Implement a Stopwatch

Question

Implement a simple digital Stopwatch, which will display the time elapsed in seconds and minutes, as described below.

Important

Please read both Display and Controls sections !

Display

Time elapsed, should be displayed in the MM:SS format, by replacing the previously displayed time string "in-place" (clearing the whole or a part of the screen is also allowed).

The stopwatch must be updated at least every second.

Examples:

0 minutes, 0 seconds

00:00

0 minutes, 33 seconds

00:33

1 minute, 50 seconds

01:50

Initially, you can start with '00:00' or with any other value in range [00:00-59:59].

Once your Stopwatch reaches 59:59, it should reset to 00:00 and continue afresh.

You can use a different base (instead of decimal) or even a different numeral system if you wish, as long as you follow the general pattern.

For example 13:03 can be displayed as:

Decimal

13:03

Hexadecimal

0D:03

Base64

N:D

Quater-imaginary base

10101:3

Roman Numerals

XIII:III

Beware that if you use a non-decimal numeral system/base, it must be encoded using printable ASCII (or Unicode) characters, e.g. using two binary (unprintable) bytes for minutes and seconds is not allowed.

You must also left-pad your output with zeroes as appropriate, if your numerical system allows for that.

Replacing the separator character : with any other printable character (including digits) is also acceptable.

Controls

The stopwatch should start paused, and stay in this state, until user explicitly starts it, by pressing the 'control' key (see below).

If, while stopwatch is counting, user presses the 'control' key again, the stopwatch should pause (keeping the current time), until the 'control' key is pressed a one more time.

The 'control' key can be a single keystroke, e.g. s, or any combination of keys, e.g. Ctrl+Shift+X, but it must be 'atomic', pressing multiple keys in sequence, e.g. s then Enter, is not allowed.

The same 'control' key (or combination) must be used to pause and resume the stopwatch.

You must use a specific 'control' key, i.e. 'any key' is not allowed.

Alternatively, you can use a single or double mouse-click, instead of a keypress for 'control'.

---

Rules

• This is code-golf, the shortest answer in bytes wins;
• Standard code-golf loopholes apply;
• Your program must (theoretically) be capable of running forever.

Answer 1

SmileBASIC, 86 77 71 bytes

@L
N=N!=DIALOG(FORMAT$("%02D:%02D",F/60MOD 60,F MOD 60),,,N)F=F+1GOTO@L

DIALOG displays a textbox on the touch screen. N is the number of seconds the text box will stay on screen before it disappears. If N is 0, it stays until the user presses the button on the touch screen.

DIALOG Returns 1 if the user pressed the button, and 0 if it closed automatically. So when the user pushes the pause button, it returns 1, and the display time is set to 0, pausing the stopwatch. After the user presses the button again, we set the display time back to 1, resuming the timer. Basically, every time DIALOG returns 1, the display time is switched between 1 and 0 using !=, which is eqivilant to a logical XOR as long as both inputs are 1 or 0.

Answer 2

Python 2, 167 129 bytes

-36 bytes mostly* from using Maltysen's idea of catching ctrl-c using an exception - go give credit!
-4 bytes thanks to DLosc (init n and b to 0 rather than f())
-1 byte thanks to FlipTack (use p^=1 rather than p=1-p)
-2 bytes thanks to Felipe Nardi Batista (remove precision specifiers)

import time
f=time.time
n=b=p=0
while 1:
 try:n=[n,f()][p];t=n-b;print'\r%02d:%02d'%(t/60%60,t%60),
 except:b=[b-n+f(),b][p];p^=1

Works the same as my original, below, but with the control key sequence of ctrl+c.
(Tested by me with Python 2.7.8 on Windows 7, 64bit;
Tested by Brian Minton with Python 2.7.13 on linux, 64bit)

* also collapsed if statement to a list lookup in order to get the try as a one-liner.

My original:

import time,msvcrt as m
f=time.time
n=b=p=0
while 1:
 if m.kbhit()and m.getch()==b'p':b=[b-n+f(),b][p];p^=1
 if p:n=f()
 t=n-b;print'\r%0.2d:%0.2d'%(t/60%60,t%60),

(Tested by me with Python 2.7.8 on Windows 7, 64bit - this code, however, is Windows specific due to the use of the msvcrt library)

The control key is 'p'.

n and b are initialised to the same value at start-up, giving an "offset" of 0; p is initialised to 0, indicating a paused state.

