Programming Examples

Code form Android Calculator Design and Program

Android application to implements simple calculator
Solution
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"
    tools:context=".MainActivity">
    <TextView
        android:id="@+id/output"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toTopOf="@+id/tableLayout"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        android:textSize="40dp"
        app:layout_constraintTop_toTopOf="parent" />
    <TableLayout
        android:id="@+id/tableLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent">

        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <Button
                android:id="@+id/per"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="%" />

            <Button
                android:id="@+id/btn_ce"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="CE" />

            <Button
                android:id="@+id/btn_c"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="C" />

            <Button
                android:id="@+id/btn_div"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_weight="1"
                android:text="/" />
        </TableRow>

        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <Button
                android:id="@+id/btn_7"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="7" />

            <Button
                android:id="@+id/btn_8"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="8" />

            <Button
                android:id="@+id/btn_9"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="9" />

            <Button
                android:id="@+id/btn_mul"
                android:onClick="operatorEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_weight="1"
                android:text="x" />
        </TableRow>

        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <Button
                android:id="@+id/btn_4"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="4" />

            <Button
                android:id="@+id/btn_5"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="5" />

            <Button
                android:id="@+id/btn_6"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="6" />

            <Button
                android:id="@+id/btn_sub"
                android:onClick="operatorEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_weight="1"
                android:text="-" />
        </TableRow>

        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <Button
                android:id="@+id/btn_1"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="1" />

            <Button
                android:id="@+id/btn_2"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="2" />

            <Button
                android:id="@+id/btn_3"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="3" />

            <Button
                android:id="@+id/btn_sum"
                android:onClick="operatorEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="+" />
        </TableRow>
        <TableRow
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <Button
                android:id="@+id/btn_00"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="00" />

            <Button
                android:id="@+id/btn_0"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="0" />

            <Button
                android:id="@+id/btn_dot"
                android:onClick="numberEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="." />

            <Button
                android:id="@+id/btn_equal"
                android:onClick="equalEvent"
                android:layout_width="30pt"
                android:layout_height="30pt"
                android:layout_marginRight="3dp"
                android:layout_weight="1"
                android:text="=" />
        </TableRow>
    </TableLayout>


</androidx.constraintlayout.widget.ConstraintLayout>



MainActivity.java

package com.example.demo2;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;


public class MainActivity extends AppCompatActivity {
    TextView editText;
    boolean isNewOp=true;
    String opr="",oldvalue="";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editText=findViewById(R.id.output);

    }

    public void numberEvent(View view) {
        if(isNewOp)
            editText.setText("");
        isNewOp=false;
        String number=editText.getText().toString();
        switch(view.getId())
        {
            case R.id.btn_0:
                number+="0";
                break;
            case R.id.btn_00:
                number+="00";
                break;
            case R.id.btn_1:
                number+="1";
                break;
            case R.id.btn_2:
                number+="2";
                break;
            case R.id.btn_3:
                number+="3";
                break;
            case R.id.btn_4:
                number+="4";
                break;
            case R.id.btn_5:
                number+="5";
                break;
            case R.id.btn_6:
                number+="6";
                break;
            case R.id.btn_7:
                number+="7";
                break;
            case R.id.btn_8:
                number+="8";
                break;
            case R.id.btn_9:
                number+="9";
                break;
            case R.id.btn_dot:
                number+=".";
                break;
        }
        editText.setText(number);
    }

    public void operatorEvent(View view) {
        isNewOp=true;
        oldvalue=editText.getText().toString();
        switch(view.getId()) {
            case R.id.btn_sum:
                opr="+";
                break;
            case R.id.btn_sub:
                opr="-";
                break;
            case R.id.btn_mul:
                opr="*";
                break;
            case R.id.btn_div:
                opr="/";
                break;
        }

    }

    public void equalEvent(View view) {

        Double num1=Double.parseDouble(editText.getText().toString());
        Double num2=Double.parseDouble(oldvalue);
        Double ans=0.0;
        switch(opr)
        {
            case "+":
                ans=num1+num2;
                break;
            case "-":
                ans=num1-num2;
                break;
            case "*":
                ans=num1*num2;
                break;
            case "/":
                ans=num1/num2;
                break;
        }
        editText.setText(String.valueOf(ans));


        /*
        Calculable calc = new ExpressionBuilder("(45+9)/8").build()
        double result1=calc.calculate();

         */
       
    }
}
Output