How does a calculator work?

A calculator evaluates mathematical expressions by parsing operator precedence and applying arithmetic rules. Modern calculators respect the standard order of operations — often remembered as PEMDAS or BODMAS — where multiplication and division are evaluated before addition and subtraction, and parentheses can override the default order. Under the hood, most software calculators convert the user's input into an expression tree or use a recursive parser to produce a numeric result.

Simple arithmetic operations (addition, subtraction, multiplication, division) are fast and deterministic, but edge cases like division by zero, very large numbers, or floating-point precision require careful handling. Good calculators round display results to avoid showing spurious digits like 0.1 + 0.2 = 0.30000000000000004.

Tool description

Simple Calculator provides a familiar button-pad interface for everyday arithmetic. It evaluates expressions in real time as you type or tap, so you can see the running result before pressing equals. The calculator supports addition, subtraction, multiplication, division, percentage, sign toggling, and backspace correction.

Features

  • Live evaluation — the result updates automatically as you build the expression, so you do not have to press equals to see intermediate values.
  • Percentage support — the % key converts the current value to a percentage (divides by 100), useful for tip and discount calculations.
  • Keyboard and button input — use the on-screen button pad or type directly via keyboard for fast entry.

How it works

Expressions are evaluated using the math.js library, which handles operator precedence, large numbers, and floating-point edge cases correctly. Display symbols like ×, ÷, and − are mapped to their ASCII equivalents (*, /, -) before evaluation. Results are formatted to 12 significant figures to avoid floating-point noise in the output.

Options explained

Button Action
C Clears the expression and result entirely.
± Toggles the sign of the current value (positive ↔ negative).
% Divides the current value by 100.
÷ × − + Standard arithmetic operators.
⌫ Deletes the last entered character.
= Evaluates the expression and replaces the input with the result.