Blinking twelve

Question

Many electronic devices, specially old ones, will show a blinking 12:00 when the time has not been set. The purpose of this challenge is to recreate this.

Specifically, the task is to display 12:00 and --:-- alternatively in an infinite loop.

The period should be 1 second, divided evenly in two periods of 0.5 seconds. Here "1 second" and "evenly" can be interpreted loosely. For example, it is acceptable if the code pauses for 0.5 seconds between displaying the strings, even if the resulting period will then be a little higher than 1 second. An initial pause before displaying the first string is acceptable.

Each new string can be displayed either by replacing the former string or in a new line. Trailing whitespace is allowed, except that if each new string is on a different line there should be no empty lines between consecutive strings.

Shortest code in bytes wins.

Answer 1

Q/KDB+, 61 Bytes

s:("12:00";"--:--")
b:1b
.z.ts:{b::not b;show s[b]}
\t 500

Explanation:

s:("12:00";"--:--")

Assign the values we wish to show in a list.

b:1b

Assign a boolean variable to flip between 0 and 1 easily.

.z.ts:{b::not b;show s[b]}

This is a KDB+ function which is invoked in set intervals by the timer function (\t) http://code.kx.com/wiki/Reference/dotzdotts
This executes the code inside the curly braces when \t is set. Show the value in s and then flipping the value of b between 0 and 1.

\t 500

Effectively calls .z.ts every 500ms.

Answer 2

Pushy, 22 bytes (non-competing)

`--:`wO`12:0`&["500oWF

This answer makes use of the two stacks, by flipping between them, printing the characters in turn:

`--:`    \ Push these characters to stack 1
 w       \ Mirror around center, yielding "--:--"
 O       \ On the second stack...
 `12:0`  \ Push these characters
 &       \ Duplicate the last (for :00)

 [        \ Infinitely:
  "       \   Print the current stack
  500oW   \   Wait 500 milliseconds
  F       \   Swap stacks
          \ (Implicit end loop)

The oW command is part of a set of experimental commands that postdate the challenge, making this answer non-competing.

Answer 3

Windows PowerShell, 46 55 bytes

function a{sleep -m 500;cls};for(){"12:00";a;"--:--";a}

Original Code:

a{sleep -m 500;cls};for(){"12:00";a;"--:--";a}
^ this won't work on other PCs. No idea why.

Answer 4

Powershell, 46 45 bytes

-1 byte, thanks @AdmBorkBork

for(){('12:00','--:--')[$i++%2]
sleep -m 500}

Answer 5

C# (.NET Core), 138 131 127 bytes

class H{static int Main(){for(int n=1;;System.Threading.Thread.Sleep(500))System.Console.WriteLine((n^=1)>0?"--:--":"12:00");}}

Try it online!

Simple one-liner code.

---

C# (.NET Core), 127 bytes

class H{static int Main(){for(int n=1;;System.Threading.Thread.Sleep(500))System.Console.Write((n^=1)>0?"\r--:--":"\r12:00");}}

Try it online!

This code has same length with the code above, it does replace previous line.

---

-7 bytes by using for loops.
-4 bytes by using ternary operator.

Answer 6

Postscript 225 214

For fun only! Don't send this to a real printer!!

/Courier findfont 9 scalefont setfont{usertime 500 mod 5 lt{newpath 9 9 moveto 1 setgray 99 setlinewidth 99 99 lineto stroke 0 setgray}if newpath 9 9 moveto usertime 999 mod 500 lt{(--:--)}{(12:00)}ifelse show}loop

Try it:

gs -c '/Courier findfont 9 scalefont setfont{usertime 500 mod 5 lt{newpath 9 9 moveto 1 setgray 99 setlinewidth 99 99 lineto stroke 0 setgray}if newpath 9 9 moveto usertime 999 mod 500 lt{(--:--)}{(12:00)}ifelse show}loop'

or

cat <<eops >/tmp/blinkingTwelve.ps
%!
/Courier findfont
9 scalefont
setfont
{
  usertime 500 mod 5 lt {
    newpath
    9 9 moveto
    1 setgray
    99 setlinewidth
    99 99 lineto
    stroke
    0 setgray
  } if
  newpath
  9 9 moveto
  usertime 999 mod 500 lt {
    (--:--)
  } {
    (12:00)
  } ifelse
  show
} loop
eops

then

gs /tmp/blinkingTwelve.ps
gv /tmp/blinkingTwelve.ps

But don't try to open this with more sophisticated viewer and care about desktop thumbnailer!

Answer 7

QBasic (QB64) 55 53 Bytes

A$="12:00
B$="--:--
DO
?A$
_DELAY .5
SWAP A$,B$
LOOP

Saved 2 bytes as newline appears to terminate the string definitions.

