Get nth Character of a String in Swift

In this tutorial, we will explore different methods to obtain the Nth character of a string in Swift.

We will primarily focus on using the index() method and demonstrate a recommended approach using a String extension.

Using the index() Method

The index() method is a powerful tool in Swift that helps us access characters at specific positions in a string. Let’s go through the steps to get the Nth character of a string using this method.

Algorithm

1. Prepare an input string.
2. Call the index() method with the target offset.
3. Use the position index as a subscript to the input string.
4. Store the Nth character.

Now, have a look at the example below.

import Foundation

let inputString = "Swift Programming"
let characterIndex = 7

let index = inputString.index(inputString.startIndex, offsetBy: characterIndex)
let nthCharacter = inputString[index]

print("Character at \(characterIndex) is \(nthCharacter)")

Explanation:

• inputString is the string from which we want to extract the Nth character.
• characterIndex represents the position of the desired character in the string (zero-based index).
• index() method is called on inputString to obtain the index of the character at the specified position.
• nthCharacter is assigned the value of the character at the calculated index.
• Finally, a print statement displays the character at the specified index.

Output:

Character at 7 is r

This confirms that the character at index 7 in the string “Swift Programming” is indeed ‘r‘.

Using String Extension

Extending Swift’s String type with a custom subscript is a recommended way to make the code more readable and reusable. Let’s create a String extension to achieve this.

Example

import Foundation

extension String {
    subscript(_ characterIndex: Int) -> Character {
        return self[index(startIndex, offsetBy: characterIndex)]
    }
}

let inputString = "Swift Programming"
let characterIndex = 12

let nthCharacter = inputString[characterIndex]

print("Character at \(characterIndex) is \(nthCharacter)")

Explanation:

• The String type is extended with a subscript that takes an integer characterIndex and returns the character at that index using the index() method.
• inputString is the string from which we want to extract the Nth character.
• characterIndex represents the position of the desired character in the string (zero-based index).
• The custom subscript is used to access the Nth character in a more concise way.
• Finally, a print statement displays the character at the specified index.

Output:

Character at 12 is m

This confirms that the character at index 12 in the string “Swift Programming” is ‘m‘.

If you need to get a substring instead of a character, modify the extension as follows:

import Foundation

extension String {
    subscript(_ characterIndex: Int) -> Substring {
        return self[index(startIndex, offsetBy: characterIndex)..<index(startIndex, offsetBy: characterIndex+1)]
    }
}

Explanation:

• The String type is extended with a subscript that takes an integer characterIndex and returns a Substring representing the character at that index.
• The ..< operator is used to create a half-open range representing the single character.

Conclusion

Obtaining the Nth character of a string in Swift is a common operation. Whether you use the index() method directly or create a String extension, the goal is to make your code more readable and maintainable. Choose the method that best suits your needs.