Create an HTML form with input fields and a dropdown for operations, using method="post". 2. Use PHP to retrieve inputs via $_POST, validate with is_numeric(), and perform calculations using switch-case. 3. Check for division by zero before dividing and display an error message if needed. 4. Enhance with CSS styling, preserve input values after submission, and use htmlspecialchars() for security.

If you are trying to build a simple calculator using PHP, it can be achieved with basic programming logic and web form handling. Here are the steps to implement a functional PHP calculator:

The operating environment of this tutorial: Dell XPS 13, Windows 11

1. Create the HTML Form for Input

This step involves designing a user interface where users can input two numbers and select an operation (addition, subtraction, multiplication, division). The form will send data to the PHP script for processing.

• Create an HTML form using method="post" to securely pass values to the PHP handler
• Include input fields for the first number, second number, and a dropdown or radio buttons for the operator
• Add a submit button labeled "Calculate" to trigger the computation

2. Process the Calculation Using PHP Logic

The backend PHP script retrieves the submitted form data, validates it, performs the selected arithmetic operation, and returns the result.

• Use $_POST['fieldname'] to retrieve user inputs from the form
• Apply conditional statements like if-elseif-else or switch-case to determine which mathematical operation to perform
• Ensure proper error handling for invalid operators or non-numeric inputs using is_numeric()
• Store the result in a variable and display it back to the user on the same page

3. Handle Division by Zero Safely

One common issue in calculator programs is dividing by zero, which causes runtime errors. This step ensures that such cases are caught before execution.

• Before performing division, check if the second number is zero
• Use a condition such as if ($num2 == 0) to detect zero denominator
• Display a user-friendly message like "Division by zero is not allowed" instead of executing the operation

4. Enhance User Experience with Visual Feedback

Improve the appearance and usability of the calculator by adding CSS styling and showing clear output formatting.

• Wrap the result in a bordered div with distinct background color for visibility
• Preserve the original input values in the form after submission so users don’t have to re-enter them
• Use htmlspecialchars() when outputting data to prevent XSS attacks