SWAP makes all the difference. For vanilla QBASIC replace _DELAY with SLEEP S where S is an integer in seconds, but then the frequency is wrong.

Answer 8

Haskell, 79 bytes

import System.Posix.Unistd
m=(>>usleep 500000).putStrLn
g=m"12:00">>m"--:--">>g

m is a helper function that waits half a second before printing its argument. The main function g calls m "12:00", then m "--:--" and then itself again.

Answer 9

S.I.L.O.S, 61 bytes

lbla
def p printLine
p 12:00
wait 500
p --:--
wait 500
GOTO a

Try it online!

Unfortunately TIO will just do nothing forever, as it waits until execution to print this. But, if you are eager to test, you can use the GitHub link.

Answer 10

Arduino CC, 79 bytes

void loop(){Serial.print("12:00");delay(500);Serial.print("--:--");delay(500);}

I have no experience with C/C++, so I don't really know how I can golf this.

Answer 11

Processing, 69 bytes

void draw(){println("12:00");delay(500);println("--:--");delay(500);}

Answer 12

Python 2, 68 Bytes

import time
while 1:
 for i in'12:00','--:--':print i;time.sleep(.5)

Answer 13

Java, 152 151 bytes (Thanks @AlexRacer)

public class c{public static void main(String[] a)throws Exception{int i=1;while(i>0){System.out.println(i++%2<1?"--:--":"12:00");Thread.sleep(500);}}}

Try it here! * (this compiler prints only once a second, couldn't find a better one)

Answer 14

C, 77 bytes

#import<windows.h>
i;f(){for(;;i^=1)Sleep(83*printf(i?"\r--:--":"\r12:00"));}

Answer 15

GameMaker Language, 47 bytes

a="12:00"if 9<c mod 20a="--:--"draw_text(0,0,a)

(Assuming a room speed of 20 fps)

Answer 16

Scala, 100 bytes

object C extends App{var p=1>2;while(2>1){p= !p;println(if(p)"12:00"else"--:--");Thread.sleep(500)}}

Answer 17

HTML + CSS, 147, 148 142 Bytes

*{font-family:Courier;left 0;background-color:white;position:absolute}@keyframes d{0%,49%{left:0}50%,to{left:-10em}}a{animation:d 1s infinite}

12:00<a>--:--

Explanation:

Basically, this uses two HTML elements: A text node containing 12:00 and an <a> tag containing --:--.

The selector in the CSS applies to both elements, giving both absolute positioning 0 to the left. This allows both elements to overlap. Then, I gave both elements a monospace font, making each take up equal widths. Finally, I set the background color to white, making sure that the <a> tag hides the text it overlaps.

Then, I use an animation to move the <a> tag offscreen every .5 seconds. To do this, the animation lasts one second, and shows the tag for the first 49%, then hides it for the last 50%.

Oh - finally, Courier is shorter than monospace, saving 3 bytes, but it might not work in all browsers/operating systems.

Update: +1 Byte

Turns out that Monaco isn't on everyone's computer. changed to using Courier instead at the expense of a byte.

Update: -6 Bytes

Forgot to remove a bit of whitespace. Oops.

Non minified code:

* {
  position: absolute;
  left: 0;
  font-family: Courier;
  background-color: white;
}
@keyframes d {
  0%, 49% {
    left: 0
  }
  50%, to {
    left: -10em
  }
}
a{animation: d 1s infinite}

12:00<a>--:--

Answer 18

tcl, 49

while 1 {lmap x 12:00\ --:-- {puts $x;after 500}}

Can be tried on https://goo.gl/8gXPzC

Thanks to people on tcl IRC channel.

tcl, 51

while 1 {puts 12:00;after 500;puts --:--;after 500}

Can be tried on https://goo.gl/Hb3sHq

Answer 19

PHP, 48 bytes

for(;;usleep(5e5))echo($n^=1)?"
12:00":"
--:--";

Run with -nr.

Replace instead of multiple lines with \r instead of \n (+2 bytes):

for(;;usleep(5e5))echo($n^=1)?"\r12:00":"\r--:--";

Answer 20

R 69 65 61 bytes

y=1;while(1){cat('\r',c('12:00','--:--')[y]);Sys.sleep(.5);y=(y==1)+1}

while(1){cat('\r12:00');Sys.sleep(.5);cat('\r--:--');Sys.sleep(.5)}

f=Sys.sleep;while(1){cat('\r12:00');f(.5);cat('\r--:--');f(.5)}

First time using the f = blah_function() trick, and it saved a few bytes. Used \r to replace existing string.

