Control Structures

if condition
  # code
elsif another_condition
  # code
else
  # code
end

unless condition
  # code
end

result = condition ? true_value : false_value

case value
when 1
  "one"
when 2..5
  "few"
else
  "many"
end

while condition
  # code
end

until condition
  # code
end

for item in collection
  # code
end

collection.each do |item|
  # code
end

5.times do |i|
  puts i
end

1.upto(5) { |i| puts i }
5.downto(1) { |i| puts i }

loop do
  break if condition
end

(1..10).each do |num|
  next if num.even?
  puts num
end

i = 0
while i < 5
  i += 1
  redo if i == 3  # Repeats iteration when i == 3
  puts i
end

numbers = [1, 2, 3, 4]
squares = numbers.map { |n| n * n }  # [1, 4, 9, 16]

even = numbers.select { |n| n.even? }  # [2, 4]

odd = numbers.reject { |n| n.even? }   # [1, 3]

first_even = numbers.find { |n| n.even? }  # 2

has_even = numbers.any? { |n| n.even? }  # true
all_even = numbers.all? { |n| n.even? }  # false

sum = numbers.inject(0) { |sum, n| sum + n }  # 10

begin
  # risky code
rescue StandardError => e
  puts "Error: #{e.message}"
ensure
  # always executed
end

raise "Something went wrong"
raise ArgumentError, "Invalid argument"

# && and ||
result = true && false  # false
result = true || false  # true

# With method calls
user && user.name  # Safe navigation

puts "Hello" if condition
puts "Goodbye" unless condition

begin
  # code
end while condition

# Instead of:
if condition
  x = 1
else
  x = 2
end

# Use:
x = condition ? 1 : 2

# Ruby 2.3+
user&.name&.upcase
# Equivalent to: user && user.name && user.name.upcase

case [1, 2, 3]
in [1, *rest]
  puts "Starts with 1, rest: #{rest}"
in [x, y, z] if x > y
  puts "x > y"
else
  puts "No match"
end