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Structure
Loops

Perform an action multiple times based on a boolean condition, checked before the first action (WHILE .. DO)

Starting with a variable x=1, Print the sequence "1,2,4,8,16,32,64,128," by doubling x and checking that x is less than 150.
ruby
x=1
while x < 150
puts x
x <<= 1
end
cpp
int x = 1;

while (x < 150) { x *= 2; Console::Write("{0},", x); }
Console::WriteLine();
for (int x = 1; x < 150; x *= 2) { std::cout << x << ","; }
std::cout << std::endl;
fsharp
let mutable x = 1
while x < 150 do printf "%d, " x ; (x <- x * 2) done
// The problem is clearly geared towards imperative languages ;-)
// No need to mutate any variable, here's how to do it loop-free functional:
let rec powers2 i = seq { if i < 150 then yield i; yield! powers2 (i*2) }
powers2 1 |> Seq.iter (fun i -> printf "%i, " i)
clojure
(take-while #(< % 150) (iterate #(* 2 %) 1))
groovy
x = 1
while (x < 150) {
print x + ","
x *= 2
}
println()

Perform an action multiple times based on a boolean condition, checked after the first action (DO .. WHILE)

Simulate rolling a die until you get a six. Produce random numbers, printing them until a six is rolled. An example output might be "4,2,1,2,6"
ruby
# Ruby has no DO..WHILE construct. Need to write it as a WHILE
rnd = 0
while (rnd != 6)
rnd = rand(6)+1
print rnd
print "," if (rnd!=6)
end
begin
rnd = rand(6)+1
print rnd
print "," if rnd!=6
end while rnd != 6
# This uses Enumerators, ad it becomes almost functional style...

games = Enumerator.new do |yielder|
yielder.yield rand(6) + 1 while true
end

puts games.take_while {|roll| roll != 6}.join(",")
cpp
Random^ rnd = gcnew Random;

int dice = rnd->Next(1, 7); Console::Write("{0}", dice);
do { Console::Write(",{0}", (dice = rnd->Next(1, 7))); } while (dice != 6);
Console::WriteLine();
fsharp
open System
let rand = Random()

Seq.initInfinite (fun _ -> rand.Next(1, 7))
|> Seq.takeWhile (fun x -> x < 6)
|> fun items -> String.Join(",", items)
|> function s when s = "" -> printfn "6" | s -> printfn "%s,6" s
clojure
(loop [r (rand-int 6)]
(if (= r 5)
nil
(do
(println r)
(recur (rand-int 6)))))
groovy
// Groovy has no do..while; use a normal while
int dice = 0
while (dice != 6) {
dice = Math.random() * 6 + 1
print dice
if (dice != 6) print ','
}

Perform an action a fixed number of times (FOR)

Display the string "Hello" five times like "HelloHelloHelloHelloHello"
ruby
puts "Hello"*5
5.times { print "Hello" }
cpp
for(int i = 0; i < 5; ++i) Console::Write("Hello");
for(int i = 5; i > 0; --i) Console::Write("Hello");
dotimes(5, hello);
fill_n(ostream_iterator<string>(cout), 5, "Hello");
fsharp
for i = 1 to 5 do printf "Hello" done
dotimes 5 (fun () -> printf "Hello")
// Repetition via ranging over a List type(index ignored)
for _ in list do printf "Hello" done
// Repetition via ranging over a Sequence type(index ignored)
for _ in sequence do printf "Hello" done
// Repetition via ranging over an Array type(index ignored)
for _ in array do printf "Hello" done
clojure
(dotimes [_ 5]
(print "Hello"))
groovy
println "Hello" * 5
5.times { print "Hello" }; println()

Perform an action a fixed number of times with a counter

Display the string "10 .. 9 .. 8 .. 7 .. 6 .. 5 .. 4 .. 3 .. 2 .. 1 .. Liftoff!"
ruby
10.downto(1) { |n| print n, " .. " }
puts "Liftoff!"
cpp
for(int i = 10; i != 0; --i) Console::Write("{0} .. ", i);
Console::WriteLine("Liftoff!");
fsharp
for i = 10 downto 1 do printf "%d .. " i done
printfn "Liftoff!"
// Repetition via ranging over a Sequence type
for i in {10 .. -1 .. 1} do printf "%d .. " i done ; printfn "Liftoff!"
clojure
(dotimes [i 10]
(print (str (- 10 i) " .. ")))

(println "Liftoff!")
groovy
10.downto(1) { print it + " .. " }
println "Liftoff!"