Variables & Built-in Data Types

Primitive Types Overview

Dart provides several built-in types that cover most use cases:

Strings

Strings in Dart are UTF-16 encoded. You can use single or double quotes:

// Both are valid
var name = 'Dart';
var greeting = "Hello, Dart!";

// Multi-line strings
var paragraph = '''
This is a
multi-line string in Dart.
''';

// String interpolation
var version = 3;
print('Dart $version is great');    // Dart 3 is great
print('${name.toUpperCase()}!');    // DART!

// Raw strings (no escape processing)
var path = r'C:\Users\file.txt';

Numbers: int and double

var age = 25;           // int
var pi = 3.14159;       // double
var precise = 2.0;      // double (even without decimal part)

// Type conversions
var intToDouble = pi.toInt();       // 3
var doubleToInt = age.toDouble();   // 25.0
var parsed = int.parse('42');      // 42
var formatted = pi.toStringAsFixed(2); // '3.14'

Booleans

var isActive = true;
var isLoggedIn = false;

// Dart has strict boolean checking
// Only `true` is truthy — no implicit conversion
var value = 1;
// if (value) { }  // ❌ ERROR: int is not bool
if (value > 0) { } // ✅ Correct

Collection Literals vs Constructors

Prefer collection literals ([], {}, {}) over named constructors. They're more concise and the Dart analyzer recommends them:

// ✅ Preferred: collection literals
var list = [1, 2, 3];
var map = {'key': 'value'};
var set = {1, 2, 3};

// ⚠️ Also valid but verbose
var list = List.filled(3, 0);
var map = Map<String, String>();

Common List Operations

Master these list operations — you'll use them in every Dart and Flutter project:

Lists

Ordered, indexable collections. Dart 3 has both legacy List and fixed-length List:

// Growable list
var fruits = [‘Apple’, ‘Banana’, ‘Cherry’];
fruits.add('Date');
fruits.removeAt(1);

// List operations
print(fruits.length);       // 3
print(fruits[0]);           // Apple
print(fruits.contains('Date')); // true

// Spread operator
var more = [...fruits, 'Elderberry'];

// List properties
var numbers = [3, 1, 4, 1, 5];
numbers.sort();
print(numbers);             // [1, 1, 3, 4, 5]

// Map and where
var doubled = numbers.map((n) => n * 2).toList();
var evens = numbers.where((n) => n % 2 == 0).toList();

Maps

Key-value pairs, similar to dictionaries or hash maps in other languages:

var user = {
  'name': 'Alice',
  'age': 28,
  'email': '[email protected]',
};

// Access values
print(user['name']);        // Alice

// Add / update entries
user['role'] = 'admin';
user['age'] = 29;

// Check key existence
if (user.containsKey('email')) {
  print('Email exists');
}

// Iterate
user.forEach((key, value) {
  print('$key: $value');
});

Sets

Unordered collections of unique elements:

var tags = {'dart', 'flutter', 'mobile'};
tags.add('web');
tags.add('dart');  // Duplicate ignored

print(tags.length);  // 4

// Set operations
var a = {1, 2, 3};
var b = {2, 3, 4};

print(a.union(b));         // {1, 2, 3, 4}
print(a.intersection(b));  // {2, 3}
print(a.difference(b));    // {1}

Type Inference: var, final, const

// var — type inferred, mutable
var name = 'Alice';
name = 'Bob';  // ✅ Allowed

// final — type inferred, immutable (set once)
final timestamp = DateTime.now();
// timestamp = DateTime.now();  // ❌ ERROR

// const — compile-time constant
const maxRetries = 3;
const appName = 'dftacademy';
// maxRetries = 5;  // ❌ ERROR

Real-World Example: Shopping Cart

Modeling an e-commerce cart using Dart's data types:

void main() {
  // Cart item as a Map
  var item = {
    'id': 1001,
    'name': 'Wireless Mouse',
    'price': 29.99,
    'quantity': 2,
    'inStock': true,
    'tags': {'electronics', 'peripheral'},
  };

  // Cart as a list of items
  var cart = <Map<String, dynamic>>[item];

  // Calculate totals
  var subtotal = 0.0;
  for (var cartItem in cart) {
    var price = cartItem['price'] as double;
    var qty = cartItem['quantity'] as int;
    subtotal += price * qty;
  }

  print('Cart items: ${cart.length}');
  print('Subtotal: \$${subtotal.toStringAsFixed(2)}');
  print('Item tags: ${item['tags']}');
}

Summary

• Dart has rich built-in types: String, int, double, bool, List, Map, Set
• Use var, final, and const for variable declarations
• final = run-time constant; const = compile-time constant
• Collections support powerful methods: map, where, reduce