如何用安卓工作室制作科学计算器安卓 App？
原文:https://www . geeksforgeeks . org/如何制作科学计算器-Android-app-use-Android-studio/
计算器是每个安卓设备上都有的应用程序。这个应用程序是预装的，或者我们也可以从 Play Store 安装另一个应用程序。对于大学生来说，做任何计算都是最常用的应用之一。在本文中，我们将看一下使用 Kotlin 在 Android 中构建一个简单的科学计算器应用。
注意:要构建一个简单的计算器应用请参考这篇文章如何使用 Android Studio 构建一个简单的计算器应用？
我们将在本文中构建什么？
我们将构建一个科学计算器，在其中我们将执行一些数学运算，如加法、减法、平方根、阶乘等。下面给出了一个示例视频，以了解我们将在本文中做什么。
分步实施
第一步:创建新项目
要在安卓工作室创建新项目，请参考如何在安卓工作室创建/启动新项目。注意选择 Java 作为编程语言。
第二步:给 colors.xml 文件添加新的颜色
导航到应用程序>RES>values>colors . XML文件，并为不同的颜色添加下面的代码。代码中添加了注释，以便更详细地了解。
可扩展标记语言
<?xml version="1.0" encoding="utf-8"?>
<resources>
<color name="purple_200">#0F9D58</color>
<color name="purple_500">#0F9D58</color>
<color name="purple_700">#0F9D58</color>
<color name="teal_200">#FF03DAC5</color>
<color name="teal_700">#FF018786</color>
<color name="black">#FF000000</color>
<color name="white">#FFFFFFFF</color>
<!--three different shades of black color-->
<color name="blac_shade_1">#292D36</color>
<color name="black_shade_2">#272B33</color>
<color name="black_shade_3">#22252D</color>
<color name="yellow">#ffa500</color>
</resources>
步骤 3:使用 activity_main.xml 文件
导航到应用程序> res >布局> activity_main.xml 并将下面的代码添加到该文件中。下面是 activity_main.xml 文件的代码。
可扩展标记语言
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/black_shade_3"
tools:context=".MainActivity">
<TextView
android:id="@+id/idTVSecondary"
android:layout_width="match_parent"
android:layout_height="70dp"
android:background="@color/black_shade_3"
android:gravity="bottom"
android:maxLines="1"
android:padding="10dp"
android:paddingTop="30dp"
android:text=""
android:textAlignment="viewEnd"
android:textColor="@color/white"
android:textSize="15sp"
tools:ignore="RtlCompat" />
<TextView
android:id="@+id/idTVprimary"
android:layout_width="match_parent"
android:layout_height="100dp"
android:layout_below="@id/idTVSecondary"
android:background="@color/black_shade_3"
android:gravity="bottom"
android:maxLines="1"
android:padding="10dp"
android:text=""
android:textAlignment="viewEnd"
android:textColor="#fff"
android:textSize="50sp"
tools:ignore="RtlCompat" />
<androidx.cardview.widget.CardView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_below="@id/idTVprimary"
android:background="@color/blac_shade_1"
app:cardCornerRadius="4dp"
app:cardElevation="2dp">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="7"
android:background="@color/blac_shade_1"
android:orientation="vertical">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:weightSum="7">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:orientation="horizontal">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:weightSum="4">
<Button
android:id="@+id/bac"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="AC"
android:textColor="@color/yellow"
android:textSize="15sp"
tools:targetApi="lollipop" />
<Button
android:id="@+id/bc"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="C"
android:textColor="@color/yellow"
android:textSize="15sp" />
<Button
android:id="@+id/bbrac1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="("
android:textColor="#ffa500"
android:textSize="15sp" />
<Button
android:id="@+id/bbrac2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text=")"
android:textColor="#ffa500"
android:textSize="15sp" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:orientation="horizontal">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:weightSum="5">
<Button
android:id="@+id/bsin"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="sin"
android:textAllCaps="false"
android:textColor="#ffa500"
android:textSize="15sp" />
<Button
android:id="@+id/bcos"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="cos"
android:textAllCaps="false"
android:textColor="#ffa500"
android:textSize="15sp" />
<Button
android:id="@+id/btan"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="tan"
android:textAllCaps="false"
android:textColor="#ffa500"
android:textSize="15sp" />
<Button
android:id="@+id/blog"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="log"
android:textAllCaps="false"
android:textColor="#ffa500"
android:textSize="15sp" />
<Button
android:id="@+id/bln"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="ln"
android:textAllCaps="false"
android:textColor="#ffa500"
android:textSize="15sp" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:orientation="horizontal">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:weightSum="5">
<Button
android:id="@+id/bfact"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="x!"
