Logical operators evaluate the relationship between two or more Boolean expressions and return a true or false value. There are several operators that we can use: &&, ||, and !.

The logical AND operator (&&) returns true if and only if the expressions on both sides of the operator return true.

var isSunny = true
var temp = 85

if (isSunny && temp > 80) {
  println("Wear sunglasses.")
}
// Prints: Wear sunglasses.

Since isSunny is true and temp has a value above 80, the expression inside the condition becomes true so Wear sunglasses. is outputted to the terminal.

The logical OR operator (||) will only return true if at least one of the Boolean expressions being compared has a true value.

var isSnowing = false
var temp = 38

if (isSnowing || temp < 40 ) {
  println("Wear a scarf.")
}
// Prints: Wear a scarf.

Even though the first value isSnowing is false, the full expression will return true because the other Boolean expression, temp < 40, is true.

The logical NOT operator, denoted by !, will evaluate the truth value of a Boolean expression and then return its inverse. For example:

var isSnowing = true
println(!isSnowing) // Prints: false

We can even add ! before a multi-part expression. By adding the ! operator to our previous code example, the Boolean expression now returns a false value:

var isSnowing = false
var temp = 38

if (!(isSnowing || temp < 40)) {
  println("Wear a scarf.")
}
// This program will not have any output.

Note: The truth tables displayed on the right side of the screen display the various outcomes of Boolean expressions being evaluated using logical operators.