Strings and Characters

A string is a piece of text, like a word or sentence, and a character is just one single letter or symbol from that text.

In this page:

A String holds a sequence of text, while a Character holds exactly one visible character, often used when processing text one symbol at a time.

Example: Declaring Strings and Characters

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let greeting: String = "Hello"
let firstLetter: Character = "H"
print("\(greeting) starts with \(firstLetter)")

Strings can be joined together with the + operator, or embedded into other strings using interpolation with \(expression).

Example: Concatenation and Interpolation

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let first = "Swift"
let second = "Lang"
let combined = first + " " + second
print(combined)
print("Combined has \(combined.count) characters")

Strings expose useful properties like .count, .isEmpty, .uppercased(), and .lowercased() for common text operations.

Example: Common String Properties and Methods

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let message = "Hello, Swift!"
print("Uppercase: \(message.uppercased())")
print("Length: \(message.count)")
print("Is empty: \(message.isEmpty)")

Since strings can't be indexed by integer, the idiomatic way to visit each character is to iterate over the string directly in a for-in loop.

Note: This correctly handles Unicode characters that might be built from multiple underlying scalars.

Example: Iterating Over Characters

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let word = "Swift"
for letter in word {
    print(letter)
}

Common Mistakes

Trying to index a String with an integer like str[0]; Swift strings use String.Index because of Unicode, not plain integer offsets.
Using + to build a large string in a loop repeatedly, which is less efficient than appending with += or building an array and joining.
Forgetting that a Character can represent a multi-scalar grapheme cluster (like an emoji with a modifier), not just a single simple letter.

Chapter Summary

String represents text, and Character represents a single grapheme cluster (visible character).
Strings can't be indexed with plain integers; use .first, .last, or String.Index navigation instead.
String interpolation (\(value)) and concatenation (+) both build new strings.
Swift strings are fully Unicode-correct, which is why simple integer indexing isn't allowed.

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