An algorithm is a recipe for solving a problem. This section discusses broad problems in computer science and how to solve them, all in the context of PHP. These problems are inherent in any programming endeavor, but in most cases PHP makes handling them easier. However, the particular circumstances of the Web offer the seasoned programmer a new set of challenges. This section brings these issues to your attention.
Chapter 21 examines sorting and searching, along with a related topic, random numbers. Although PHP has built-in functions for sorting data, this chapter explores the theory behind sorting. This gives you the knowledge to code custom sorting functions when the need arises.
Chapter 22 discusses parsing and string evaluation. Much of this chapter is about regular expressions, a powerful way to describe patterns that are compared to strings. These are useful for validating user input.
Chapter 23 describes integrating PHP with a database. MySQL is used in the examples because it's Open Source. Databases allow you to manipulate data in powerful ways and are necessary for many Web applications.
Chapter 24 is about network issues, such as sending HTTP headers. Because PHP scripts execute as Web pages, network issues appear frequently.
Chapter 25 explores generating graphics with PHP. It develops examples that create buttons and graphs dynamically.
