Swift Program to Find Sum of Digits of a Number using Recursion

Swift – Find Sum of Digits of a Number using Recursion

In this tutorial, we will learn how to find the sum of the digits of a number using recursion in Swift. We will understand the concept, write an algorithm, and implement the solution step by step with a complete Swift program and output.

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Understanding the Problem

Finding the sum of the digits of a number involves adding all its digits together. For example:

• The sum of digits of 123 is 1 + 2 + 3 = 6.
• The sum of digits of -456 is 4 + 5 + 6 = 15 (ignoring the sign).
• The sum of digits of 0 is 0.

We will use recursion to break down the problem into smaller subproblems and add the digits until the number becomes 0.

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Algorithm to Find Sum of Digits Using Recursion

1. Take the number as input.
2. Base Case: If the number is 0, return 0.
3. Recursive Case:
   1. Extract the last digit using number % 10.
   2. Add it to the result of the recursive call for number / 10.

This algorithm processes each digit of the number recursively until the base case is reached.

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Step-by-Step Implementation in Swift

1. Define the Base Case

Create a function that returns 0 when the input number is 0:

func sumOfDigits(_ number: Int) -> Int {
    if number == 0 {
        return 0 // Base case: Return 0 if the number is 0
    }
    return 0 // Placeholder for recursive case
}

2. Add the Recursive Case

Add logic to calculate the last digit and recursively call the function for the rest of the number:

func sumOfDigits(_ number: Int) -> Int {
    let num = abs(number) // Handle negative numbers
    if num == 0 {
        return 0 // Base case
    }
    return (num % 10) + sumOfDigits(num / 10) // Recursive case
}

Explanation:

• abs(number): Ensures that the function works for negative numbers by taking the absolute value.
• num % 10: Extracts the last digit of the number.
• num / 10: Removes the last digit from the number.
• (num % 10) + sumOfDigits(num / 10): Adds the last digit to the sum of the digits of the remaining number.

3. Test the Function

Let’s test the function with some example inputs:

// Test cases
print("Sum of digits in 123: \(sumOfDigits(123))")    // Output: 6
print("Sum of digits in -456: \(sumOfDigits(-456))")  // Output: 15
print("Sum of digits in 0: \(sumOfDigits(0))")        // Output: 0

Complete Swift Program

Here’s the complete Swift program to find the sum of the digits of a number using recursion:

main.swift

import Foundation

// Recursive function to find the sum of digits of a number
func sumOfDigits(_ number: Int) -> Int {
    let num = abs(number) // Handle negative numbers
    if num == 0 {
        return 0 // Base case
    }
    return (num % 10) + sumOfDigits(num / 10) // Recursive case
}

// Test cases
print("Sum of digits in 123: \(sumOfDigits(123))")    // Output: 6
print("Sum of digits in -456: \(sumOfDigits(-456))")  // Output: 15
print("Sum of digits in 0: \(sumOfDigits(0))")        // Output: 0

Output:

Sum of digits in 123: 6
Sum of digits in -456: 15
Sum of digits in 0: 0
Program ended with exit code: 0

Xcode Screenshot: