Dart Basics

Learn the Dart programming language fundamentals

🎯 Introduction to Dart

Dart is a modern, object-oriented programming language developed by Google. It's easy to learn with familiar syntax, supports strong typing, and powers Flutter applications with excellent performance and developer productivity. 


// Your first Dart program
void main() {
  print('Hello, Dart!');
  
  var name = 'Flutter';
  var year = 2024;
  
  print('Welcome to $name in $year');
}

Output: 

Hello, Dart!
Welcome to Flutter in 2024

Dart Fundamentals

📦

Variables

Store and manage data 

var name = 'John';
int age = 25;
String city = 'NYC';
🔢

Data Types

Different kinds of values 

int, double
String, bool
List, Map
⚡

Functions

Reusable code blocks 

void greet() {
  print('Hi!');
}
🏗️

Classes

Object-oriented programming 

class Person {
  String name;
}

🔹 Variables and Data Types

Declaring and using variables in Dart:

🔸 Variable Declaration 


// Using var (type inference)
var name = 'Alice';        // String
var age = 30;              // int
var height = 5.8;          // double
var isStudent = true;      // bool

// Explicit type declaration
String city = 'New York';
int year = 2024;
double price = 99.99;
bool isActive = false;

// Final (runtime constant)
final currentDate = DateTime.now();

// Const (compile-time constant)
const pi = 3.14159;

void main() {
  print('Name: $name');
  print('Age: $age');
  print('City: $city');
}

Output: 

Name: Alice
Age: 30
City: New York

🔹 Basic Data Types

Common data types in Dart: 


void main() {
  // Numbers
  int count = 42;              // Integer
  double temperature = 98.6;   // Decimal
  num value = 100;             // Can be int or double
  
  // Strings
  String greeting = 'Hello';
  String name = "Dart";
  String message = '''
    Multi-line
    string
  ''';
  
  // Booleans
  bool isTrue = true;
  bool isFalse = false;
  
  // Lists (Arrays)
  List<int> numbers = [1, 2, 3, 4, 5];
  var fruits = ['Apple', 'Banana', 'Orange'];
  
  // Maps (Key-Value pairs)
  Map<String, int> ages = {
    'Alice': 25,
    'Bob': 30,
  };
  
  // Print examples
  print('Count: $count');
  print('First fruit: ${fruits[0]}');
  print('Alice age: ${ages['Alice']}');
}

Output: 

Count: 42
First fruit: Apple
Alice age: 25

🔹 Functions

Creating and using functions: 


// Basic function
void greet() {
  print('Hello!');
}

// Function with parameters
void sayHello(String name) {
  print('Hello, $name!');
}

// Function with return value
int add(int a, int b) {
  return a + b;
}

// Arrow function (short syntax)
int multiply(int a, int b) => a * b;

// Optional parameters
void introduce(String name, [int? age]) {
  print('Name: $name');
  if (age != null) {
    print('Age: $age');
  }
}

// Named parameters
void createUser({required String name, int age = 18}) {
  print('User: $name, Age: $age');
}

void main() {
  greet();
  sayHello('Alice');
  
  var sum = add(5, 3);
  print('Sum: $sum');
  
  var product = multiply(4, 5);
  print('Product: $product');
  
  introduce('Bob', 25);
  createUser(name: 'Charlie');
}

Output: 

Hello!
Hello, Alice!
Sum: 8
Product: 20
Name: Bob
Age: 25
User: Charlie, Age: 18

🔹 Control Flow

If statements, loops, and conditions: 


void main() {
  // If-else statement
  int age = 20;
  if (age >= 18) {
    print('Adult');
  } else {
    print('Minor');
  }
  
  // For loop
  for (int i = 1; i <= 3; i++) {
    print('Count: $i');
  }
  
  // For-in loop
  var fruits = ['Apple', 'Banana', 'Orange'];
  for (var fruit in fruits) {
    print(fruit);
  }
  
  // While loop
  int count = 0;
  while (count < 3) {
    print('While: $count');
    count++;
  }
  
  // Switch statement
  var grade = 'A';
  switch (grade) {
    case 'A':
      print('Excellent!');
      break;
    case 'B':
      print('Good!');
      break;
    default:
      print('Keep trying!');
  }
}

Output: 

Adult
Count: 1
Count: 2
Count: 3
Apple
Banana
Orange
While: 0
While: 1
While: 2
Excellent!

