11/17 Boolean Values and Operations

Often we have to compare different expressions or variables. Boolean variables only have 2 values, true and false or 1 and 0 (1 corresponds to true, 0 corresponds to false).

Bitwise operations:

AND, * (logic product)

• 0 * 0 = 0

• 1 * 0 = 0

• 0 * 1 = 0

• 1 * 1 = 1

OR, + (logic sum)

• 0 + 0 = 0

• 1 + 0 = 1

• 0 + 1 = 1

• 1 + 1 = 1

NOT, ! (logic negation)

• !0 = 1

• !1 = 0

XOR, ⊕ or ^

• 0 ^ 0 = 0

• 1 ^ 0 = 1

• 0 ^ 1 = 1

• 1 ^ 1 = 0

XNOR, ⊙ (opposite of ⊕)

• 0 ⊙ 0 = 1

• 1 ⊙ 0 = 0

• 0 ⊙ 1 = 0

• 1 ⊙ 1 = 1

Order of Precedence: () > ! > * > ⊕ = ⊙ > +

Boolean Expressions:

== equal to

!= not equal to

< less than

> greater than

<= less than or equal to

>= greater than or equal to

Logical Operators:

! Logical NOT

&& Logical AND

• a&&b is true only if both a and b are true

|| Logical OR

• a||b is true if a or b or both are true

Comparison:

• char types are compared by ACSII values

• Strings are compared by ACSII values of each character from left to right

• When paring two double or float values, we often compare the difference with a small enough value because of round off errors

• A boolean variable x == true is the same as x

Selected Operators and their Precedence:

• [] Array element access

• ++, --, ! Increment, decrement, Boolean not

• *, /, % Multiplication, division, remainder

• +, - Addition, subtraction

• <, <=, >, >= Comparisons

• ==, != Equal, not equal

• && Boolean and

• || Boolean or

• = Assignment