Start by clarifying the requirements: what kind of calculator (basic arithmetic, scientific, expression parser), input format, and expected operations. Then outline a design that separates concerns: tokenization, parsing (e.g., shunting-yard or recursive descent), and evaluation. Discuss trade-offs between simplicity and extensibility, and consider edge cases like operator precedence, parentheses, and error handling.
Pro tip: Demonstrate production-level thinking by discussing how you would test the calculator (unit tests for parsing and evaluation) and how you would handle invalid input gracefully, rather than just focusing on the happy path.
Ask questions to understand the scope: basic operations vs. scientific functions, input as string or tokens, support for variables, and error handling expectations.
Decide on a modular design: separate tokenizer, parser, and evaluator. Discuss using shunting-yard for infix to postfix conversion or recursive descent for direct evaluation.
Explain how to manage precedence (e.g., using a stack or grammar rules) and support parentheses for grouping. Mention associativity for operators like exponentiation.
Describe how to evaluate the parsed expression, including handling division by zero, invalid tokens, and mismatched parentheses. Discuss returning meaningful errors.
Talk about how to extend the calculator (e.g., adding functions, variables) and the importance of unit tests for each component and edge cases.
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