🔹 Classes and Objects

Object-oriented programming in Dart: 


// Define a class
class Person {
  // Properties
  String name;
  int age;
  
  // Constructor
  Person(this.name, this.age);
  
  // Method
  void introduce() {
    print('Hi, I am $name and I am $age years old.');
  }
  
  // Getter
  bool get isAdult => age >= 18;
}

// Class with named constructor
class User {
  String username;
  String email;
  
  User(this.username, this.email);
  
  // Named constructor
  User.guest() : username = 'Guest', email = '[email protected]';
}

void main() {
  // Create objects
  var person1 = Person('Alice', 25);
  person1.introduce();
  print('Is adult: ${person1.isAdult}');
  
  var person2 = Person('Bob', 16);
  person2.introduce();
  print('Is adult: ${person2.isAdult}');
  
  var user = User.guest();
  print('Username: ${user.username}');
}

Output: 

Hi, I am Alice and I am 25 years old.
Is adult: true
Hi, I am Bob and I am 16 years old.
Is adult: false
Username: Guest

🔹 Lists and Collections

Working with lists and maps: 


void main() {
  // Lists
  List<String> fruits = ['Apple', 'Banana', 'Orange'];
  
  // Add items
  fruits.add('Mango');
  
  // Access items
  print('First: ${fruits[0]}');
  print('Length: ${fruits.length}');
  
  // Loop through list
  for (var fruit in fruits) {
    print(fruit);
  }
  
  // List methods
  fruits.remove('Banana');
  print('Contains Apple: ${fruits.contains('Apple')}');
  
  // Maps
  Map<String, int> scores = {
    'Alice': 95,
    'Bob': 87,
    'Charlie': 92,
  };
  
  // Access map values
  print('Alice score: ${scores['Alice']}');
  
  // Add to map
  scores['David'] = 88;
  
  // Loop through map
  scores.forEach((name, score) {
    print('$name: $score');
  });
}

Output: 

First: Apple
Length: 4
Apple
Banana
Orange
Mango
Contains Apple: true
Alice score: 95
Alice: 95
Bob: 87
Charlie: 92
David: 88

🔹 Null Safety

Dart's null safety features: 


void main() {
  // Non-nullable variable (cannot be null)
  String name = 'Alice';
  // name = null; // Error!
  
  // Nullable variable (can be null)
  String? nickname = null;
  nickname = 'Ally';
  
  // Null-aware operators
  String? username;
  
  // ?? operator (default value if null)
  String displayName = username ?? 'Guest';
  print('Display: $displayName');
  
  // ?. operator (safe navigation)
  print('Length: ${username?.length}');
  
  // ! operator (assert non-null)
  String? confirmedName = 'Bob';
  String definite = confirmedName!;
  print('Definite: $definite');
  
  // Late variables
  late String description;
  description = 'Initialized later';
  print(description);
}

Output: 

Display: Guest
Length: null
Definite: Bob
Initialized later

🔹 Dart for Flutter

How Dart concepts apply to Flutter: 


import 'package:flutter/material.dart';

// Classes for widgets
class MyButton extends StatelessWidget {
  final String text;
  final VoidCallback onPressed;
  
  // Constructor with named parameters
  MyButton({required this.text, required this.onPressed});
  
  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: onPressed,
      child: Text(text),
    );
  }
}

// Using the widget
void main() {
  runApp(
    MaterialApp(
      home: Scaffold(
        body: Center(
          child: MyButton(
            text: 'Click Me',
            onPressed: () {
              print('Button clicked!');
            },
          ),
        ),
      ),
    ),
  );
}

🧠 Test Your Knowledge

Which keyword is used for compile-time constants in Dart?