Introduction to Variables

##Objectives

1. Define a variable.
2. Create and reassign variables.
3. Define pass-by-value as it relates to variables

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Variables in Ruby

Much like in math, variables are words or characters that hold values. In algebra, however, variables are only placeholders for numbers. In Ruby, a variable can point to almost any type of value including numbers, strings, arrays, and hashes.

Creating Variables

Variables are assigned values using = ("equal sign"), called the assignment operator. Variable names are typically all lower case and, in the case of multiple words, the words are separated by underscores.

current_president = "Barack Obama"
puts "In 2014, the president was #{current_president}."

The code above will print In 2014, the president was Barack Obama..

Note: The syntax of #{current_president} simply injects the value of the variable current_president into the string. This is called Interpolation and we'll cover it later - but think of it as "In 2014, the president was" + current_president where you are adding that value to a string.

Reassigning Variables

Now the variable current_president is equal to the string Barack Obama. Let's say somehow Stephen Colbert got elected as president for 2016. To update current_president, you would just reassign the variable much in the same way that you first defined it:

current_president = "Barack Obama"
puts "In 2014, the president was #{current_president}."

current_president = "Stephen Colbert"
puts "Now, it being the year 2016, the president is #{current_president}."

This will print out:

In 2014, the president was Barack Obama.
Now, it being the year 2016, the president is Stephen Colbert.

Variable Example

Within this repository is a file named variables.rb with some examples you can read and play with.

'This is data, it is a string. Strings start with " "'

"Part of being data, or a string, is that ruby doesn't interpret it."

puts 1+1
puts "1+1"

example = "The word 'example' is equal to this sentence, it's a named variable."

puts example
puts example
puts example

puts "variables are any previously undefined word that"
puts "starts with a lowercase letter."

Running this file will print:

2
1+1
The word 'example' is equal to this sentence, it's a named variable.
The word 'example' is equal to this sentence, it's a named variable.
The word 'example' is equal to this sentence, it's a named variable.
variables are any previously undefined word that
starts with a lowercase letter.

Resources

• ZetCode Ruby Variables
• Wikibooks: Ruby Programming/Syntax/Variables and Constants
• RubyMonk on Interpolation of Variables in Strings