输入普通算术表达式，例如 (379*11900)+(75*20000)。计算器先算乘除再算加减，并显示每一步化简过程。
销售额增长了多少？促销价是多少？利率是上涨了 1% 还是 1 个百分点？百分比看似简单，但选错基数，答案就会改变。
百分比就是以一百为分母的比率。所有百分比计算都取决于能否选对基数(分母)，日常中的大多数情况都属于以下四种之一。
① A 的 B% 是多少？ A × B ÷ 100 (80,000 的 15% = 12,000)
② A 是 B 的百分之几？ A ÷ B × 100 (12 ÷ 48 × 100 = 25%)
③ 从 A 到 B 的变化率 (B − A) ÷ A × 100 (200 → 250 = +25%)
④ A 增加/减少 B% 后 A × (1 ± B ÷ 100) (50,000 + 20% = 60,000)四个基本的百分比公式、百分比与百分点的区别、为什么打八折再打九折不是七折，以及如何从含税价中拆出税额。阅读指南 →
想要自己的版本？把下面的任务提示词粘贴到 AI 聊天中，或将技能文件保存到 AI 编程助手。其中包含我们开发此工具时整理的功能、边界情况和测试用例。
提示词和技能以英文提供，AI 工具在任何语言环境下都能很好地理解。
直接粘贴到 Claude、ChatGPT、Gemini 等 AI 聊天中即可。
You are an experienced full-stack web developer. Build a web tool called "分步公式计算器" that meets the requirements below.
## Goal
Build a calculator that evaluates expressions with arithmetic and parentheses and shows each intermediate step.
## Core features
- +, −, ×, ÷, parentheses and decimals
- Step-by-step working that follows operator precedence
- Accept thousands separators
- Copy result
- Recent history
## Inputs
- An expression string
## Outputs
- Final result
- List of intermediate results
## Edge cases and handling rules
- Implement a parser; never use eval
- Report mismatched parentheses with their position
- Handle division by zero
- Keep precision for large numbers and decimals (decimal arithmetic)
## Implementation requirements
- Build it as a single page (HTML, CSS, JavaScript) that runs entirely in the browser, and never send the user's input to a server.
- Make the UI responsive and easy to use on mobile; label every input and keep everything keyboard accessible.
- Add a Copy button for results and show clear, friendly error messages for invalid input.
- Keep the core logic in functions separate from the UI so it can be unit-tested.
## Definition of done (test cases)
- (379*11900)+(75*20000) = 6010100 with steps 4510100 and 1500000
- 2+3*4 = 14
- 1/0 shows an error
First outline your implementation plan in at most five lines, then write the complete code, and finally explain how to check the test cases above.在 Claude Code 等 AI 编程助手中保存为 .claude/skills/build-expression-calculator/SKILL.md，以后开发或修改此工具时可重复使用。
---
name: build-expression-calculator
description: Use when building or changing a 分步公式计算器 tool. Build a calculator that evaluates expressions with arithmetic and parentheses and shows each intermediate step.
---
# Build: 分步公式计算器
## Goal
Build a calculator that evaluates expressions with arithmetic and parentheses and shows each intermediate step.
## Workflow
1. Review the required features, inputs and outputs below and ask about anything missing first.
2. Implement the core logic as pure functions separate from the UI.
3. Check the logic against the test cases in the verification list.
4. Build a responsive UI with an input form, a result area and a Copy button.
5. Reproduce each edge case listed under Rules and refine the error messages.
## Core features
- +, −, ×, ÷, parentheses and decimals
- Step-by-step working that follows operator precedence
- Accept thousands separators
- Copy result
- Recent history
## Inputs
- An expression string
## Outputs
- Final result
- List of intermediate results
## Rules
- Implement a parser; never use eval
- Report mismatched parentheses with their position
- Handle division by zero
- Keep precision for large numbers and decimals (decimal arithmetic)
- Build it as a single page (HTML, CSS, JavaScript) that runs entirely in the browser, and never send the user's input to a server.
## Verification
- [ ] (379*11900)+(75*20000) = 6010100 with steps 4510100 and 1500000
- [ ] 2+3*4 = 14
- [ ] 1/0 shows an error