Flutt

import 'package:flutter/material.dart';

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => new _MyAppState();
}

class _MyAppState extends State<MyApp> {
  final TextEditingController _ageController = new TextEditingController();
  final TextEditingController _heightController = new TextEditingController();
  final TextEditingController _weightController = new TextEditingController();


  double bmi = 0.0;

  _calculateClicked() {
    setState(() {
          int age = int.parse(_ageController.text);
          double height = double.parse(_heightController.text);
          int weight = int.parse(_weightController.text);


          void calculatebmi(){
            double inches = height*12;
            bmi = weight/2;
          }
          calculatebmi();
        });
  }

  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      debugShowCheckedModeBanner: false,
      title: "Bmi challenge app",
      home: new Scaffold(
        appBar: new AppBar(
          title: Text('BMI'),
          centerTitle: true,
          backgroundColor: Colors.pink,
        ),
        body: new Column(
          children: <Widget>[
            new Center(
              child: new Image(
                image: new NetworkImage(
                  "http://www.simpleimageresizer.com/_uploads/photos/761d18ce/bmi-logo-880x655_1_20.png",
                ),
              ),
            ),
            new Card(
                color: Colors.grey[300],
                child: new Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: <Widget>[
                    new Padding(
                      padding: EdgeInsets.only(bottom: 25.0, top: 15.0),
                      child: new TextField(
                        controller: _ageController,
                        decoration: new InputDecoration(
                            icon: new Icon(
                              Icons.person_outline,
                            ),
                            hintText: "Age",
                            hintStyle: new TextStyle(fontSize: 17.0)),
                      ),
                    ),
                    new Padding(
                      padding: EdgeInsets.only(bottom: 25.0),
                      child: new TextField(
                        controller: _heightController,
                        decoration: new InputDecoration(
                            icon: new Icon(
                              Icons.insert_chart,
                            ),
                            hintText: "Height in feet",
                            hintStyle: new TextStyle(fontSize: 17.0)),
                      ),
                    ),
                    new Padding(
                      padding: EdgeInsets.only(bottom: 25.0),
                      child: new TextField(
                        controller: _weightController,
                        decoration: new InputDecoration(
                            icon: new Icon(
                              Icons.line_weight,
                            ),
                            hintText: "Weight in lb",
                            hintStyle: new TextStyle(fontSize: 17.0)),
                      ),
                    ),
                    new Padding(
                        padding: new EdgeInsets.only(bottom: 15.0),
                        child: new MaterialButton(
                          onPressed: _calculateClicked(),
                          color: Colors.pink,
                          child: new Text(
                            "Calculate",
                            style: new TextStyle(color: Colors.white),
                          ),
                          minWidth: 100.0,
                          height: 45.0,
                        )),
                  ],
                )),
            new Padding(
              padding: EdgeInsets.only(top: 15.0),
              child: new Text("Your BMI: $bmi"),
            )
          ],
        ),
      ),
    );
  }
}