Intro to Ruby - Conditionals

Overview

The following is a brief example of conditional logic in the Ruby language. Most of this should be familiar to you from other languages but convenience syntax like “unless” (opposite of “if”) might be new to you. As a rule of thumb, try not to use an “unless” with an “else” expression even though it would be syntactically correct. This is generally frowned upon and one should use the “if”, “else” expressions instead (much easier to read). Go ahead, study and play with the code yourself.

Code

class MerDeNoms
  NAMES = ["Billy", "Charlie", "Merideth", "Dirk", "Sandra"]

  def print_names
    NAMES.each {|name| puts name}
  end

  def has_name? name
    puts NAMES.include?(name) ? "#{name} is found." : "#{name} is not found."
  end

  def print_speciality name
    puts "#{name} is not special." unless NAMES.include?(name)
  end

  def print_bio name
    date = ""
    if name == "Billy" then date = "1970"
    elsif name == "Charlie" then date = "1950"
    elsif name == "Merideth" then date = "1977"
    elsif name == "Dirk" then date = "1990"
    elsif name == "Sandra" then date = "2000"
    else date = "?"
    end
    puts "#{name} was born in #{date}."
  end

  def print_status name
    description = ""
    case name
    when "Billy" then description = "is sleeping."
    when "Sandra" then description = "is hungry."
    else description = "is day dreaming."
    end
    puts "#{name} #{description}"
  end
end

names = MerDeNoms.new

# An example of the ternary operator.
puts "01 Ternary\n\n"
names.has_name? "Fred"

# An example of the "unless" statement.  NOTE: You could also use the "if" statement in this manner as well.
puts "\n02 Unless\n\n"
names.print_speciality "Fred"

# An example of elsif logic.
puts "\n03 ElseIf \n\n"
names.print_bio "Dirk"

# An example of the case statement.
puts "\n04 Case \n\n"
names.print_status "Dirk"

Output

01 Ternary

Fred is not found.

02 Unless

Fred is not special.

03 ElseIf

Dirk was born in 1990.

04 Case

Dirk is day dreaming.

Download

The code above is provided as a Ruby script so that you can quickly execute all the examples above if you like. Just download, unzip, and type the following to execute all examples via the command line: ruby 11-conditionals.rb.

What’s Next

Loops

Tags: Ruby

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