Minutes command in TeX

There is no expandable way to access the time in hours and minutes in Knuth TeX, which can only do arithmetic via register assignments.

Well, there might be, with some recursion magic.

It's much easier if you allow e-TeX extensions:

longdeffirstoftwo#1#2{#1}
longdefsecondoftwo#1#2{#2}
defminutes{computeminutestime}
defcomputeminutes#1{%
  ifnum#1<60
    expandafterfirstoftwo
  else
    expandaftersecondoftwo
  fi
  {#1}{expandaftercomputeminutesexpandafter{thenumexpr#1-60relax}}%
}
defhours{expandaftercomputehourstime}
defcomputehours#1{thenumexpr(#1-computeminutes{#1})/60relax}

deflongtime{printlongtimetime}
defprintlongtime#1{%
  ifnumcomputehours{#1}<10 0ficomputehours{#1}%
  :%
  ifnumcomputeminutes{#1}<10 0ficomputeminutes{#1}%
}

hours, minutes, longtime

computehours{955}, computeminutes{955}, printlongtime{955}

computehours{905}, computeminutes{905}, printlongtime{905}

computehours{37}, computeminutes{37}, printlongtime{37}

computehours{0}, computeminutes{0}, printlongtime{0}

bye

Why doing the long way? Because division in numexpr rounds, rather than truncate.

The final examples are meant to emulate different times.

With expl3 (that can also be used in plain TeX):

input expl3-generic

ExplSyntaxOn

cs_new:Npn minutes { int_to_arabic:n { c_sys_minute_int } }
cs_new:Npn hours { int_to_arabic:n { c_sys_hour_int } }
cs_new:Npn longtime
 {
  int_compare:nT { c_sys_hour_int < 10 } { 0 }
  hours
  :
  int_compare:nT { c_sys_minute_int < 10 } { 0 }
  minutes
 }

ExplSyntaxOff

I give much simpler calculation of minutes and hours than egreg:

defhours{numexpr (time+30)/60-1relax}
defminutes{numexpr time-60*hours relax}

thehours, theminutes

bye

Well, there might be, with some recursion magic.

Here it is then, a minute macro that works in ANY engine :)

It differs from wipet's minutes because his macro emulates a TeX register which you can access with the, while with this one you can't, because Knuth's TeX doesn't have fake registers like ε-TeX's numexpr.

catcode`@=11
defminute{numberexpandaftermin@ithetime{}{}{};}
defmin@i#1#2#3#4#5;{min@ii#1#2#3#4;}
defmin@ii#1;{ifnum#1>59 expandaftermin@iinumbermin@decr@hourelse #1fi}
defmin@decr@hourelse#1fi{fimin@reverse#1{}{};}
defmin@reverse#1#2#3#4#5;{min@minus@sixty#4#3#2#100;}
defmin@afterfi#1#2fi{fimin@re@reverse#1{}{};}
defmin@re@reverse#1#2#3#4#5;{#4#3#2#1;}
defmin@minus@sixty#1#2#3#4#5;{ifcase#2
     min@minus@one{#3}{#4}{#14}ormin@minus@one{#3}{#4}{#15}%
  ormin@minus@one{#3}{#4}{#16}ormin@minus@one{#3}{#4}{#17}%
  ormin@minus@one{#3}{#4}{#18}ormin@minus@one{#3}{#4}{#19}%
  ormin@afterfi{#10#3#4}ormin@afterfi{#11#3#4}%
  ormin@afterfi{#12#3#4}ormin@afterfi{#13#3#4}%
  fi}
defmin@minus@one#1#2#3{ifcase#1 min@minus@one{#2}{}{#39}% 0
  ormin@afterfi{#30#2}ormin@afterfi{#31#2}ormin@afterfi{#32#2}%
  ormin@afterfi{#33#2}ormin@afterfi{#34#2}ormin@afterfi{#35#2}%
  ormin@afterfi{#36#2}ormin@afterfi{#37#2}ormin@afterfi{#38#2}%
  fi}
catcode`@=12

edefx{minute}showx

end

The algorithm is really stupid. It takes the tokens from the expansion of thetime, and successively subtracts 60 from that, until what remains is less than 60, and returns that. The subtraction, in the lack of numexpr, is done by a ten-way ifcase that looks at the tens digit of the number, and returns the value subtracted (no arithmetic was harmed in the making of this code :)