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package com.example.nabeel.myapplicationtutorial2;

import android.app.Activity;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;

public class CoolCalc extends Activity implements View.OnClickListener {
    Button zeroBtn, oneBtn, twoBtn, threeBtn, fourBtn, fiveBtn, sixBtn, sevenBtn, eightBtn, nineBtn, clearBtn;
    ImageButton addBtn, subtractBtn, multiplyBtn, divideBtn,calcBtn;
    TextView resultView;
    String runningNumber = "";
    String leftValueStr = "";
    String rightValueStr = "";
    Operation currentOperation;
    int result = 0;

    public enum Operation{
        ADD, SUBTRACT, MULLTIPLY, DIVIDE, EQUAL;
    }


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

    }
    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.zeroBtn:
                numberPressed(0);
                break;
            case R.id.oneBtn:
                numberPressed(1);
                break;
            case R.id.twoBtn:
                numberPressed(2);
                break;
            case R.id.threeBtn:
                numberPressed(3);
                break;
            case R.id.fourBtn:
                numberPressed(4);
                break;
            case R.id.fiveBtn:
                numberPressed(5);
                break;
            case R.id.sixBtn:
                numberPressed(6);
                break;
            case R.id.sevenBtn:
                numberPressed(7);
                break;
            case R.id.eightBtn:
                numberPressed(8);
                break;
            case R.id.nineBtn:
                numberPressed(9);
                break;
            case R.id.addBtn:
                processOperation(Operation.ADD);
                break;
            case R.id.subtractBtn:
                processOperation(Operation.SUBTRACT);
                break;
            case R.id.multiplyBtn:
                processOperation(Operation.MULLTIPLY);
                break;
            case R.id.divideBtn:
                processOperation(Operation.DIVIDE);
                break;
            case R.id.clearBtn:
                leftValueStr = "";
                rightValueStr= "";
                currentOperation = null;
                runningNumber = "";
                result = 0;
                resultView.setText("0");
                break;
            case R.id.calcBtn:
                processOperation(Operation.EQUAL);
                break;
        }


    }

    private void init() {
        //inialize all xml attributes
        zeroBtn = findViewById(R.id.zeroBtn);
        oneBtn = findViewById(R.id.oneBtn);
        twoBtn = findViewById(R.id.twoBtn);
        threeBtn = findViewById(R.id.threeBtn);
        fourBtn = findViewById(R.id.fourBtn);
        fiveBtn = findViewById(R.id.fiveBtn);
        sixBtn = findViewById(R.id.sixBtn);
        sevenBtn = findViewById(R.id.sevenBtn);
        eightBtn = findViewById(R.id.eightBtn);
        nineBtn = findViewById(R.id.nineBtn);
        clearBtn = findViewById(R.id.clearBtn);

        resultView = findViewById(R.id.resultView);

        addBtn = findViewById(R.id.addBtn);
        subtractBtn = findViewById(R.id.subtractBtn);
        multiplyBtn = findViewById(R.id.multiplyBtn);
        divideBtn = findViewById(R.id.divideBtn);
        calcBtn = findViewById(R.id.calcBtn);

        //set listeners
        zeroBtn.setOnClickListener(this);
        oneBtn.setOnClickListener(this);
        twoBtn.setOnClickListener(this);
        threeBtn.setOnClickListener(this);
        fourBtn.setOnClickListener(this);
        fiveBtn.setOnClickListener(this);
        sixBtn.setOnClickListener(this);
        sevenBtn.setOnClickListener(this);
        eightBtn.setOnClickListener(this);
        nineBtn.setOnClickListener(this);
        resultView.setOnClickListener(this);
        addBtn.setOnClickListener(this);
        subtractBtn.setOnClickListener(this);
        multiplyBtn.setOnClickListener(this);
        divideBtn.setOnClickListener(this);
        calcBtn.setOnClickListener(this);
        clearBtn.setOnClickListener(this);
    }

    void numberPressed( int number ){
        runningNumber +=String.valueOf(number);
        resultView.setText(runningNumber);
    }
    void processOperation(Operation operation){
        if (currentOperation != null){
            if (runningNumber != null){
                rightValueStr = runningNumber;
                runningNumber = "";

                switch (currentOperation){
                    case ADD:
                        result = Integer.parseInt(leftValueStr) + Integer.parseInt(rightValueStr);
                        break;
                    case SUBTRACT:
                        result = Integer.parseInt(leftValueStr) - Integer.parseInt(rightValueStr);
                        break;
                    case MULLTIPLY:
                        result = Integer.parseInt(leftValueStr) * Integer.parseInt(rightValueStr);
                        break;
                    case DIVIDE:
                            result = Integer.parseInt(leftValueStr) / Integer.parseInt(rightValueStr);
                        break;
                }

                leftValueStr = String.valueOf(result);
                resultView.setText(leftValueStr);
            }
            }
        else {
            leftValueStr = runningNumber;
            runningNumber = "";
        }
        currentOperation = operation;

