Simple Calculator

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:padding="8dp"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/input_num_1"
        android:layout_width="0dp"
        android:layout_height="50dp"
        android:layout_marginEnd="10dp"
        android:inputType="numberDecimal"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/input_num_2"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/input_num_2"
        android:layout_width="0dp"
        android:layout_height="50dp"
        android:inputType="numberDecimal"
        app:layout_constraintLeft_toRightOf="@+id/input_num_1"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/add_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="+"
        android:layout_margin="5dp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/sub_button"
        app:layout_constraintTop_toBottomOf="@id/input_num_1"/>

    <Button
        android:id="@+id/sub_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="-"
        android:layout_margin="5dp"
        app:layout_constraintLeft_toRightOf="@+id/add_button"
        app:layout_constraintRight_toLeftOf="@+id/multiply_button"
        app:layout_constraintTop_toBottomOf="@id/input_num_1" />

    <Button
        android:id="@+id/multiply_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="*"
        android:layout_margin="5dp"
        app:layout_constraintLeft_toRightOf="@+id/sub_button"
        app:layout_constraintRight_toLeftOf="@+id/divide_button"
        app:layout_constraintTop_toBottomOf="@id/input_num_2"/>

    <Button
        android:id="@+id/divide_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="/"
        android:layout_margin="5dp"
        app:layout_constraintLeft_toRightOf="@+id/multiply_button"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@id/input_num_2" />

    <TextView
        android:id="@+id/output_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/sub_button"
        />


</androidx.constraintlayout.widget.ConstraintLayout>