PHP: Forming strings with loops

Loops also allow you to generate strings. This is a common task for web development. It's merely basic aggregation using interpolation or concatenation.

One especially popular task among interviewers is to do a string reversal. There are lots of ways to solve it, but the most basic is by iterating each character. Have a look at how this function works:

<?php

reverse('Hexlet'); // telxeH

The general idea of a string reversal is that you take characters one by one from the beginning of the string and then connect them together in reverse order. Sounds like a piece of cake. Now let's examine it:

<?php

function reverse($str)
{
    $i = 0;
    // A neutral element in terms of strings is an empty string
    $result = '';

    while ($i < strlen($str)) {
        $currentChar = $str[$i];
        // Join it together it in reverse order
        $result = "{$currentChar}{$result}";
        // The same through concatenation
        // $result = $currentChar . $result;
        $i = $i + 1;
    }

    return $result;
}

$name = 'Bran';
reverse($name); // 'narB'
// Neutral element check
reverse(''); // ''

https://replit.com/@hexlet/php-basics-loops-using-reverse

Perhaps the only tricky part here is getting a feel of how the string itself is built. Since each next character is attached to the resulting string on the left, the string ends up reversed.

Instructions

Implement the mysubstr() function, which extracts a substring of a specified length from a string. It takes two arguments (string and length) and returns a substring starting from the first character:

Call example:

<?php

$str = 'If I look back I am lost';
mysubstr($str, 1); // 'I'
mysubstr($str, 7); // 'If I lo'

https://replit.com/@hexlet/php-basics-edge-cases-mysubstr

Use the same approach as you did for the function to flip the string from the lesson: assemble the resulting string in a loop by looping through the initial string up to a certain point.