Whenever the control key is pressed the value of p is switched. When switching from a paused state to an active state b is updated to a new value keeping any current offset from the previous active state(s) with b-n.

During an active state n is repeatedly updated to the current time by calling time.time().

The difference between n and b, t, is then the total number of seconds (including a fractional part) elapsed during active state(s).

The minutes elapsed are then t/60 and each of the minutes and seconds are displayed mod 60 with (t/60%60,t%60). Leading zeros are prepended for each using string formatting of the integer part with '...%0.2d...'. Printing a tuple (the trailing ,) where the first item has a leading carriage return (the \r) causes the previously printed text to be overwritten.

Answer 3

Python - 160 159 143 bytes

Thanks to @JonathanAllan for saving me 18 bytes!

Only uses builtin libraries, so the control key is ctrl-c, catching it with an except keyboardInterrupt.

import time
Z=0
print'00:00'
while 1:exec"try:\n while 1:\n  %s\nexcept:1\n"*2%(1,"print'\033c%02d:%02d'%divmod(Z%3600,60);Z+=1;time.sleep(1)")

Answer 4

QBasic, 213 211 bytes

Control key is tab. Leaving this running may cause laptop fires. You have been warned.

DO
WHILE k$<>CHR$(9)
k$=INKEY$
LOCATE 1
?CHR$(48+m\10);CHR$(48+(m MOD 10));":";CHR$(48+(d MOD 60)\10);CHR$(48+(d MOD 10))
IF r THEN
n=TIMER
d=v+n-b+86400
m=d\60MOD 60
END IF
WEND
k$=""
v=v+n-b
r=1-r
b=TIMER
LOOP

Here it is in action, pausing at 10, 15, and 20 seconds:

Ungolfed and commented

' Outer loop runs forever
DO
  ' The WHILE-WEND loop runs until tab is pressed
  WHILE key$ <> CHR$(9)
    key$ = INKEY$
    ' Output the stopwatch value at top left of screen
    LOCATE 1
    ' Unfortunately, QBasic's PRINT USING doesn't have a format for printing
    ' with leading zeros, so we have to do it manually by printing the
    ' 10s digit and the 1s digit
    PRINT CHR$(48 + minute \ 10); CHR$(48 + (minute MOD 10));
    PRINT ":";
    PRINT CHR$(48 + second \ 10); CHR$(48 + (second MOD 10))
    ' Update the current time if the running flag is set
    IF running THEN now = TIMER
    ' Take the difference between now and the last time we started the
    ' stopwatch, plus the amount of saved time from previous runs,
    ' plus 86400 to account for the possibility of running over midnight
    ' (since TIMER is the number of seconds since midnight, and QBasic's
    ' MOD doesn't handle negative values like we would need it to)
    diff = saved + now - lastStarted + 86400
    second = diff MOD 60
    minute = diff \ 60 MOD 60
  WEND
  ' If we're outside the WHILE loop, the user pressed tab
  key$ = ""
  ' Add the previous run's time to the saved amount
  saved = saved + now - lastStarted
  ' Toggle running between 0 and 1
  running = 1 - running
  ' If we're starting, we want to put the current time in lastStarted;
  ' if we're stopping, it doesn't matter
  lastStarted = TIMER
LOOP

Note that values of TIMER are floating-point. This doesn't affect the output, since MOD and \ truncate to integers. But it does add accuracy to the amount of saved time: if you pause the timer right before a tick, you'll see when you start it up again that the number changes in less than a second.

Answer 5

bash + Unix utilities, 90 or 93 bytes

90-byte version:

trap d=\$[!d] 2;for((n=0;;)){((d|!n))&&dc<<<DP60dod*d$n\r%+n|colrm 1 4&&: $[n++];sleep 1;}

93-byte version:

trap d=\$[!d] 2;for((n=0;;)){((d|!n))&&dc<<<DP60dod*$n+n|colrm 1 4&&n=$[(n+1)%3600];sleep 1;}

Ctrl-C is the resume/pause character. A space is the delimiter between minutes and seconds.

