About This Expression Calculator
Basic Calculator III is a common interview challenge. It asks you to evaluate a string expression. The expression may contain addition, subtraction, multiplication, division, spaces, and nested parentheses. This tool turns that idea into a practical page. You can enter a custom expression. You can choose normal decimal division. You can also choose integer truncation. That mode matches many coding test rules.
Why Operator Order Matters
A simple left to right scan is not enough. Multiplication and division must run before addition and subtraction. Parentheses must run before everything outside them. Unary signs must also be handled. For example, -3*(2+5) should become -21. The parser used here follows that order with a small grammar. It reads expressions, then terms, then factors. That approach keeps the calculation clear.
Useful Coding Practice
The calculator is useful when checking stack based solutions, recursive descent solutions, or test cases. You can paste a LeetCode style expression and compare the answer. You can adjust precision when you want decimal study. You can inspect steps when the expression is confusing. The exported files also help save examples for revision.
Input Safety And Limits
Only digits, spaces, decimal points, operators, and parentheses are accepted. This keeps the evaluator focused on arithmetic. The page rejects missing parentheses, extra symbols, invalid numbers, and division by zero. It also gives diagnostics, such as length, operator count, and maximum nesting depth. These values help you understand expression complexity.
Better Test Design
Good practice cases should include short expressions and deep expressions. They should include negative values, repeated operators, and nested groups. They should also include division cases. This is important because truncation can change answers. A strong test set exposes mistakes in precedence, sign handling, and recursive returns. Use the table below as a start. Then create your own cases and compare them with your coded solution.
Practical Reading Tips
Read each result with the selected mode in mind. Decimal mode is best for math checks. Truncated mode is best for interview replicas. When a result looks wrong, enable steps first. Then add parentheses to isolate one section. This habit makes debugging faster. It also improves your mental model of expression parsers over repeated drills.