Adding and subtracting within a range of numbers and looping round - php

Question

I'm wondering how I would go about the addition and subtraction of numbers in a set range and which would loop back on themselves, example below;
Range: 1 - 10
So if I now had the number 7 and added 5 to it, I would want the number go to 2
8, 9, 10, loop around to 1, 2.
And the same if I subtracted, so I have the number 3 and I subtract 4 so I should be left with 9.
2, 1, loop around to 10, 9
I hope this makes sense.
Thanks.

Answer 1

You can use % operator.
It calculates remainder after division.
For example:
$d = 10;
$x = 7;
$y = 5;
echo ($x + $y) % $d;
gives 2;
With negative values you can just remove MINUS

Answer 2

Use the modulus operator.
result = (a + b) % 10;

Answer 3

You can use modulo function like (7+5)%10 = 2

Answer 4

Try this:
$range = range(1,10);
$min = min($range);
$max = max($range);
function operate( $a, $b, $operation ) {
global $max, $min;
switch( $operation ) {
case '+':
$a += $b;
break;
case '-':
$a -= $b;
break;
}
if( $a < $min ) {
return $max + $a;
} else if( $a > $max ) {
return $a - $max;
}
}
Hope it helps.

Answer 5

You can do this with code like
$range = array('from' => 3, 'to' => 13);
$dist = $range['to'] - $range['from'];
$a = 7;
$b = 14;
echo ($dist + ($a % $range['to'] - $b % $range['to'])) % $dist; // $a - $b
echo ($dist + ($a % $range['to'] + $b % $range['to'])) % $dist; // $a + $b

Answer 6

Modulo will do the trick as others have shown, but you must also account for the lower end of the range.
E.g. looping an arbitrary value within an hour range will work since it's zero-based. But if you want to loop a value within a month range you will get into trouble with the last day, because:
31 % 31 = 0
So you will loop to zero when you should remain on 31.
To deal with any range, you need to do this:
$min = 5;
$max = 15;
$value = 25; // The range is 11, so we want this turned into 14
$range = $max - $min + 1;
$value = (($value-$min) % $range) + $min;
To deal with values below minimum:
$range = $max - $min + 1;
$value = ($min - $value) % $range;
$value = $max - ($value - 1);