The difference between the two versions is that the 90-byte program will work for 2^63 seconds (at which point, bash will give me an integer overflow).

The 93-byte version will truly work forever.

The original problem included the requirement: "Your program must (theoretically) be capable of running forever."

If running for 2^63 seconds is sufficient to meet that requirement, then the 90-byte solution works. That duration is more than 20 times the age of the universe!

If the program needs to be able to run for longer than that, I'll have to go with the 93-byte solution.

---

I should probably point out that this solution, as well as at least some of the others posted, will very slowly fall behind the true elapsed time. This slippage is because the program is sleeping for one second between each execution of the body of the loop, but the body of the loop does take some tiny amount of time to execute. This will be inconsequential in practice.

Answer 6

Batch, 132 bytes

set/ar=0,m=s=100
:l
cls
@choice/t 1 /d y /m %m:~1%:%s:~1% /n
set/as+=r,m+=c=s/160,s-=c*60,m-=m/160*60,r^^=%errorlevel%-1
goto l

Pressing n will (un)pause the timer. The output flicker can be reduced at a cost of three (or four) bytes.

Answer 7

Pure bash, 141 bytes

set -m
while ! read -t 1;do printf '\r%02i:%02i' $[s=s>3598?0:s+1,s/60] $[s%60];done&trap 'fg>/dev/null' TSTP
printf '00:00'
kill -STOP $!
read

This uses nothing but Bash builtins (no external tools). The control character is Ctrl-Z, so that standard SIGTSTP handling pauses the stopwatch.

• set -m enables job control, which is usually off in a script.
• A subshell process is backgrounded (&).
  • read -t 1 waits one second for input from the user, then fails.
  • The until loop continues as long as read keeps failing.
  • printf outputs the correctly-padded and -formatted time
  • $[s=s>3598?0:s+1,s/60] arithmetic expansion first computes the updated time, checking whether to wrap and otherwise incrementing the seconds counter s, and then returns the floored division s/60.
  • $[s%60] gives the seconds remainder.
• The outer script sets up a trap handler for TSTP, the signal Ctrl-Z generates. When Ctrl-Z is pressed while the outer script is running, it will run fg>/dev/null and put the subshell back into the foreground. >/dev/null is necessary to stop fg printing out the subshell command every time.
• The script prints the initial 00:00 and sends a STOP signal to the child process $!, which will pause the process.
• read waits for input forever, keeping the script alive.

If Ctrl-Z is pressed while the subshell is foregrounded, it will pause execution and return the outer script to the foreground, where it will wait silently. If the outer script is foregrounded, the trap handler will resume the subshell's execution, and it will count up again.

Answer 8

HTML + JavaScript (ES6), 191 192 187 183 174 bytes

<b onclick='b=b?clearInterval(b):setInterval("a.innerHTML=`${(d=(((c=a.innerHTML.split`:`)[1]>58)+c[0])%60)>9?d:`0`+d}:${(e=++c[1]%60)>9?e:`0`+e}",1e3)'onload='b=0'id=a>00:00

Explanation

Click the timer to start or pause the stopwatch. As such, a single click is the control key. The separator between the two values is a colon.

Whenever the user clicks the click, the value of b is checked. It is initialised to 0 which evaluates to false, so a string of code is evaluated every 1000 milliseconds. This sets the variable to the id of the interval, so it can be stopped later. If b contains a number, it evaluates to true, so the interval is stopped. This returns the value undefined, so the cycle continues.

The string of code changes the html of the element with id a (the stopwatch). First the minutes are parsed by taking the previous stopwatch value, splitting it by the colon, and getting the minutes value, which is increased by 0 if the value of the seconds is not 59 (greater than 58), and 1 otherwise, modulo 60. Then this value is padded. Then comes the colon, and lastly, the seconds. The code simply gets the old value, increases it by 1, takes modulo 60 and optionally pads it.

Answer 9

C 309 179 bytes

f(){m=0,s=0;A: while(getchar()^'\n'){if(s++==59){if(m++==59)m=0;s=0;}printf("\r%02d:%02d",m,s);sleep(1);system("clear");if(getchar()=='\n'){break;}}while(getchar()^'\n'){}goto A;}

Ungolfed version:

void f()
{
   int m=0,s=0;

   A: while(getchar()^'\n')
      {           
       if(s++==59)
       {
         if(m++==59)
           m=0;

         s=0;
       }
       printf("\r%02d:%02d",m,s);
       sleep(1);  
       system("clear");

        if(getchar()=='\n')
        {
          break;
        }
      }

       while(getchar()^'\n')
       {}
       goto A ;
}

Usage: Press Enter to Pause and Resume the Stopwatch.

