Interactive Ruby¶

We begin our exploration of Ruby with the interactive Ruby shell (irb). Open up a terminal and type:

shell> irb --simple-prompt
>>

Make sure that you can get irb working before you move on.

Ruby as a calculator¶

At the simplest level, you can use ruby as a calculator. Try this:

shell> irb --simple-prompt
>> 1 + 2
=> 3
>> 4 - 3
=> 1

Ruby understands all the basic arithmetic operators that you would expect:

To get out of irb type exit:

shell> irb --simple-prompt
>> 1 + 2
=> 3
>> exit
shell>

You should play around with these for a bit. Try this:

>> 3 * 2
=> 6
>> 4 / 2
=> 2
>> 3 - 5
=> -2
>> 3 / 2
=> 1

Notice what happens when you try to divide 3 by 2: the result is 1.

What happened? It turns out that Ruby understands two different classes of numbers:

Integers

An integer is a whole number, like 1, 2, -5, etc. When you operate using only integers, Ruby will give you an Integer answer.

3/2 is 1.5, but that is not an integer, so Ruby gives you 1 instead.

Floats

A float is a number with decimal places, like 3.14, 1.5, 3.0, etc. When you operate with Floats Ruby gives you a Float answer. For example:

shell> irb --simple-prompt
>> 3.0 / 2.0
=> 1.5

More operators

Before we wrap up this chapter, let’s look at two more operators:

Notice how the remainder operator ‘%’ behaves with decimals. In this example, 2 goes twice into 5.1 and there is 1.1 left over.