initProject.dart

// Copyright (c) 2019, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Calculator'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  final String title;

  const MyHomePage({
    Key? key,
    required this.title,
  }) : super(key: key);

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _answer = 0;
  List<int> list = [];

  void _mem(int x) {
    setState(() {
      _answer = x;
      if (list.length == 2) {
        list[0] = list[1];
        list[1] = x;
      } else {
        list.add(x);
      }
    });
  }

  void _sum() {
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Text("${_answer}"),
          FloatingActionButton(
            onPressed: ()=>_mem(1),
            tooltip: 'Increment',
            child: const Text("1"),
          ),
          FloatingActionButton(
            onPressed: ()=>_mem(2),
            tooltip: 'Increment',
            child: const Text("2"),
          ),
          FloatingActionButton(
            onPressed: () {
             setState((){
               if(list.length == 2)
               _answer= list[0]+list[1];
             });
            },
            tooltip: 'Increment',
            child: const Icon(Icons.add),
          ),
        ],
      ),
    );
  }
}