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Concept
Common operator notation
Résumé
In programming languages, scientific calculators and similar common operator notation or operator grammar is a way to define and analyse mathematical and other formal expressions. In this model a linear sequence of tokens are divided into two classes: operators and operands.
Operands are objects upon which the operators operate. These include literal numbers and other constants as well as identifiers (names) which may represent anything from simple scalar variables to complex aggregated structures and objects, depending on the complexity and capability of the language at hand as well as usage context. One special type of operand is the parenthesis group. An expression enclosed in parentheses is typically recursively evaluated to be treated as a single operand on the next evaluation level.
Each operator is given a position, precedence, and an associativity. The operator precedence is a number (from high to low or vice versa) that defines which operator takes an operand that is surrounded by two operators of different precedence (or priority). Multiplication normally has higher precedence than addition, for example, so 3+4×5 = 3+(4×5) ≠ (3+4)×5.
In terms of operator position, an operator may be prefix, postfix, or infix. A prefix operator immediately precedes its operand, as in −x. A postfix operator immediately succeeds its operand, as in x! for instance. An infix operator is positioned in between a left and a right operand, as in x+y. Some languages, most notably the C-syntax family, stretches this conventional terminology and speaks also of ternary infix operators (a?b:c). Theoretically it would even be possible (but not necessarily practical) to define parenthesization as a unary bifix operation.
Operator associativity
Operator associativity determines what happens when an operand is surrounded by operators of the same precedence, as in 1-2-3: An operator can be left-associative, right-associative, or non-associative. Left-associative operators are applied to operands in left-to-right order while right-associative operators are the other way round.
Source officielle
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