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Loops and Iterators¶

Loop Method¶

The loop constructs loops through a block of code until the condition is false. If you don't put an end condition the loop will run infinitely.

i = 0
loop do
    i += 1
    puts "Hello World"
    break if i == 2
end
Hello World
Hello World
=> nil

We can continue with the loop by using the next keyword as follows :

i = 0
loop do
  i += 1
  next if i == 2
  puts i
  break if i == 5
end

While Loop¶

The syntax for the while is :

while (boolean condition)
#code statement
end

The while will run as long as the condition is true.

i = 0
while i < 5
  i += 1
  puts i
end

Until Loop¶

until is the negated form of the while statement :

i = 0
until i >= 5
  i += 1
  puts i
end

The same statement with while :

i = 0
while i < 5
  i += 1
  puts i
end

While and Until- Alternative Syntax¶

The while statement have alternative syntax. We can put the statement at the beginning of the while statement as follows :

i = 0
puts "#{ i += 1 }" while i < 5

until alternative syntax¶

The until also have an alternative syntax as follows :

i = 0
puts "#{ i += 1 }" until i == 5

Do..While Alternative Syntax¶

i = 0
begin
  puts i
  i += 1
end while i < 5

For Loop¶

You can use the traditional for loop as in other languages as follows :

for i in 1..5
  puts i
end

Alternative `for` statement¶

An alternative for the for statement is to use the times methods :

5.times {|i| puts i}

Step¶

We can use a step function to choose th upper boundary in what steps we would like to loop as follows :

1.step(10,2) { |i| puts i}

`case` statement¶

You use the case statement instead of using multiple if/elsif/else statements :

lang = "fr"

dog = case lang
  when "en"
    "dog"
  when "es"
    "perro"
  when "fr"
    "chien"
  when "de"
    "Hund"
  else "dog"
end

And when using symbols :

lang = :de

doggy = case lang
  when :en then "dog"
  when :es then "perro"
  when :fr then "chien"
  when :de then "Hund"
end
puts doggy

We can also use ranges with the case statement :

scale = 8

out = case scale
  when 0 then "lowest"
  when 1..3; "medium-low"
  when 4..5; "medium"
  when 6..7; "medium-high"
  when 8..9; "high"
  when 10; "highest"
  else "off scale"
end
puts "Scale: " + outs

The ; and then are used when we put the statement on the same line. We could have written the same as follows :

scale = 8

out = case scale
  when 0
    "lowest"
  when 1..3
    "medium-low"
  when 4..5
    "medium"
  when 6..7
    "medium-high"
  when 8..9
    "high"
  when 10
    "highest"
  else
    "off scale"
end
puts "Scale: " + out

We could also use complicated logical operations in the when clause.