4 Operators | KaiGuoV5

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4.1 Operators Precedence

Precedence	Operator	Description	Associativity
1	`a++ a-—`	Suffix/postfix increment and decrement	Left-to-right
2	`+a -a ++a --a ! not ∼`	Plus/minus, Prefix increment/decrement,Logical/Bitwise Not	Right-to-left
3	`a*b a/b a%b`	Multiplication, division, and remainder	Left-to-right
4	`a+b a-b`	Addition and subtraction	Left-to-right
5	`<< >>`	Bitwise left shift and right shift	Left-to-right
6	`< <= > >=`	Relational operators	Left-to-right
7	`== !=`	Equality operators	Left-to-right
8	`&`	Bitwise AND	Left-to-right
9	`ˆ`	Bitwise XOR	Left-to-right
10	`\|`	Bitwise OR	Left-to-right
11	`&& and`	Logical AND	Left-to-right
12	`\|\| or`	Logical OR	Left-to-right
13	`+= -= *= /= %= <<= >>= &= ˆ= \|=`	Compound	Right-to-left

Unary operators have higher precedence than binary operators

Standard math operators (+, *, etc.) have higher precedence than

comparison, bitwise, and logic operators

Comparison operators have higher precedence than bitwise and logic operators

Bitwise operators have higher precedence than logic operators

Compound assignment operators +=, -=, *=, /=, %=, ˆ=, !=, &=, >>= , <<= have lower priority

The comma operator has the lowest precedence (see next slides)

Important: sometimes parenthesis can make an expression verbose... but they can help!

4.2 Prefix/Postfix Increment/Decrement Semantic

Prefix Increment/Decrement ++i , --i

Update the value

Return the new (updated) value

Postfix Increment/Decrement i++ , i--

Save the old value (temporary)

Update the value

Return the old (original) value

Prefix/Postfix increment/decrement semantic applies not only to built-in types but also to objects

4.3 Assignment, Compound, and Comma Operators

Assignment and compound assignment operators have right-to-left associativity and their expressions return the assigned value

The comma operator⋆ has left-to-right associativity. It evaluates the left expression, discards its result, and returns the right expression

4.4 Spaceship Operator

C++20 provides the three-way comparison operator <=> , also called spaceship operator, which allows comparing two objects in a similar way of strcmp . The operator returns an object that can be directly compared with a positive, 0, or negative integer value

The semantic of the spaceship operator can be extended to any object and can greatly simplify the comparison operators overloading

4.5 Safe Comparison Operators

C++20 introduces a set of functions <utility> to safely compare integers of different types (signed, unsigned)

example: