calculator.dart

import 'package:flutter/material.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  var x, y, sum;
  
  final TextEditingController a = new TextEditingController(text: '0');
  final TextEditingController b = new TextEditingController(text: '0');
  void _sum(){
    setState(() {
      x = int.parse(a.text);
      y = int.parse(b.text);      
      sum = x + y;
    });
  }
  void _calculate(String operation){
    if (operation == "+"){
      setState(() {
        x = int.parse(a.text);
        y = int.parse(b.text);      
        sum = x + y;
      });
    } else if(operation == "-"){
      setState(() {
        x = int.parse(a.text);
        y = int.parse(b.text);      
        sum = x - y;
      });
    } else if(operation == "*"){
      setState(() {
        x = int.parse(a.text);
        y = int.parse(b.text);      
        sum = x * y;
      });
    } else if(operation == "/"){
      setState(() {
        x = int.parse(a.text);
        y = int.parse(b.text);      
        sum = x / y;
      });
    }
    
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: new AppBar(
        title: new Text("CalCI"),
      ),
      body:  new Container(
        padding: EdgeInsets.all(40),
        child: new Center(
          child:  new Column(
            children: <Widget>[
              new Text(
                "Output: " + this.sum.toString(),
                style: new TextStyle(
                  fontSize: 20,
                  fontWeight: FontWeight.bold,

                ),
              ),
              new TextField(
                keyboardType: TextInputType.number,
                controller: a,
                decoration: new InputDecoration(
                  hintText: "Enter No:",
                  labelText: "Enter first number"
                ),
              ),
              new TextField(
                keyboardType: TextInputType.number,
                controller: b,
                decoration: new InputDecoration(
                  hintText: "Enter No:",
                  labelText: "Enter second number"
                ),
              ),
              new Padding(padding: EdgeInsets.only(
                top: 50
              )),
              new Row(
                children: <Widget>[
                  new RaisedButton(
                    onPressed: ()=> _calculate('+'), 
                    child: new Text("+"),
                    
                    ),
                  new RaisedButton(
                    onPressed: ()=> _calculate('-'), 
                    child: new Text("-"),
                    ),
                ],
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              ),
              new Row(
                children: <Widget>[
                  new RaisedButton(
                    onPressed: ()=> _calculate('*'), 
                    child: new Text("*"),
                    
                    ),
                  new RaisedButton(
                    onPressed: ()=> _calculate('/'), 
                    child: new Text("/"),
                    ),
                ],
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              )
            ],
            mainAxisAlignment: MainAxisAlignment.center,
          ),
        ),
    ),
    );
  }
}