android:textAllCaps="false"
android:textColor="#ffa500"
android:textSize="15sp" />
<Button
android:id="@+id/bsquare"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="x²"
android:textAllCaps="false"
android:textColor="#ffa500"
android:textSize="15sp" />
<Button
android:id="@+id/bsqrt"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="√"
android:textColor="#ffa500"
android:textSize="15sp" />
<Button
android:id="@+id/binv"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="1/x"
android:textAllCaps="false"
android:textColor="#ffa500"
android:textSize="15sp" />
<Button
android:id="@+id/bdiv"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="÷"
android:textColor="#ffa500"
android:textSize="15sp" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:orientation="horizontal">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:weightSum="4">
<Button
android:id="@+id/b7"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="7"
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/b8"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="8"
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/b9"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="9"
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/bmul"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="×"
android:textColor="#ffa500"
android:textSize="15sp" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:orientation="horizontal">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:weightSum="4">
<Button
android:id="@+id/b4"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="4"
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/b5"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="5"
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/b6"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="6"
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/bminus"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="-"
android:textColor="#ffa500"
android:textSize="15sp" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:orientation="horizontal">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:weightSum="4">
<Button
android:id="@+id/b1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="1"
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/b2"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="2"
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/b3"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="3"
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/bplus"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="+"
android:textColor="#ffa500"
android:textSize="15sp" />
</LinearLayout>
</LinearLayout>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_weight="1"
android:orientation="horizontal">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="horizontal"
android:weightSum="4">
<Button
android:id="@+id/bpi"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="π"
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/b0"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="0"
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/bdot"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="."
android:textColor="#fff"
android:textSize="15sp" />
<Button
android:id="@+id/bequal"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_margin="3dp"
android:layout_weight="1"
android:backgroundTint="@color/black_shade_2"
android:padding="6dp"
android:text="="
android:textColor="#ffa500"
android:textSize="15sp" />
</LinearLayout>
</LinearLayout>
</LinearLayout>
</LinearLayout>
</androidx.cardview.widget.CardView>
</RelativeLayout>
第 4 步:使用T2【主活动. kt】文件
转到 MainActivity.kt 文件，参考以下代码。下面是 MainActivity.kt 文件的代码。代码中添加了注释，以更详细地理解代码。
我的锅
import android.os.Bundle
import android.widget.Button
import android.widget.TextView
import android.widget.Toast
import androidx.appcompat.app.AppCompatActivity
class MainActivity : AppCompatActivity() {
// creating variables for our text view and button
lateinit var tvsec: TextView
lateinit var tvMain: TextView
lateinit var bac: Button
lateinit var bc: Button
lateinit var bbrac1: Button
lateinit var bbrac2: Button
lateinit var bsin: Button
lateinit var bcos: Button
lateinit var btan: Button
lateinit var blog: Button
lateinit var bln: Button
lateinit var bfact: Button
lateinit var bsquare: Button
lateinit var bsqrt: Button
lateinit var binv: Button
lateinit var b0: Button
lateinit var b9: Button
lateinit var b8: Button
lateinit var b7: Button
lateinit var b6: Button
lateinit var b5: Button
lateinit var b4: Button
lateinit var b3: Button
lateinit var b2: Button
lateinit var b1: Button
lateinit var bpi: Button
lateinit var bmul: Button
lateinit var bminus: Button
lateinit var bplus: Button
lateinit var bequal: Button
lateinit var bdot: Button
lateinit var bdiv: Button
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// initializing all our variables.
tvsec = findViewById(R.id.idTVSecondary)
tvMain = findViewById(R.id.idTVprimary)
bac = findViewById(R.id.bac)
bc = findViewById(R.id.bc)
bbrac1 = findViewById(R.id.bbrac1)
bbrac2 = findViewById(R.id.bbrac2)
bsin = findViewById(R.id.bsin)
bcos = findViewById(R.id.bcos)
btan = findViewById(R.id.btan)
blog = findViewById(R.id.blog)
bln = findViewById(R.id.bln)
bfact = findViewById(R.id.bfact)
bsquare = findViewById(R.id.bsquare)
bsqrt = findViewById(R.id.bsqrt)
binv = findViewById(R.id.binv)
b0 = findViewById(R.id.b0)
b9 = findViewById(R.id.b9)
b8 = findViewById(R.id.b8)
b7 = findViewById(R.id.b7)
b6 = findViewById(R.id.b6)
b5 = findViewById(R.id.b5)
b4 = findViewById(R.id.b4)
b3 = findViewById(R.id.b3)
b2 = findViewById(R.id.b2)
b1 = findViewById(R.id.b1)
bpi = findViewById(R.id.bpi)
bmul = findViewById(R.id.bmul)
bminus = findViewById(R.id.bminus)
bplus = findViewById(R.id.bplus)
bequal = findViewById(R.id.bequal)
bdot = findViewById(R.id.bdot)
bdiv = findViewById(R.id.bdiv)
// adding on click listener to our all buttons.
