Building a Simple PHP Calculator – A Beginner Project

If you're just starting out with PHP or looking for a practical beginner project to enhance your web development skills, a calculator is a perfect way to apply basic PHP concepts like forms, variables, conditionals, and arithmetic operations. In this post, I’ll walk you through how I built a simple calculator using PHP, HTML, and a little bit of CSS, and explain the key parts of the project.

Project Objective

Create a web-based calculator that can perform basic arithmetic operations:

• Addition
• Subtraction
• Multiplication
• Division

The calculator will take two numbers and an operator as input from the user, then display the result when the form is submitted.

Tools & Technologies Used

• PHP – Backend logic
• HTML – User interface structure
• CSS – Basic styling for a cleaner UI (optional)
• Local Server – XAMPP or similar to run PHP locally

Project Code Breakdown

1. HTML Form

The form collects two numbers and the desired operation from the user.

<form method="post">
  <input type="number" name="num1" placeholder="Enter first number" required>
  <input type="number" name="num2" placeholder="Enter second number" required>
  <select name="operator" required>
    <option value="">Select Operation</option>
    <option value="add">Add (+)</option>
    <option value="subtract">Subtract (-)</option>
    <option value="multiply">Multiply (*)</option>
    <option value="divide">Divide (/)</option>
  </select>
  <button type="submit" name="calculate">Calculate</button>
</form>

2. PHP Logic

This PHP block handles the logic when the form is submitted.

<?php
$result = "";

if (isset($_POST['calculate'])) {
  $num1 = $_POST['num1'];
  $num2 = $_POST['num2'];
  $operator = $_POST['operator'];

  switch ($operator) {
    case "add":
      $result = $num1 + $num2;
      break;
    case "subtract":
      $result = $num1 - $num2;
      break;
    case "multiply":
      $result = $num1 * $num2;
      break;
    case "divide":
      if ($num2 != 0) {
        $result = $num1 / $num2;
      } else {
        $result = "Error: Division by zero";
      }
      break;
    default:
      $result = "Invalid operation selected";
  }
}
?>

3. Displaying the Result

After form submission, the result is displayed below the form:

<?php if ($result !== ""): ?>
  <h3>Result: <?php echo $result; ?></h3>
<?php endif; ?>

Optional Styling (CSS)

To make the interface cleaner:

<style>
  form {
    margin: 50px auto;
    text-align: center;
  }
  input, select, button {
    padding: 10px;
    margin: 5px;
    font-size: 16px;
  }
</style>

What You Learned

• How to use HTML forms to send data to a PHP script
• Basic PHP syntax for handling form input
• Using conditionals and switch-case for logic flow
• How to perform simple error handling (like division by zero)

Possible Improvements

• Add keyboard support
• Add history of calculations using session or local storage
• Improve styling with a modern frontend framework like Bootstrap
• Extend functionality with more operations like exponents, modulus, etc.

Final Thoughts

This simple calculator project was a great way to get hands-on experience with PHP and server-side logic. It’s an ideal project for beginners and can be expanded in many creative ways. If you're learning PHP, I highly recommend trying this project out yourself!

Let me know if you have any questions or want help with your version of the calculator!

Thanks for reading! 👨‍💻