Ruby - loop, while, until, for, each, (..) 2020

Let's print out even numbers up to 10. We'll use loop:

#!/usr/bin/ruby
# loop.rb
# How to loop

n = 0

loop do
   n += 1
   next unless (n % 2) == 0
   break if n > 10
   puts n
end

Output:

$ ./loop.rb
2
4
6
8
10

Let's print out even numbers up to 10. This time, we'll use while:

#!/usr/bin/ruby
# while.rb
# How to while

n = 0

while (n <= 10)
   n += 1
   next unless (n % 2) == 0
   puts n
end

Output:

$ ./while.rb
2
4
6
8
10

Let's print out even numbers up to 10. This time, we'll use until:

#!/usr/bin/ruby
# until.rb
# How to until

n = 0

until (n > 10)
   n += 1
   next unless (n % 2) == 0
   puts n
end

Output:

$ ./until.rb
2
4
6
8
10

Let's print out even numbers up to 10. This time, we'll use for:

#!/usr/bin/ruby
# for.rb
# How to for

list = [0,1,2,3,4,5,6,7,8,9,10]
for n in list
   next unless (n % 2) == 0
   puts "#{n}"
end

Output:

$ ./for.rb
0
2
4
6
8
10

If we want the output in one line, we can use print instead:

#!/usr/bin/ruby
# for2.rb
# How to for

list = [0,1,2,3,4,5,6,7,8,9,10]
for n in list
   next unless (n % 2) == 0
   print "#{n} "
end

Output:

$ ./for2.rb
0 2 4 6 8 10

Let's print out even numbers up to 10. This time, we'll use each:

#!/usr/bin/ruby
# each.rb
# How to each

list = [0,1,2,3,4,5,6,7,8,9,10]
list.each do |n|
   next unless (n % 2) == 0
   print "#{n}, "
end

Output:

$ ./each.rb
0, 2, 4, 6, 8, 10,

We can simplify a little bit by using range(n1..n10)

#!/usr/bin/ruby
# range.rb
# How to range

(0..10).each do |n|
   next unless (n % 2) == 0
   print "#{n}, "
end

Output:

$ ./range.rb
0, 2, 4, 6, 8, 10,