Standard Calculator
Basic arithmetic calculator with expression support.
About the Standard Calculator
A plain arithmetic calculator that accepts a whole expression at once, so you can type 12+7*3 and get the answer rather than pressing keys one at a time.
How to use it
- Type the full expression.
- Use + - * / and parentheses.
- The answer updates as you type.
The formula
A basic calculator looks like it has no rules worth knowing. It has two, and both surprise people.
Chain entry: each operator acts on the running total, left to right
Algebraic entry: the whole expression is evaluated by precedence
Type 2 + 3 × 4 into a simple pocket calculator and many return 20, because they add first and then multiply the running total. Type it into one that respects precedence and you get 14, because multiplication binds tighter. Neither is broken — they are answering different questions, and knowing which you are holding matters.
The percent key is the other trap. On most calculators, 200 + 10% gives 220, because % is interpreted as 'per cent of the running total'. On others it gives 200.1, reading 10% as 0.1. The key has never been standardised.
Worked examples
| Keys pressed | Chain result | Precedence result | Why |
|---|---|---|---|
| 2 + 3 × 4 = | 20 | 14 | left to right vs multiply first |
| 100 − 10 % = | 90 | 99.9 | % of total vs % as 0.01 |
| 1 ÷ 3 × 3 = | 0.9999999 | 1 | rounding at the display limit |
| 0.1 + 0.2 = | 0.3 | 0.30000000000000004 | binary floating point |
The last two rows are not calculator faults but consequences of how computers store numbers. A third cannot be written exactly in decimal, and a tenth cannot be written exactly in binary — so 0.1 + 0.2 lands a hair above 0.3 in almost every programming language on earth. Most calculators hide this by rounding the display, which is a design choice rather than a fix.
Common mistakes
- Assuming every calculator applies precedence. Many simple ones evaluate strictly left to right. Test yours with 2 + 3 × 4: if it says 20, use brackets or reorder your entry.
- Trusting the percent key without checking. Its behaviour differs between models and is genuinely ambiguous. For anything that matters, multiply by the decimal yourself.
- Chaining a long calculation without checking intermediates. One mistyped digit is invisible in a final answer. Glance at the running total as you go.
- Expecting exact decimal arithmetic. Binary floating point cannot represent 0.1 exactly. For money, work in whole cents and divide at the end.
Terms explained
- Chain entry
- Applying each operation to the running total in sequence, ignoring precedence. Common on simple calculators.
- Algebraic entry
- Evaluating a whole expression by the standard order of operations.
- Running total
- The accumulated result, updated with each operator press.
- Floating point
- How computers store fractional numbers in binary. Fast, and not exactly decimal.
- Memory keys
- M+ adds to a stored value, M− subtracts, MR recalls it and MC clears it. Useful for accumulating subtotals.
- CE and C
- CE clears the current entry only; C clears everything. Pressing the wrong one loses more work than intended.
Common questions
- Why does my calculator give a different answer to my phone?
- Almost certainly order of operations. Simple calculators often work left to right, while phone and computer calculators apply precedence. 2 + 3 × 4 is 20 on one and 14 on the other.
- What does the percent key actually do?
- It depends on the model, which is why it causes so much confusion. Most treat 200 + 10% as 10% of 200; some treat it as adding 0.1. Multiplying by the decimal yourself removes all doubt.
- Why is 0.1 + 0.2 not exactly 0.3?
- Because binary cannot represent a tenth exactly, in the same way decimal cannot represent a third. The tiny error is normally hidden by display rounding.
- What is the difference between C and CE?
- C clears the entire calculation; CE clears only the number you just typed. CE lets you fix a mistyped entry without starting again.
- How do the memory keys work?
- M+ adds the displayed value to memory, M− subtracts it, MR recalls it and MC clears it. They are ideal for totalling several subtotals without writing anything down.
- Should I use brackets?
- Whenever the order matters and you are not certain how your calculator behaves. They cost nothing and remove every ambiguity.
- Why does 1 ÷ 3 × 3 not give exactly 1?
- Because the calculator rounds a third to its display precision, then multiplies the rounded value. Some calculators keep extra hidden digits and do return 1.
- How should I handle money calculations?
- Work in whole cents where you can and round only at the end. Rounding at each intermediate step is how totals drift by a penny.