Grading system

main.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';
import 'package:flutter/services.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: 'Grading System'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  final String title;

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

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final TextEditingController _subjectController = TextEditingController();
  final TextEditingController _gradeController = TextEditingController();

  String output = "";
  String error = "";

  Text displayOutput() {
    if (error.isNotEmpty) {
      return Text(
        error,
        style: const TextStyle(fontSize: 20.0, color: Colors.red),
      );
    } else {
      return Text(
        output,
        style: const TextStyle(fontSize: 20.0, color: Colors.green),
      );
    }
  }

  void _calculateGrade() {
    print('running');
    // Check if the user has entered a subject and grade
    if (_subjectController.text.isEmpty || _gradeController.text.isEmpty) {
      error = "Please enter both grade and subject";
      return;
    }

    // Check if the user has entered a valid grade
    if (_gradeController.text.contains(".") ||
        _gradeController.text.contains("-") ||
        _gradeController.text.contains("+")) {
      error = "Please enter a valid grade";
      return;
    }

    // Check if the user has entered a valid subject
    final gradeValue = int.parse(_gradeController.text);
    final subjectValue = _subjectController.text;

    // Calculate the grade and set the output
    if (gradeValue >= 80) {
      output = "Your grade for $subjectValue is A";
    } else if (gradeValue >= 60) {
      output = "Your grade for $subjectValue is B";
    } else if (gradeValue >= 50) {
      output = "Your grade for $subjectValue is C";
    } else if (gradeValue >= 40) {
      output = "Your grade for $subjectValue is D";
    } else {
      output = "Your grade for $subjectValue is F";
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Padding(
              padding: const EdgeInsets.all(15.0),
              child: Row(
                children: [
                  Expanded(
                    child: TextField(
                      controller: _subjectController,
                      keyboardType: TextInputType.text,
                      decoration: const InputDecoration(
                        hintText: 'Enter Subject',
                        border: OutlineInputBorder(),
                        contentPadding: EdgeInsets.symmetric(
                          horizontal: 10.0,
                          vertical: 10.0,
                        ),
                      ),
                      onChanged: (value) {
                        // Clear the output and error
                        output = "";
                        error = "";
                        setState(() {});
                      },
                    ),
                  ),
                  const SizedBox(width: 10),
                  Expanded(
                    child: TextField(
                      controller: _gradeController,
                      maxLength: 3,
                      keyboardType: TextInputType.number,
                      inputFormatters: <TextInputFormatter>[
                        FilteringTextInputFormatter.digitsOnly
                      ],
                      decoration: const InputDecoration(
                        hintText: 'Enter Score',
                        border: OutlineInputBorder(),
                        counterText: "",
                        contentPadding: EdgeInsets.symmetric(
                          horizontal: 10.0,
                          vertical: 10.0,
                        ),
                      ),
                      onChanged: (value) {
                        // Clear the output and error
                        output = "";
                        error = "";
                        setState(() {});
                      },
                    ),
                  ),
                ],
              ),
            ),
            const SizedBox(height: 20.0),
            displayOutput(),
            const SizedBox(height: 20.0),
            ElevatedButton(
              onPressed: () {
                _calculateGrade();
                setState(() {});
              },
              child: const Text('Calculate'),
            ),
          ],
        ),
      ),
    );
  }
}