The Well-Grounded Rubyist, Second Edition

6.1. Conditional code execution

Allow a user access to a site if the password is correct. Print an error message unless the requested item exists. Concede defeat if the king is checkmated. The list of uses for controlling the flow of a program conditionally—executing specific lines or segments of code only if certain conditions are met—is endless. Without getting too philosophical, we might even say that decision making based on unpredictable but discernible conditions is as common in programming as it is in life.

Ruby gives you a number of ways to control program flow on a conditional basis. The most important ones fall into two categories:

• if and related keywords
• Case statements

We’ll look at both in this section.

6.1.1. The if keyword and ...