Strings, Numbers, Boolean Values, Lists, and Other Data Types in Dart

    Dart provides several built-in data types for storing and working with different kinds of
    information. Understanding strings, numbers, Boolean values, lists, sets, maps, and other
    data types is essential for developing Flutter applications. JustAcademy's Flutter curriculum
    includes Dart Programming Fundamentals covering variables, data types, operators, and
    collections such as List, Set, and Map. :contentReference[oaicite:0]{index=0}
 

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1. What Are Data Types in Dart?

    A data type defines the kind of value that can be stored and used in a Dart program.
    Different data types are useful for different types of information.
 

For example:

String name = "Rahul";
int age = 25;
double price = 499.99;
bool isLoggedIn = true;

    Here:
 

   
• String stores text.

   
• int stores whole numbers.

   
• double stores decimal numbers.

   
• bool stores true or false.

 

2. Main Dart Data Types

3. Strings in Dart

    A String represents a sequence of characters and is used for storing text.
    Strings are commonly used for names, messages, addresses, descriptions, URLs, labels,
    and other textual information.
 

Creating a String

String name = "Rahul";
String city = "Mumbai";
String course = "Flutter Development";

Single Quotes

String message = 'Hello Dart';

Double Quotes

String message = "Hello Dart";

    Both single and double quotes can be used for ordinary Dart strings.
 

4. String Interpolation

    String interpolation allows variables and expressions to be inserted directly into a string.
    Dart uses the $ symbol for this purpose.
 

String name = "Rahul";
int age = 25;

print("My name is $name");
print("I am $age years old");

Output:

My name is Rahul
I am 25 years old

Using Expressions

int price = 500;
int quantity = 3;

print("Total: ${price * quantity}");

Output:

Total: 1500

5. Common String Properties and Methods

length

String name = "Flutter";

print(name.length);

Output:

7

toUpperCase()

String name = "flutter";

print(name.toUpperCase());

toLowerCase()

String name = "FLUTTER";

print(name.toLowerCase());

contains()

String course = "Flutter Development";

print(course.contains("Flutter"));

trim()

String name = "  Rahul  ";

print(name.trim());

replaceAll()

String text = "Hello Java";

String result = text.replaceAll("Java", "Dart");
print(result);

split()

String data = "Dart,Flutter,Firebase";

List<String> items = data.split(",");
print(items);

6. Multiline Strings

    Triple quotes can be used to create multiline strings.
 

String message = '''
Welcome to Dart.
Learn Flutter.
Build mobile applications.
''';

print(message);

7. Numbers in Dart

    Dart provides numeric types for working with numbers. The most commonly used numeric types
    are int, double, and num.
 

8. int – Integer Numbers

    The int type is used for whole numbers without a fractional part.
 

int age = 25;
int students = 100;
int score = 95;
int year = 2026;

Arithmetic with int

int a = 20;
int b = 10;

print(a + b);
print(a - b);
print(a * b);
print(a ~/ b);
print(a % b);

    The ~/ operator performs integer division.
 

9. double – Decimal Numbers

    The double type is used for numbers that can contain a fractional or decimal
    component.
 

double price = 499.99;
double percentage = 85.5;
double temperature = 32.7;

Example

double price = 499.99;
double discount = 50.50;

double finalPrice = price - discount;
print(finalPrice);

10. num – General Numeric Type

    The num type can represent both integer and double values.
 

num value = 100;

value = 99.50;
print(value);

    This is useful when a numeric value may be either an integer or a decimal.
 

11. Number Operations

Dart supports common arithmetic operations.

int a = 20;
int b = 6;

print(a + b);  // Addition
print(a - b);  // Subtraction
print(a * b);  // Multiplication
print(a / b);  // Division
print(a ~/ b); // Integer division
print(a % b);  // Remainder

12. Useful Number Methods

abs()

int number = -25;

print(number.abs());

round()

double price = 99.60;

print(price.round());

floor()

double price = 99.90;

print(price.floor());

ceil()

double price = 99.10;

print(price.ceil());

13. Boolean Values in Dart

    The bool type represents one of two logical values:
    true or false.
 

bool isLoggedIn = true;
bool isAdmin = false;
bool isAvailable = true;

Using Boolean Values with if

bool isLoggedIn = true;

if (isLoggedIn) {
  print("Welcome to the application");
} else {
  print("Please log in");
}

14. Boolean Expressions

    Comparison operators produce Boolean values.
 

int age = 25;

print(age > 18);
print(age == 25);
print(age != 30);

Output:

true
true
true

15. Logical Operators

    Multiple Boolean expressions can be combined using logical operators.
 

