Kotlin Program to Convert Decimal to Binary

You can convert a decimal number to binary in Kotlin using Integer.toBinaryString(decimalNumber) or by repeatedly dividing the number by 2 and collecting remainders.

Examples

Input0

Output0

Input10

Output1010

Input255

Output11111111

How to Think About It

To convert a decimal number to binary, think of dividing the number by 2 repeatedly and noting the remainder each time. These remainders, read in reverse order, form the binary number. Alternatively, Kotlin provides a built-in function to do this conversion easily.

Algorithm

1

Get the decimal number as input.

2

If the number is 0, return "0" as binary.

3

While the number is greater than 0, divide it by 2 and store the remainder.

4

Collect all remainders in reverse order to form the binary string.

5

Return the binary string.

Code

kotlin

fun main() {
    val decimalNumber = 10
    val binaryString = Integer.toBinaryString(decimalNumber)
    println("Binary of $decimalNumber is $binaryString")
}

Output

Binary of 10 is 1010

Dry Run

Let's trace the decimal number 10 through the code using the manual division method.

1

Initial number

decimalNumber = 10

2

Divide by 2 and get remainder

10 / 2 = 5 remainder 0

3

Divide quotient by 2 and get remainder

5 / 2 = 2 remainder 1

4

Repeat division

2 / 2 = 1 remainder 0

5

Repeat division

1 / 2 = 0 remainder 1

6

Collect remainders in reverse

Remainders collected: 0,1,0,1 reversed to 1010

Quotient	Remainder
10	0
5	1
2	0
1	1

Why This Works

Step 1: Using built-in function

The Integer.toBinaryString() function converts the decimal number directly to its binary string representation.

Step 2: Manual conversion logic

Dividing the number by 2 and collecting remainders simulates how binary numbers are formed, with each remainder representing a binary digit.

Step 3: Reversing remainders

The binary digits are collected from least significant to most significant bit, so reversing the remainders gives the correct binary number.

Alternative Approaches

Manual division and string building

kotlin

fun decimalToBinary(num: Int): String {
    if (num == 0) return "0"
    var number = num
    val binary = StringBuilder()
    while (number > 0) {
        binary.append(number % 2)
        number /= 2
    }
    return binary.reverse().toString()
}

fun main() {
    val decimalNumber = 10
    println("Binary of $decimalNumber is ${decimalToBinary(decimalNumber)}")
}

This method shows the step-by-step logic but is longer than using the built-in function.

Using Kotlin extension function

kotlin

fun Int.toBinary(): String = Integer.toBinaryString(this)

fun main() {
    val decimalNumber = 10
    println("Binary of $decimalNumber is ${decimalNumber.toBinary()}")
}

This approach wraps the built-in function in an extension for cleaner code.

Complexity: O(log n) time, O(log n) space

Time Complexity

The algorithm divides the number by 2 repeatedly until it reaches 0, which takes about log base 2 of n steps.

Space Complexity

The space needed is proportional to the number of binary digits, which is also about log base 2 of n.

Which Approach is Fastest?

Using the built-in Integer.toBinaryString() is fastest and simplest, while manual methods are educational but slower.

Approach	Time	Space	Best For
Built-in function	O(log n)	O(log n)	Quick and simple conversion
Manual division	O(log n)	O(log n)	Learning and understanding binary conversion
Extension function	O(log n)	O(log n)	Cleaner syntax using built-in method