Algorithm

An algorithm is a recipe for carrying out a computational task. For example, every child learns in elementary school how to perform long addition of two natural numbers: “add the right-most digits of the two numbers and write down the sum as the right-most digit of the result. But if the sum is 10 or more, write only the right-most digit and add the leading digit to the sum of the next two digits to the left, etc.” We have all learned similar simple procedures for long subtraction, multiplication and division of two numbers. These are all actually simple algorithms. Like any algorithm, each is a procedure that works on inputs (two numbers for the problems above) and produces an output (the result). The same procedure will work on any input, no matter how long it is. While we can carry out simple algorithms on small inputs by hand, computers are needed for more complex algorithms or for longer inputs. As with long addition, a complex task is broken down into simple steps that can be repeated many times, as needed. Algorithms are often displayed for human readers in a short form that summarizes their salient features.