The "Do While False" idiom

Question

Do While False

At work today one of my colleagues was describing the use-case for do while(false). The person he was talking to thought that this was silly and that simple if statements would be much better. We then proceeded to waste half of our day discussing the best manner to write something equivalent to:

do
{
   //some code that should always execute...

   if ( condition )
   {
      //do some stuff
      break;
   }

   //some code that should execute if condition is not true

   if ( condition2 )
   {
       //do some more stuff
       break;
   }

   //further code that should not execute if condition or condition2 are true

}
while(false);

This is an idiom which is found in c quite often. Your program should produce the same output as the below pseudo-code depending on the conditions.

do
{
   result += "A";

   if ( C1)
   {
      result += "B";
      break;
   }

   result += "C"

   if ( C2 )
   {
       result += "D";
       break;
   }

   result += "E";

}
while(false);

print(result);

Therefore the input could be:

1. C1 = true, C2 = true
2. C1 = true, C2 = false
3. C1 = false, C2 = true
4. C1 = false, C2 = false

and the output should be:

1. "AB"
2. "AB"
3. "ACD"
4. "ACE"

This is code-golf so answers will be judged on bytes. Standard loopholes are banned.

Yes this is a simple one, but hopefully we will see some creative answers, I'm hoping the simplicity will encourage people to use languages they are less confident with.

Answer 1

Japt, 19 bytes

"A{U?'B:'C+(V?'D:'E

Test it online!

Fun fact: This would be 16 bytes if it weren't for a bug:

"A{U?"B:C{V?"D:E

Answer 2

Kotlin, 50 bytes

It is interesting what one can do with string templates.

{a,b->"A${if(a)"B" else "C${if(b)"D" else "E"}"}"}

Try Here

Answer 3

Mouse-2002, 23 bytes

??"A"["B"|"C"["D"|"E"]]

Switches on two inputs, which each should be either 0 for false or anything else for true.

Ungolfed, as a function:

#Y,?,?;

$Y 1% a: 2% b:
  "A"
  a [
    "B"
  |
    "C"
    b [
      "D"
    |
      "E"
    ]
  ]
$

Brackets just test if the top of the stack is true, and | is else.

This is a translation of @Cᴏɴᴏʀ O'Bʀɪᴇɴ's ES6 answer.

Answer 4

PHP 4.1, 19 bytes

I was expecting it to be harder, but well. It was really fun!

<?=A,$A?B:C.($B^t);

This expects 2 parameters/values, passed as strings over POST/GET/SESSION/COOKIE... The key A will have the first value, the key B will have the 2nd.
The result will be sent to STDOUT.

Answer 5

DUP, 29 bytes

['A,^['B,]['C,$['D,]['E,]?]?]

Try it here!

Anonymous lambda. Usage:

1 0['A,^['B,]['C,$['D,]['E,]?]?]!

Explanation

[                           ] {lambda}
 'A,                          {output A}
    ^                         {check if arg1 is truthy}
     [   ][               ]?  {conditional}
      'B,                     {if so, output B}
           'C,                {otherwise, output C...}
              $               {...and check if arg2 is truthy}
               [   ][   ]?    {conditional}
                'D,           {if so, output D}
                     'E,      {otherwise, output E}

Answer 6

><> (Fish), 30 bytes

"A"o$1+.
"<"DC"v"CE
o "B"|>oo;

This code uses the two variables (using the initial stack) to move the pointer to (C2, C1+1) You can try it here

Answer 7

Perl, 19 + 1 (-p switch) = 20 bytes

$ perl -pe '$_=l.$_^-su;s/B./B/'
00
ACE
01
ACD
10
AB
11
AB

Uses string XOR and a bareword with leading hyphen. Ungolfed:

$_ = ('l' . $_) ^ '-su';
s/B./B/;

Answer 8

𝔼𝕊𝕄𝕚𝕟, 18 chars / 23 bytes

`A⏜î?⍘B:`C⏜í?⍘D:⍘E

Try it here (Firefox only).

It's pretty much a fusion of conditional statements.

Note: ⏜ basically takes all code up to an optional ⏝, interprets the code, and replaces that block in the code with the result. This is the first time I've used this in a submission, but it works quite well. Self-modifying code FTW!

Answer 9

QBIC, 39 34 bytes

EDIT: Found out that QBasic (and by extension QBIC) doesn't need an =1 to test if an input is true, so removed those.