Explanation:

• Wait for Enter keystroke, break the first while loop and wait until next Enter comes.
• Upon next Enter keystroke, goto first while loop and resume counting.

Now, I know goto is a bad coding practice in C, but I could not figure out another way.

Answer 10

Javascript in Chrome console, 143 bytes

f=document,m=s=g=i=0;setInterval(()=>{if(g%2){m=(i/60|0)%60;s=i++%60}f.write((m>9?m:'0'+m)+':'+(s>9?s:'0'+s));f.close();f.onclick=()=>g++},1e3)

When entered in console it inits the counter to 00:00 and then enables the control which is keypress on the document.

Not much magic going on, notably the (i/60)|0 floors the number

Done and tested in Chrome console

Answer 11

Javascript, 124 bytes

s=i=1,setInterval("s&&(d=document).close(d.write(`0${i/60%60|0}:`.slice(-3)+`0${i++%60}`.slice(-2))),d.onclick=_=>s=!s",1e3)

The 'control key' is a click on the document. To test this, paste the code in the console or in a html file inside the <script> tag.

Explanation:

let s = 1
let i = 1
setInterval(() => {
    //If s = true then check after the "&&" operator else false
    s && (d = document).close( //put the document variable inside the d variable, so now i don't need to use anymore the long word 'document, then i close the document
            d.write( //Write into the document the next string
                `0${i/60%60|0}:`.slice(-3) + `0${i++%60}`.slice(-2) //Here is the magic, here I update the 'i' variable and convert the 'i' value to minutes and seconds
            ) 
        ),
        d.onclick = _ => s = !s //Add onclick event to the document, if s = true then s = false, if s = false then s = true
}, 1e3) //1e3 = 1000

Tested in Chrome

Answer 12

C# 220 Bytes

using static System.Console;
using static System.DateTime;
class P
{
    static void Main()
    {
        var l = Now;
        var d = l-l;
        for( var r = 1<0;;Write($"\r{d:mm\\:ss}"))
        {
            if (KeyAvailable&&ReadKey(1<2).KeyChar == 's')
            {
                l = Now;
                r = !r;
            }
            if (r)
                d -= l - (l = Now);
        }

    }
}

Golfed

using static System.Console;using static System.DateTime;class P{static void Main(){var l=Now;var d=l-l;for(var r=1<0;;Write($"\r{d:mm\\:ss}")){(KeyAvailable&&ReadKey(1<2).KeyChar=='s'){l=Now;r=!r;}if(r)d-=l-(l=Now);}}}

Using the s key to start/stop. Whole program works by remembering the TimeDelta using DateTime.Now

Most C#-Magic here comes from the C# 7.0 feature using static.

Answer 13

PHP, 94 91 bytes

I assume that 32 is the key code for the space bar (which it probably is not);
I currently have no way to test ncurses. But the rest of the code works fine.

for($s=[STDIN];;)echo date("\ri:s",$t+=$r^=stream_select($s,$n,$n,1)&&32==ncurses_getch());

starts at 00:00, but increments immediately when pause ends

If You (like me) don´t have ncurses, You can test by replacing the second date parameter with $t+=$r^=!rand(sleep(1),19); or $t+=$r^=++$x%20<1+sleep(1);. (sleep always returns 0.)

breakdown

for($s=[STDIN];                     // set pointer for stream_select
    ;                               // infinite loop:
)
    echo date("\ri:s",                  // 5. print CR + time
        $t+=                            // 4. increment $t if watch is running
        $r^=                            // 3. then toggle pause
            stream_select($s,$n,$n,1)   // 1. wait 1 second for a keystroke
            &&32==ncurses_getch()       // 2. if keystroke, and key==space bar
    ;

