Strings in Ruby

Use double or single quotes to define strings.

single quotes: wont be able to perform string interpolation.

first_name = 'Curtis '
last_name = 'W'

puts first_name + last_name
# => Curtis W

String interpolation

#{} is used to interpolate a string.
only works when you use double quotes " ".

puts "Hello #{first_name}#{last_name}"
# => Hello Curtis W

puts 'Hello #{first_name}#{last_name}'
# => Hello #{first_name}#{last_name} NOT what we wanted.

String methods

How do you determine if something is a string? We use the .class method.

puts 'Hello'.class
# => String

first_name = 'Curtis '
last_name = 'W'

full_name = "#{first_name} #{last_name}"
puts full_name.length
# => 9

p full_name.empty?
# => false

How do you replace a word in a string?

use the .gsub method.

sentence = "Welcome to the jungle"

puts sentence.gsub('jungle', 'forest')
# => Welcome to the forest

Useful string methods

.upcase: converts a string to uppercase.
.chars: returns an array of characters.

p 'Hello'.chars
# => ["H", "e", "l", "l", "o"]

.reverse: reverses a string.
.length or .size: returns the length of a string.
.count: returns the number of times a character appears in a string.

p 'Hello'.count('l')
# => 2

.include?: returns true if a string includes a character.

"hEllo wOrlD".include?("w")
# => true
"hEllo wOrlD".include?("1")
# => false

.split: splits a string into an array of substrings.

p "1,2,3,4,5".split(',')
# => ["1", "2", "3", "4", "5"]

Variable Assignment

= is used to assign a value to a variable.

Take a look at the following example:

name = "Curtis"
new_name = name
name = "Oh no! CHANGED!"

puts new_name # => "Curtis"
puts name # => "Oh no! CHANGED!"

The variable new_name is assigned the value of name. It passes this value in memory. Therefore, when we reassign name, it will NOT change the value of new_name.

Escaping characters

\ is used to escape characters.

puts 'Curtis said 'Hello, world!'' # => will throw an error. We have quotes inside quotes. We need to escape them.

puts 'Curtis said \'Hello, world!\'' # => Curtis said 'Hello, world!'

\n is used to create a new line.
\t is used to represent a tab.
\b is used to represent a backspace.
\s is used to represent a space.

Getting input from users

How do we get input from users? We primarily use the gets or gets.chomp methods.

gets.chomp: gets input from the user. Returns a string.

puts "What is your fist name?"
name = gets.chomp
puts "Hello #{name}, nice to meet you!"

# => What is your fist name?
# => Curtis
# => Hello Curtis, nice to meet you!

Another example:

puts "Enter a number to multiply by 2"
number = gets.chomp.to_i # converts the input to an integer.
puts "Your number multiplied by 2 is #{number * 2}"
# => Your number multiplied by 2 is 10

#######
puts "What is your first name?"
first = gets.chomp

puts "what is your last name?"
last = gets.chomp

def full_name_length(first, last)
  puts "name is #{first.length + last.length} characters long"
end

full_name_length(first, last)
# => name is 8 characters long

Numbers in Ruby

Can enter a repl by typing irb in the terminal.

> 1 + 1
=> 2

> 10 / 4
=> 2

# However, we are missing the decimal. To fix this, we can use the `.to_f` method.
> 10.to_f / 4
=> 2.5

# Or could add the decimal to the number.
> 10.0 / 4
=> 2.5

.to_f is a method that converts a number to a float.

Doing the same thing with variables:

x = 5
y = 10
puts y / x
=> 2

Can have a string multiplied by a number:

puts "I am a line"
puts "-" * 10
puts "I am below the line"

=>
# I am a line
# ----------
# I am below the line

Creates a line of dashes.

Can do something very similar with the .times method.

5.times { puts "hi" }

# =>  hi
#     hi
#     hi
#     hi
#     hi

3.times { puts rand(10)} # Random number between 0 and 9.
#  => 3
#     5
#     7

Convert string to integer

If the string can be converted to a number, we can use the .to_i method.

puts "5".to_i
=> 5

If you convert a string that cannot be converted to a number, it will return 0.

Example calculation:

puts "Simple calculator"
25.times { print "-" }
puts
puts "Enter the first number"
num1 = gets.chomp.to_i
puts "Enter the second number"
num2 = gets.chomp.to_i
puts "The first number multiplied by the second number is #{num1 * num2}"

=>
# Simple calculator
# -------------------------
# Enter the first number
# 5
# Enter the second number
# 10
# The first number multiplied by the second number is 50

Can use any operator:

puts "Simple calculator"
25.times { print "-" }
puts ""
puts "Enter the first number"
num1 = gets.chomp.to_i
puts "Enter the operator"
op = gets.chomp # + - * /
puts "Enter the second number"
num2 = gets.chomp.to_i
operation = "#{num1} #{op} #{num2}"
puts eval(operation).to_s

Operators in Ruby

Good article on operators in Ruby: here

Operator	Description	Example
`==`	Checks if two values are equal.
`!=`	Checks if two values are not equal.	`a != b`
`>`	Checks if one value is greater than another.	`a > b`
`<`	Checks if one value is less than another.	`a < b`
`<=>`	Combined comparison operator. Returns `0` if equal, `1` if greater, `-1` if less.	`a <=> b`
`.eql?()`	Checks if two values are equal.	`10.eql?(10.0) => false`