View Category
Structure
Conditionals

Perform an action if a condition is true (IF .. THEN)

Given a variable name, if the value is "Bob", display the string "Hello, Bob!". Perform no action if the name is not equal.
csharp
if (name == "Bob") Console.WriteLine("Hello, {0}!", name);
erlang
if (Name == "Bob") -> io:format("Hello, ~s!~n", [Name]) ; true -> false end.
case Name of "Bob" -> io:format("Hello, ~s!~n", [Name]) ; _ -> false end.
Name == "Bob" andalso (begin io:format("Hello, ~s!~n", [Name]), true end).
cpp
if (name == "Bob") Console::WriteLine("Hello, {0}!", name);
if (name == "Bob") std::cout << "Hello, " << name << "!" << std::endl;
clojure
(def person "Bob")
(if (= person "Bob")
(println "Hello, Bob!"))
go
if name == "Bob" {
fmt.Println("Hello", name)
}

Perform different actions depending on a boolean condition (IF .. THEN .. ELSE)

Given a variable age, if the value is greater than 42 display "You are old", otherwise display "You are young"
csharp
int age = 41;

if (age > 42)

System.Console.WriteLine("You are old");
else
System.Console.WriteLine("You are young");


erlang
if Age > 42 -> io:format("You are old~n") ; true -> io:format("You are young~n") end.
Message = if Age > 42 -> "old" ; true -> "young" end, io:format("You are ~s~n", [Message]).
case Age > 42 of true -> io:format("You are old~n") ; false -> io:format("You are young~n") end.
case Age of _ when Age > 42 -> io:format("You are old~n") ; _ -> io:format("You are young~n") end.
Message = case Age of _ when Age > 42 -> "old" ; _ -> "young" end, io:format("You are ~s~n", [Message]).
Age > 42 andalso (begin io:format("You are old~n"), true end) orelse (begin io:format("You are young~n"), true end).
(fun (X) when X > 42 -> io:format("You are old~n"); (_) -> io:format("You are young~n") end)(Age).
(fun () when Age > 42 -> io:format("You are old~n"); () -> io:format("You are young~n") end)().
io:format("You are ~s~n", [if Age > 42 -> "old" ; true -> "young" end]).
cpp
if (age > 42) Console::WriteLine("You are old");
else Console::WriteLine("You are young");
Console::WriteLine("You are {0}", (age > 42 ? "old" : "young"));
std::printf("You are %s\n", (age > 42 ? "old" : "young"));
clojure
(def age 41)
(if (> age 42) "You are old" "You are young")

Perform different actions depending on several boolean conditions (IF .. THEN .. ELSIF .. ELSE)

csharp
if (age > 84) Console.WriteLine("You are really ancient");
else if (age > 30) Console.WriteLine("You are middle-aged");
else Console.WriteLine("You are young");
Console.WriteLine("You are {0}", ((age > 84) ? "really ancient" : (age > 30) ? "middle-aged" : "young"));
erlang
if
Age > 84 -> io:format("You are really ancient~n");
Age > 30 -> io:format("You are middle-aged~n");
true -> io:format("You are young~n")
end.
case Age of
_ when Age > 84 -> io:format("You are really ancient~n");
_ when Age > 30 -> io:format("You are middle-aged~n");
true -> io:format("You are young~n")
end.
cpp
if (age > 84) Console::WriteLine("You are really ancient");
else if (age > 30) Console::WriteLine("You are middle-aged");
else Console::WriteLine("You are young");
Console::WriteLine("You are {0}", (age > 84 ? "really ancient" : age > 30 ? "middle-aged" : "young"));
std::cout << "You are " << (age > 84 ? "really ancient" : age > 30 ? "middle-aged" : "young") << std::endl;
clojure
(println
(condp <= age
84 "You are really ancient"
30 "You are middle aged"
"You are young"))

