Intro to Methods

Warmup

• What do you know about methods from your prework?
• How have you organized your code up to this point?
• What tools have you used if you wanted to perform actions multiple times?

Defining Methods without Parameters

# converter.rb
def print_welcome
  puts 'Welcome to Converter!'
end

print_welcome
print_welcome
print_welcome

Try it!

Create a method print_welcome in a new file doubler.rb that prints the message Welcome to Doubler!

Defining Methods with Parameters

• Input: temperature in Fahrenheit
• Output: temperature in Celsius

# converter.rb
# ... print_welcome

def convert_to_celsius(temperature)
  ((temperature) - 32) * 5.0 / 9.0).round(2)
end

print_welcome
convert_to_celsius(32)

Return Values

• What a method returns
• What a variable would capture if set equal to the results of this method
• Separate from what a method does
• In Ruby, methods return the last line

Printing Values that are Returned

# converter.rb
# ... print_welcome

def convert_to_celsius(temperature)
  ((temperature) - 32) * 5.0 / 9.0).round(2)
end

print_welcome
convert_to_celsius(32)

Try It!

• Define a method doubler that takes a single argument and doubles it.
• Call that method three times and save the returns to variables.
• Print those values held in those variables to the screen.

Calling Methods from Other Methods

# converter.rb
# ... print_welcome, convert_to_celsius

def print_converted(temperature)
  converted = convert_to_celsius(temperature)
  puts "#{temperature} degrees Farenheit is equal to #{converted} degrees Celsius."
end

print_converted(32)
print_converted(35)

Try it!

• Add a method print_double which accepts an argument and prints a phrase in the form 3 doubled is 6.
• If you have time, see if you can determine what print_double returns. Why might that be?

Layers of Abstraction

# converter.rb

def convert(first, second, third)
  print_welcome
  print_converted(first)
  print_converted(second)
  print_converted(third)
end

# print_welcome, convert_to_celsius, etc.

convert(32, 35, 100)
convert(12, 45, 65)

Try It!

• Create a high level method for your doubler.rb file that wraps these other methods into one.

Basic Classes

class NameOfClass
  # stuff
end

Converter Class

# converter.rb

class Converter
  # convert, print_welcome, convert_to_celsius, print_converted
end

converter = Converter.new
converter.convert(32, 35, 100)
converter.convert(12, 45, 65)

Things to Notice

• We create a new instance of a class
• We call our methods on that instance

Try It!

• Wrap your existing methods from double.rb in a Doubler class
• Adjust your code so that the output when you run ruby doubler.rb is the same as it was before you created the class

Summary

• How do we define methods in Ruby?
• What is the difference in how we define a method that takes arguments from one that does not.
• Why do we use methods?
• How do we define a simple class in Ruby?