Page 150 - DCAP408_WEB_PROGRAMMING

Web Programming

Notes Logical Operator

The logical operators evaluate expressions and then return a true or false value based on the result.
Operator What does it do? Example/Explanation
&& Looks at two expressions if day='friday'&&date=13 then alert("Are You
and returns a value of Superstitious?")
"true" if both expressions Compares the value of the day and the value of the date. If
are true. it is true that today is a Friday and if it is also true that the
date is the 13th, then an alert box pops up with the
message "Are You Superstitious?"
|| Looks at two expressions if day='friday'&&date=13 then alert("Are You
and returns a value of Superstitious?") else if day='friday'||date=13 then
"true" if either one—but alert("Aren't you glad it isn't Friday the 13th?")
not both—of the Compares the value of the day and the value of the date. If
expressions are true. it is true that today is a Friday and if it is also true that the
date is the 13th, then an alert box pops up with the
message "Are You Superstitious?" If both are not true, the
script moves onto the next line of code...
Which compares the value of the day and the value of the
date. If either one—but not both—is true, then an alert box
pops up with the message "Aren't you glad it isn't Friday
the 13th?"

Computational Operator

The computational operators perform a mathematical function on a value or values, and return
a single value.

Operator What does it do? Example/Explanation
+ Adds two values together counter+2
Returns the sum of the counter plus 2
- Subtracts one value from counter-2
another Returns the sum of the counter minus 2
* Multiplies two values counter*10
Returns the result of the variable times 10
/ Divides the value on the counter/2
left by the one on the right Divides the current value of the counter by 2 and returns
and returns the result the result
++X Increments the value, and ++counter
then returns the result Looks at the current value of the counter, increments it by
one, and then returns the result. If the counter has a value
of 3, this equation returns the value of 4.
X++ Returns the value, and counter++
then increments the value Returns the value of the counter, then increments the
counter. If the counter has a value of 3, this equation
returns the value of 3, then sets the counter value to 4.
--X Decreases the value, and --counter
then returns the result Looks at the current value of the counter, decreases it by
one, and then returns the result. If the counter has a value
of 7, this equation returns the value of 6.
X-- Returns the value, and counter--
then decreases the value Returns the value of the counter, then decrease the
counter value. If the counter has a value of 7, this
equation returns the value of 7, then sets the counter
value to 6.

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