I'm writing a script that needs to identify every 7th number where the first number of the sequence is 0 (so the sequence is 6, 13, 20, 27, 34, 41, 48, etc.)
Here's what I've got so far (which works in a limited way), but I'd prefer to write a loop so that the values in the sequence don't have to be hardcoded:
<?php
$x = 7;
if ($x === 6 || $x === 13 || $x === 20 || $x === 27 || $x === 34 || $x === 41 || $x === 48) {
$result = 1;
} else {
$result = 0;
}
echo $result;
?>
Thanks in advance for any advice!
Update: Here's my updated script using @robbieaverill 's solution and checking the values against an array. There are many great solutions here, thanks everyone!
<?php
$divisor = 7;
$limit = 500;
$sequence = array();
for ($i = 0; $i <= $limit; $i++) {
if (is_int(($i + 1) / $divisor)) {
$sequence[] = $i;
}
}
$x = 41;
if (in_array($x, $sequence, true)) {
$result = 1;
} else {
$result = 0;
}
echo $result;
?>
The output here is 1, indicating that if the value of $x is 41 it is found within the $sequence array.
There's probably a bunch of different ways you could do this. If you need to identify numbers that are evenly divisible by 7 (plus one, because you're zero based), you could do something like this:
$divisor = 7;
$limit = 100; // when do you want to stop searching?
for ($i = 0; $i <= $limit; $i++) {
if (is_int(($i + 1) / $divisor)) {
var_dump($i);
}
}
Note that is_int() is checking whether the divided result is a whole number, it'd return false for a decimal/floating point number.
A solution like this would work also.
$index = 0;
for($i = 0; $i <= 700; $i++){
if($index == 6){
echo $i . "<br/>";
$index = 0;
} else {
$index++;
}
}
will output 6 13 20 27 34 41 48 55
And here's another way of doing that using the modulus operator:
<?php
$start = 0;
$sequence = 7;
$limit = 100;
for ($i=$start; $i<$limit; $i++) {
// if the divition of the current number / the sequence is a full number (there is no remainder) and we're not at 0
if(($i+1) % $sequence == 0 && $i!=0) {
echo $i . "<br>";
}
}
// output:
6
13
20
27
34
41
48
55
62
69
76
83
90
97
Since you said "that needs to identify every 7th number" you maybe only wanna check if a given number is one of a 7th, meaning you want a function to test. Then this could help:
function isMultipleOf($input, $sequence) {
if(($input+1) % $sequence == 0 && $input!=0) {
return true;
} else {
return false;
}
}
$check = 601;
echo isMultipleOf($check, $sequence); // true/1;
$check = 2;
echo isMultipleOf($check, $sequence); // false;
In General we could write an arithmetic sequence like this:
{a, a+d, a+2d, a+3d, ... }
Where a = 6 (the first term) d = 7 (the "common difference" between terms)
so we can have {a, a+d, a+2d, a+3d, ... }
{6, 6+7, 6+2×7, 6+3×7, ... }
{6, 13, 20, 27, ... } so we can have a rule
x[n] = a + d(n−1)
which can be written in php as below
<?php
$a=6;
$n=10; //number of terms
$d=7;
for($i=1;$i<=10;$i++){
echo $term=$a+($i-1)*$d;
echo "<br>";
}
?>
Add 1 to sequential number $i and use modulus n and return $i % 7 == 0.
E.g.
function isNth(int $i, int $nth, int $offset = -1): bool
{
return !(($i - $offset) % $nth);
}
Usage example:
foreach ([0,1,2,3,4,5,6,7,8,9,10,11,12,13] as $number)
{
if (isNth($number, 7)) print "$number
";
}
// will print 6
13
foreach ([1,2,3,4,5,6,7,8,9,10,11,12,13,14] as $number)
{
if (isNth($number, 7, 0)) print "$number
";
}
// will print 7
14
So if you have a list of number best thing would be
<?php
$list = array(0,1,8,89,785,0,789785,56,8,9,1,2,3,2);
for($i = 0; $i < count($list);$i++){
if($list[$i] === 0){
echo "Found and occurence. Value is ".($list[$i+7])."<br>";
}
}
?>
Will output Found and occurence. Value is 56 Found and occurence. Value is 3
Consider using range to generate the series:
$begin = 6;
$end = 48;
$step = 7;
$seq = range($begin, $end, $step);
print_r($seq);
Then you can check if a number is in that series using in_array:
if (in_array(41, $seq)) // ...
This is in no way efficient, but it's an obvious implementation that works very well for small series. By small I mean thousands of entries or fewer.