AND Operator

bool isLoggedIn = true;
bool isVerified = true;

bool canAccess = isLoggedIn && isVerified;
print(canAccess);

OR Operator

bool isAdmin = false;
bool isManager = true;

bool hasPermission = isAdmin || isManager;
print(hasPermission);

NOT Operator

bool isBlocked = false;

print(!isBlocked);

16. Lists in Dart

    A List is an ordered collection of values. Lists are commonly used when
    multiple related items need to be stored together.
 

List<String> fruits = [
  "Apple",
  "Banana",
  "Mango"
];

17. List Indexing

    List indexes start from 0.
 

List<String> fruits = [
  "Apple",
  "Banana",
  "Mango"
];

print(fruits[0]);
print(fruits[1]);
print(fruits[2]);

Output:

Apple
Banana
Mango

18. Adding Items to a List

List<String> fruits = [
  "Apple",
  "Banana"
];

fruits.add("Mango");
print(fruits);

19. Removing Items from a List

List<String> fruits = [
  "Apple",
  "Banana",
  "Mango"
];

fruits.remove("Banana");
print(fruits);

20. List Length

List<int> numbers = [10, 20, 30, 40];

print(numbers.length);

Output:

4

21. Looping Through a List

List<String> languages = [
  "Dart",
  "Flutter",
  "Java",
  "Python"
];

for (String language in languages) {
  print(language);
}

22. List of Numbers

List<int> marks = [
  80,
  85,
  90,
  95
];

int total = 0;
for (int mark in marks) {
  total += mark;
}
print("Total: $total");

23. List of Objects

    Lists can also contain objects created from classes.
 

class Student {
  String name;

  Student(this.name);
}
void main() {
  List<Student> students = [
    Student("Rahul"),
    Student("Amit"),
    Student("Priya")
  ];
  for (Student student in students) {
    print(student.name);
  }
}

24. Set Data Type

    A Set is a collection where each value occurs only once.
 

Set<String> skills = {
  "Dart",
  "Flutter",
  "Firebase"
};

Adding a Set Value

skills.add("REST API");

Duplicate Values

Set<String> languages = {
  "Dart",
  "Flutter",
  "Dart"
};

print(languages);

    The duplicate "Dart" value is not stored as a second distinct element.
 

25. Map Data Type

    A Map stores information using key-value pairs. Maps are especially useful
    for structured data and JSON-like information.
 

Map<String, dynamic> user = {
  "name": "Rahul",
  "age": 25,
  "city": "Mumbai"
};

Accessing Map Values

print(user["name"]);
print(user["age"]);
print(user["city"]);

Adding a New Key-Value Pair

user["email"] = "[email protected]";

Updating a Value

user["age"] = 26;

26. Object Data Type

    Object is a general Dart type that can represent values that are objects.
 

Object value = "Hello";

value = 100;
value = true;

    Because the static type is Object, operations specific to a particular
    type may require type checking or casting.
 

27. dynamic Data Type

    The dynamic type allows a variable to contain values of different types.
 

dynamic value = 100;

value = "Hello";
value = true;
print(value);

    dynamic can be useful when working with data whose type is not known in advance,
    but unnecessary use can reduce the benefits of Dart's static type checking.
 

28. Null and Nullable Types

    Dart supports null safety. A normal non-nullable variable cannot contain null.
 

String name = "Rahul";

    If a value is allowed to be null, add ? to the type.
 

String? middleName;

middleName = null;

Nullable Number

int? age;

age = null;
age = 25;

29. final and const

    Dart also provides final and const for values that should not
    be reassigned.
 

final

final String name = "Rahul";

// name = "Amit"; // Invalid

const

const double pi = 3.14159;
const int maxUsers = 100;

30. Difference Between Common Data Types

31. Type Inference with var

    Dart can infer the type of a variable from its initial value.
 

var name = "Rahul";
var age = 25;
var price = 99.99;
var loggedIn = true;

print(name);
print(age);
print(price);
print(loggedIn);

    The inferred types are effectively String, int,
    double, and bool.
 

32. Generic Lists

    Generic type parameters allow you to specify what kind of values a collection should contain.
 

List<String> names = [
  "Rahul",
  "Amit",
  "Priya"
];

List<int> ages = [
  20,
  25,
  30
];

33. Generic Sets

Set<String> technologies = {
  "Dart",
  "Flutter",
  "Firebase"
};

34. Generic Maps

Map<String, int> marks = {
  "Rahul": 90,
  "Amit": 85,
  "Priya": 95
};

    Here, keys are strings and values are integers.
 

