A Calculator in PHP is a simple application that performs basic arithmetic operations like addition, subtraction, multiplication, and division. It can be built with either a Graphical User Interface (GUI) using HTML/CSS with PHP backend, or a Command Line Interface (CLI) version that runs in the terminal.

Types:

1. GUI Calculator (Web-based)

• Built with HTML/CSS for the frontend and PHP for backend processing.
• Users enter numbers and operations through buttons or input fields.
• PHP handles the calculation logic and displays the result dynamically.

2. CLI Calculator (Console-based)

• Runs in the terminal or command prompt.
• User inputs numbers and operation symbols manually.
• PHP processes inputs using readline() or command-line arguments and prints the result.

⚙️ Features (for both types):

• Basic operations: Add, Subtract, Multiply, Divide
• Input validation (avoid divide by zero, invalid entries)
• Clear or reset function (for GUI)
• Simple, fast, and lightweight

How it Works (Basic Flow):

GUI:

1. User enters numbers and selects operation via web form.
2. Form submits data to a PHP script.
3. PHP calculates the result and returns it to the same or another page.
4. Result is displayed on screen.

CLI:

1. User runs PHP script and enters values in the console.
2. PHP captures input using readline() or arguments ($argv[]).
3. Performs calculation and prints result to the console.

Benefits:

• Simple project for learning PHP basics.
• Teaches form handling (GUI) or command-line interaction (CLI).
• Can be easily expanded into a scientific calculator.
• Useful for understanding logic flow, conditionals, and user input handling.