<?php
/**
 * This function returns
 * the Total no. of vowels
 * present in the given
 * string using a simple
 * method of looping
 * through all the
 * characters present in
 * the string.
 *
 * @param string $string
 * @return int   $noOfVowels
 */
function countVowelsSimple(string $string)
{
    if (empty($string)) {
        throw new \Exception('Please pass a non-empty string value');
    }

    $noOfVowels = 0;
    $vowels     = ['a', 'e', 'i', 'o', 'u']; // Vowels Set
    $string     = strtolower($string); // For case-insensitive checking
    $characters = str_split($string); // Splitting the string to a Character Array.

    foreach ($characters as $character) {
        if (in_array($character, $vowels)) {
            $noOfVowels++;
        }
    }

    return $noOfVowels;
}

/**
 * This function returns
 * the Total no. of vowels
 * present in the given
 * string using a
 * regular expression.
 *
 * @param string $string
 * @return int
 */
function countVowelsRegex(string $string)
{
    if (empty($string)) {
        throw new \Exception('Please pass a non-empty string value');
    }
    $string = strtolower($string); // For case-insensitive checking

    return preg_match_all('/[a,e,i,o,u]/', $string);
}