Answer 14

Bash, 65 bytes

trap d=\$[!d] 2;for((;;)){ printf "\r%(%M:%S)T" $[n+=d];sleep 1;}

Note that it must be written to a file script to work correctly, or else, try:

bash -c 'trap d=\$[!d] 2;for((;;)){ printf "\r%(%M:%S)T" $[n+=d];sleep 1;}'

Extended version to explain it:

trap d=\$[!d] 2                     # flip d for each INT (ctrl-c) signal.
for((n=0;;)){                       # repeat forever the code inside the {...}
                                    # The n=0 is not strictly needed.
    printf "\r%(%M:%S)T" "$[n+=d]"  # Print Minute:Second string calculated from 
                                    # the n value, increment by the value of d.
                                    # If IFS is not numeric (0-9), then, the
                                    # quotes around "$[n+=d]" could be removed.
    sleep 1                         # wait for 1 second.
}

The %(...)T format to printf is valid in bash 5+.

Answer 15

C (gcc), 121 115 bytes

p,r;g(){r^=1;}main(t,b){for(b=time(signal(2,g));;r?p=t:(b+=t!=p))t=time(0)-b,printf("\r%02d:%02d  ",t/60%60,t%60);}

Try it online!

Sets a signal handler for SIGINT, which is triggered by pressing control-C. We keep a time offset in b, and display the wall clock time minus the time offset. If we are paused, increment the time base everytime the wall clock ticks to freeze the displayed time.

Thanks to @ceilingcat for shaving off 6 bytes!

Answer 16

Zsh + Gnu date, 242 bytes

Featuring 1/100ths of a second! It requires an interactive terminal, but here's a TIO link anyway.
Hit Enter to start/stop the timer; Ctrl-C to exit.

u(){p=`gdate +%s`;q=`gdate +%N`;}
f(){read -t0.01&&{read;break};unset REPLY}
g(){while :;{u;t=$[p-a];s=$[t%60];m=$[(t%3600-s)/60]
echo "\r`printf %02d:%02d $m $s`.$q[1,2]\c";f;}}
<<<ready;read;u;a=$p
while :;{f;echo "\r\e[2A\c";u;a=$[p-t];g;}

Comments (a bit out of date):

u()echo $[`gdate +%s%N`/1000]       # fn:unix timestamp extended to µs
v()gdate +%s                        # fn:unix time, in s
f(){read -t0.01 -r&&{read -r;break;} # fn:listens for "Enter"
                      ;unset REPLY;}

g(){while :;                        # fn:rolling stopwatch
    {q=`u`;t=$[`v`-a]               #    t=time diff from baseline (s)
    ;echo "\r`printf %02d:%02d      #    format output
    $[(t%3600-s)/60] $s`            #    minutes:seconds
    .${q:10:2}\c";                  #    .xx = partial seconds
    f;}}                            #    listen for "Enter"

                                    # Execution starts here!
<<<ready;read;u;a=$p                # Wait for "Enter"; get baseline $a

while :;{                           # Main program loop
         f;                         # listen for an "Enter"
           echo "\r\e[2A\c"         # go up 1 line of the console
a=$[`v`-t]                          # reset the baseline
                ;g;}                # begin the stopwatch

Answer 17

Commodore BASIC (C64/TheC64 Mini, VIC-20, PET, C16/+4) - 147 tokenized and BASIC bytes

 0?"{clear}":geta$:ifa$<>" "thengoto
 1ti$="000000"
 2fori=.to1:?"{home}"mid$(ti$,3,2)":"mid$(ti$,5,2):geta$:b$=ti$:i=-(a$=" "):nE:pO198,.
 3geta$:ifa$<>" "then3
 4ti$=b$:goto2

{clear} in the listing is SHIFT+CLR/HOME which outputs as one PETSCII character when following an opening quotation mark, whereas {home} is the CLR/HOME key without the shift on the same condition of following an opening quotation mark.

Use the space bar as the control key.

To work with the Commodore 128 in BASIC 7, change the listing in the following lines:

 0?"{clear}":geta$:ifa$<>" "thengoto0
 2fori=.to1:?"{home}"mid$(ti$,3,2)":"mid$(ti$,5,2):geta$:b$=ti$:i=-(a$=" "):nE:poK198,.

Adds an extra seven tokens to the count (as all numbers are stored in BASIC as 7 bytes, so goto10 is 8 tokenized bytes whereas goto is only 1).