<< RETURN: Coding / Kotlin / Coding with Kotlin
Objective
The Simple calculator application should be able to perform most of what a Basic calculator can do. There won’t be any complex arithmetic such as power, logarithms, exponents, or modulo.
However it can perform the following:
- Addition
- Subtraction
- Multiplication
- Division
- Negation (Adding/Removing negative sign)
- Add Floating point
- Clear Output
Compose Multiplatform Example
Kotlin
import androidx.compose.material.MaterialTheme
import androidx.compose.desktop.ui.tooling.preview.Preview
import androidx.compose.foundation.layout.*
import androidx.compose.material.Button
import androidx.compose.material.Text
import androidx.compose.material.TextField
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.unit.dp
import androidx.compose.ui.window.Window
import androidx.compose.ui.window.application
val specialOps: Set<String> = setOf("+", "-", "x", "/")
@Composable
@Preview
fun App() {
var text by remember { mutableStateOf("Press any key to begin...") }
MaterialTheme {
Column(modifier = Modifier.fillMaxSize().padding(10.dp, 10.dp, 10.dp, 10.dp),
horizontalAlignment = Alignment.Start) {
Row(modifier = Modifier.fillMaxWidth().padding(5.dp, 5.dp),
verticalAlignment = Alignment.Top) {
TextField(
value = text,
onValueChange = { text = it },
label = { Text("Output") },
modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 0.dp),
readOnly = true
)
Button(
modifier = Modifier.padding(0.dp, 10.dp, 0.dp, 0.dp).height(55.dp),
onClick = {
text = "Press any key to begin..."
}) {
Text("CLEAR")
}
}
Row(modifier = Modifier.fillMaxWidth().padding(5.dp, 5.dp),
verticalAlignment = Alignment.CenterVertically) {
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text == "Press any key to begin..." || text.contains("Error")) {
text = "1"
}
else {
text += "1"
}
}) {
Text("1")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text == "Press any key to begin..." || text.contains("Error")) {
text = "2"
}
else {
text += "2"
}
}) {
Text("2")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text == "Press any key to begin..." || text.contains("Error")) {
text = "3"
}
else {
text += "3"
}
}) {
Text("3")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text != "Press any key to begin..." || !text.contains("Error")) {
if (!specialOps.contains(text.last().toString())) {
if ("^[~.0-9]+[+-x/][.0-9]+".toRegex().matches(text)) {
text = calculate(text) + "+"
}
else {
text += "+"
}
}
}
}) {
Text("+", fontWeight = FontWeight.Bold)
}
}
}
Row(modifier = Modifier.fillMaxWidth().padding(5.dp, 5.dp),
verticalAlignment = Alignment.CenterVertically) {
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text == "Press any key to begin..." || text.contains("Error")) {
text = "4"
}
else {
text += "4"
}
}) {
Text("4")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text == "Press any key to begin..." || text.contains("Error")) {
text = "5"
}
else {
text += "5"
}
}) {
Text("5")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text == "Press any key to begin..." || text.contains("Error")) {
text = "6"
}
else {
text += "6"
}
}) {
Text("6")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text != "Press any key to begin..." || !text.contains("Error")) {
if (!specialOps.contains(text.last().toString())) {
if ("^[~.0-9]+[+-x/][.0-9]+".toRegex().matches(text)) {
text = calculate(text) + "-"
}
else {
text += "-"
}
}
}
}) {
Text("-", fontWeight = FontWeight.Bold)
}
}
}
Row(modifier = Modifier.fillMaxWidth().padding(5.dp, 5.dp),
verticalAlignment = Alignment.CenterVertically) {
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text == "Press any key to begin..." || text.contains("Error")) {
text = "7"
}
else {
text += "7"
}
}) {
Text("7")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text == "Press any key to begin..." || text.contains("Error")) {
text = "8"
}
else {
text += "8"
}
}) {
Text("8")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text == "Press any key to begin..." || text.contains("Error")) {
text = "9"
}
else {
text += "9"
}
}) {
Text("9")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text != "Press any key to begin..." || !text.contains("Error")) {
if (!specialOps.contains(text.last().toString())) {
if ("^[~.0-9]+[+-x/][.0-9]+".toRegex().matches(text)) {
text = calculate(text) + "x"
}
else {
text += "x"
}
}
}
}) {
Text("x", fontWeight = FontWeight.Bold)
}
}
}
Row(modifier = Modifier.fillMaxWidth().padding(5.dp, 5.dp),
verticalAlignment = Alignment.CenterVertically) {
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (!specialOps.contains(text.last().toString()) || !text.contains("Error"))
text = performNegation(text)
}) {
Text("+/-")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text == "Press any key to begin..." || text.contains("Error")) {
text = "0"
}
else {
text += "0"
}
}) {
Text("0")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
text = addDot(text)
}) {
Text(".")
