calc.dart

import 'package:flutter/material.dart';
// import 'calcs.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  bool operand = false;
  String result = " ";
  final ButtonStyle style = ElevatedButton.styleFrom(textStyle: const TextStyle(fontSize: 20));

  @override
  Widget build(BuildContext context) {
    var padding = MediaQuery.of(context).padding;
    double width = MediaQuery.of(context).size.width;
    double height= MediaQuery.of(context).size.height - padding.top - padding.bottom;
    return Scaffold(
      appBar: AppBar(title: Text("Calculator")),
      body: Center(
        child: Column(
          children: <Widget>[
            Row(
              children: <Widget>[
                    Padding(
                      padding: const EdgeInsets.fromLTRB(20.0, 50.0, 0.0, 50.0),
                      child: Text(result, style: TextStyle(fontSize: 25.0)),
                    ),
              ],
            ),
            Row( children: [
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult("1"), child: Text("1"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult("2"), child: Text("2"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult("3"), child: Text("3"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult("4"), child: Text("4"), style: style),
              ),
            ]),
            Row( children: [
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult("5"), child: Text("5"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult("6"), child: Text("6"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult("7"), child: Text("7"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> deleteLast(), child: Text("<-"), style: style),
              ),
            ]),
            Row( children: [
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult("8"), child: Text("8"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult("0"), child: Text("9"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult("0"), child: Text("0"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> finalResult(Calculations().calculations(result)), child: Text("="), style: style),
              ),
            ]),
            Row( children: [
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult(" + "), child: Text("+"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult(" - "), child: Text("-"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult(" * "), child: Text("*"), style: style),
              ),
              SizedBox(
                height: width/4,
                width: width/4,
                child: ElevatedButton(onPressed: ()=> changeResult(" / "), child: Text("/"), style: style),
              ),
            ]),
          ],
        ),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }

  void deleteLast() {
    if ((result != null) && (result.length > 0)) {
      setState(() {
        if(result[result.length-1] == " ") {
          result = result.substring(0, result.length - 3);
          operand = false;
        } else
          result = result.substring(0, result.length - 1);
      });
    }
  }

  void changeResult(String s) {
    setState(() {
      if (s == " + " || s == " - " || s == " * " || s == " / ") {
        if (operand == false) {
          result += s;
          operand = true;
        }
      } else
        result += s;
    });
  }

  void finalResult(String s) {
    print("A");
    setState(() {
      result = s;
    });
  }
}



class Calculations {
  String calculations(String s) {
    int finalNumber = 0;
    int num1 = firstNumber(s);
    int num2 = secondNumber(s);
    for (int i = 0; i < s.length; i++) {
      if (s[i] == "+")
        return (num1 + num2).toString();
      else if (s[i] == "-")
        return (num1 - num2).toString();
      else if (s[i] == "*")
        return (num1 * num2).toString();
      else if (s[i] == "/")
        return (num1 / num2).toString();
    }

    return finalNumber.toString();
  }

  int firstNumber(String s) {
    int num1 = 0;
    for (int i = 0; i < s.length; i++) {
      if (s[i] == " ")
        break;

      num1 = num1 * 10 + int.parse(s[i]);
    }

    return num1;
  }

  int secondNumber(String s) {
    int num2 = 0;
    bool start = false;
    for (int i = 0; i < s.length; i++) {
      if (s[i] == "+" || s[i] == "-" || s[i] == "*" || s[i] == "/")
        start = true;
      if (s[i] == " ")
        continue;

      num2 = num2 * 10 + int.parse(s[i]);
    }

    return num2;
  }
}