Flutter conditional statement with output of jsondecode var

I want to show different images for different outputs of JSONdecode. I get var between 01d and 50d. For example, when it gives out 04d, I want to show Image 'assets/night.png' and for 05d, I want to show Image 'assets/afternoon.png' and more. I am a complete beginner with flutter, this is what I thought about:

var current_icon;

  Future getWeather () async {
    http.Response response = await http.get(Uri.parse("https://api.openweathermap.org/data/2.5/weather?q=city&appid=****"));
    var results = jsonDecode(response.body);
    setState(() {
      this.current_icon = results['weather'][0]['icon'];
    });
  }
@override
  void initState () {
    super.initState();
    this.getWeather();
  }

and then put it in my container here:

new Container(
    height: double.infinity,
    width: double.infinity,
    child: new Image(
          image: (What should I do here?),
          fit: BoxFit.cover,
       ),
    ),