Calculator App

# Calculator App PRD

## Overview
Build a fully functional calculator application that supports basic arithmetic, scientific operations, keyboard input, and maintains a calculation history.

## Requirements
- Basic arithmetic operations: addition, subtraction, multiplication, division
- Scientific operations: sin, cos, tan, log, square root, power (x^y)
- Correct order of operations (PEMDAS/BODMAS)
- Decimal number support with proper formatting
- Full keyboard input support (number keys, operators, Enter to evaluate, Escape to clear)
- Calculation history showing the last 10 calculations with expressions and results
- Clear button (C) and backspace button to delete last character
- Percent button that converts current value to percentage
- Memory store (MS) and memory recall (MR) functionality
- Responsive layout that works on mobile and desktop
- Error handling for division by zero (display "Error" or "Infinity")
- Parentheses support for grouping expressions
- Copy result to clipboard with a button click

## Tech Stack
- HTML, CSS, JavaScript (vanilla or any framework)
- No calculator libraries — build the evaluation logic yourself

## Scoring Criteria
- **Functional (40%)**: Basic and scientific operations work, keyboard input works, history displays
- **Quality (20%)**: Clean code, handles edge cases (double operators, leading zeros), no crashes
- **Fidelity (25%)**: All features implemented including memory, parentheses, clipboard copy
- **Speed (15%)**: Time bonus