Basic Calculator

A basic calculator performs the four fundamental arithmetic operations — addition, subtraction, multiplication, and division — on two numbers at a time. It mirrors the behavior of a classic pocket calculator: enter a number, press an operator, enter the next number, and press equals to see the result.

Unlike a scientific or expression calculator, this tool evaluates strictly left-to-right as operators are pressed and does not apply the standard order of operations (PEMDAS / BODMAS). That makes it fast and predictable for everyday calculations like splitting bills or summing receipts, but the wrong tool for expressions with mixed operators where precedence matters.

Suppose you bought 3 items at $4.50, 2 items at $7.00, and want to apply a 10% discount on the total.

• 3 × 4.50 = 13.50
• 2 × 7.00 = 14.00
• 13.50 + 14.00 = 27.50
• 27.50 × 10 % → 27.50 × 0.10 = 2.75 (the discount)
• 27.50 − 2.75 = 24.75 (final total)

Notice each step is performed individually. If you tried to enter 3 × 4.50 + 2 × 7.00 in one go on a left-to-right calculator, you'd get (3 × 4.50 = 13.50) + 2 = 15.50, then × 7.00 = 108.50 — completely wrong.

• Quick everyday math — adding receipts, calculating tips, splitting a bill.
• Single-operation calculations — a simple multiplication or division you'd otherwise do mentally.
• Step-by-step worked problems where you control which operation happens when.
• Sanity checks on numbers from a spreadsheet or invoice.
• Teaching arithmetic to children — a basic calculator's simplicity matches early-grade math expectations.

• Assuming PEMDAS. Entering 2 + 3 × 4 returns 20 here, not 14. Compute multiplication and division first as separate steps.
• Misusing the % key. It only divides by 100; it does not automatically apply a percentage to the previous number.
• Forgetting to clear (C) between unrelated calculations. A leftover pending operator can silently fold into your next entry.
• Trusting division-by-zero results. Any answer that came from dividing by 0 is mathematically undefined.
• Floating-point rounding surprises — sums like 0.1 + 0.2 may show a tiny trailing decimal. Round to 2 places for currency.