b1.setOnClickListener {
// on below line we are appending
// the expression to our text view.
tvMain.text = (tvMain.text.toString() + "1")
}
b2.setOnClickListener {
// on below line we are appending
// the expression to our text view.
tvMain.text = (tvMain.text.toString() + "2")
}
b3.setOnClickListener {
// on below line we are appending
// the expression to our text view.
tvMain.text = (tvMain.text.toString() + "3")
}
b4.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "4")
}
b5.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "5")
}
b6.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "6")
}
b7.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "7")
}
b8.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "8")
}
b9.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "9")
}
b0.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "0")
}
bdot.setOnClickListener {
tvMain.text = (tvMain.text.toString() + ".")
}
bplus.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "+")
}
bdiv.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "/")
}
bbrac1.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "(")
}
bbrac2.setOnClickListener {
tvMain.text = (tvMain.text.toString() + ")")
}
bpi.setOnClickListener {
// on clicking on pi button we are adding
// pi value as 3.142 to our current value.
tvMain.text = (tvMain.text.toString() + "3.142")
tvsec.text = (bpi.text.toString())
}
bsin.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "sin")
}
bcos.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "cos")
}
btan.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "tan")
}
binv.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "^" + "(-1)")
}
bln.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "ln")
}
blog.setOnClickListener {
tvMain.text = (tvMain.text.toString() + "log")
}
bminus.setOnClickListener {
// on clicking on minus we are checking if
// the user has already a minus operation on screen.
// if minus operation is already present
// then we will not do anything.
val str: String = tvMain.text.toString()
if (!str.get(index = str.length - 1).equals("-")) {
tvMain.text = (tvMain.text.toString() + "-")
}
}
bmul.setOnClickListener {
// if mul sign is not present in our
// text view then only we are adding
// the multiplication operator to it.
val str: String = tvMain.text.toString()
if (!str.get(index = str.length - 1).equals("*")) {
tvMain.text = (tvMain.text.toString() + "*")
}
}
bsqrt.setOnClickListener {
if (tvMain.text.toString().isEmpty()) {
// if the entered number is empty we are displaying an error message.
Toast.makeText(this, "Please enter a valid number..", Toast.LENGTH_SHORT).show()
} else {
val str: String = tvMain.text.toString()
// on below line we are calculation
// square root of the given number.
val r = Math.sqrt(str.toDouble())
// on below line we are converting our double
// to string and then setting it to text view.
val result = r.toString()
tvMain.setText(result)
}
}
bequal.setOnClickListener {
val str: String = tvMain.text.toString()
// on below line we are calling an evaluate
// method to calculate the value of expressions.
val result: Double = evaluate(str)
// on below line we are getting result
// and setting it to text view.
val r = result.toString()
tvMain.setText(r)
tvsec.text = str
}
bac.setOnClickListener {
// on clicking on ac button we are clearing
// our primary and secondary text view.
tvMain.setText("")
tvsec.setText("")
}
bc.setOnClickListener {
// on clicking on c button we are clearing
// the last character by checking the length.
var str: String = tvMain.text.toString()
if (!str.equals("")) {
str = str.substring(0, str.length - 1)
tvMain.text = str
}
}
bsquare.setOnClickListener {
if (tvMain.text.toString().isEmpty()) {
// if the entered number is empty we are displaying an error message.
Toast.makeText(this, "Please enter a valid number..", Toast.LENGTH_SHORT).show()
} else {
// on below line we are getting the expression and then calculating the square of the number
val d: Double = tvMain.getText().toString().toDouble()
// on below line we are calculating the square.
val square = d * d
// after calculating the square we
// are setting it to text view.
tvMain.setText(square.toString())
// on below line we are setting
// the d to secondary text view.
tvsec.text = "$d²"
}
}
bfact.setOnClickListener {
if (tvMain.text.toString().isEmpty()) {
// if the entered number is empty we are displaying an error message.
