问在foreach循环中减去两个数字，并显示每个结果的结果。

EN

    <?php

        setlocale(LC_MONETARY, 'en_GB'); 

        // LET US IMAGINE FOR A MOMENT THAT $wrap_query->result() CONTAINS
        // THE FOLLOWING SIMULATED DATA MIMICKING YOUR DATA STRUCTURE...
        $simulatedWrap1     = new stdClass();
        $simulatedWrap2     = new stdClass();
        $simulatedWrap3     = new stdClass();

        $simulatedWrap1->wrap_date  = "2016-08-07";
        $simulatedWrap1->wrap_total = 10000.00;

        $simulatedWrap2->wrap_date  = "2016-08-06";
        $simulatedWrap2->wrap_total = 12000.00;

        $simulatedWrap3->wrap_date  = "2016-08-05";
        $simulatedWrap3->wrap_total = 8000.00;

        $rWrapCollection    = [
            $simulatedWrap1,
            $simulatedWrap2,
            $simulatedWrap3,
        ];

        // MAKE A COPY OF THE MAIN ARRAY COLLECTION
        // THIS WOULD BE USED WITHIN THE LOOP TO MOVE THE ARRAY CURSOR
        // TO THE NEXT ELEMENT WITHIN THE COLLECTION
        $rWrapClone         = $rWrapCollection;

        // JUST FOR FUN: EXPLICITLY MOVE THE CURSOR TO THE FIRST
        // ELEMENT IN THE COLLECTION
        current($rWrapClone);

        // CREATE AND INITIALIZE A VARIABLE $output TO AN EMPTY STRING.
        // THIS VARIABLE WILL HOLD THE HTML CONTENT GENERATED WITHIN THE LOOP
        $output             = "";

        foreach ($rWrapCollection as $index=>$wrap){
            // MOVE THE CURSOR TO THE NEXT ITEM & CATCH THE VALUE IN A VARIABLE 
            $nextWrap       = next($rWrapClone);
            $output        .= date("D d M Y", strtotime($wrap->wrap_date)) . " - ";
            $output        .= money_format('%n', $wrap->wrap_total);

            // IF THERE IS STILL ANY NEXT ITEM, THEN CALCULATE
            // THE DIFFERENCE BETWEEN THE CURRENT & NEXT ITEM       
            if($nextWrap){
                $difference = $wrap->wrap_total - $nextWrap->wrap_total;
                $output    .= " (" . money_format('%n',$difference) . ")";
            }

            $output .= "<br />";
        }

        echo $output;

        //PRODUCES:
        Sun 07 Aug 2016 - £10,000.00 (-£2,000.00)
        Sat 06 Aug 2016 - £12,000.00 (£4,000.00)
        Fri 05 Aug 2016 - £8,000.00

    <?php

        $output         = "";
        $resultsCopy    = $wrap_query->result();
        current($resultsCopy);

        foreach ($wrap_query->result()  as $wrap) {
            $nexWrap        = next($resultsCopy);
            $output        .= date("D d M Y", strtotime($wrap->wrap_date)) . " - ";
            $output        .= money_format('%n', $wrap->wrap_total);

            if($nexWrap){
                $difference = $wrap->wrap_total - $nexWrap->wrap_total;
                $output    .= " (" . money_format('%n',$difference) . ")";
            }

            $output .= "<br />";
        }

        echo $output;

$previous = null;
foreach ($wrap_query->result() as $wrap) {
    if ($previous) {
        echo " (" .money_format('%n', $previous->wrap_total - $wrap->wrap_total) .")<br>";
    }
    echo date("D d M Y", strtotime($wrap->wrap_date))." - ";
    echo money_format('%n', $wrap->wrap_total);
    $previous = $wrap;   // set previous to current
}