Control Structures

Conditional Statements

#if statement
if true
  "if statement"
elsif false
  "else if, optional"
else
  "else, also optional"
end

#case/switch statement
grade = 'B'    
case grade
 when 'A'
   puts "Hooray!"
 when 'B'
   puts "OK job"
 when 'C'
   puts "You can do better"
 when 'F'
   puts "You failed!"
 else
   puts "Alternative grading system, eh?"
end

#=> OK job

#case with ranges
grade = 72
case grade
    when 90..100
      puts "Hooray!"
    when 80...90
      puts "OK job"
    when 70...80
      puts "You can do better"   
    else
      puts "You failed!"
end

#=> You can do better

Ruby Loops

# A for loop in Ruby uses a Range:
for counter in 1..5
  puts "iteration #{counter}"
end
#=> iteration 1
#=> iteration 2
#=> iteration 3
#=> iteration 4
#=> iteration 5

#while loop
counter = 1
while counter <= 5 do
  puts "iteration #{counter}"
  counter += 1
end
#=> iteration 1
#=> iteration 2
#=> iteration 3
#=> iteration 4
#=> iteration 5

Each and Blocks

Instead of For Loops, rubyists usually use the "each" method and pass it a block. A block is a bunch of code that you can pass to a method like "each". The "each" method of a range runs the block once for each element of the range. The block below is passed a counter as a parameter.

(1..5).each do |counter|
  puts "iteration #{counter}"
end
#=> iteration 1
#=> iteration 2
#=> iteration 3
#=> iteration 4
#=> iteration 5

# You can also surround blocks in curly brackets:
(1..5).each {|counter| puts "iteration #{counter}"}

# The contents of data structures can also be iterated using each.
array.each do |element|
  puts "#{element} is part of the array"
end
hash.each do |key, value|
  puts "#{key} is #{value}"
end