<?php
// get the base frequency
$startingFrequency = 0;

// get the contents given by the advent_of_code website
$fContents = file_get_contents("external_contents/day_1.txt");

// loop through each line of the contents (delimit by new line)
foreach((array) explode(PHP_EOL, $fContents) as $number) {
    // make sure the number is numeric
    if(is_numeric($number)) {
        // add the number to the starting frequency
        $startingFrequency += $number;
    }
}

// return the end result
echo "End result: " . $startingFrequency;