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length and methods

Learn .length and String methods.

length and methods

You find how many characters a String has with the .length property: "Welcome".length evaluates to 7. .length is a property, not a method; no parentheses needed.

To upper-case the letters you use .toUpperCase(), to lower-case them .toLowerCase(). For example "book".toUpperCase() returns "BOOK". These methods do not change the original string; they return a new one.

Methods return a new string

Important: .toUpperCase() and .toLowerCase() do not modify the original string. String name = "Alex"; name.toUpperCase(); produces a new string "ALEX" but name stays "Alex".

To keep the result you assign it to a new variable: String big = name.toUpperCase();. Now big is "ALEX" and name is "Alex". Strings in Dart are immutable; every method call creates a new string.

Practice Upper-case the city

Declare a String variable city with the value "Paris". Declare a new variable big and assign the result of city.toUpperCase() to it. Then print big with print(big);. The output on a single line must be PARIS.

Starter code

main.dart
// Declare city, build big with toUpperCase and print it

Sample solution

main.dart
String city = "Paris";
var big = city.toUpperCase();
print(big);

Expected output

PARIS

Questions and answers

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

1 Write the length call

Question 
String word = "Welcome";
print(word____);
Answer 
String word = "Welcome";
print(word.length);

Explanation: .length gives the character count of the String.

2 What does "book".toUpperCase() return?

main.dart
"book".toUpperCase()
  • "book"
  • "Book"
  • "BOOK" Correct answer
  • true

Explanation: toUpperCase upper-cases all letters: BOOK.

3 Match each method to its job

Term Meaning
.length Character count
.toUpperCase() Upper-cases letters
.toLowerCase() Lower-cases letters
print(x) Prints to screen

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