Fairly simple implementation:

f = Sys.sleep;      #store function for repeated usage
while(1){
    cat('\r12:00'); #print 12
    f(.5);          #sleep
    cat('\r--:--'); #print --
    f(.5)           #sleep again
}

Answer 21

REXX, 60, 54 bytes

d.='--:--'
d.1='12:00'
a=1
do b=0
  sleep(.5)
  a=\a
  say d.a
  end

(Indented for readability)

Edit: Turns out that the most naïve solution is even shorter:

do b=0
say '12:00'
sleep(.5)
say '--:--'
sleep(.5)
end

Tested with Regina REXX interpreter; some older implementations may not have the Delay function at all, or it may only support whole seconds.

Answer 22

Lua, 94 bytes

Unfortunately Lua has no built-in sleep function, so a loop is necessary.

x=1 z=os.clock while 1 do x=-x print(x<0 and"12:00"or"--:--") y=z()+.5 repeat until z()>y end

As a bonus, here's a Windows only one which is 109 bytes and which clears the screen each time:

x=1 z=os.clock while 1 do x=-x print(x<0 and"12:00"or"--:--") y=z()+.5 repeat until z()>y os.execute"cls"end

Answer 23

Python 2, 92 bytes

import time
t=0
while 1:u=t%2;v='--'*u;w=1-u;print v+'12'*w+':'+v+'00'*w;t+=1;time.sleep(.5)

Try it online!

Explanation

import time                                   Import the time module
t=0                                           Set a counter, 't', to 0
while 1:                                      Trigger an infinite loop
    u = t%2                                   Let 'u' be the remainder of t/2. This will alternate between 0 and 1 
    w = 1 - u                                 Let 'w' be the opposite of u
    v = '--'*u                                Python lets the repetition of strings by multiplying them by an int. Here we are either mulitplying by 1 (no effect) or 0 (turns it to an empty string)
    print v + '12'*w + ':' + v + '00'*w       Concatonating 4 strings and printing them. We are using string multiplication again on the '12' and '00'
    t += 1                                    Increment the counter variable
    time.sleep(0.5)                           Wait half a second

Answer 24

*><>, 30 bytes

cn"00:"ooo5Sdo"--:--"ooooo5Sdo

Online test.

I feel this is much simpler and more different than redstarcoder's algorithm, and thus I posted it as separate.

Replaces output in-place.

Answer 25

8th, 62 58 51 bytes

: p . cr .5 sleep ; : f "12:00" p "--:--" p recurse ;

When invoked, the word f will display blinking twelve according the "new line" format. This code leverages "tail-call elimination" implemented in 8th.

The following code (95 bytes long) will let word f display blinking twelve according the "replacing the former string" format:

: p 0 0 con:gotoxy con:print ; 
: f con:cls repeat "12:00" p .5 sleep "--:--" p .5 sleep again ;

Answer 26

ForceLang, 79 bytes

def d datetime.wait 500
def w io.writeln
label 1
w "12:00"
d
w "--:--"
d
goto 1

---

And here's a version in 125 bytes that actually clears the screen each time and blinks:

set z string.char 8
def d datetime.wait 500
set z z+z+z+z+z
label 1
io.write "12:00"
d
io.write z+"--:--"
d
io.write z
goto 1

Answer 27

SmileBASIC, 35 bytes

WAIT 30?"12:00
WAIT 30?"--:--
EXEC.

WAIT times are in frames (1/60 second), and EXEC. restarts the program (equivilant to EXEC 0 which runs the code that's in slot 0)

Version that clears the screen and adds 6 bytes:

WAIT 30CLS?"12:00
WAIT 30CLS?"--:--
EXEC.

Answer 28

Excel VBA (Win, Excel 32 bit Only), 97 Bytes

In a module:

Because VBA's Application.Wait() method cannot handle input for time periods of less than one second, a declaration of the kernel32 sleep method is used for the 500 ms wait period.

Declare Sub Sleep Lib "kernel32" (ByVal s&)

Note: 64-bit versions of VBA (VB7) require a PtrSafe tag after the Declare tag, and changing the ByVal s& call to ByVal s as LongPtr.

In the vbe immediates window:

Do:DoEvents:?"12:00":Sleep 500:?"--:--":Sleep 500:Loop

Answer 29

PKod, 26 bytes

PKod is an esoteric language that only has one accessible variable

Code:

l12=:o00yyl=-oo=:o=-ooyy<

Explanation:
l - if first char in code, print any NOP chars found
12 - two NOP chars to print
=: - set variable as :
00 - two more NOP chars
o - print variable's corresponding ascii char
y - wait 0.25 seconds
l - if not first char in code, clear the console
=-oo - set variable as - and print twice
< - go back to the start of the code

Answer 30

Dart, 103 bytes

import'dart:io';f({i=1}){while(i>0){print(i++%2>0?"12:00":"--:--");sleep(Duration(milliseconds:500));}}

Try it online!

Sometimes I hate how verbose and strongly typed Dart has to be :D