Logical operations

It’s often useful to combine various conditions:

if age < 12 || height < 1.2
	"You are allowed on the ride."
else
	 "Try a different helter-skelter. There's nothing for you here."
end

In the above snippet of code, the || means OR. If the person is under 12 or is smaller than 1.2m they are allowed on the ride.

Logical operations

Ruby has three ways of combining conditions:

and (&&)

If you use an && the output is true only if both inputs are true. You can write this in terms of a truth table:

false && false #=> false
false && true  #=> false
true  && false #=> false
true  && true  #=> true

or (||)

If you use the || the output is true if at least one of the inputs is true. || means one or the other or both:

false || false #=> false
false || true #=> true
true || false #=> true
true || true #=> true

not (!)

The ! is not. It is a quick way of reversing the truth of the condition:

!false #=> true
!true #=> false

1 > 2 && 3 > 4

1==1 || 10 ==9

!(5<6)

(1<=2 && 3>4) || (3 <= 4 && "ham")

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