실생활 앱 (계산기)

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

class CalculatorApp extends StatefulWidget {
  const CalculatorApp({super.key});

  @override
  State<CalculatorApp> createState() => _CalculatorAppState();
}

class _CalculatorAppState extends State<CalculatorApp> {
  final keys = ['7', '8', '9', '+', '4', '5', '6', '-', '1', '2', '3', '×', 'C', '0', '=', '÷', '(', ')', '^', '√'];
  String expression = '';
  String answer = '0';

  void press(String key) {
    setState(() {
      if (key == 'C') {
        expression = '';
        answer = '0';
      } else if (key == '=') {
        answer = calculate(expression);
      } else {
        expression += key;
      }
    });
  }

  String calculate(String value) {
    // 실제 앱에서는 expression parser 패키지를 붙이면 더 안전합니다.
    // 여기서는 수식 상태와 답 상태를 분리하는 구조를 보여줍니다.
    return value.isEmpty ? '0' : '계산 결과';
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Row(
          children: [
            Expanded(child: Text('수식란: \${expression.isEmpty ? '0' : expression}')),
            Expanded(child: Text('답란: $answer')),
          ],
        ),
        GridView.count(
          shrinkWrap: true,
          crossAxisCount: 4,
          children: keys.map((key) {
            return ElevatedButton(
              onPressed: () => press(key),
              child: Text(key),
            );
          }).toList(),
        ),
      ],
    );
  }
}

Card(
  child: Padding(
    padding: const EdgeInsets.all(20),
    child: Column(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        const Text(
          '계산기',
          style: TextStyle(fontSize: 22, fontWeight: FontWeight.w900),
        ),
        const SizedBox(height: 16),
        Row(
        children: [
          Expanded(child: Text('수식란: $expression')),
          Expanded(child: Text('답란: $answer')),
        ],
      ),
      const SizedBox(height: 12),
      GridView.count(
        shrinkWrap: true,
        crossAxisCount: 4,
        children: keys.map((key) {
          return FilledButton.tonal(
            onPressed: () => calculate(key),
            child: Text(key),
          );
        }).toList(),
      )
      ],
    ),
  ),
)