PHP - how count percent of each value in array

Use array_map():

$a = array(10, 15, 20, 25, 30);
$a = array_map(function($value) { return $value * 1.05; }, $a);

Gives: array(10.5, 15.75, 21, 26.25, 31.5);

The array_map function should be the solution you are looking for (documentation here).

I guess you'll have to create a function like this :

function fivePercent($n)
{
    return($n * 1.05);
}

And use array_map to call it on each number in your array :

$b = array_map("fivePercent", $a);

edit : Working code here.

edit 2 : According to the answer here, it is faster to use foreach, but since you asked not to use it, calling a named function is much faster than writing the function in the array_map call. Anyway, it doesn't matter with small arrays, just consider this when you have a lot of numbers to deal with.

Here is your custom function,

$arr = array_map(function($i){
        return $i+($i*0.05);
    }, $arr);
    print_r($arr);

Here is working code.

array_map — Applies the callback to the elements of the given arrays

function myfunction($num)
{
  return($num + ($num * .05));
}

$a=array(10, 15, 20, 25, 30);
print_r(array_map("myfunction",$a));

Output:

Array ( [0] => 10.5 [1] => 15.75 [2] => 21 [3] => 26.25 [4] => 31.5 )

Use Array_map function of php

$a = array(10, 15, 20, 25, 30);
$arrReturn = array_map("increment", $a);
print_r($arrReturn);

function increment($n){
    $return = $n + ($n * .5);
    return $return;
}

Of course, a language construct can be used to loop the array and an as proven by several other answers array_map() will do the job, but when you want to apply a user function to every element in an array, that is what array_walk() is designed for. The values are "modified by reference" as they are iterated instead of creating a whole new array then overwriting the old data with the new returned array.

Use the Mulitplication Assignment Operator to apply the 5% boost to each value encountered.

Code: (Demo)

function fivePercentIncrease(&$value) {
    $value *= 1.05;
}

$a = [10, 15, 20, 25, 30];

array_walk($a, 'fivePercentIncrease');

var_export($a);

Or via an anonymous function: (Demo)

$a = [10, 15, 20, 25, 30];

array_walk($a, function(&$value) { $value *= 1.05; });

var_export($a);

Or via an anonymous function using PHP7.4's arrow function syntax: (Demo)

$a = [10, 15, 20, 25, 30];

array_walk($a, fn(&$value) => $value *= 1.05);

var_export($a);