Computer Science Programming Basics in Ruby

3.3 What Is a Variable?

A variable is a piece of data attached to a name. In algebra, a variable like x in the equation x = y + 2 indicates that x and y can take on many different values. In most programming languages, variables are defined just as in algebra and can be assigned different values at different times. In a computer, they refer to a location in memory. Although this is a simple concept, variables are the heart of almost every program you write. The Pythagorean theorem is shown in Figure 3-1, and it uses three variables: A, B, and C.

Figure 3-1. Pythagorean theorem

A, B, and C are the variable names, and they each represent a number. To create a variable in Ruby, simply use the format variable_name = value, where variable_name is the name of your variable and value is the value you would like it to have. The equal sign (=) behaves differently in Ruby from the way it does in algebra. In Ruby, = means “assign the RHS (righthand side) to the variables in the (LHS) lefthand side.” The code snippet y = x + 2 means compute the value of x + 2 and store the result into the variable y. In algebra, y = x + 2 simply explains a relationship between variables x and y.

An easy way to test things in Ruby is with irb (once Ruby is properly installed), the Interactive Ruby Shell. Enter irb from a command prompt; you can see that it is very easy to create variables. The following example ...