How to convert a number to its English word representation in Kotlin

How to convert a number to its English word representation in Kotlin.

Here's a detailed step-by-step tutorial on how to convert a number to its English word representation in Kotlin:

Step 1: Define a function to handle single-digit numbers

First, let's define a function that can convert a single-digit number to its English word representation. We'll call this function convertSingleDigit.

private fun convertSingleDigit(num: Int): String {
    return when (num) {
        0 -> "zero"
        1 -> "one"
        2 -> "two"
        3 -> "three"
        4 -> "four"
        5 -> "five"
        6 -> "six"
        7 -> "seven"
        8 -> "eight"
        9 -> "nine"
        else -> throw IllegalArgumentException("Invalid input: $num")
    }
}

Step 2: Define a function to handle two-digit numbers

Next, let's define a function that can convert a two-digit number to its English word representation. We'll call this function convertTwoDigits.

private fun convertTwoDigits(num: Int): String {
    if (num < 10) {
        return convertSingleDigit(num)
    } else if (num < 20) {
        return when (num) {
            10 -> "ten"
            11 -> "eleven"
            12 -> "twelve"
            13 -> "thirteen"
            14 -> "fourteen"
            15 -> "fifteen"
            16 -> "sixteen"
            17 -> "seventeen"
            18 -> "eighteen"
            19 -> "nineteen"
            else -> throw IllegalArgumentException("Invalid input: $num")
        }
    } else {
        val tensDigit = num / 10
        val onesDigit = num % 10
        val tensWord = when (tensDigit) {
            2 -> "twenty"
            3 -> "thirty"
            4 -> "forty"
            5 -> "fifty"
            6 -> "sixty"
            7 -> "seventy"
            8 -> "eighty"
            9 -> "ninety"
            else -> throw IllegalArgumentException("Invalid input: $num")
        }
        val onesWord = convertSingleDigit(onesDigit)
        return "$tensWord-$onesWord"
    }
}

Step 3: Define a function to handle three-digit numbers

Now, let's define a function that can convert a three-digit number to its English word representation. We'll call this function convertThreeDigits.

private fun convertThreeDigits(num: Int): String {
    val hundredsDigit = num / 100
    val remainingDigits = num % 100
    val hundredsWord = convertSingleDigit(hundredsDigit) + " hundred"
    return if (remainingDigits == 0) {
        hundredsWord
    } else {
        hundredsWord + " " + convertTwoDigits(remainingDigits)
    }
}

Step 4: Define the main conversion function

Finally, let's define the main function that can convert any positive integer to its English word representation. We'll call this function convertToWord.

fun convertToWord(num: Int): String {
    if (num == 0) {
        return "zero"
    }
    if (num < 0) {
        return "minus " + convertToWord(-num)
    }
    val billions = num / 1_000_000_000
    val millions = (num / 1_000_000) % 1_000
    val thousands = (num / 1_000) % 1_000
    val remainingDigits = num % 1_000

    val result = StringBuilder()

    if (billions > 0) {
        result.append(convertThreeDigits(billions)).append(" billion ")
    }

    if (millions > 0) {
        result.append(convertThreeDigits(millions)).append(" million ")
    }

    if (thousands > 0) {
        result.append(convertThreeDigits(thousands)).append(" thousand ")
    }

    if (remainingDigits > 0) {
        result.append(convertThreeDigits(remainingDigits))
    }

    return result.toString().trim()
}

Step 5: Testing the conversion function

Let's test our convertToWord function with some sample inputs:

fun main() {
    println(convertToWord(0)) // Output: zero
    println(convertToWord(42)) // Output: forty-two
    println(convertToWord(123)) // Output: one hundred twenty-three
    println(convertToWord(1000)) // Output: one thousand
    println(convertToWord(1_000_000)) // Output: one million
    println(convertToWord(1_234_567_890)) // Output: one billion two hundred thirty-four million five hundred sixty-seven thousand eight hundred ninety
}

That's it! You now have a complete implementation to convert a number to its English word representation in Kotlin.