未定义的变量：php 网络应用程序中的 monthly_error

Question

这是一道作业题，但我想问的是我错在哪里。我一直在寻找，看不出哪里出错了。当我运行应用程序时，出现以下错误：
未定义的变量：monthly_rate

在这一行中：
$monthly_rate_f = number_format($monthly_rate, 2).'%';

这是应用程序的完整代码：

<?php
    // get the data from the form
    $investment = filter_input(INPUT_POST, 'investment', FILTER_VALIDATE_FLOAT);
    $interest_rate = filter_input(INPUT_POST, 'interest_rate', FILTER_VALIDATE_FLOAT);
    $years = filter_input(INPUT_POST, 'years', FILTER_VALIDATE_INT);

    // validate investment
    if ($investment === FALSE ) {
        $error_message = 'Investment must be a valid number.';
    } else if ( $investment <= 0 ) {
        $error_message = 'Investment must be greater than zero.';
    // validate interest rate
    } else if ( $interest_rate === FALSE )  {
        $error_message = 'Interest rate must be a valid number.';
    } else if ( $interest_rate <= 0 ) {
        $error_message = 'Interest rate must be greater than zero.';
    // validate years
    } else if ( $years === FALSE ) {
        $error_message = 'Years must be a valid whole number.';
    } else if ( $years <= 0 ) {
        $error_message = 'Years must be greater than zero.';
    } else if ( $years > 30 ) {
        $error_message = 'Years must be less than 31.';
    // set error message to empty string if no invalid entries
    } else {
        $error_message = '';
    }

    // if an error message exists, go to the index page
    if ($error_message != '') {
        include('index.php');
        exit();
    }

    // calculate the future value
    $future_value = $investment;
    if (isset($_POST["monthly"])) {
        $compounded_monthly = "Yes";
        $months = $years * 12;
        $monthly_rate = $interest_rate / 12;
        for ($i = 1; $i <= $months; $i++) {
            $future_value = $future_value + ($future_value * $monthly_rate * .01);
        }
    } else {
        for ($i = 1; $i <= $years; $i++) {
            $future_value = $future_value + ($future_value * $interest_rate * .01);
        }
    }

    // apply currency and percent formatting
    $investment_f = '$'.number_format($investment, 2);
    $yearly_rate_f = $interest_rate.'%';
    $future_value_f = '$'.number_format($future_value, 2);
    $monthly_rate_f = number_format($monthly_rate, 2).'%';
?>

<!DOCTYPE html>
<html>
<head>
    <title>Future Value Calculator</title>
    <link rel="stylesheet" type="text/css" href="main.css"/>
</head>
<body>
    <main>
        <h1>Future Value Calculator</h1>

        <label>Investment Amount:</label>
        <span><?php echo $investment_f; ?></span><br>

        <?php
        if (isset($_POST["monthly"])) {
            echo "<label>Monthly Interest Rate:</label>";
            echo "<span>".$monthly_rate_f."</span><br>";
            echo" <label>Number of Months:</label>";
            echo "<span>".$months."</span><br>";
            echo" <label>Future Value:</label>";
            echo"<span>".$future_value_f."</span><br>";
            echo"Compound Monthly:".$compounded_monthly."</br>";
        } else {
            echo "<label>Yearly Interest Rate:</label>";
            echo "<span>".$yearly_rate_f."</span><br>";
            echo" <label>Number of Years:</label>";
            echo "<span>".$years."</span><br>";
            echo" <label>Future Value:</label>";
            echo"<span>".$future_value_f."</span><br>";
        }
        ?>

    </main>
</body>
</html>

Answer 1

$monthly_rate 仅在条件的一半中定义：

if (isset($_POST["monthly"])) {
    $monthly_rate = $interest_rate / 12;
} else {
    // ...
}

因此，如果您的程序到达该语句的 else 分支，则它不会被定义，但无论如何您稍后仍会尝试使用它：

    $monthly_rate_f = number_format($monthly_rate, 2).'%';

您可以将此行移到定义 $monthly_rate 的第一个分支中。

未定义的变量：php 网络应用程序中的 monthly_error

Undefined variable: monthly_error in php web application

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