Toast.makeText(this, "Please enter a valid number..", Toast.LENGTH_SHORT).show()
} else {
// on below line we are getting int value
// and calculating the factorial value of the entered number.
val value: Int = tvMain.text.toString().toInt()
val fact: Int = factorial(value)
tvMain.setText(fact.toString())
tvsec.text = "$value`!"
}
}
}
fun factorial(n: Int): Int {
// this method is use to find factorial
return if (n == 1 || n == 0) 1 else n * factorial(n - 1)
}
fun evaluate(str: String): Double {
return object : Any() {
// on below line we ar creating variable
// for tracking the position and char pos.
var pos = -1
var ch = 0
// below method is for moving to next character.
fun nextChar() {
// on below line we are incrementing our position
// and moving it to next position.
ch = if (++pos < str.length) str[pos].toInt() else -1
}
// this method is use to check the extra space
// present int the expression and removing it.
fun eat(charToEat: Int): Boolean {
while (ch == ' '.toInt()) nextChar()
// on below line we are checking the char pos
// if both is equal then we are returning it to true.
if (ch == charToEat) {
nextChar()
return true
}
return false
}
// below method is to parse our
// expression and to get the ans
// in this we are calling a parse
// expression method to calculate the value.
fun parse(): Double {
nextChar()
val x = parseExpression()
if (pos < str.length) throw RuntimeException("Unexpected: " + ch.toChar())
return x
}
// in this method we will only perform addition and
// subtraction operation on the expression.
fun parseExpression(): Double {
var x = parseTerm()
while (true) {
if (eat('+'.toInt())) x += parseTerm() // addition
else if (eat('-'.toInt())) x -= parseTerm() // subtraction
else return x
}
}
// in below method we will perform
// only multiplication and division operation.
fun parseTerm(): Double {
var x = parseFactor()
while (true) {
if (eat('*'.toInt())) x *= parseFactor() // multiplication
else if (eat('/'.toInt())) x /= parseFactor() // division
else return x
}
}
// below method is use to parse the factor
fun parseFactor(): Double {
//on below line we are checking for addition
// and subtraction and performing unary operations.
if (eat('+'.toInt())) return parseFactor() // unary plus
if (eat('-'.toInt())) return -parseFactor() // unary minus
// creating a double variable for ans.
var x: Double
// on below line we are creating
// a variable for position.
val startPos = pos
// on below line we are checking
// for opening and closing parenthesis.
if (eat('('.toInt())) { // parentheses
x = parseExpression()
eat(')'.toInt())
} else if (ch >= '0'.toInt() && ch <= '9'.toInt() || ch == '.'.toInt()) {
// numbers
while (ch >= '0'.toInt() && ch <= '9'.toInt() || ch == '.'.toInt()) nextChar()
// on below line we are getting sub string from our string using start and pos.
x = str.substring(startPos, pos).toDouble()
} else if (ch >= 'a'.toInt() && ch <= 'z'.toInt()) {
// on below function we are checking for the operator in our expression.
while (ch >= 'a'.toInt() && ch <= 'z'.toInt()) nextChar()
val func = str.substring(startPos, pos)
// calling a method to parse our factor.
x = parseFactor()
// on below line we are checking for square root.
x =
if (func == "sqrt") Math.sqrt(x)
// on below line we are checking for sin function
// and calculating sin function using Math class.
else if (func == "sin") Math.sin(
Math.toRadians(x)
// on below line we are calculating the cos value
) else if (func == "cos") Math.cos(
Math.toRadians(x)
// on below line we are calculating
// the tan value of our expression.
) else if (func == "tan")
Math.tan(Math.toRadians(x))
// on below line we are calculating
// log value of the expression.
else if (func == "log")
Math.log10(x)
// on below line we are calculating
// ln value of expression.
else if (func == "ln") Math.log(x)
// f we get any error then
// we simply return the exception.
else throw RuntimeException(
"Unknown function: $func"
)
} else {
// if the condition not satisfy then we are returning the exception
throw RuntimeException("Unexpected: " + ch.toChar())
}
// on below line we are calculating the power of the expression.
if (eat('^'.toInt())) x = Math.pow(x, parseFactor()) // exponentiation
return x
}
// at last calling a parse for our expression.
}.parse()
}
}
现在运行您的应用程序，查看应用程序的输出。
输出:
