Dart Basics: From Entry Point to Collections

If you're coming to Dart from another language, most of it will feel familiar — but the details are worth getting right from day one. This is a whirlwind tour of the fundamentals: the entry point, variables, types, control flow, and the core collections you'll use in every program.

The entry point

Every Dart program starts at a top-level main function.

void main() {
  print('Hello, Dart');
}

// It can also take command-line arguments:
void main(List<String> args) {
  print('You passed ${args.length} args');
}

Variables

Use var to let Dart infer the type, or write the type explicitly. Use final for a value set once, and const for a compile-time constant.

var count = 3;          // inferred as int
int total = 10;         // explicit
final name = 'Ada';     // set once, at runtime
const pi = 3.14159;     // compile-time constant

late String greeting;   // initialized later, but before first use
greeting = 'Hi';

Rule of thumb: reach for final by default and only use var when the value genuinely changes.

Data types

The core built-in types:

int age = 30;
double price = 9.99;
num anything = 5;       // int or double
String title = 'Dart';
bool isReady = true;
List<int> scores = [1, 2, 3];
Map<String, int> ages = {'Ada': 36};
Object o = 'anything';  // the root type
dynamic d = 'no checks';// opts out of static checking — avoid

Strings support interpolation with $ and ${...}:

final user = 'Sam';
print('Welcome, $user — you have ${scores.length} scores');

Control flow

if / else if / else work as you'd expect, and there's a ternary for short cases.

if (age >= 18) {
  print('adult');
} else {
  print('minor');
}

final label = age >= 18 ? 'adult' : 'minor';

switch handles multi-way branches, and in modern Dart it can be an expression:

final tier = switch (score) {
  >= 90 => 'A',
  >= 80 => 'B',
  _ => 'C',
};

Lists

An ordered, growable collection.

final fruits = <String>['apple', 'banana'];
fruits.add('cherry');
print(fruits[0]);        // apple
print(fruits.length);    // 3
print(fruits.contains('banana')); // true

// Transform without a loop:
final upper = fruits.map((f) => f.toUpperCase()).toList();
final short = fruits.where((f) => f.length <= 5).toList();

Loops

Classic for, for-in, and while:

for (var i = 0; i < 3; i++) {
  print(i); // 0 1 2
}

for (final fruit in fruits) {
  print(fruit);
}

var n = 3;
while (n > 0) {
  n--;
}

Dart also has collection-for and collection-if for building lists inline:

final widgets = [
  const Header(),
  for (final f in fruits) Chip(label: f),
  if (isReady) const Footer(),
];

Sets

An unordered collection of unique values.

final tags = <String>{'dart', 'flutter'};
tags.add('dart');       // ignored — already present
print(tags.length);     // 2
print(tags.contains('flutter')); // true

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

Maps

Key–value pairs.

final capitals = <String, String>{
  'Iraq': 'Baghdad',
  'Japan': 'Tokyo',
};
capitals['Egypt'] = 'Cairo';
print(capitals['Japan']);           // Tokyo
print(capitals.containsKey('Iraq')); // true

for (final entry in capitals.entries) {
  print('${entry.key} -> ${entry.value}');
}

Functions

Functions are first-class. Use arrow syntax for one-liners, and named or optional parameters for clarity.

int add(int a, int b) => a + b;

String greet(String name, {String greeting = 'Hello'}) => '$greeting, $name';

greet('Ada');                 // Hello, Ada
greet('Ada', greeting: 'Hi'); // Hi, Ada

Where to go next

That's the toolkit for everyday Dart. Next, learn how these pieces come together in classes and objects — the foundation of Dart's object-oriented model — and lean into the type system: the more precise your types, the more the compiler helps you.