How To Create Calculator App For Android

Introduction

Nonety percent of people today use Android smartphones. In our day to day life, we perform mathematical operations with the help of a calculator. Thus, I will show you how to create Calculator app for an Android, using Android Studio. Android is the Kernel based operating system. It allows the user, to modify GUI components and the source code.

Requirements

• Android Studio.
• Little bit XML and JAVA knowledge.

Download link (Android Studio): https://developer.android.com/studio/index.html.

Steps to be followed are given below.

Carefully follow my steps to create Calculator app for an Android and I have included the source code given below.

Step 1

Open an Android Studio. Start the new project.

Step 2

Put the Application name and company domain. If you wish to use C++ for coding the project, mark the Include C++ support, followed by clicking Next.

Step 3

Select the Android minimum SDK. Afterwards, you chose the minimum SDK and it will show the approximate percentage of the people, who use SDK, followed by clicking Next.

Step 4

Choose the basic activity, followed by clicking Next.

Step 5

Put the activity name and layout name. Android Studio basically takes Java class name, which is provided by you in the activity name.

Step 6

Go to activity_calc.xml, followed by clicking the bottom text. This XML file contains the designing code for an Android app in the activity_calc.xml; copy and paste the code given below.

activity_calc.xml code

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent">
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/linearLayout1"
        android:layout_marginLeft="10pt"
        android:layout_marginRight="10pt"
        android:layout_marginTop="3pt">
        <EditText
            android:layout_weight="1"
            android:layout_height="wrap_content"
            android:layout_marginRight="5pt"
            android:id="@+id/etNum1"
            android:layout_width="match_parent"
            android:inputType="numberDecimal">
        </EditText>
        <EditText
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:layout_marginLeft="5pt"
            android:id="@+id/etNum2"
            android:layout_width="match_parent"
            android:inputType="numberDecimal">
        </EditText>
    </LinearLayout>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/linearLayout2"
        android:layout_marginTop="3pt"
        android:layout_marginLeft="5pt"
        android:layout_marginRight="5pt">
        <Button
            android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:layout_weight="1"
            android:text="+"
            android:textSize="15pt"
            android:id="@+id/btnAdd">
        </Button>
        <Button
            android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:layout_weight="1"
            android:text="-"
            android:textSize="15pt"
            android:id="@+id/btnSub">
        </Button>
        <Button
            android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:layout_weight="1"
            android:text="*"
            android:textSize="15pt"
            android:id="@+id/btnMult">
        </Button>
        <Button
            android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:layout_weight="1"
            android:text="/"
            android:textSize="15pt"
            android:id="@+id/btnDiv">
        </Button>
    </LinearLayout>
    <TextView
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:layout_marginLeft="5pt"
        android:layout_marginRight="5pt"
        android:textSize="12pt"
        android:layout_marginTop="3pt"
        android:id="@+id/tvResult"
        android:gravity="center_horizontal">
    </TextView>
</LinearLayout>

Step 8

In CalcActivity.java, copy and paste the code of Java programming given below, which is the backend language for an Android. Do not replace your package name, else an app will not run. The code given below contains my package name. 

CalcActivity.java code

package ganeshannt.calc;

import android.app.Activity;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
public class CalcActivity extends Activity implements
        OnClickListener
{
    EditText input1;
    EditText input2;
    Button addition;
    Button subtraction;
    Button multiplication;
    Button division;
    TextView tvResult;
    String oper = "";
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_calc);
        input1 = (EditText) findViewById(R.id.etNum1);
        input2 = (EditText) findViewById(R.id.etNum2);
        addition = (Button) findViewById(R.id.btnAdd);
        subtraction = (Button) findViewById(R.id.btnSub);
        multiplication = (Button) findViewById(R.id.btnMult);
        division = (Button) findViewById(R.id.btnDiv);
        tvResult = (TextView) findViewById(R.id.tvResult);
        // set a listener
        addition.setOnClickListener(this);
        subtraction.setOnClickListener(this);
        multiplication.setOnClickListener(this);
        division.setOnClickListener(this);
    }
    @Override
    public void onClick(View v)
    {
        // TODO Auto-generated method stub
        float num1 = 0;
        float num2 = 0;
        float result = 0;
        // check if the fields are empty
        if (TextUtils.isEmpty(input1.getText().toString())
                || TextUtils.isEmpty(input2.getText().toString()))
        {
            return;
        }
        // read EditText and fill variables with numbers
        num1 = Float.parseFloat(input1.getText().toString());
        num2 = Float.parseFloat(input2.getText().toString());

        // defines the button that has been clicked and performs the corresponding operation
        // write operation into oper, we will use it later for output
        switch (v.getId())
        {
            case R.id.btnAdd:
                oper = "+";
                result = num1 + num2;
                break;
            case R.id.btnSub:
                oper = "-";
                result = num1 - num2;
                break;
            case R.id.btnMult:
                oper = "*";
                result = num1 * num2;
                break;
            case R.id.btnDiv:
                oper = "/";
                result = num1 / num2;
                break;
            default:
                break;
        }

        // form the output line
        tvResult.setText(num1 + " " + oper + " " + num2 + " = " + result);
    }
}

Step 9

This is our user interface of the Application. Click Make project option.

Step 10

Run the Application, followed by choosing the virtual machine. Click OK.

Deliverables

Here, we successfully created Calculator app for an Android, using an Android Studio Application, which was created and executed.

Addition operation

Subtraction operation

Divide operation

Multiplication operation

If you have any doubts, just comment below.