০ ২। Dart প্রোগ্রামিং ভাষার মৌলিক বিষয়সমূহ

var name = 'John'; // টাইপ ইনফার্ড
String surname = 'Doe'; // এক্সপ্লিসিট টাইপ
final age = 30; // রানটাইমে ইনিশিয়ালাইজড, পরে চেঞ্জ করা যাবে না
const PI = 3.14159; // কম্পাইল টাইমে ইনিশিয়ালাইজড

int number = 42;
double price = 9.99;
String message = 'Hello';
bool isTrue = true;

dynamic value = 'Can be anything';
value = 42; // Valid

if (condition) {
  // code
} else if (anotherCondition) {
  // code
} else {
  // code
}

for (var i = 0; i < 5; i++) {
  print(i);
}

while (condition) {
  // code
}

switch (variable) {
  case value1:
    // code
    break;
  case value2:
    // code
    break;
  default:
    // code
}

int add(int a, int b) {
  return a + b;
}

void greet(String name, [String? title]) {
  print('Hello ${title ?? ''} $name');
}

void introduce({required String name, int? age}) {
  print('I am $name${age != null ? ' and I am $age years old' : ''}');
}

var multiply = (int a, int b) => a * b;

List<int> numbers = [1, 2, 3, 4, 5];
numbers.add(6);
print(numbers[0]); // 1

Set<String> uniqueNames = {'Alice', 'Bob', 'Charlie'};
uniqueNames.add('Alice'); // Won't be added (duplicate)

Map<String, int> ages = {
  'Alice': 30,
  'Bob': 25,
  'Charlie': 35,
};
print(ages['Bob']); // 25

class Person {
  String name;
  int age;

  Person(this.name, this.age);

  void introduce() {
    print('I am $name and I am $age years old');
  }
}

var person = Person('John', 30);
person.introduce();

class Student extends Person {
  String school;

  Student(String name, int age, this.school) : super(name, age);

  @override
  void introduce() {
    super.introduce();
    print('I study at $school');
  }
}

String? name;
print(name?.toUpperCase()); // null

String? input;
String result = input ?? 'Default';

Future<String> fetchData() async {
  await Future.delayed(Duration(seconds: 2));
  return 'Data fetched';
}

void main() async {
  print('Fetching data...');
  String result = await fetchData();
  print(result);
}

try {
  int result = 12 ~/ 0; // IntegerDivisionByZeroException
} on IntegerDivisionByZeroException {
  print('Cannot divide by zero');
} catch (e) {
  print('An error occurred: $e');
} finally {
  print('This always executes');
}

class Vector {
  final int x, y;
  Vector(this.x, this.y);

  Vector operator +(Vector v) => Vector(x + v.x, y + v.y);
  Vector operator *(int scalar) => Vector(x * scalar, y * scalar);
}