}
}
Column(modifier = Modifier.padding(10.dp, 10.dp, 10.dp, 10.dp)) {
Button(onClick = {
if (text != "Press any key to begin..." || !text.contains("Error")) {
if (!specialOps.contains(text.last().toString())) {
if ("^[~.0-9]+[+-x/][.0-9]+".toRegex().matches(text)) {
text = calculate(text) + "/"
}
else {
text += "/"
}
}
}
}) {
Text("/", fontWeight = FontWeight.Bold)
}
}
Button(modifier = Modifier.padding(10.dp, 0.dp, 10.dp, 10.dp).height(51.dp).width(80.dp).align(Alignment.Top),
onClick = {
if (text != "Press any key to begin..." || !text.contains("Error")) {
if (!specialOps.contains(text.last().toString())) {
if (text.last().toString() == ".") {
text += "0"
}
text = calculate(text)
}
}
}) {
Text("=", fontWeight = FontWeight.ExtraBold)
}
}
}
}
}
fun main() = application {
Window(onCloseRequest = ::exitApplication, title = "Simple Calculator") {
App()
}
}
fun addDot(mainEqn: String): String
{
return if (specialOps.contains(mainEqn.last().toString())) {
mainEqn + "0."
} else {
val myList = mainEqn.split("+", "-", "x", "/")
if (myList.size == 2 && !(myList[1].contains("."))) {
"$mainEqn."
} else if (myList.size == 1 && !(myList[0].contains("."))) {
"$mainEqn."
} else {
mainEqn
}
}
}
fun calculate(mainEqn: String): String
{
val isDouble = (mainEqn.contains('.') || mainEqn.contains('/'))
val numArr = mainEqn.split("+", "-", "x", "/")
val num = if (mainEqn.contains('+')) {
parseNegation(numArr[0]).toDouble() + parseNegation(numArr[1]).toDouble()
} else if (mainEqn.contains('-')) {
parseNegation(numArr[0]).toDouble() - parseNegation(numArr[1]).toDouble()
} else if (mainEqn.contains('x')) {
parseNegation(numArr[0]).toDouble() * parseNegation(numArr[1]).toDouble()
} else if (mainEqn.contains('/')) {
if (parseNegation(numArr[1]).toDouble() == 0.0) {
return "Divide by Zero Error"
} else {
parseNegation(numArr[0]).toDouble() / parseNegation(numArr[1]).toDouble()
}
} else {
parseNegation(mainEqn).toDouble()
}
return if (isDouble) {
num.toString().replace("-", "~")
} else {
num.toInt().toString().replace("-", "~")
}
}
fun parseNegation(numStr: String): String
{
return if (numStr.contains("~")) {
"-${numStr.substring(1, numStr.length)}"
}
else {
numStr
}
}
fun performNegation(numStr: String): String
{
val myList = numStr.split("+", "-", "x", "/")
if (myList.size == 2) {
if (myList.last().contains("~")) {
for (i in numStr.indices) {
if (specialOps.contains(numStr[i].toString())) {
return numStr.substring(0, i + 1) + numStr.substring(i + 2, numStr.length)
}
}
} else {
for (i in numStr.indices) {
if (specialOps.contains(numStr[i].toString())) {
return numStr.substring(0, i + 1) + "~" + numStr.substring(i + 1, numStr.length)
}
}
}
} else if (myList.size == 1) {
return if (myList[0].contains("~")) {
numStr.substring(1, numStr.length)
} else {
"~$numStr"
}
}
return numStr
}
The above is the full code for the Simple Calculator. If you have a working Compose Multiplatform project, you should be able to just copy and paste.
Github
If for some reason copy + paste doesn’t work for you, another option is to download the full Simple Calculator project from my Github repository.
Next Up
Once you’re done with this, you can check out Hashing with Kotlin using Compose Multiplatform.