# Precedence and Associativity in C++

## Precedence and Associativity

• The sequence of operators and operands that reduces to a single value after the evaluation is called an expression
• If 2*3 is evaluated nothing great ,it gives 6 but if 2*3+2 is 6+2 =8 or 2*6=12.To avoid this confusion rules of  Precedence and associativity are used ## Precedence

Operator precedence gives priorities to operators while evaluating an expression

Example: when 2*3+2 is evaluated  output is 8 but not 12 because the * operator is having more priority than + hence 2*3 is  evaluated first followed by 6+2.

## Operator precedence table

• Operator precedence table gives the detail list of priorities for each and every operator
• Operators are listed from higher priority to lower
PrecedenceOperatorDescriptionAssociativity
1`::`Scope resolutionLeft-to-right
2`++`   `--`Suffix/postfix increment and decrement
`type()` `type{}`Function-style typecast
`()`Function call
`[]`Array subscripting
`.`Element selection by reference
`->`Element selection through pointer
3`++`   `--`Prefix increment and decrementRight-to-left
`+`   `-`Unary plus and minus
`!`   `~`Logical NOT and bitwise NOT
`(type)`C-style type cast
`*`Indirection (dereference)
`&`Address-of
`sizeof`Size-of
`new``new[]`Dynamic memory allocation
`delete``delete[]`Dynamic memory deallocation
4`.*`   `->*`Pointer to memberLeft-to-right
5`*`   `/`   `%`Multiplication, division, and remainder
6`+`   `-`Addition and subtraction
7`<<`   `>>`Bitwise left shift and right shift
8`<`   `<=`For relational operators < and ≤ respectively
`>`   `>=`For relational operators > and ≥ respectively
9`==`   `!=`For relational = and ≠ respectively
10`&`Bitwise AND
11`^`Bitwise XOR (exclusive or)
12`|`Bitwise OR (inclusive or)
13`&&`Logical AND
14`||`Logical OR
15`?:`Ternary conditional operatorRight-to-left
`=`Direct assignment (provided by default for C++ classes)
`+=`   `-=`Assignment by sum and difference
`*=`   `/=`   `%=`Assignment by product, quotient, and remainder
`<<=`   `>>=`Assignment by bitwise left shift and right shift
`&=`   `^=`   `|=`Assignment by bitwise AND, XOR, and OR
16`throw`Throw operator (for exceptions)
17`,`CommaLeft-to-right

#### Example1

Evaluate 5*4+(3+2)

• Parenthesis is having the highest priority
5*4+5
• Among * and +,* is having the highest priority
20 + 5= 25 is the final output

#### Example 2

Arithmetic operators for having higher priority than relational operators

Observe the difference With Parenthesis  and without Parenthesis

`5<4+5<4 5<9<4// 5<9 gives 1 1<4 =1`
`(5>4)+(5>4)//5>4 is true 1+12`

## Associativity

Associativity determines in which direction operators  are to be evaluated if they are under the same priority i.e

1. Left to Right
2. Right to Left

#### Example

5*3/2
15/2
7

Here * and / are having the same level of priority but it associativity is given as left to right. hence evaluate* followed by /

#### Note

From the Operator precedence table, we can conclude  except for   group 3 and group 15 all the remaining operators are having associativity as,`left to right`

## C++ program to demonstrate operator precedence and associativity

`main() {int a = 20,b = 10,c = 15 d = 5,e;e = (a + b) * c / d; // ( 30 * 15 ) / 5cout << "Value of (a + b) * c / d is :" << e << endl ;e = ((a + b) * c) / d; // (30 * 15 ) / 5cout << "Value of ((a + b) * c) / d is :" << e << endl ;e = (a + b) * (c / d); // (30) * (15/5)cout << "Value of (a + b) * (c / d) is :" << e << endl ;e = a + (b * c) / d; // 20 + (150/5)cout << "Value of a + (b * c) / d is :" << e << endl ;}`

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