Replacing a conditional with many branches with a switch/case statement

Many languages support more compact forms of branching than just if ... then ... else such as switch or case or match. Use such a form to add an appropriate placing suffix to the numbers 1..40, e.g. 1st, 2nd, 3rd, 4th, ..., 11th, 12th, ... 39th, 40th
csharp
public static string GetOrdinal(int i)
{
if (i > 10 && i < 20) return i.ToString() + "th";
switch (i % 10)
{
case 1:
return i.ToString() + "st";
case 2:
return i.ToString() + "nd";
case 3:
return i.ToString() + "rd";
default:
return i.ToString() + "th";
}
}
public static string GetOrdinal(int i)
{
if (i > 10 && i < 20) return i.ToString() + "th";
switch (i % 10)
{
case 1:
return i.ToString() + "st";
break;
case 2:
return i.ToString() + "nd";
break;
case 3:
return i.ToString() + "rd";
break;
default:
return i.ToString() + "th";
break;
}
}
erlang
Suffix = case Num of
N when N > 10, N < 20 -> "th";
N when N rem 10 =:= 1 -> "st";
N when N rem 10 =:= 2 -> "nd";
N when N rem 10 =:= 3 -> "rd";
_ -> "th"
end,
io_lib:format("~w~s", [Num, Suffix])
cpp
#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
int num,i,x;
cout<<"Enter the range:";
cin>>num;
for(i=1;i<=num;i++)
{
x=i%10;
switch(i)
{
case 11:
case 12:
case 13:cout<<i<<"th ";
continue;
}
switch(x)
{
case 1: cout<<i<<"st ";break;
case 2: cout<<i<<"nd ";break;
case 3: cout<<i<<"rd ";break;
default: cout<<i<<"th ";
}
}
getch();
}
clojure
(def n 112)

(println (str n
(let [rem (mod n 100)]
(if (and (>= rem 11) (<= rem 13))
"th"
(condp = (mod n 10)
1 "st"
2 "nd"
3 "rd"
"th")))))
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.
csharp
int x = 1;

while (x < 150)
{
x *= 2;
Console.Write("{0},", x);
}
erlang
X = 1, print_while_X_less_150(X).
Pred = fun (X) -> X < 150 end,
Action = fun (X) -> io:format("~B,", [X]), X * 2 end,
X = 1,

while_do(Pred, Action, X).
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;
clojure
(take-while #(< % 150) (iterate #(* 2 %) 1))

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"
csharp
System.Random die = new System.Random();
int roll;

do
{
roll = die.Next(1, 6);
Console.Write(roll);
if (roll < 6) Console.Write(",");
}
while (roll != 6);
erlang
Pred = fun (DiceRoll) -> DiceRoll =/= 6 end,
Action = fun (DiceRoll) -> io:format("~B,", [DiceRoll]), dice_roll() end,

do_while(Pred, Action, dice_roll()).
-module(dice).
-export([start/0]).

start() ->
roll(dice_roll()).

roll(6) ->
io:format("6~n", []);
roll(N) ->
io:format("~B,", [N]),
roll(dice_roll()).

dice_roll() -> random:uniform(6).
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();
clojure
(loop [r (rand-int 6)]
(if (= r 5)
nil
(do
(println r)
(recur (rand-int 6)))))

Perform an action a fixed number of times (FOR)

Display the string "Hello" five times like "HelloHelloHelloHelloHello"
csharp
string text = "Hello";

for (int i = 0; i < 5; i++)
{
Console.Write(text);
}
erlang
dotimes(5, fun () -> io:format("Hello") end).
lists:foreach(fun (_) -> io:format("Hello") end, lists:seq(1, 5)).
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");
clojure
(dotimes [_ 5]
(print "Hello"))

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!"
csharp
for (int i = 10; i > 0; i--)
{
Console.Write("{0} .. ", i);
}

Console.WriteLine("Liftoff!");
erlang
fromto(10, 1, -1, fun (X) -> io:format("~B .. ", [X]) end), io:format("Liftoff!~n").
lists:foreach(fun (X) -> io:format("~B .. ", [X]) end, lists:seq(10, 1, -1)), io:format("Liftoff!~n").
cpp
for(int i = 10; i != 0; --i) Console::Write("{0} .. ", i);
Console::WriteLine("Liftoff!");
clojure
(dotimes [i 10]
(print (str (- 10 i) " .. ")))

(println "Liftoff!")