我的php计算没有显示结果

Question

我有一个非常愚蠢的问题。我正在从 mysql 中提取收入和支出的总额，然后我想从收入中减去支出。由于某种原因，结果不是剩下的，而是显示了收入数字 - 支出数字。

代码如下

function total_by_type_between_dates($type, $start, $end){

    global $uc_con;

    $start  = strtotime ($start);

    $end    = strtotime ($end);

    $sql    = "SELECT SUM(amount) AS total FROM account WHERE `time` > $start && `time` < $end &&  `type` = '$type'";

    $result = $uc_con->query($sql);

    $row    = $result->fetch_array(MYSQLI_ASSOC);

    $total  = number_format((float)$row['total'], 2, '.', '');

    echo $total;

}

function total_expense_between_dates($start, $end){

    global $uc_con;

    $start  = strtotime ($start);

    $end    = strtotime ($end);

    $sql    = "SELECT SUM(amount) AS total FROM account WHERE `time` > $start && `time` < $end && `type` != 'income' && `type` != 'mileage'";

    $result = $uc_con->query($sql);

    $row    = $result->fetch_array(MYSQLI_ASSOC);

    $total  = number_format((float)$row['total'], 2, '.', '');

    return $total;

}

echo total_by_type_between_dates('income', $date_begining, $date_ending)-total_expense_between_dates($date_begining, $date_ending);

奇怪的是结果显示如下：2770.69-407.42而不是2363.29

谁能告诉我可能是什么原因造成的

Answer 1

您的total_by_type_between_dates函数正在回显其结果而不是返回它。所以你的echo&nbsp;total_by_type_between_dates('income',&nbsp;$date_begining,&nbsp;$date_ending)-total_expense_between_dates($date_begining,&nbsp;$date_ending);有效地echo&nbsp;total_by_type_between_dates('income',&nbsp;$date_begining,&nbsp;$date_ending); echo&nbsp;null-total_expense_between_dates($date_begining,&nbsp;$date_ending);并且null在数字上下文中被视为 0，因此您看到的结果是：2770.69-407.42改变echo&nbsp;$total;在total_by_type_between_dates到return&nbsp;$total;并且代码将按预期工作。3v4l.org 上的精简演示