    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".CoolCalc"
    android:background="@android:color/white">


    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="165dp"
            android:id="@+id/result_text"
            android:background="@android:color/holo_blue_light"
            android:orientation="vertical">

            <TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:id="@+id/resultView"
                android:layout_gravity="end"
                android:gravity="right"
                android:textColor="@android:color/black"
                android:text=""
                android:paddingTop="50dp"
                android:textSize="45sp" />

        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="100dp"
            android:orientation="horizontal"
            android:weightSum="4">

            <Button
                android:id="@+id/sevenBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="?android:attr/colorForeground"
                android:text="7"
                android:textColor="#000000"
                android:textSize="30dp" />

            <Button
                android:id="@+id/eightBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="?android:attr/colorForeground"
                android:text="8"
                android:textColor="#000000"
                android:textSize="30dp" />

            <Button
                android:id="@+id/nineBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="?android:attr/colorForeground"
                android:text="9"
                android:textColor="#000000"
                android:textSize="30dp" />

            <ImageButton
                android:id="@+id/divideBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="#ffffff"
                android:padding="16dp"
                android:src="@drawable/icon_divide" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="100dp"
            android:orientation="horizontal">

            <Button
                android:id="@+id/fourBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="?android:attr/colorForeground"
                android:text="4"
                android:textColor="#000000"
                android:textSize="30dp" />

            <Button
                android:id="@+id/fiveBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="?android:attr/colorForeground"
                android:text="5"
                android:textColor="#000000"
                android:textSize="30dp" />

            <Button
                android:id="@+id/sixBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="?android:attr/colorForeground"
                android:text="6"
                android:textColor="#000000"
                android:textSize="30dp" />

            <ImageButton
                android:id="@+id/multiplyBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="#ffffff"
                android:padding="16dp"
                android:src="@drawable/icon_multiplication" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="100dp"
            android:orientation="horizontal">

            <Button
                android:id="@+id/oneBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="?android:attr/colorForeground"
                android:text="1"
                android:textColor="#000000"
                android:textSize="30dp" />

            <Button
                android:id="@+id/twoBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="?android:attr/colorForeground"
                android:text="2"
                android:textColor="#000000"
                android:textSize="30dp" />

            <Button
                android:id="@+id/threeBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="?android:attr/colorForeground"
                android:text="3"
                android:textColor="#000000"
                android:textSize="30dp" />

            <ImageButton
                android:id="@+id/subtractBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="#ffffff"
                android:padding="16dp"
                android:src="@drawable/icon_minus" />
        </LinearLayout>

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="100dp"
            android:orientation="horizontal"
            android:weightSum="4">

            <LinearLayout
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="2"
                android:background="?android:attr/colorForeground"
                android:gravity="center"
                android:orientation="vertical">

                <Button
                    android:layout_width="110dp"
                    android:layout_height="wrap_content"
                    android:id="@+id/clearBtn"
                    android:background="#45c4cd"
                    android:text="CLEAR"
                    android:textColor="#ffffff"
                    android:textSize="30sp" />

            </LinearLayout>

            <Button
                android:id="@+id/zeroBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="?android:attr/colorForeground"
                android:text="0"
                android:textColor="#000000"
                android:textSize="30dp" />

            <ImageButton
                android:id="@+id/addBtn"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:background="#ffffff"
                android:padding="16dp"
                android:src="@drawable/add" />
        </LinearLayout>

    </LinearLayout>
    <ImageButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/calcBtn"
        android:layout_alignParentEnd="true"
        android:layout_marginTop="130dp"
        android:layout_marginEnd="50dp"
        android:background="@android:color/white"
        android:contentDescription="@null"
        android:src="@drawable/equal"
        tools:ignore="RtlSymmetry" />


</RelativeLayout>