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substring

Learn to take parts of a string with substring.

substring

To take a part of a String you use the .substring(start, end) method. start is inclusive, end is exclusive: "DartLang".substring(0, 4) returns "Dart". Indexing is zero-based.

If you omit the second parameter it goes to the end of the String: "DartLang".substring(4) returns "Lang". Negative indices are not supported; keep indices within the String length to avoid errors.

Start and end rules

In substring the start index exists in the string and is included in the result. The end index is excluded; it means "take up to here". "welcome".substring(0, 3) takes the letters w, e, l and returns "wel".

Both parameters must be between 0 and length. start cannot be greater than end; otherwise an error is thrown. Practical tip: the number of characters taken is end - start.

Practice Take the first 4 characters

Declare a String variable word with the value "DartLang". Declare a new variable first and assign the result of word.substring(0, 4) to it. Then print first with print(first);. The output on a single line must be Dart.

Starter code

main.dart
// Declare word, assign the first 4 chars to first via substring, print it

Sample solution

main.dart
String word = "DartLang";
var first = word.substring(0, 4);
print(first);

Expected output

Dart

Questions and answers

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

1 Match the call to its meaning

Term Meaning
substring(0, 3) First 3 characters
substring(2) From index 2 to end
substring(0, 1) First character
substring(1, 3) Middle part

2 Write the substring call

Question 
String word = "Dart";
print(word____);
Answer 
String word = "Dart";
print(word.substring(0, 3));

Explanation: .substring(0, 3) takes the first 3 characters.

3 What does "welcome".substring(0, 3) return?

main.dart
"welcome".substring(0, 3)
  • "welc"
  • "w"
  • "lco"
  • "wel" Correct answer

Explanation: substring(0, 3) takes indices 0, 1, 2: wel.

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