PHP - get array value if next element is not series - php

Question

Here is my array
$array = array( 0 => 10, 1 => 9, 2 => 8, 3 => 6, 4=> 4 );
I want to get array value 6. because, 7 is missing before this value/series is break.
Please help me how can I do it easy & fast method.

Answer 1

The sequence could be calculated by subtracting the first value from the second value. Then you could for example use a for loop to loop through the values of the array and check if there is also a next value available by checking if there is an index + 1.
Then if that is the case you can subtract the current value in the loop from the next value and check if that result equals the step size.
If that is not the case, the next value of the iteration is the value that breaks the sequence and you can break out of the loop.
$array = [10,9,8,6,4];
if (count($array) > 2) {
$step = $array[0] - $array[1];
for ($i = 0; $i < count($array); $i++) {
if (isset($array[$i + 1]) && $array[$i] - $array[$i + 1] !== $step) {
$wrongValue = $array[$i + 1];
echo sprintf(" The step count is %d, but after %d comes %d which breaks the sequence.",
$step, $array[$i], $wrongValue
);
break;
}
}
}
Demo

Answer 2

<?php
$sequence =
[
0 => 10,
1 => 9,
3 => 8,
4 => 6,
5 => 4
];
$last = null;
foreach($sequence as $k => $v)
{
if(!is_null($last) && $last - $v > 1)
break;
$last = $v;
}
var_dump($k, $v);
Output:
int(4)
int(6)

Answer 3

Loop through it, save the previous values and compare with current one:
<?php
function findMissing($array) {
$missing = [];
foreach($array as $key => $val) {
if(isset($previousValue) && $previousValue-1!=$val) {
echo "not in series: ".($previousValue-1) .", returning ".$val."<br>\n";
$missing[] = $val;
}
$previousValue=$val;
}
return $missing;
}
// USAGE:
$array = array( 0 => 10, 1 => 9, 2 => 8, 3 => 6, 4=> 4 );
findMissing($array);
// not in series: 7, returning 6
// not in series: 5, returning 4
$array2 = array( 10, 9, 8, 6, 5 );
$missingValues = findMissing($array2);
// not in series: 7, returning 6
var_dump($missingValues);
// array(1) { [0]=> int(6) }

Answer 4

I'm not sure I understand what you want to achieve, but let's start it here.
UPDATED:
for($i = 0; $i < count($array); ++$i) {
if($i > 0) {
if($array[$i] != ($array[$i-1]-1)) {
echo($array[$i]);
break;
}
}
}
Output:
6