mini calculator app with four buttons (Add, Subtract, Multiply, Divide). Each button will call the same style of function with arguments.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Mini Calculator',
      theme: ThemeData(primarySwatch: Colors.indigo),
      home: const CalculatorPage(),
    );
  }
}

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

  @override
  State<CalculatorPage> createState() => _CalculatorPageState();
}

class _CalculatorPageState extends State<CalculatorPage> {
  final TextEditingController _num1Controller = TextEditingController();
  final TextEditingController _num2Controller = TextEditingController();
  final TextEditingController _resultController = TextEditingController();

  ///  Function with arguments (operation chosen by operator)
  void calculate(double a, double b, String operator) {
    double result = 0;

    switch (operator) {
      case '+':
        result = a + b;
        break;
      case '-':
        result = a - b;
        break;
      case '*':
        result = a * b;
        break;
      case '/':
        if (b != 0) {
          result = a / b;
        } else {
          _resultController.text = "Cannot divide by 0";
          return;
        }
        break;
    }

    setState(() {
      _resultController.text = result.toString();
    });
  }

  ///  Helper to safely parse numbers
  void _onOperationPressed(String operator) {
    final double? num1 = double.tryParse(_num1Controller.text);
    final double? num2 = double.tryParse(_num2Controller.text);

    if (num1 != null && num2 != null) {
      calculate(num1, num2, operator);
    } else {
      setState(() {
        _resultController.text = "Invalid input";
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text("Mini Calculator")),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Column(
          children: [
            TextField(
              controller: _num1Controller,
              keyboardType: TextInputType.number,
              decoration: const InputDecoration(
                labelText: "Enter first number",
                border: OutlineInputBorder(),
              ),
            ),
            const SizedBox(height: 12),
            TextField(
              controller: _num2Controller,
              keyboardType: TextInputType.number,
              decoration: const InputDecoration(
                labelText: "Enter second number",
                border: OutlineInputBorder(),
              ),
            ),
            const SizedBox(height: 16),

            ///  Row of operation buttons
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: [
                ElevatedButton(
                  onPressed: () => _onOperationPressed('+'),
                  child: const Text("+"),
                ),
                ElevatedButton(
                  onPressed: () => _onOperationPressed('-'),
                  child: const Text("-"),
                ),
                ElevatedButton(
                  onPressed: () => _onOperationPressed('*'),
                  child: const Text("×"),
                ),
                ElevatedButton(
                  onPressed: () => _onOperationPressed('/'),
                  child: const Text("÷"),
                ),
              ],
            ),

            const SizedBox(height: 20),
            TextField(
              controller: _resultController,
              readOnly: true,
              decoration: const InputDecoration(
                labelText: "Result",
                border: OutlineInputBorder(),
              ),
            ),
          ],
        ),
      ),
    );
  }
}