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There are various ways in which calculators interpret keystrokes. One can categorize calculators into two main types: 1) single-step or immediate execution calculators and 2) expression or formula calculators. On a formula calculator one types in an expression and then presses 'Enter' to evaluate the expression.〔Formula Calculators Pty Ltd (page on the Internet ); 2009. Available from: http://fCalculators.com〕〔Moisey Oysgelt (Formula Calculator page on the Internet ); 2000. Available from: http://www.alemoi.com/math〕〔Haxial Software Pty Ltd (Product page on the Internet ); 2001. Available from: http://www.haxial.com/products/calculator〕 There are various systems for typing in an expression: infix, postfix, natural display, etc. On an immediate execution calculator, the user presses a key for each operation, by pressing keys to calculate all the intermediate results, before the final value is shown.〔Microsoft’s Windows Operating System Calculator Accessory; 2001. Available on a Windows PC at: Start/All Programs/Accessories/Calculator〕〔MotionNET (page on the Internet ); 2006. Available from: http://www.motionnet.com/calculator〕〔Flow Simulation Ltd (Calc98 page on the Internet ); 2008. Available from: http://www.calculator.org/jcalc98.html〕 ==Immediate execution== With the immediate execution mode (also known as ''chain calculation mode'') of operation each binary operation is executed as soon as the next operator is pressed, therefore the order of operations in a mathematical expression is not taken into account. Scientific calculators have buttons for brackets and these calculators ''can'' take order of operation into account. Also for unary operations like √ or x2 the number is entered first then the operator. Simple four-function calculators, such as those included with most operating systems, usually use this input method. The first example has been given twice. The first version is for simple calculators, showing how it is necessary to rearrange operands in order to get the correct result. The second version is for scientific calculators, where operator precedence is observed. The immediate execution calculators are based on a mixture of infix and postfix notation: binary operations are infix but unary operations are postfix. Because operators are applied one at a time, the user must work out which operator button to use at each stage and this can lead to problems.〔Harold Thimbleby. A new calculator and why it is necessary, Computing Science, Middlesex University, London, UK; September 1998. Available from: http://www.uclic.ucl.ac.uk/harold/srf/allcalcs.pdf〕〔Neville Holmes. Truth and Clarity in Arithmetic, University of Tasmania; 2003. Available from: http://standards.computer.org/sabminutes/2003Wint/Truth%20and%20Clarity%20in%20Arithmetic%20-%20Neville%20Holmes.pdf〕 When discussing these problems, Professor Harold Thimbleby has pointed out that button-operated calculators “… require numbers and operation signs to be punched in a certain order, and mistakes are easy to make and hard to spot”.〔http://www.physorg.com. Professor devises easier calculator; June 2005. Available from: http://www.physorg.com/news4773.html〕 Problems can occur because, for anything but the simplest calculation, to work out the value of a written formula, the user of a button-operated calculator is required to: * Rearrange the formula so that the value can be calculated by pressing buttons one at a time, while taking operator precedence and parentheses into account. * Use memory buttons to ensure that operations are applied in the correct order. * Use the special buttons +/− and 1/x, that do not correspond to operations in the formula, for non-commutative operators. Mistakes can be hard to spot because: * For the above reasons, the sequence of button presses may bear little resemblance to the original formula. * The operation carried out when a button is pressed is not always the same as the button, but a previously entered operation. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Calculator input methods」の詳細全文を読む スポンサード リンク
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