• Lisp

(defparameter x 13)
(defvar s)
(setf s (format nil "~B" x))

• Clojure

(defn s
  [x]
  (pprint/cl-format nil "~b" x))

• C++

std::string ToBinary(int x) {
  std::array<char, 64> buf;
  auto[ptr, ec] = std::to_chars(buf.data(), buf.data() + buf.size(), x, 2);
  auto s = std::string(buf.data(), ptr);
  return s;
}

• C++

std::bitset<sizeof(x)*8> y(x);
auto s = y.to_string();

• C#

String s = Convert.ToString(x,2);

• C#

String s = Convert.ToString(x,2).PadLeft(16, '0');

• D

auto s = to!string(x,2);

• Dart

var s = x.toRadixString(2);

• Elixir

s = Integer.to_string(x, 2)

• Elixir

Integer.digits(x, 2) |> Enum.join("")

• Erlang

S = io_lib:format("~.2B~n", [X]).

• Fortran

write (unit=s,fmt='(B32)') x

• Fortran

write (unit=s,fmt='(B0)') x

• Go

s := strconv.FormatInt(x, 2)

• Go

s := fmt.Sprintf("%b", x)

• Haskell

foldl (\acc -> (++ acc) . show) "" . unfoldr (\n -> if x == 0 then Nothing else Just (x `mod` 2, x `div` 2))

• Haskell

s x = showIntAtBase 2 intToDigit x ""

• JS

let s = x.toString(2);

• Java

String s = Integer.toBinaryString(x);

• Lua

local s = {}

while x > 0 do
    local tmp = math.fmod(x,2)
    s[#s+1] = tmp
    x=(x-tmp)/2
end

s=table.concat(s)

• PHP

$s = sprintf("%b", $x);

• Pascal

var Iter,n:integer;
[...]
  S := '';
  for Iter := 0 to n do
    s:= Char(Ord('0')+(x shr Iter) and 1) + S;   

• Pascal

var
  _x: Integer;
  _s: String;
begin
  _s := IntToBin(_x,8*SizeOf(Integer));
end.

• Perl

$s = sprintf "%b", $x;

• Python

s = '{:b}'.format(x)

• Python

s = format(x, 'b')

• Ruby

s = x.to_s(2)

• Rust

let s = format!("{x:b}");

• Rust

let s = format!("{:b}", x);

• Scala

val s = x.toString(2)

• Scheme

(define (binary-representation x)
  (let loop ([N x]
             [s '()])
    (let ([NN (arithmetic-shift N -1)])
      (cond [(zero? N) (list->string s)]
            [(odd? N) (loop NN (cons #\1 s))]
            [else (loop NN (cons #\0 s))]))))