CodeBlanks Logo Icon CodeBlanks
Login Register

Summary - Lists

Combine add, map and where to write a class list.

Summary - Lists

In this group you learned List creation, index access, add/remove, length/contains and the map/where methods. Now we will combine them to write a class-list application.

The app will append grades to a list with add and filter those 50 and above with where. This structure combines data entry and filtering; it is the core of a real grade-tracking app.

Plan

We will build the class-list app step by step: (1) declare an empty List<int>; (2) add a few grades with add; (3) filter those 50 and above with where; (4) convert the result to a List with .toList(); (5) print with print.

This structure is the skeleton of a real grade-tracking app too. Dropping low grades and listing the passing ones is common in schools and workplaces. Remember to convert the Iterable returned by where with .toList().

Practice Class list app

Declare an empty int list with var grades = <int>[];. Add four grades with grades.add(40);, grades.add(55);, grades.add(70);, grades.add(30);. Declare a variable passing and assign the result of grades.where((g) => g >= 50).toList() to it. Print passing with print(passing);. The output on a single line must be [55, 70].

Starter code

main.dart
// Declare grades, add with add, filter with where and print

Sample solution

main.dart
var grades = <int>[];
grades.add(40);
grades.add(55);
grades.add(70);
grades.add(30);
var passing = grades.where((g) => g >= 50).toList();
print(passing);

Expected output

[55, 70]

Questions and answers

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

1 Write the add call

Question 
var grades = <int>[];
grades____;
grades.add(90);
print(grades);
Answer 
var grades = <int>[];
grades.add(85);
grades.add(90);
print(grades);

Explanation: .add(85) appends 85 to the list.

2 Which methods fit adding, filtering 50+ and transforming?

main.dart
// class list
  • add + where + map Correct answer
  • add + map + fold
  • remove + length + contains
  • add + sort + print

Explanation: add appends, where filters, map transforms.

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