Calculator App

Original prompt

Create a working calculator app.
Choose the technology yourself.
Run it.
Test it.
Fix any issues you find.
Do not ask me questions unless you are genuinely blocked.

Chinese translation

创建一个可工作的计算器应用。技术由你自行选择。运行它、测试它，并修复发现的所有问题。除非确实受阻，否则不要向我提问。

Expected outcome

The deliverable should be a calculator application that actually runs and has been tested and repaired, using a technology stack chosen by the implementer. Minimum capabilities include digit and decimal entry, the four basic operations, clear, backspace, sign toggle, and equals. A strong implementation should also handle precedence, chained calculations, keyboard input, error states, and number formatting. The calculation core should be deterministic; division by zero, malformed expressions, overflow, and floating-point display noise should be handled intelligibly without crashing the UI. The handoff should include run instructions, a test method, and evidence that discovered defects were fixed.

Additional verification guidance

• Run the real app and use both buttons and keyboard for basic, chained, decimal, negative, and precedence-sensitive calculations against known results.
• Cover cases such as `0.1 + 0.2`, division by zero, repeated decimal points, leading operators, long input, overflow, and recovery after an error.
• Check state-machine consistency for clear, backspace, sign toggle, repeated equals, and consecutive operators, with no console exceptions.
• Review keypad layout, focus, readability, and touch targets on desktop and narrow screens; run automated tests and a full regression after fixes.