CodeIgniter BMI计算器无法运行，求问题排查与修复方案

Let's walk through the errors you're seeing and fix your calculator step by step:

The Errors Explained #

• Undefined index: submit: Your submit button doesn't have a name attribute, so $_GET['submit'] doesn't exist when the form is submitted. Also, your form uses the default GET method, but we should switch to POST (more secure, and aligns with CodeIgniter's best practices).
• Undefined variable: weight/height: When the page loads for the first time (before form submission), you're trying to use $weight and $height variables that haven't been defined yet.
• Division by zero: Same as above—on initial page load, $height is undefined, so $height * $height evaluates to 0, causing a division by zero when calculating BMI.

Fixed View Code #

<div id="container"> 
    <h1>BMI and Blood Pressure Calculator</h1> 
    <div id="body"> 
        <p>This webpage allows users to calculate their BMI and Blood Pressure by entering in their values into the boxes</p> 
        </br> 
        <p>Please enter in your details below (use meters for height, kilograms for weight)</p>
        <!-- Add method="post" and action to submit to same page -->
        <form method="post" action=""> 
            <br /> 
            <br />Patient Information 
            <br />Height (m) <input type="text" name="height" size="12" maxlength="20" value="<?php echo $this->input->post('height') ?? ''; ?>"> 
            <br />Weight (kg) <input type="text" name="weight" size="12" maxlength="20" value="<?php echo $this->input->post('weight') ?? ''; ?>"> 
            <br /> 
            <br /><input type="reset" value="Clear Form"> 
            <!-- Add name="submit" to detect form submission -->
            <br /><input type="submit" name="submit" value="Submit Information"> 
        </form> 
    </div> 

    <?php
    // Only run BMI logic when form is submitted
    if ($this->input->post('submit')) {
        // Get and clean up POST values
        $height = trim($this->input->post('height'));
        $weight = trim($this->input->post('weight'));

        // Validate inputs to avoid invalid calculations
        if (!empty($height) && !empty($weight) && is_numeric($height) && is_numeric($weight) && $height > 0) {
            function bmi($height, $weight) {
                return $weight / ($height * $height);
            }

            $bmi = bmi($height, $weight);
            $bmi = round($bmi, 2); // Round for readability

            // Determine BMI category
            if ($bmi <= 15) {
                $output = "Very severely underweight";
            } elseif ($bmi > 15 && $bmi <= 16 ) {
                $output = "Severely underweight";
            } elseif ($bmi > 16 && $bmi <= 18.5) {
                $output = "Underweight";
            } elseif ($bmi > 18.5 && $bmi <= 25) {
                $output = "Normal";
            } elseif ($bmi > 25 && $bmi <= 30) {
                $output = "Overweight";
            } elseif ($bmi > 30 && $bmi <= 35) {
                $output = "Obesity class 1";
            } elseif ($bmi > 35 && $bmi <= 40) { // Fixed typo: $num → $bmi
                $output = "Obesity class 2";
            } else { // Catch all values over 40
                $output = "Obesity class 3";
            }

            // Display result
            echo "<p>Your BMI is " . $bmi . " and you are : " . $output . "</p>";
        } else {
            // Show error for invalid inputs
            echo "<p style='color: red;'>Please enter valid, non-zero numeric values for height and weight!</p>";
        }
    }
    ?>
</div>

Key Fixes Made #

1. Form Setup: Added method="post" to the form and name="submit" to the submit button, so we can reliably detect form submission using CodeIgniter's built-in input methods.
2. Conditional Execution: Wrapped all BMI calculation logic inside a submission check—this prevents the code from running on initial page load, eliminating undefined variable errors.
3. Input Validation: Added checks to ensure inputs are non-empty, numeric, and height is greater than 0—stops division by zero and invalid value issues.
4. Bug Squashing: Fixed the typo $num to $bmi in one conditional, and adjusted the last category to properly catch all values over 40.
5. User Experience: Added input value retention (so users don't lose their entries after submission) and rounded BMI for readability, plus an error message for invalid inputs.

内容的提问来源于stack exchange，提问作者user9776860