import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*
import javax.script.ScriptEngineManager

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // Set click listeners for the number buttons
        button0.setOnClickListener { appendNumber("0") }
        button1.setOnClickListener { appendNumber("1") }
        button2.setOnClickListener { appendNumber("2") }
        button3.setOnClickListener { appendNumber("3") }
        button4.setOnClickListener { appendNumber("4") }
        button5.setOnClickListener { appendNumber("5") }
        button6.setOnClickListener { appendNumber("6") }
        button7.setOnClickListener { appendNumber("7") }
        button8.setOnClickListener { appendNumber("8") }
        button9.setOnClickListener { appendNumber("9") }
        buttonDot.setOnClickListener { appendNumber(".") }

        // Set click listeners for the operator buttons
        buttonAdd.setOnClickListener { setOperator("+") }
        buttonSubtract.setOnClickListener { setOperator("-") }
        buttonMultiply.setOnClickListener { setOperator("*") }
        buttonDivide.setOnClickListener { setOperator("/") }

        // Set click listener for the equals button
        buttonEquals.setOnClickListener { calculateResult() }

        // Set click listener for the clear button
        buttonClear.setOnClickListener { clearInput() }
    }

    private fun appendNumber(number: String) {
        inputTextView.append(number)
    }

    private fun setOperator(operator: String) {
        inputTextView.append(operator)
    }

    private fun calculateResult() {
        val input = inputTextView.text.toString()
        val result = try {
            // Evaluate the input string as a mathematical expression
            val engine = ScriptEngineManager().getEngineByName("rhino")
            engine.eval(input) as Double
        } catch (e: Exception) {
            // If there's an error, show an error message
            inputTextView.setTextColor(resources.getColor(R.color.colorError))
            return
        }
        inputTextView.text = result.toString()
    }

    private fun clearInput() {
        inputTextView.text = ""
        inputTextView.setTextColor(resources.getColor(R.color.colorPrimaryDark))
    }
}

Kotlin online compiler

Write, Run & Share Kotlin code online using OneCompiler’s Kotlin online compiler for free. It’s a modern and fast online playground for Kotlin, supporting the latest version and ideal for learning, experimenting, and sharing code instantly.

About Kotlin

Kotlin is a statically typed, modern programming language developed by JetBrains. It runs on the JVM and is fully interoperable with Java. Kotlin is concise, expressive, and safe, and it’s officially supported by Google for Android app development.

Sample Code

The following is a simple Kotlin program that prints a greeting:

fun main() {
    println("Hello, OneCompiler!")
}

Taking inputs (stdin)

OneCompiler’s Kotlin editor supports stdin. You can provide input using the I/O tab. Here's a sample program that reads a line of input and prints a greeting:

fun main() {
    print("Enter your name: ")
    val name = readLine()
    println("Hello, $name")
}

Syntax Basics

Variables

val name: String = "OneCompiler"  // Immutable
var age: Int = 25                 // Mutable

Kotlin supports type inference, so explicit types are optional:

val city = "Hyderabad"
var count = 10

Conditionals

val score = 85
if (score >= 50) {
    println("Pass")
} else {
    println("Fail")
}

Loops

For loop

for (i in 1..5) {
    println(i)
}

While loop

var i = 1
while (i <= 5) {
    println(i)
    i++
}

Do-While loop

var j = 1
do {
    println(j)
    j++
} while (j <= 5)

Functions

fun add(a: Int, b: Int): Int {
    return a + b
}

fun greet(name: String) = "Hello, $name"

Collections

val items = listOf("apple", "banana", "cherry")
for (item in items) {
    println(item)
}

This guide provides a quick reference to Kotlin programming syntax and features. Start coding in Kotlin using OneCompiler’s Kotlin online compiler today!