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Ruby Conditionals

Overview

Decision structures, also called decision trees, conditional statements, or if/else statements, are fundamental to computer programming. Conditional statements are a sequence of well-defined instructions that produce a unique output based on the value of the input. Conditionals follow a flowchart-like structure.

Learning Objectives

  • can define the syntax of a conditional statement in Ruby
  • can reproduce the syntax of string interpolation in Ruby

Vocabulary

  • if/elsif/else
  • unless
  • gets
  • chomp
  • #{}

Additional Resources

Process

  • cd into the ruby-challenges repository
  • Create a new branch: conditionals-initials1-initials2 (ex. conditionals-aw-sp)
  • touch a file with no spaces and .rb extension: conditionals-student1-student2.rb (ex. conditionals-austin-sarah.rb)
  • Open the folder in a text editor
  • Code!

If/Else/End

Conditionals in Ruby use the keywords if else and end. Simple evaluations in Ruby don't need to be wrapped in () and code blocks don't have {} so indentation is super important. Just like JavaScript the else block is a catch all and does not take an evaluation.

my_num = 10
if my_num == 10
  puts 'Your number is 10!'
else
  puts 'Your number is not 10.'
end

If/Elsif/Else/End

To add additional evaluations to an if/else code block, Ruby offers the keyword elsif. After the if statement you may use as many elsif statements as you want. Ending with an else will capture all the leftover possibilities.

my_num = 20
if my_num == 10
  puts 'Your number is 10!'
elsif my_num < 10
  puts "#{my_num} is less than 10."
elsif my_num > 10
  puts "#{my_num} is greater than 10."
else
  puts 'Something went wrong.'
end

Unless

Ruby also offers unless as a way to make conditional statements. Unless is just like if !(...). It is just like an if in reverse. It's a conditional statement that executes only if the condition is false instead of true.

my_num = 10
unless my_num > 20
  puts "#{my_num} is not greater than 20."
else
  puts "#{my_num} is greater than 20."
end

Input

Ruby has the unique ability to not only produce an outcome in the terminal but to take user input in the terminal. The command for user input in the terminal is an action called called gets. It is a bit like prompt() in JavaScript. And just like prompt() the input value from gets needs to be stored in a variable to access later.

> puts 'Enter your name'
=> "Enter your name"

> name = gets
# gets provides a blank line that accepts user input as a string
LEARN Student
=> "LEARN Student\n"

> puts "Hello, #{name}. How are you today?"
"Hello, LEARN Student
. How are you today?"

The string output from gets includes the return character you type to enter the user input. Ruby has a command called chomp that removes any additional line breaks and white space from the end of a string.

> puts 'Enter your name'
=> "Enter your name"

> name = gets.chomp
=> "LEARN Student"

> puts "Hello, #{name}. How are you today?"
=> "Hello, LEARN Student. How are you today?"

Challenge: Rock, Paper, Scissors

Story: As user 1, I can see a prompt in the terminal asking me to type either "rock", "paper", or "scissors".

Story: As user 2, I can see a prompt in the terminal asking me to type either "rock", "paper", or "scissors".

Story: As a user, I can see a message in the terminal saying if user 1 or user 2 won the round.

Story: As a user, I can see a message in the terminal saying if there was a tie.

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