Booleans

A boolean is a value that can only ever be true or false, like answering yes or no to a question.

In this page:

A Bool variable holds either true or false, often as the result of a comparison.

Example: Declaring Booleans

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let isSwiftFun = true
let isDifficult = false
print("Is Swift fun? \(isSwiftFun)")
print("Is it too difficult? \(isDifficult)")

Comparing two values with ==, !=, <, >, <=, or >= always produces a Bool result.

Example: Comparison Operators Produce Booleans

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let age = 20
let isAdult = age >= 18
print("Is an adult: \(isAdult)")

The && (logical AND), || (logical OR), and ! (logical NOT) operators combine or invert boolean values to build more complex conditions.

Example: Combining Booleans with Logical Operators

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let hasTicket = true
let hasID = false
let canEnter = hasTicket && hasID
print("Can enter: \(canEnter)")
print("Missing ID: \(!hasID)")

Common Mistakes

Comparing a boolean to true explicitly, e.g. if isReady == true, instead of the cleaner if isReady.
Assuming any non-zero number counts as true like in C; Swift's Bool is a distinct type and numbers are never implicitly converted to booleans.
Forgetting that && and || short-circuit, so a later expression might not even be evaluated.

Chapter Summary

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