Dart - Complete Beginner’s Guide

What is Dart? Dart is the language for building mobile apps with Flutter. It’s modern, fast, and makes beautiful apps for iOS and Android. If you love clean syntax, you’ll love Dart!

1. Getting Started

Your First Program

void main() {
  print("Hello, Dart!");
  // Output: Hello, Dart!
}

Variables and Types

// Explicit types
String name = "Alice";
int age = 25;
double height = 5.7;
bool isStudent = true;

// Type inference (Dart figures it out)
var city = "New York";      // String
var score = 95;             // int
var temperature = 98.6;     // double
var active = true;          // bool

// Dynamic (any type - use rarely!)
dynamic something = 42;
something = "now I'm a string";

// Constants
const pi = 3.14159;         // Compile-time constant
final name = "John";        // Runtime constant

2. Strings

String Basics

// Single or double quotes
String single = 'Hello';
String double = "World";

// String interpolation
String name = "Alice";
String greeting = "Hello, $name!";
print(greeting);  // "Hello, Alice!"

// With expressions
int age = 25;
String message = "I am ${age + 1} years old";
print(message);   // "I am 26 years old"

// Multi-line strings
String multiLine = """
This is a
multi-line
string
""";

String Methods

String text = "Hello World";

text.length;               // 11
text.toUpperCase();        // "HELLO WORLD"
text.toLowerCase();        // "hello world"
text.contains("World");    // true
text.startsWith("Hello");  // true
text.endsWith("World");    // true
text.substring(0, 5);      // "Hello"
text.replaceAll("World", "Dart");  // "Hello Dart"

3. Numbers and Math

Numbers

// Integers
int count = 10;
int negative = -5;

// Doubles (decimals)
double pi = 3.14159;
double result = 10 / 3;    // Always double

// Arithmetic
10 + 5;          // 15
10 - 3;          // 7
4 * 3;           // 12
15 / 3;          // 5.0 (division always returns double)
15 ~/ 3;         // 5 (integer division)
17 % 5;          // 2 (remainder)

// Math functions
import 'dart:math';
sqrt(16);        // 4.0
pow(2, 3);       // 8.0
sin(pi/2);       // 1.0

4. Lists (Arrays)

Creating and Using Lists

// List of integers
List<int> numbers = [1, 2, 3, 4, 5];

// List of strings
List<String> colors = ["red", "blue", "green"];

// Type inference
var mixed = [1, "hello", true];    // List<Object>

// Empty list
List<int> empty = [];

// Access elements
numbers[0];       // 1
numbers[2];       // 3
numbers.last;     // 5
numbers.first;    // 1

// Length
numbers.length;   // 5

List Methods

List<int> nums = [3, 1, 4, 1, 5, 9];

// Add elements
nums.add(2);                    // Adds 2 to end
nums.addAll([6, 5, 3]);        // Add multiple
nums.insert(0, 10);            // Insert at position

// Remove elements
nums.remove(5);                // Remove first occurrence
nums.removeAt(0);              // Remove by index
nums.removeLast();             // Remove last

// Other operations
nums.contains(4);              // true
nums.indexOf(4);               // 2
nums.sort();                   // [1, 1, 2, 3, 4, 5, 6, 9]
nums.reversed.toList();        // Reverse
nums.join(", ");               // "1, 1, 2, 3, 4, 5"

5. Maps (Dictionaries)

Creating Maps

// Map with string keys
Map<String, String> person = {
  "name": "John",
  "city": "New York",
  "job": "Developer"
};

// Map with various types
Map<String, dynamic> user = {
  "name": "Alice",
  "age": 25,
  "isActive": true
};

// Access values
person["name"];     // "John"
person["age"];      // null (key doesn't exist)

// Add/Update
person["email"] = "john@example.com";
person["name"] = "Jane";  // Update

// Remove
person.remove("city");

Map Methods

Map<String, int> scores = {
  "Alice": 90,
  "Bob": 85,
  "Charlie": 92
};

// Keys and values
scores.keys;       // [Alice, Bob, Charlie]
scores.values;     // [90, 85, 92]

// Check
scores.containsKey("Alice");    // true
scores.containsValue(90);       // true

// Iteration
scores.forEach((name, score) {
  print("$name: $score");
});

6. Control Flow

If Statements

int age = 18;

if (age >= 18) {
  print("You can vote");
} else if (age >= 13) {
  print("You're a teenager");
} else {
  print("You're a child");
}

