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# Simple print statement
puts "Hello, World!"

# Method definition
def greet(name)
  "Hello, #{name}!"
end

puts greet("Ruby Developer")

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# Single-line comment

=begin
Multiline comment
Can span multiple lines
=end

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# Integer
age = 30
big_number = 1_000_000  # Underscores for readability

# Float
pi = 3.14159

# String
name = "Ruby"
interpolated = "Hello, #{name}!"

# Boolean
is_true = true
is_false = false

# Nil
nothing = nil

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# Array
fruits = ["apple", "banana", "cherry"]
mixed_array = [1, "two", :three]

# Hash (Dictionary)
person = {
  name: "Alice",
  age: 30,
  city: "New York"
}

# Symbol
status = :active

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# Local variable
local_var = 42

# Instance variable
@instance_var = "I belong to an instance"

# Class variable
@@class_var = "Shared across all instances"

# Global variable
$global_var = "Accessible everywhere"

# Constant
DAYS_IN_WEEK = 7
PI = 3.14159

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a = 10
b = 3

puts a + b   # Addition: 13
puts a - b   # Subtraction: 7
puts a * b   # Multiplication: 30
puts a / b   # Division: 3
puts a % b   # Modulo: 1
puts a ** 2  # Exponentiation: 100

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a = 5
b = 10

puts a == b  # Equal to: false
puts a != b  # Not equal to: true
puts a < b   # Less than: true
puts a > b   # Greater than: false
puts a <= b  # Less than or equal to: true
puts a >= b  # Greater than or equal to: false

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true_value = true
false_value = false

puts true_value && false_value  # Logical AND: false
puts true_value || false_value  # Logical OR: true
puts !true_value                # Logical NOT: false

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# If-else
x = 10
if x > 5
  puts "x is greater than 5"
elsif x == 5
  puts "x is equal to 5"
else
  puts "x is less than 5"
end

# Ternary operator
result = x > 5 ? "Greater" : "Less or Equal"

# Case statement
grade = 'B'
case grade
when 'A'
  puts "Excellent!"
when 'B'
  puts "Good job!"
when 'C'
  puts "Satisfactory"
else
  puts "Needs improvement"
end

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# While loop
count = 0
while count < 5
  puts count
  count += 1
end

# For loop
(1..5).each do |num|
  puts num
end

# Times loop
5.times do |i|
  puts "Iteration #{i}"
end

# Loop control
10.times do |i|
  break if i > 5
  next if i.even?
  puts i
end

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# Method definition
def greet(name = "World")
  "Hello, #{name}!"
end

puts greet         # "Hello, World!"
puts greet("Ruby") # "Hello, Ruby!"

# Multiple return values
def multiple_values
  [1, 2, 3]
end

a, b, c = multiple_values

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# Lambda
multiply = ->(x, y) { x * y }
puts multiply.call(3, 4)  # 12

# Proc
multiply_proc = Proc.new { |x, y| x * y }
puts multiply_proc.call(3, 4)  # 12

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# Block with yield
def demonstrate_block
  puts "Before yield"
  yield if block_given?
  puts "After yield"
end

demonstrate_block { puts "Inside block" }

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class Person
  # Accessor methods
  attr_accessor :name, :age

  # Constructor
  def initialize(name, age)
    @name = name
    @age = age
  end

  # Instance method
  def introduce
    "Hi, I'm #{@name}, #{@age} years old"
  end
end

person = Person.new("Alice", 30)
puts person.introduce

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class Employee < Person
  attr_accessor :company

  def initialize(name, age, company)
    super(name, age)
    @company = company
  end

  def work_info
    "Works at #{@company}"
  end
end

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module Swimmable
  def swim
    "I can swim!"
  end
end

class Fish
  include Swimmable
end

fish = Fish.new
puts fish.swim  # "I can swim!"

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begin
  # Risky code
  result = 10 / 0
rescue ZeroDivisionError => e
  puts "Error: #{e.message}"
ensure
  puts "This always runs"
end

# Custom exception
class CustomError < StandardError; end

def raise_custom_error
  raise CustomError, "Something went wrong"
end

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# Writing to a file
File.open("example.txt", "w") do |file|
  file.puts "Hello, File!"
end

# Reading from a file
File.read("example.txt")

# Appending to a file
File.open("example.txt", "a") do |file|
  file.puts "Another line"
end

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# RSpec example
RSpec.describe Calculator do
  it "adds two numbers" do
    expect(Calculator.add(2, 3)).to eq(5)
  end
end