_!_!~a_>?@AB._X]~b_>?@ACD._E?@ACE.

---

Original answer:

_!_!~a=1_>?@AB._X]~b=1_>?@ACD._X]?@ACE.

Takes two numerical inputs and tests these in straight-forward IF's. No fancy OR logic and array indexes here, unfortunately.

Answer 10

C, 42 bytes (long version); 31 (short version)

The existing submissions seem inconsistent with regards to whether the variables must be named C1 and C2, and whether actually printing the results is required, so I've done a long and short version.

This approach takes advantage of the fact that most of the possibilities for each index differ by only one bit.

Long version:

char s[4]={65,67-C1,69*!C1&69-C2};puts(s);

Short version:

char s[4]={65,67-a,69*!a&69-b};

Answer 11

ForceLang,124 bytes

def f io.readnum()
set w io.write
set g goto
w "A"
if f
g L
w "C"
if f
g M
w "E"
g N
label L
w "B"
g N
label M
w "D"
label N

Answer 12

D, 35 bytes

(int a,int b)=>a?"AB":"AC"+"ED"[b];

Hey, look, D has lambdas.

Hey, look, D is JavaScript, but longer. :^(

Copied verbatim from Conor's ES6 answer. c:

Answer 13

Go, 120 bytes

func w(b bool,d bool)(r string){
for i:=true;i;i=!i{
r+="A"
if b{r+="B"
break}
r+="C"
if d{r+="D"
break}
r+="E"}
return}

Go has only one loop structure, for, but you can simulate a do-while loop with for i := true; i; i = expr.

Edit: It also happens that Go's switch statement is flexible enough to replicate this.

switch {
case true:
    r += "A"
    if b {
        r += "B"
        break
    }
    r += "C"
    if d {
        r += "D"
        break
    }
    r += "E"
}

Answer 14

FALSE, 16 bytes

$"A"'C+,~['E+,]?

Input values are on the stack (first C2 then C1), false is 0 and true is -1 (this is normal in FALSE)

Answer 15

SMBF, 39 bytes

Each _ represents a null literal \x00 and is used for readability. I've successfully tested it for all test cases. except the third, because I haven't found a way to test that input on my interpreter, since I'd need stdin to be \x00\x01. I know it works, though, because I used the exact same method for testing C2 as I did for testing C1.

<.<,[<]<<.[>]>[<<<]<<<<,[<]<<.DE__BC__A

Explanation:

<.          print A
<,          read C1
[<]         if true, move left one
<<.         move left 2 and print (C if false, B if true)
[>]>        move to C1
[<<<]       if true, our output is done, so move all the way left, so further code is NOP
<<<<,       move left 4 and read C2
[<]         if true, move left one
<<.         move left 2 and print (E if false, D if true)
DE_ BC_ A   data on the tape

I think this will do the same for the same byte count, reusing B and C by adding 2 to each:

<.<,[<]<<.[>]>[<<]<<++<++>>,[<]<<.BC__A

Answer 16

Hexagony, 28 26 25 bytes

A;?.));?~..>);@</E"+;@}/>

-2 bytes by moving up the printing of AB

-1 byte by incrementing to C instead

Try it online!

Expanded:

   A ; ? . 
  ) ) ; ? ~ 
 . . > . ; @ 
< / E " + ; @ 
 } / > . . . 
  . . . . . 
   . . . .

---

Uses the value of the second input to get the last char, removing the need for another costly branch:

"E" + (-1*C2)

Credit to @JoKing
Alternatively I could have also just subtracted the value which doesn't save any bytes though:

"E" - C2

Answer 17

CJam, 25 bytes

'Aq~[{'C\['E'D]=}{;'B}]=~

Try it online

Not the best way to do it, but it works.

Answer 18

Jolf, 16 bytes

+'A?j'B+'C."DE"J

Simple. Try this one here!

Aother one, using that other Pyth answer's approach:

11 characters, 18 UTF-8 bytes. You can try this one here.

~T."૎્««"Ιj
          ^-- that's a capital Iota, converting input to binary

Answer 19

Brainbash, 43 bytes

----[>+<----]>++.>#{<+.>}-{<++.+>#-{<+>}<.}

Brainbash is BF with two tapes and more stuff. We're only using one this time. Let's take a look:

----[>+<----]>++.

