For Loops

Array Iteration

colors = ["red", "green", "blue"]
for color in colors
  puts color
end

Two-variable form gives index, value:

for i, color in colors
  puts "#{i}: #{color}"
end

Single-variable form gives keys:

config = {"host" => "localhost", "port" => 3000}
for k in config
  puts k
end
# prints host, port

Two-variable form gives key, value:

for k, v in config
  puts "#{k} = #{v}"
end

Iterate from 0 to N-1:

for i in 5
  puts i
end
# prints 0, 1, 2, 3, 4

Use range(start, end) to iterate from start to end-1:

for i in range(3, 7)
  puts i
end
# prints 3, 4, 5, 6

range() also works as a standalone function that returns an array:

arr = range(5)
# arr is [0, 1, 2, 3, 4]

Stop the loop early:

for n in [1, 2, 3, 4, 5]
  if n == 4
    break
  end
  puts n
end
# prints 1, 2, 3

Skip to the next iteration:

for n in [1, 2, 3, 4, 5]
  if n % 2 == 0
    next
  end
  puts n
end
# prints 1, 3, 5

break and next work in while loops too.