<?php
function properCase( $string ) {
    $array = explode(' ', strtolower($string));
    $cidade = '';
    $ignorar = array( 'do', 'dos', 'da', 'das' );
 
    foreach ($array as $ar) {
        if( !in_array ( $ar, $ignorar ) ) {
           $ar = ucfirst( $ar );
        }
        $cidade .= $ar.' ';
    }
    return trim( $cidade );
}
 
echo properCase( 'PORTO DE GALINHAS' ).PHP_EOL;
echo properCase( 'HOSPITAL DOS PLANTADORES DE CANA' ).PHP_EOL;
echo properCase( 'rua do vergueiRO' ).PHP_EOL;

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