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Expressions can be represented in prefix, postfix or infix notations and conversion from one form to another may be accomplished using a stack. Many compilers use a stack to parse syntax before translation into low-level code. Most programming languages are context-free languages, allowing them to be parsed with stack-based machines.
Infix notation may also be distinguished from function notation, where the name of a function suggests a particular operation, and its arguments are the operands. An example of such a function notation would be S(1, 3) in which the function S denotes addition ("sum"): S (1, 3) = 1 + 3 = 4.
An operator which is non-associative cannot compete for operands with operators of equal precedence. In Prolog for example, the infix operator :-is non-associative, so constructs such as a :- b :- c are syntax errors. Unary prefix operators such as − (negation) or sin (trigonometric function) are typically associative prefix operators.
In computer programming, an operator is a programming language construct that provides functionality that may not be possible to define as a user-defined function (i.e. sizeof in C) or has syntax different than a function (i.e. infix addition as in a+b).
For example, to add 3 and 4 together, the expression is 3 4 + rather than 3 + 4. The conventional notation expression 3 − 4 + 5 becomes 3 (enter) 4 − 5 + in reverse Polish notation: 4 is first subtracted from 3, then 5 is added to it. The concept of a stack, a last-in/first-out construct, is integral to the left-to-right evaluation of RPN.
Infix notation, the common arithmetic and logical formula notation, such as "a + b − c". Polish notation or "prefix notation", which places the operator before the operands (arguments), such as "+ a b". Reverse Polish notation or "postfix notation", which places the operator after the operands, such as "a b +".
For example, a CPU starts an addition operation by routing the operands from their sources (typically processor registers) to the ALU's operand inputs, while simultaneously applying a value to the ALU's opcode input that configures it to perform an addition operation. At the same time, the CPU enables the destination register to store the ALU ...
Immediate-execution calculators are based on a mixture of infix and postfix notation: binary operations are done as infix, but unary operations are postfix. Because operators are applied one-at-a-time, the user must work out which operator key to use at each stage, and this can lead to problems.