Implement a basic calculator that evaluates a string with +, -, *, /, and parentheses.

Evaluating arithmetic with precedence and nested parentheses is a parsing problem, and a stack handles both cleanly. The traps are operator precedence, multi-digit numbers, and the sign of truncated division. Here is a single-pass solution.

Updated Aug 2026 · Grounded in real Applied AI Engineer interview loops and written to a senior-engineer editorial bar.