How to separate large numbers with spaces kotlin

Question

I have a calculator app and I want it to show large numbers with spaces between them when users enter their input. Currently, they don't have spaces between them like this: 10000; 100000; 1000000. I want them to show like this: 10 000; 100 000; 1 000 000. The second one looks much neater.

Here is my code

 class CalculatorActivity : AppCompatActivity() {

@Suppress("PrivatePropertyName")
private var DigitOnScreen = StringBuilder(12)
private var operation: Char = ' '
private var leftHandSide: Double = 0.0
private var rightHandSide: Double = 0.0
private lateinit var binding: ActivityCalculatorBinding


override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    binding = ActivityCalculatorBinding.inflate(layoutInflater)
    setContentView(binding.root)

    binding.resultId.text = "0"

    initializeButtons()
}

private fun initializeButtons() {
    functionalButtons()
    operationalButtons()
    numericalButtons()
}

/**
 * This function initializes all of our numerical buttons from
 *  [0 - 9]
 */
private fun numericalButtons() {

    binding.oneBtn.setOnClickListener {
        appendToDigitOnScreen("1")
    }

    binding.twoBtn.setOnClickListener {
        appendToDigitOnScreen("2")
    }

    binding.threeBtn.setOnClickListener {
        appendToDigitOnScreen("3")
    }

    binding.fourBtn.setOnClickListener {
        appendToDigitOnScreen("4")
    }

    binding.fiveBtn.setOnClickListener {
        appendToDigitOnScreen("5")
    }

    binding.sixBtn.setOnClickListener {
        appendToDigitOnScreen("6")
    }

    binding.sevenBtn.setOnClickListener {
        appendToDigitOnScreen("7")
    }

    binding.eightBtn.setOnClickListener {
        appendToDigitOnScreen("8")
    }

    binding.nineBtn.setOnClickListener {
        appendToDigitOnScreen("9")
    }

    binding.zeroBtn.setOnClickListener {
        appendToDigitOnScreen("0")
    }

    binding.dotBtn.setOnClickListener {
        appendToDigitOnScreen(".")
    }

}

/**
 *  Insert the button been clicked onto the screen so user can see
 *  inputs for the button clicked
 */

private fun appendToDigitOnScreen(digit: String) {

    // Add each digit to our string builder
    DigitOnScreen.append(digit)

    // display it on the screen of our mobile app
    binding.resultId.text = DigitOnScreen.toString()
}

/**
 *  Initialize the operation keys in our calculator like the
 *  addition key, subtraction key and the likes
 */
private fun operationalButtons() {

    binding.additionBtn.setOnClickListener {
        selectOperation('A')
    }

    binding.subtractBtn.setOnClickListener {
        selectOperation('S')
    }

    binding.divideBtn.setOnClickListener {
        selectOperation('D')
    }

    binding.multipyBtn.setOnClickListener {
        selectOperation('M')
    }

}

/**
 * Function to assign operational sign to our math calculations
 */
private fun selectOperation(c: Char) {

    operation = c
    leftHandSide = DigitOnScreen.toString().toDouble()
    DigitOnScreen.clear()
    binding.resultId.text = "0"
}

/**
 * Handles functional operations in out application like
 * clear button, backspace button and the clear everything button
 */
private fun functionalButtons() {

    binding.clearEverythingBtn.setOnClickListener {
        DigitOnScreen.clear()
        binding.resultId.text = "0"
    }

    binding.clearBtn.setOnClickListener {

        if (DigitOnScreen.isEmpty()) {
            return@setOnClickListener
        } else {
            clearDigit()
        }
    }

    binding.backspaceBtn.setOnClickListener {
        if (DigitOnScreen.isEmpty()) {
            return@setOnClickListener
        } else {
            clearDigit()
        }
    }

    binding.equalBtn.setOnClickListener {
        performMathOperation()
    }

}


/**
 *  This function performs our Math Operation which is then showed on the screen.
 */
private fun performMathOperation() {

    rightHandSide = DigitOnScreen.toString().toDouble()


    when (operation) {

        'A' -> {
            val sum = OperationsHelper.add(leftHandSide, rightHandSide)
            binding.resultId.text = sum.toString()
            DigitOnScreen.clear()
            DigitOnScreen.append(sum)
        }
        'S' -> {
            val subtract = OperationsHelper.subtract(leftHandSide, rightHandSide)
            binding.resultId.text = subtract.toString()
            DigitOnScreen.clear()
            DigitOnScreen.append(subtract)
        }
        'M' -> {
            val multiply = OperationsHelper.multiply(leftHandSide, rightHandSide)
            binding.resultId.text = multiply.toString()
            DigitOnScreen.clear()
            DigitOnScreen.append(multiply)
        }
        'D' -> {
            val divide = OperationsHelper.divide(leftHandSide, rightHandSide)
            binding.resultId.text = divide.toString()
            DigitOnScreen.clear()
            DigitOnScreen.append(divide)
        }

    }

}

/**
 *  This function remove the last digit on the screen.
 */
private fun clearDigit() {

    val length = DigitOnScreen.length

    DigitOnScreen.deleteCharAt(length - 1)
    if (length <= 0) {
        binding.resultId.text = "0"
    }else{
        binding.resultId.text = DigitOnScreen.toString()
    }

}

Answer 1

you can solve it like this for example :

val x = "10000000"
val s:StringBuilder = java.lang.StringBuilder("")
x.mapIndexed{ index, c ->
    if ((index+1)%3 ==0){
        s.append(" ")
    }
    s.append(c)
}
println(s)

you need to store the value of all digts -> and every 3 digit make a space