Boolean Logic
01-1
Boolean values
•  Are TRUE and FALSE
01-2
Boolean values
•  Are TRUE and FALSE
» Named after the English mathematician
George Boole (1815-64) who developed
Boolean algebra
01-3
Boolean values
•  Are TRUE and FALSE
•  They can be established in a number of ways
01-4
Boolean values
•  Are TRUE and FALSE
•  They can be established in a number of ways
» Declaration
01-5
Boolean values
•  Are TRUE and FALSE
•  They can be established in a number of ways
» Declaration
» Comparison
01-6
Boolean values
•  Are TRUE and FALSE
•  They can be established in a number of ways
» Declaration
» Comparison
» Boolean expression
01-7
Declaration
•  To declare a variable means to create it
01-8
Declaration
•  To declare a variable means to create it
•  Example:
» In JavaScript declare the variable
doorIsOpen and assert its value is true
var doorIsOpen = true;
01-9
Comparison
•  Comparison operators are used to establish
a relationship between objects of the same
type
01-10
Comparison operators
•  <
•  <=
less than
less than or equal to
•  === equal to (strict includes operand types)
•  !== not equal to (strict includes operand types)
•  >=
greater than or equal to
•  >
greater than
01-11
Comparison operators
•  <
•  <=
less than
less than or equal to
•  === equal to (strict includes operand types)
•  !== not equal to (strict includes operand types)
•  >=
greater than or equal to
•  >
greater than
» Comparison operators are infix and binary
01-12
Comparison operators
•  <
•  <=
less than
less than or equal to
•  === equal to (strict includes operand types)
•  !== not equal to (strict includes operand types)
•  >=
greater than or equal to
•  >
greater than
» Comparison operators are infix and binary
>  The operator is between (infix) its two
operands (binary)
01-13
Examples
•  maryAge < aliAge
•  year > 1582
•  elephantWeight <= mouseWeight
•  thisYear === 2017
•  thisYear !== leapYear
01-14
Boolean expression
•  Logical operators can be used to construct
Boolean expressions from Boolean values
01-15
Boolean expression
•  Logical operators can be used to construct
Boolean expressions from Boolean values
» The operands of the operators must be
Boolean
01-16
Logical operators
•  && and
•  | |
or
•  !
not
01-17
Boolean expression example
•  Assume the value of year is a calendar year
such as 2017
•  The following expression is true if year is a
leap year in the Gregorian calendar
( year % 4 === 0
&&
year % 100 !==0 )
||
year % 400 === 0
// Remainder of year is 0
// on division by 4
// AND
// Remainder of year is not 0
// on division by 100
// OR
// Remainder of year is 0 // on division by 400
01-18
Using the not operator
! ( year % 100 === 0 )
===
( year % 100 !== 0 )
01-19
Using the not operator
•  The following expression is true if year is a
leap year in the Gregorian calendar
( year % 4 === 0
// Remainder of year is 0
// on division by 4
&&
// AND
! ( year % 100 === 0 ) ) // Remainder of year is not 0
// on division by 100
||
// OR
year % 400 === 0
// Remainder of year is 0 // on division by 400
01-20