// Ternary operator
String status = age >= 18 ? "Adult" : "Minor";

Comparisons

5 == 5;            // true
5 != 3;            // true
5 > 3;             // true
5 < 3;             // false
5 >= 5;            // true
5 <= 4;            // false

true && false;     // false (AND)
true || false;     // true (OR)
!true;             // false (NOT)

// Null-aware operators
String? name;
name ??= "Guest";  // Assign if null
print(name ?? "Unknown");  // Use if null

7. Loops

For Loops

// Traditional for loop
for (int i = 0; i < 5; i++) {
  print(i);        // 0, 1, 2, 3, 4
}

// For-in loop (modern)
List<String> fruits = ["apple", "banana", "orange"];
for (String fruit in fruits) {
  print(fruit);
}

// forEach (with index)
fruits.asMap().forEach((index, fruit) {
  print("$index: $fruit");
});

While Loops

int count = 0;
while (count < 5) {
  print(count);
  count++;
}

// Do-while (runs at least once)
int x = 0;
do {
  print(x);
  x++;
} while (x < 3);

Break and Continue

for (int i = 0; i < 10; i++) {
  if (i == 5) {
    break;         // Exit loop
  }
  print(i);        // 0, 1, 2, 3, 4
}

for (int i = 0; i < 5; i++) {
  if (i == 2) {
    continue;      // Skip to next
  }
  print(i);        // 0, 1, 3, 4
}

8. Functions

Defining Functions

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

add(5, 3);         // 8

// Return type inferred
subtract(a, b) {
  return a - b;
}

// Optional positional parameters
greet(String name, [String greeting = "Hello"]) {
  return "$greeting, $name!";
}

greet("Alice");              // "Hello, Alice!"
greet("Bob", "Hi");          // "Hi, Bob!"

// Named parameters
void printInfo({
  required String name,
  int age = 0,
  String city = "Unknown"
}) {
  print("$name, $age, $city");
}

printInfo(name: "John", age: 30);
printInfo(name: "Jane", city: "NYC", age: 25);

Arrow Functions

// Short function
int square(int x) => x * x;

List<int> numbers = [1, 2, 3, 4];
List<int> squared = numbers.map((n) => n * n).toList();
// [1, 4, 9, 16]

9. Classes

Basic Class

class Person {
  String name;
  int age;

  // Constructor
  Person(this.name, this.age);

  // Method
  void greet() {
    print("Hello, I'm $name and I'm $age years old");
  }
}

// Create instance
Person person = Person("John", 30);
person.greet();  // "Hello, I'm John and I'm 30 years old"

Properties and Methods

class Rectangle {
  double width;
  double height;

  Rectangle(this.width, this.height);

  // Getter
  double get area => width * height;

  // Setter
  set area(double value) {
    width = value / height;
  }

  // Method
  void printDimensions() {
    print("${width}x${height}");
  }
}

Rectangle rect = Rectangle(5, 10);
print(rect.area);      // 50
rect.area = 100;       // width changes

Inheritance

class Animal {
  String name;

  Animal(this.name);

  void speak() {
    print("$name makes a sound");
  }
}

class Dog extends Animal {
  Dog(String name) : super(name);

  @override
  void speak() {
    print("$name barks!");
  }
}

Dog dog = Dog("Buddy");
dog.speak();  // "Buddy barks!"

10. Null Safety (Dart Feature!)

Non-nullable by Default

// Can't be null
String name = "John";
// name = null;  // ❌ ERROR

// Can be null
String? nickname = null;
nickname = "Johnny";

// Safe access
nickname?.length;      // null or length
nickname ?? "Unknown";  // Use default if null

// Null assertion (careful!)
int length = nickname!.length;  // Crashes if null!

11. Practical Example

Simple Calculator

void main() {
  print(calculate(10, 5, '+'));  // 15
  print(calculate(10, 5, '-'));  // 5
  print(calculate(10, 5, '*'));  // 50
  print(calculate(10, 5, '/'));  // 2.0
}

double calculate(double a, double b, String operation) {
  switch (operation) {
    case '+':
      return a + b;
    case '-':
      return a - b;
    case '*':
      return a * b;
    case '/':
      if (b == 0) throw Exception("Cannot divide by zero");
      return a / b;
    default:
      throw Exception("Unknown operation");
  }
}