for what you described... you can just divide by 10, as when working with integers, the rounding is truncated in quest (I think, lol):
game.minutes = game.minutes + (game.combat_rounds / 10)
// 5 / 10 = 0
// 10 / 10 = 1
// 14 / 10 = 1
// 15 / 10 = 1
// 19 / 10 = 1
// 20 / 10 = 2
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though, if you wanted to do more advance stuff, there's:
the 'modulus ' Operator: %
this is a division operation, except it finds the remainder
the modulus operator is great for 'cycles', such as 0-59 seconds/minutes or 0-11/0-23 hours, etc etc etc
for example:
game.military_hours = game.turns % 24
// turn: 0, hour: 0
// turn: 1, hour: 1
// turn: 23, hour: 23
// turn: 24, hour: 0
// turn: 25, hour: 1
// turn: 47, hour: 23
// turn: 48, hour: 0
game.civilian_hours = game.turns % 12
// turn: 0, hour: 0
// turn: 1, hour: 1
// turn: 11, hour: 11
// turn: 12, hour: 0
// turn: 13, hour: 1
// turn: 23, hour: 11
// turn: 24, hour: 0
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also, the modulus allows for stuff like this:
is the number even or odd?
if (game.number % 2 = 0) { msg ("The number is even") } else { msg ("The number is odd") }
// any number divided by 2, not having a remainder, is even
// 10 / 2 = 5 R 0 = even
// 11 / 2 = 5 R 1 = odd
// 19 / 2 = 9 R 1 = odd
// 20 / 2 = 10 R 0 = even
and so you can use this for many other things, which use other values besides (divisible by) 2... and probably able to use other values besides '=0' too.
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here's some links of my own work with trying to learn date+time coding:
viewtopic.php?f=18&t=4162 // this was before I knew of the modulus operator, lol
viewtopic.php?f=18&t=4317 // and here's more of me struggling with date+time coding, lol