Simple Calculator in Android

You can view new updated simple calculator with ViemModel and LiveData in my new blog  

https://androidtuts4u.blogspot.com/2021/10/simple-calculator-with-viewmodel-and.html


To create a calculator first  we need to create the layout of the calculator.
Layout  is created  using XML file given below

<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" >



 <EditText

    android:id="@+id/result_id"   

    android:layout_width="fill_parent"

    android:layout_height="120dp"

  />

 <Button

   android:id="@+id/Btn7_id"   

   android:layout_width="70dp"

   android:layout_height="60dp"

   android:layout_below="@id/result_id"

   android:text="7"

   android:onClick="btn7Clicked"

  />

 <Button

   android:id="@+id/Btn8_id"   

   android:layout_width="70dp"

   android:layout_height="60dp"

   android:layout_below="@id/result_id"

   android:layout_toRightOf="@id/Btn7_id"

   android:text="8"

   android:onClick="btn8Clicked"

  />

  <Button

   android:id="@+id/Btn9_id"   

   android:layout_width="70dp"

   android:layout_height="60dp"

   android:layout_below="@id/result_id"

   android:layout_toRightOf="@id/Btn8_id"

   android:text="9"

   android:onClick="btn9Clicked"

  />

  <Button

   android:id="@+id/Btnclear_id"   

   android:layout_width="90dp"

   android:layout_height="60dp"

   android:layout_below="@id/result_id"

   android:layout_toRightOf="@id/Btn9_id"

   android:text="clear"

   android:onClick="btnclearClicked"

  />

  <Button

   android:id="@+id/Btn4_id"   

   android:layout_width="70dp"

   android:layout_height="60dp"

   android:layout_below="@id/Btn7_id"

   android:text="4"

   android:onClick="btn4Clicked"

  /> <Button

   android:id="@+id/Btn5_id"   

   android:layout_width="70dp"

   android:layout_height="60dp"

   android:layout_below="@id/Btn8_id"

   android:layout_toRightOf="@id/Btn4_id"

   android:text="5"

   android:onClick="btn5Clicked"

  /> <Button

   android:id="@+id/Btn6_id"   

   android:layout_width="70dp"

   android:layout_height="60dp"

   android:layout_below="@id/Btn9_id"

   android:layout_toRightOf="@id/Btn5_id"

   android:text="6"

   android:onClick="btn6Clicked"

  />

  <Button

   android:id="@+id/Btnplus_id"   

   android:layout_width="90dp"

   android:layout_height="60dp"

   android:layout_below="@id/Btnclear_id"

   android:layout_toRightOf="@id/Btn6_id"

   android:text="+"

   android:onClick="btnplusClicked"

  />

  <Button

   android:id="@+id/Btn1_id"   

   android:layout_width="70dp"

   android:layout_height="60dp"

   android:layout_below="@id/Btn4_id"

   android:text="1"

   android:onClick="btn1Clicked"

  /> <Button

   android:id="@+id/Btn2_id"   

   android:layout_width="70dp"

   android:layout_height="60dp"

   android:layout_below="@id/Btn5_id"

   android:layout_toRightOf="@id/Btn1_id"

   android:text="2"

   android:onClick="btn2Clicked"

  /> <Button

   android:id="@+id/Btn3_id"   

   android:layout_width="70dp"

   android:layout_height="60dp"

   android:layout_below="@id/Btn6_id"

   android:layout_toRightOf="@id/Btn2_id"

   android:text="3"

   android:onClick="btn3Clicked"

  />

  <Button

   android:id="@+id/Btnminus_id"   

   android:layout_width="90dp"

   android:layout_height="60dp"

   android:layout_below="@id/Btnplus_id"

   android:layout_toRightOf="@id/Btn3_id"

   android:text="-"

   android:onClick="btnminusClicked"

  

  />

  

  <Button

   android:id="@+id/Btnequal_id"   

   android:layout_width="110dp"

   android:layout_height="60dp"

   android:layout_below="@id/Btn1_id"

   android:text="="

   android:onClick="btnequalClicked"

  />

   <Button

   android:id="@+id/Btndivide_id"   

   android:layout_width="90dp"

   android:layout_height="60dp"

   android:layout_below="@id/Btn1_id"

   android:layout_toRightOf="@id/Btnequal_id"

   android:text="/"

   android:onClick="btndivideClicked"

  

  />

   <Button

   android:id="@+id/Btnmulti_id"   

   android:layout_width="90dp"

   android:layout_height="60dp"

   android:layout_below="@id/Btnminus_id"

   android:layout_toRightOf="@id/Btndivide_id"

   android:text="*"

   android:onClick="btnmultiClicked"

  />

</RelativeLayout>

The java file is given below:

package com.arun.calculator;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class MainActivity extends Activity {
    
 public String str ="";
 Character op = 'q';
 int i,num,numtemp;
    EditText showResult;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
     
        showResult = (EditText)findViewById(R.id.result_id);
        
        
    }
      public void btn1Clicked(View v){
       insert(1);
       
      }
      
 public void btn2Clicked(View v){
       insert(2);
       
      }
      public void btn3Clicked(View v){
       insert(3);
       
      }
      public void btn4Clicked(View v){
       insert(4);
       
      }
      public void btn5Clicked(View v){
       insert(5);
       
      }
      public void btn6Clicked(View v){
       insert(6);
      }
      public void btn7Clicked(View v){
       insert(7);
       
      }
      public void btn8Clicked(View v){
       insert(8);
       
      }
      public void btn9Clicked(View v){
       insert(9);
       
      }
      public void btnplusClicked(View v){
       perform();
       op = '+';
   
      }
      
 public void btnminusClicked(View v){
    perform();
         op = '-';
   
      }
      public void btndivideClicked(View v){
       perform();
       op = '/';
   
      }
      public void btnmultiClicked(View v){
       perform();
       op = '*';
     
      }
      public void btnequalClicked(View v){
       calculate();
       
      }
      
 public void btnclearClicked(View v){
       reset();
      }
      private void reset() {
  // TODO Auto-generated method stub
   str ="";
   op ='q';
   num = 0;
   numtemp = 0;
   showResult.setText("");
 }
 private void insert(int j) {
    // TODO Auto-generated method stub
       str = str+Integer.toString(j);
       num = Integer.valueOf(str).intValue();
       showResult.setText(str);
       
    
   }
      private void perform() {
    // TODO Auto-generated method stub
    str = "";
    numtemp = num;
   }
      private void calculate() {
    // TODO Auto-generated method stub
    if(op == '+')
     num = numtemp+num;
    else if(op == '-')
     num = numtemp-num;
    else if(op == '/')
     num = numtemp/num;
    else if(op == '*')
     num = numtemp*num;
    showResult.setText(""+num);
   }
    
}