35. Data Types in Flutter Applications

    These Dart data types are used throughout Flutter development. For example, a product model
    may use strings for names, doubles for prices, integers for quantities, Booleans for status,
    and lists for multiple products.
 

class Product {
  String name;
  double price;
  int quantity;
  bool isAvailable;

  Product({
    required this.name,
    required this.price,
    required this.quantity,
    required this.isAvailable,
  });
}

36. Example: Product List

class Product {
  String name;
  double price;

  Product({
    required this.name,
    required this.price,
  });
}
void main() {
  List<Product> products = [
    Product(
      name: "Laptop",
      price: 55000.00,
    ),
    Product(
      name: "Mobile",
      price: 25000.00,
    ),
    Product(
      name: "Headphones",
      price: 2500.00,
    ),
  ];
  for (Product product in products) {
    print("${product.name}: ₹${product.price}");
  }
}

37. Example: User Data

void main() {
  String name = "Rahul";
  int age = 25;
  double accountBalance = 12500.50;
  bool isVerified = true;

  List<String> skills = [
    "Dart",
    "Flutter",
    "Firebase"
  ];
  Map<String, dynamic> user = {
    "name": name,
    "age": age,
    "balance": accountBalance,
    "verified": isVerified,
    "skills": skills
  };
  print(user);
}

38. Strings, Numbers, Booleans, and Collections Together

void main() {
  // String
  String studentName = "Rahul";

  // Integer
  int age = 21;
  // Double
  double percentage = 87.5;
  // Boolean
  bool passed = true;
  // List
  List<String> subjects = [
    "Dart",
    "Flutter",
    "Firebase"
  ];
  // Set
  Set<String> skills = {
    "Dart",
    "Flutter",
    "Git"
  };
  // Map
  Map<String, dynamic> student = {
    "name": studentName,
    "age": age,
    "percentage": percentage,
    "passed": passed,
    "subjects": subjects,
    "skills": skills
  };
  print(student);
}

39. Choosing the Correct Data Type

40. Common Beginner Mistakes

Using the Wrong Data Type

Incorrect:

int age = "25";

Correct:

int age = 25;

Using a String Instead of a Number

For numeric calculations, use numeric types rather than storing the number as text.

double price = 499.99;

Using Null with a Non-Nullable Type

Incorrect:

// String name = null;

Correct:

String? name = null;

Unnecessary dynamic

    If the type is already known, use a specific type instead of dynamic.
 

int age = 25;

41. Best Practices

   
• Use descriptive variable names.

   
• Choose the most appropriate data type for each value.

   
• Use String for text.

   
• Use int for whole numbers.

   
• Use double for decimal values.

   
• Use bool for true/false states.

   
• Use List for ordered collections.

   
• Use Set when duplicate values should not be stored.

   
• Use Map for key-value relationships.

   
• Use generic collection types such as List<String> where appropriate.

   
• Use nullable types only when null is a valid state.

   
• Avoid unnecessary use of dynamic.

   
• Use final when a variable should not be reassigned.

   
• Use const for compile-time constant values.

 

42. Practice Exercises

   
1. Create a String variable containing your full name.

   
2. Create an integer variable containing your age.

   
3. Create a double variable containing the price of a product.

   
4. Create a Boolean variable representing whether you are logged in.

   
5. Create a List containing five programming languages.

   
6. Create a List of integers containing five marks.

   
7. Create a Set containing five unique skills.

   
8. Create a Map containing a user's name, age, email, and city.

   
9. Write a program that calculates the total price of three products.

   
10. Write a program that checks a Boolean login status.

   
11. Create a list of students using a custom Student class.

   
12. Create a product model using String, double, int, and bool properties.

 

43. Quick Revision

   
• String: Used for text.

   
• int: Used for whole numbers.

   
• double: Used for decimal numbers.

   
• num: Used for numeric values that may be integers or doubles.

   
• bool: Stores true or false.

   
• List: Stores an ordered collection.

   
• Set: Stores unique values.

   
• Map: Stores key-value pairs.

   
• Object: Represents a general Dart object.

   
• dynamic: Allows dynamic typing.

   
• Null: Represents the absence of a value.

   
• ? Makes a type nullable.

   
• final: Allows assignment only once.

   
• const: Represents a compile-time constant.

 

44. Conclusion

    Strings, numbers, Boolean values, lists, sets, maps, and other Dart data types are the
    foundation of data handling in Flutter applications. A strong understanding of these
    types helps developers create models, process user input, handle API responses, manage
    application state, and build dynamic interfaces.
 

    JustAcademy's Flutter curriculum specifically includes Dart variables and data types,
    along with List, Set, and Map collections, as part of its Dart Programming Fundamentals
    module. :contentReference[oaicite:1]{index=1}
 

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