching with grep in Ruby
Ruby Gems
Ruby Web Frameworks
Working with APIs in Ruby
Machine Learning

# Implementing a prime number counting algorithm

In this section, we are going to create an algorithm that will find all the prime numbers between zero to 2 million. Sound exciting? In traditional programming languages, this algorithm would need hundreds of lines of code, but in Ruby, we're going to see how to implement this efficiently.

To start, let's get access to the prime library, and to do this, use this code:

`require 'prime' `

Next, store the prime numbers in an array with this code:

`prime_array = Prime.take_while{ |p| p <2_000_000 } `

In this code, we created a variable called prime_array. In this variable, we store all the prime numbers up to 2 million.

Ruby ignores underscores with integers, which is how we were able to represent the integer of 2 million with this syntax: 2_000_000. This is helpful when it comes to writing large numbers since we can...