Simple Calculator

Create a basic calculator that can perform addition, subtraction, multiplication, and division.

Creating a basic calculator with PHP, CSS, and AJAX involves a few key components:

Frontend (HTML + CSS + JavaScript/AJAX): This handles the user interface and interactions.
Backend (PHP): This handles the calculation logic and returns the results.

1. Frontend: HTML + CSS + JavaScript/AJAX

HTML (index.html):

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Simple Calculator</title>
    <link rel="stylesheet" href="styles.css">
</head>
<body>
    <div class="calculator">
        <input type="text" id="display" disabled>
        <div class="buttons">
            <button onclick="appendToDisplay('1')">1</button>
            <button onclick="appendToDisplay('2')">2</button>
            <button onclick="appendToDisplay('3')">3</button>
            <button onclick="appendToDisplay('+')">+</button>
            <button onclick="appendToDisplay('4')">4</button>
            <button onclick="appendToDisplay('5')">5</button>
            <button onclick="appendToDisplay('6')">6</button>
            <button onclick="appendToDisplay('-')">-</button>
            <button onclick="appendToDisplay('7')">7</button>
            <button onclick="appendToDisplay('8')">8</button>
            <button onclick="appendToDisplay('9')">9</button>
            <button onclick="appendToDisplay('*')">*</button>
            <button onclick="appendToDisplay('0')">0</button>
            <button onclick="appendToDisplay('.')">.</button>
            <button onclick="calculate()">=</button>
            <button onclick="appendToDisplay('/')">/</button>
            <button onclick="clearDisplay()">C</button>
        </div>
    </div>
    <script src="script.js"></script>
</body>
</html>

CSS (styles.css):

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    background-color: #f0f0f0;
}

.calculator {
    border: 1px solid #ccc;
    border-radius: 5px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
    background-color: #fff;
    padding: 10px;
    width: 200px;
}

#display {
    width: 100%;
    height: 40px;
    margin-bottom: 10px;
    text-align: right;
    font-size: 24px;
    padding: 5px;
    border: 1px solid #ccc;
    border-radius: 3px;
}

.buttons button {
    width: 45px;
    height: 45px;
    font-size: 18px;
    margin: 2px;
    border: 1px solid #ccc;
    border-radius: 3px;
    background-color: #f9f9f9;
    cursor: pointer;
}

.buttons button:hover {
    background-color: #e0e0e0;
}

JavaScript (script.js):

function appendToDisplay(value) {
    document.getElementById('display').value += value;
}

function clearDisplay() {
    document.getElementById('display').value = '';
}

function calculate() {
    var display = document.getElementById('display');
    var expression = display.value;

    if (expression) {
        var xhr = new XMLHttpRequest();
        xhr.open('POST', 'calculate.php', true);
        xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
        xhr.onload = function () {
            if (xhr.status === 200) {
                display.value = xhr.responseText;
            }
        };
        xhr.send('expression=' + encodeURIComponent(expression));
    }
}

2. Backend: PHP

PHP (calculate.php):

<?php
if (isset($_POST['expression'])) {
    $expression = $_POST['expression'];

    // Remove any potential security risks
    $expression = preg_replace('/[^0-9+\-.*\/()]/', '', $expression);

    try {
        // Evaluate the expression
        $result = eval('return ' . $expression . ';');
        echo $result;
    } catch (Exception $e) {
        echo 'Error: Invalid expression';
    }
}
?>

Explanation

Frontend (HTML + CSS + JavaScript/AJAX):
- HTML: Provides the basic structure of the calculator, including buttons for digits and operations.
- CSS: Styles the calculator to make it look better.
- JavaScript/AJAX:
  - appendToDisplay(value): Appends the clicked button's value to the display.
  - clearDisplay(): Clears the display.
  - calculate(): Sends the expression to calculate.php via AJAX, receives the result, and displays it.
Backend (PHP):
- calculate.php:
  - Receives the expression from the client.
  - Sanitizes the expression to prevent security issues.
  - Uses eval() to compute the result of the expression.
  - Returns the result to the frontend.

This setup provides a functional basic calculator with a clean interface and responsive behavior using AJAX to handle calculations.

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Source Code

PHP crash course: Simple Calculator

Simple Calculator

Create a basic calculator that can perform addition, subtraction, multiplication, and division.

1. Frontend: HTML + CSS + JavaScript/AJAX

2. Backend: PHP

Explanation