Alpha Ruby Review

Important Classes and Methods

class: String

Use strings to represent text or other non-numeric data within your program.

• Creating a string using a string literal (note you can use either single quotes or double quotes to create a string):

# Create a string using double quotes
name = "Gizmo"
# => "Gizmo"

# Create a string using single quotes
type = 'Mogwai'
# => "Mogwai"

• Joining two strings together with the + operator:

location = "China" + "Town"
# => "ChinaTown"

• Inserting variables into a string with string interpolation (note that string interpolation only works with double quotes):

name = "Gizmo"

# Interpolation works when using double quotes
greeting = "Hello, #{name}!"
# => "Hello, Gizmo!"

# But it doesn't do anything for strings in single quotes
farewell = 'Goodbye, #{name}!'
# => "Goodbye, #{name}!"

Also note that escape characters (e.g. \n) only work in double quotes as well:

sentence_with_newline = "This will have a newline at the end\n"
# => "This will have a newline at the end\n"

sentence_without_newline = 'But escape characters wont work in single quotes\n'
# => "But escape characters wont work in single quotes\\n"

• Get the length of a string with the length method:

name = "Gizmo"
name.length
# => 5

Useful String methods

• to_i: attempts to convert the string to an integer. Use this when reading user input from the command line or reading numbers from a file. Note that this will only work well if the string contains nothing but digits (e.g. "123"). If the string is non-numeric (e.g. "foo") then the to_i method will return 0 instead:

age_string = "28"
age = age_string.to_i
# => 28

# This will not work because the string doesn't contain digits...
max_number_string = "foooooooooooooooooooooo"
max_number = max_number_string.to_i
# => 0

• to_f: attempts to convert a string to a float (a number with decimals). Use case is similar to to_i. This will also convert non-numeric strings to 0.0:

"10.0".to_f
# => 10.0

"totally not a float".to_f
# => 0.0

• downcase: use this method to change the case of all uppercase letters in a string to downcase. This is useful when receiving user input and you want to match a string without worrying about case sensitivity:

location = "Boston"
location.downcase
# => "boston"

if location.downcase == "boston"
  # This will work for "Boston", "BOSTON, "boston", etc...
end

• chomp: removes a trailing newline character if there is one. This is useful when reading in user input since the user has to hit Enter to submit which also adds the newline character:

user_input = gets
# => "user types in something here\n"

# Using .chomp will ensure that the newline character is removed
user_input = gets.chomp
# => "user types in something here"

• gsub: (global substitution) replaces all occurrences of one string or pattern with another string. You typically use this if you want to clean up a string by removing all characters of a certain type or substituting them with another value (e.g. replacing all non-alphanumeric characters with an empty string will remove them). This method accepts either strings or regular expressions (regexs) as input:

input = "A string with letters, whitespace, and punctuation!"

# Let's remove the punctuation and keep the letters and whitespace
cleaned_input = input.gsub(/[^a-zA-Z\s]/, '')
# => "A string with letters whitespace and punctuation"