Calculator Application Simple with StatefulWidget

 import "package:flutter/material.dart";

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "Hello",
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.lightGreen,
      ),
      home: const FlutterApp(),
    );
  }
}

class FlutterApp extends StatefulWidget {
  const FlutterApp({super.key});

  @override
  State<StatefulWidget> createState() {
    return FlutterAppState();
  }
}

class FlutterAppState extends State<FlutterApp> {
  var no1Controller = TextEditingController();
  var no2Controller = TextEditingController();

  var result = " ";

  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () {
        FocusManager.instance.primaryFocus?.unfocus();
      },
      child: Scaffold(
        drawer: Drawer(
          child: ListView(
            padding: EdgeInsets.zero,
            children: [
              const UserAccountsDrawerHeader(
                accountName: Text("John"),
                accountEmail: Text("John@google.com"),
                currentAccountPicture: Icon(Icons.account_circle, size: 85),
              ),
              ListTile(
                leading: const Icon(Icons.message),
                title: const Text("message"),
                onTap: () {
                  Navigator.pop(context);
                },
              ),
              const Divider(thickness: 1, color: Colors.black),
              ListTile(
                leading: const Icon(Icons.account_circle),
                title: const Text("profile"),
                onTap: () {
                  Navigator.pop(context);
                },
              ),
              const Divider(thickness: 1, color: Colors.black),
              ListTile(
                leading: const Icon(Icons.settings),
                title: const Text("Settings"),
                onTap: () {
                  Navigator.pop(context);
                },
              ),
              const Divider(thickness: 1, color: Colors.black),
              ListTile(
                leading: const Icon(Icons.help_outline),
                title: const Text("Help & feedback"),
                onTap: () {
                  Navigator.pop(context);
                },
              ),
              const Divider(thickness: 1, color: Colors.black),
              ListTile(
                leading: const Icon(Icons.restore_from_trash),
                title: const Text("Trash"),
                onTap: () {
                  Navigator.pop(context);
                },
              ),
            ],
          ),
        ),
        appBar: AppBar(
          title: const Text(
            "Flutter Calculator",
            style: TextStyle(fontWeight: FontWeight.bold),
          ),
          centerTitle: true,
          backgroundColor: Colors.grey,
        ),
        body: Center(
          child: Container(
            color: Colors.white,
            width: 300.0,
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                TextField(
                  keyboardType: TextInputType.number,
                  controller: no1Controller,
                  decoration: InputDecoration(
                    hintText: "Enter the First Value...",
                    labelText: "First Value",
                    border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(11.0),
                    ),
                  ),
                ),
                const SizedBox(height: 30.0),
                TextField(
                  keyboardType: TextInputType.number,
                  controller: no2Controller,
                  decoration: InputDecoration(
                    hintText: "Enter the Second Value...",
                    labelText: "Second Value",
                    border: OutlineInputBorder(
                      borderRadius: BorderRadius.circular(11.0),
                    ),
                  ),
                ),
                const SizedBox(height: 50.0),
                Row(
                  mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                  children: [
                    ElevatedButton(
                      onPressed: () {
                        var no1 = int.parse(no1Controller.text);
                        var no2 = int.parse(no2Controller.text);

                        /*var no1 = int.parse(no1Controller.text.toString());
                      var no2 = int.parse(no2Controller.text.toString());*/

                        /*A string can be cast to an integer using the int.parse() method in Dart.
                      The method takes a string as an argument and converts it into an integer*/

                        var sum = no1 + no2;

                        result = "The sum of $no1 and $no2 = $sum";

                        setState(
                          () {},
                        );
                      },
                      style: ElevatedButton.styleFrom(
                        backgroundColor: Colors.blue,
                      ),
                      child: const Text(
                        "Add",
                        style: TextStyle(
                            fontWeight: FontWeight.bold, color: Colors.white),
                      ),
                    ),
                    //SizedBox(width: 10,),

                    ElevatedButton(
                      onPressed: () {
                        var no1 = int.parse(no1Controller.text.toString());
                        var no2 = int.parse(no2Controller.text.toString());

                        var sub = no1 - no2;

                        result = "The subtraction of $no1 and $no2 = $sub";

                        setState(
                          () {},
                        );
                      },
                      style: ElevatedButton.styleFrom(
                        backgroundColor: Colors.blue,
                      ),
                      child: const Text(
                        "sub",
                        style: TextStyle(
                            fontWeight: FontWeight.bold, color: Colors.white),
                      ),
                    ),
                    //SizedBox(width: 10,),

                    ElevatedButton(
                      onPressed: () {
                        var no1 = int.parse(no1Controller.text.toString());
                        var no2 = int.parse(no2Controller.text.toString());

                        var mul = no1 * no2;

                        result = "The Multiplication of $no1 and $no2 = $mul";

                        setState(
                          () {},
                        );
                      },
                      style: ElevatedButton.styleFrom(
                        backgroundColor: Colors.blue,
                      ),
                      child: const Text(
                        "Mul",
                        style: TextStyle(
                            fontWeight: FontWeight.bold, color: Colors.white),
                      ),
                    ),
                    //SizedBox(width: 10,),

                    ElevatedButton(
                      onPressed: () {
                        var no1 = int.parse(no1Controller.text.toString());
                        var no2 = int.parse(no2Controller.text.toString());

                        var div = no1 / no2;

                        result = "The Division of $no1 and $no2 = $div";
                        /*To limit the digits after point below technique is used*/
                        /*result = "The Division of $no1 and $no2 = ${div.toStringAsFixed(4)}";*/

                        setState(
                          () {},
                        );
                      },
                      style: ElevatedButton.styleFrom(
                        backgroundColor: Colors.blue,
                      ),
                      child: const Text(
                        "Div",
                        style: TextStyle(
                            fontWeight: FontWeight.bold, color: Colors.white),
                      ),
                    ),
                  ],
                ),
                Padding(
                  padding: const EdgeInsets.all(21),
                  child: Text(
                    result,
                    style: const TextStyle(fontSize: 25, color: Colors.black),
                  ),
                ),
              ],
            ),
          ),
        ),
      ),
    );
  }
}