This sets the first cell to A and outputs it.

>#

This move to the next cell and takes numeric input

{<+.>}

This is an if statement. If the numeric input is one, then we'll increment the previous cell and output it, outting B.

-

This transforms 1 to 0 (falsey) and 0 to 255. It's effectively a boolean NOT as far as the next if statement is concerned.

{<++.

If the current bit, output a C.

+>#

Change it do a D and take some input

-

"Negate it"

{<+>}

If it was a zero, output an increment and return to input cell.

<.}

Move to destination cell and out it.

---

I could use the "heat death of the universe" to save two bytes, using >+[+[<]>>+<+]>, but that didn't complete in the online interpreter, which can be found in the link in the header.

Answer 20

MATLAB, 31 28 bytes

@(x,y)[65,67-x,~x*(69-y),'']

This anonymous function will match all the test cases. The first input is condition 1 and the second input is condition 2. The string will be returned.

The function also works with Octave. You can try it online here.

Simply create the anonymous function by running the command above, then call the function. Running this for example:

ans(0,1)

Will return:

ACD 

Answer 21

C, 54 bytes

Since the story started with a loop, I decided to stick to that. Not the shortest of solutions; but certainly one of the more obscure ones.

Function f takes two integer parameters as input (1 = true, 0 = false), and outputs AB, ACD or ACE to stdout.

f(a,b){for(int x=64;~putchar(++x)<<a&4;x+=x&2?!b:!a);}

Answer 22

Nustack, 27 bytes

a"AB"*"AC"b{"E"}{"D"}if + |

Thanks to Morgan Thrapp and her Python answer for giving me the inspiration for this one.

Explanation:

a"AB"* /* Repeat "AB" 0 or 1 times, depending on if a is #t or #f. The result ("" or "AB") is put on the stack */
"AC" /* Put "AC" on the stack */
b{"E"}{"D"}if /* If b is true, push "E", else push "D" */
+ /* Concatenate the top two strings on the stack, push the result ("ACE" or "ACD") */
| /* Right now the stack looks like (x y). If x is truthy (not empty), keep x, else keep y */

Answer 23

Javascript, 43 Bytes

A different (more intuitive?) way to do it in JS. The name parseInt is not inductive of Code Golfing :P

"A"+["CE","CD","B","B"][parseInt(x+""+y,2)]

Test:

var cases = ["00","01","10","11"];
    
for (i=0;i<4;i++) {
   var x = cases[i][0];
   var y = cases[i][1];
   document.write("A"+["CE","CD","B","B"][parseInt(x+""+y,2)]+"<br>")
}

Answer 24

Ruby, 31 bytes

Anonymous function; assign to a variable to test its output.

->x,y{?A+(x ??B:?C+(y ??D:?E))}

Answer 25

SmileBASIC, 32 bytes

INPUT A,B?"A"+"CB"[A]+"ED"[B]*!A

Answer 26

C++, 57 52 bytes

[](auto c,auto&s){s="AC";c[0]?--s[1],s:s+='E'-c[1];}

First argument should be an indexable collection (vector, array, etc) of conditions, and second argument is the string to write to.

Assumes that the runtime character set has B and C contiguous, and D and E also contiguous (both are true for common codings such as ASCII and EBCDIC).

Demo

auto const f = [](auto c,auto&s){s="AC";c[0]?--s[1],s:s+='E'-c[1];};

#include<array>
#include<iostream>
#include<string>
int main()
{
    std::string s;

    for (bool c1: {true, false})
        for (bool c2: {true, false})
            f(std::array{c1, c2}, s),std::cout << s << '\n';
}

Answer 27

Forth (gforth), 54 bytes

I had orignally planned on using emit for this, but realized that direct string output was shorter (61 vs 54 bytes)

: f if ." AB" else if ." ACD" else ." ACE" then then ;

Try it online!

Explanation

If C1 is true, it prints AB, otherwise it prints ACD if C2 is true, and ACE if C2 is false

Code Explanation

: f                \ start a new word definition
   if              \ if c1 is true
      ." AB"       \ print "AB"
   else            \ if c1 is false
      if           \ if c2 is true
         ." ACD"   \ print "ACD"
      else         \ if c2 is false
         ." ACE"   \ print "ACE"
      then         \ end the inner if
   then            \ end the outer if
;                  \ end the word defintion