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Summary - Variables

Combine var, final, const and null safety to write a profile program.

Summary - Variables

In this group you learned five ways to declare variables in Dart: var (type inference), final (runtime constant), const (compile-time constant), late (deferred init) and nullable types (?).

Combining them you can write a real profile program. We will practice with two small tasks.

In later lessons we will use these keywords for function parameters, class fields and collections too. The foundation is laid here.

Practice Profile program

Inside void main() declare three variables: var name = 'Alex', final age = 25, const city = 'London'. Then print with print('$name $age $city').

Starter code

main.dart
// Declare three variables and print them

Sample solution

main.dart
void main() {
  var name = 'Alex';
  final age = 25;
  const city = 'London';
  print('$name $age $city');
}

Expected output

Alex 25 London

Practice Final profile

Inside void main() declare final name = 'Zoe' and const birthYear = 1995. Print with print('$name $birthYear').

Starter code

main.dart
// Write a profile with final and const

Sample solution

main.dart
void main() {
  final name = 'Zoe';
  const birthYear = 1995;
  print('$name $birthYear');
}

Expected output

Zoe 1995

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Which is a compile-time constant?

  • var
  • final
  • const Correct answer
  • late

Explanation: const is set at compile time.

2 Nullable email

Question 
String? email = ____;
Answer 
String? email = null;

Explanation: email can be null right now.

3 All variable concepts

Term Meaning
var Type inference
final Immutable
const Compile-time
String? Nullable

All lessons in Beginner

1 Dart basics

  1. What is Dart?
  2. Your first program
  3. dart run
  4. Comments
  5. String interpolation
  6. Summary - Dart basics

2 Variables

  1. var and type
  2. final
  3. const
  4. late
  5. Null safety
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. bool and String
  4. Type inference
  5. dynamic
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Null-aware operators
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String interpolation
  3. length and methods
  4. substring
  5. contains and indexOf
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. switch
  4. Pattern matching
  5. Ternary
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. for-in
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Lists

  1. Creating lists
  2. List access
  3. add and remove
  4. length and contains
  5. List methods
  6. Summary - Lists

11 Sets and Maps

  1. Set
  2. Set operations
  3. Map
  4. Map operations
  5. Map iteration
  6. Summary - Sets and Maps

12 Functions

  1. Defining functions
  2. Return values
  3. Arrow functions
  4. Optional parameters
  5. First-class functions
  6. Summary - Functions

13 Null safety in depth

  1. Nullable types
  2. Null-aware operators
  3. The ! operator
  4. late
  5. Null check
  6. Summary - Null safety

14 Class basics

  1. class
  2. Constructor
  3. Instance variables
  4. Methods
  5. this
  6. Summary - Class basics

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. split and join
  2. replace
  3. trim and pad
  4. RegExp
  5. StringBuffer
  6. Summary - Advanced strings

17 Enums

  1. Defining enums
  2. Enum values
  3. Enhanced enums
  4. switch with enum
  5. Enum and patterns
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. The Exception class
  5. on clause
  6. Summary - Exceptions

19 Async basics

  1. Future
  2. async/await
  3. then
  4. Future.error
  5. Future.wait
  6. Summary - Async basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together