Swift Decimal to Binary Conversion – 4 New Approaches Explained Simply

What You'll Learn

In this Swift guide, you'll learn how to convert a decimal number into its binary form using 4 unique and beginner-friendly methods.

These examples are different from our first Swift article and provide even more ways to understand the logic behind binary number generation.

Why You Might Need This

• Build custom number conversion tools for iOS/macOS.

• Understand binary systems for low-level Swift apps.

• Learn Swift control flows like loops, recursion, and logic operators.

• Practice problems for coding interviews or student projects.

Binary Conversion Using While Loop with Prepending

// Convert decimal to binary using a while loop and string prepending
func decimalToBinaryLoop(_ number: Int) -> String {
    if number == 0 { return "0" }
    var num = number
    var binary = ""

    while num > 0 {
        binary = String(num % 2) + binary
        num /= 2
    }

    return binary
}

print("Binary of 27:", decimalToBinaryLoop(27))

Steps Explained

1. Start with an empty string binary.

2. Divide the number by 2 each time and store the remainder.

3. Prepend (+) each remainder to the front of the string.

4. Stop when the number becomes 0.

Output

Recursive Binary Conversion (Optimized)

// Recursive method to convert decimal to binary with fallback for 0
func decimalToBinaryRecursive(_ number: Int) -> String {
    if number == 0 { return "" }
    return decimalToBinaryRecursive(number / 2) + String(number % 2)
}

let result = decimalToBinaryRecursive(33)
print("Binary of 33:", result.isEmpty ? "0" : result)

Steps Explained

1. Use recursion to divide the number until it reaches 0.

2. On each return, append the remainder (% 2) to form the binary string.

3. If the result is empty (i.e., number was 0), return "0".

Output

Bitwise Shift and Append Strategy

// Bitwise method to extract binary digits using shifts
func decimalToBinaryBitwise(_ number: Int) -> String {
    if number == 0 { return "0" }
    var result = ""
    var started = false

    for i in (0..<32).reversed() {
        let bit = (number >> i) & 1
        if bit == 1 { started = true }
        if started { result.append(String(bit)) }
    }

    return result
}

print("Binary of 40:", decimalToBinaryBitwise(40))

Steps Explained

1. Use >> to shift bits and & 1 to check if that bit is 1 or 0.

2. Begin building the binary only after the first 1 appears (to skip leading 0s).

3. Append bits to result.

Output

Swift’s Built-in Conversion Method (Revisited)

// Using Swift’s toString radix:2 conversion
func decimalToBinaryBuiltIn(_ number: Int) -> String {
    return String(number, radix: 2)
}

print("Binary of 14:", decimalToBinaryBuiltIn(14))

Steps Explained

1. Swift has a built-in way to convert numbers to any base using String(_:radix:).

2. Passing radix: 2 converts the number to binary.

Output

Wrapping Up

These four Swift programs demonstrate a diverse set of logic structures — including while loops, recursion, bitwise operators, and built-in shortcuts — for converting decimal numbers into binary.

This reinforces key Swift programming skills while deepening your understanding of binary computation.