Calculator

Activity Main (XML)
-------------------


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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="fill_parent"
    android:orientation="vertical"
    android:layout_height="wrap_content"
    android:gravity="center"
    tools:context="com.example.work.myapplication.MainActivity">


    <EditText
        android:id="@+id/disp"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:hint="Enter the values"
        android:textSize="30sp"
        android:layout_marginBottom="25dp"/>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal"
        android:gravity="center">

        <Button
            android:id="@+id/one"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="1"/>

        <Button
            android:id="@+id/two"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="2"/>

        <Button
            android:id="@+id/three"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="3"/>

        <Button
            android:id="@+id/add"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="+"/>

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal"
        android:gravity="center">

        <Button
            android:id="@+id/four"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="4"/>

        <Button
            android:id="@+id/five"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="5"/>

        <Button
            android:id="@+id/six"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="6"/>

        <Button
            android:id="@+id/sub"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="-"/>

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal"
        android:gravity="center">

        <Button
            android:id="@+id/seven"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="7"/>

        <Button
            android:id="@+id/eight"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="8"/>

        <Button
            android:id="@+id/nine"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="9"/>

        <Button
            android:id="@+id/mul"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="*"/>

    </LinearLayout>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal"
        android:gravity="center">

        <Button
            android:id="@+id/zero"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="0"/>

        <Button
            android:id="@+id/cancel"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="CLR"/>

        <Button
            android:id="@+id/equal"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="="/>

        <Button
            android:id="@+id/div"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="/"/>

    </LinearLayout>


</LinearLayout>





============================

Main_Activity (Java)
--------------------------

package com.example.work.myapplication;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends AppCompatActivity {

    Button one, two, three, four, five, six, seven, eight, nine, zero, add, sub, mul, div, cancel, equal;
    EditText disp;
    int a;
    int b;
    boolean addition, subtraction, multiplication, division;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);


        one=(Button) findViewById(R.id.one);
        two=(Button) findViewById(R.id.two);
        three=(Button) findViewById(R.id.three);
        four=(Button) findViewById(R.id.four);
        five=(Button) findViewById(R.id.five);
        six=(Button) findViewById(R.id.six);
        seven=(Button) findViewById(R.id.seven);
        eight=(Button) findViewById(R.id.eight);
        nine=(Button) findViewById(R.id.nine);
        zero=(Button) findViewById(R.id.zero);
        add=(Button) findViewById(R.id.add);
        sub=(Button) findViewById(R.id.sub);
        mul=(Button) findViewById(R.id.mul);
        div=(Button) findViewById(R.id.div);
        cancel=(Button) findViewById(R.id.cancel);
        equal=(Button) findViewById(R.id.equal);
        disp=(EditText) findViewById(R.id.disp);

        one.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                disp.setText(disp.getText() + "1");
            }
        });

        two.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                disp.setText(disp.getText() + "2");
            }
        });

        three.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                disp.setText(disp.getText() + "3");
            }
        });

        four.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                disp.setText(disp.getText() + "4");
            }
        });

        five.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                disp.setText(disp.getText() + "5");
            }
        });

        six.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                disp.setText(disp.getText() + "6");
            }
        });

        seven.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                disp.setText(disp.getText() + "7");
            }
        });

        eight.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                disp.setText(disp.getText() + "8");
            }
        });

        nine.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                disp.setText(disp.getText() + "9");
            }
        });

        zero.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                disp.setText(disp.getText() + "0");
            }
        });

        add.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (disp == null)
                {
                    disp.setText("");
                }
                else {
                    a = Integer.parseInt(disp.getText() + "");
                    addition = true;
                    disp.setText(null);
                }
            }
        });


        sub.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (disp == null)
                {
                    disp.setText("");
                }
                else {
                    a = Integer.parseInt(disp.getText() + "");
                    subtraction = true;
                    disp.setText(null);
                }
            }
        });

        mul.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (disp == null)
                {
                    disp.setText("");
                }
                else {
                    a = Integer.parseInt(disp.getText() + "");
                    multiplication = true;
                    disp.setText(null);
                }
            }
        });

        div.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (disp == null)
                {
                    disp.setText("");
                }
                else {
                    a = Integer.parseInt(disp.getText() + "");
                    division = true;
                    disp.setText(null);
                }
            }
        });


        cancel.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v)
            {
                disp.setText("");
            }
        });



        equal.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                b = Integer.parseInt(disp.getText() + "");

                if (addition == true){
                    disp.setText(a + b +"");
                    addition=false;
                }

                if (subtraction == true){
                    disp.setText(a - b +"");
                    subtraction=false;
                }

                if (multiplication == true){
                    disp.setText(a * b +"");
                    multiplication=false;
                }

                if (division == true){
                    disp.setText(a / b +"");
                    division=false;
                }
            }
        });








    }
}


=====================