Editing precedence

The [[awk]] programming language uses rules of *precedence* to determine the order in which [[operator]]s within an [[expression]] are used during evaluation. The order that [[operator]]s are evaluated within an [[expression]] are predetermined by the intepreter and the [[operator]]s with the highest priority are evaluated first. An [[neophite|inexperienced programmer]] may expect the following programming line to produce a result of 35. However, this actually produces a value of 23, because [[multiplication]] has a higher precedence than [[addition]], so it is performed first. {{{ print 3 + 4 * 5 # This produces 23 because multiplication is done before addition }}} == _Using parentheses to control the order of evaluation_ It is possible to change the order in which [[operator]]s within an [[expression]] are evaluated by using [[parentheses]] enclosures. In the following example, the [[expression]] produces a value of 35, because the [[parentheses]] have a higher precedence than [[multiplication]], so their contents are evaluated first: {{{ print (3 + 4) * 5 # The parentheses cause the addition to be evaluated before the multiplication }}} == _Groups of operators or functions within parentheses have the same precedence as normal_ Groups of [[operator]]s or [[function]]s within parentheses have the same precedence as they normal would. In the following example, the [[multiplication]] within the [[parentheses]] occurs before the [[addition]]: {{{ print 3 * (4 + 2 * 3) # Within the parentheses 2 * 3 is evaluated before 4 is added }}} == _Operators of equal precedence are evaluated from left to right_ Operators of equal precedence are evaluated from left to right. In the following example, the [[addition]] and [[subtraction]] operators have equal precedence, so the [[operator]]s are evaluated from left to right. This means that the [[subtraction]] takes place before the [[addition]], because the [[subtraction]] operator occurs on the left side of the [[expression]] before the [[addition]]: {{{ print 5 - 2 + 1 }}} == _Side Effects_ An expression that changes the value of one of its components during evaluation, may produce [[side effects]] and the results that it produces may vary depending on which version of [[awk]] is being used. In the following example code, the [[awk]] interpreter may produce a value of 8 or 9, depending on whether or not the [[assignment]] in [[parentheses]] affects the value outside. {{{ BEGIN { # Changing the number variable in the middle of the expression may introduce side effects result = (number = 4) + number # This expression may produce a value of 8 or 9 depending on the awk version print "The result is " result } }}} == Within an expression, each operator has a predetermined precedence == Within an [[expression]], each [[operator]] is has a predetermined position, precedence, and [[associativity]]. === Operator Position === The position of the [[operator]] is the position of [[operator]] as a component within the [[expression]], and relates to other components within the [[expression]]: 12 + (2 x -4) + 5^2 The above [[expression]] contains the following [[component]]s: | Position | Component | Notes | 1 | 12 | The first component is the number 12. This is also the first element | 2 | + | The second component is the [[plus]] operator. This is the first operator | 3 | ( | The third component is the opening bracket. The expression (2 x !-4) is the second element | 4 | 2 | The fourth component is the number 2. This is the first element of the second element | 5 | x | The fifth component is the [[multiplication]] operator. This is the first operator in the second element | 6 | - | The sixth component is the [[minus]] operator. This is the second operator in the second element | 7 | 4 | The seventh component is the number 4. This is the second element of the second element | 8 | ) | The eighth component is the closing bracket. | 9 | + | The ninth component is the [[plus]] operator. This is the sixth operator. | 10 | 5 | The tenth component is the number 5. The expression 5^2 is the third element | 11 | ^ | The eleventh component is the [[caret]] exponent operator. This is the seventh operator | 12 | 2 | The twelfth component is the number 2. This is the third component of the third expression * Note that the brackets have been dropped for evaluation, so the expression is now 2 x -4 === Prefix, Postfix, Infix An [[operator]] is either a [[prefix]] operator, a [[postfix]] operator or an [[infix]] operator depending upon is positioning within the [[expression]]. ==== Prefix Operators A [[prefix]] operator immediately precedes its [[operand]]. The [[unary]] operators used to indicate whether a [[number]] is [[positive]] or [[negative]] is a [[prefix]] operator: ==== Postfix Operators A [[postfix]] operator immediately follows its [[operand]] within an expression. ==== Infix Operators An [[infix]] operator is positioned between its left and right [[operand]]s: === Precedence The [[precedence]] of an [[operator]] is determined by a numerical [[value]] representing the priority of the [[operator]] whilst determining the order in which the [[operator]]s will be evaluated. Note that [[operator]]s to be evaluated first have a higher value. ==== Competing for Operands **Operands go to the operator with the highest level of precedence** In cases where two [[operator]]s of different precedences compete for the same [[operand]], the [[operand]] belongs to the [[operator]] with the highest precedence: 3 + 4 * 5 In the above expression, both the [[plus]] operator and the [[multiplication]] operator are competing for the second element (numeral 4) as an [[operand]]. Because the [[multiplication]] operator has the higher precedence, it owns the [[operand]], so the number 4 is associated with the [[multiplication]] operator, rather than the [[addition]] operator. === Operators of equal precedence are evaluated from left to right In cases where two [[operator]]s of the same precedence compete for [[operand]]s, the [[operand]] belongs to the [[operator]] on the left: 6 + 5 - 3 In the above expression, because both the [[addition]] and [[subtraction]] operator have equal precedence, the second element (numeral 5) belongs to the addition [[operator]], so the [[expression]] is evaluated mathematically as: (6 + 5) - 3

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This change is a minor edit.

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