PHP: For loop

A while loop works perfectly for situations where the number of iterations isn't known in advance, e.g., finding a prime number. When we do know the number of iterations, it's better to use a for loop.

Let's have a look at a function that reverses strings using a for loop:

<?php

function reverseString($str)
{
    $result = '';

    for ($i = 0; $i < strlen($str); $i += 1) {
        $currentChar = $str[$i];
        $result = "{$currentChar}{$result}";
    }

    return $result;
}

https://replit.com/@hexlet/php-basics-for-reversestring

You can read it like this: «the loop with index $i repeats until $i < strlen($str) and after each step increases $i by 1».

1. The initial counter value. This code runs exactly once before the first iteration.
2. Predicate condition to decide when cycle repeats. It's executed on each iteration. This is exactly what we have with while
3. Description of the counter change. This code is executed at the end of each iteration.

Other than that, it works exactly the same as a while loop.

Instructions

Implement a function called sumOfSeries(), which counts the sum of a series of integers. A series is given using two numbers, a start number and an end number.

The function takes two number arguments and returns the sum of the series. For example, if you pass 4 and 7 as arguments, the sum will be 4 + 5 + 6 + 7 = 22.

<?php

sumOfSeries(1, 2); // 3
sumOfSeries(1, 3); // 6
sumOfSeries(4, 7); // 22

If the initial and final numbers are equal, the result will be the same number:

<?php

sumOfSeries(1, 1); // 1