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String interpolation

Learn to embed values in strings with \$ and \${}.

String interpolation

In Dart you use interpolation to embed a variable or expression inside a string. For a simple variable the $ prefix is enough: "Welcome $name". For an expression (method call, operation) you need curly braces: "Length: ${name.length}".

Interpolation is more readable than concatenating strings with +. Writing "Welcome $name" instead of "Welcome " + name is the Dart way. Any valid Dart expression can be embedded.

$ vs ${}

$ embeds only a variable name: "$name". If you want a method call or operation you must use ${}: "${name.toUpperCase()}". Without braces, $name.toUpperCase() makes Dart embed only $name and treat the rest as plain text.

Rule: $ for a simple variable, ${} for an expression. When unsure, ${} always works.

Practice Print with interpolation

Declare a String variable name with the value "Alex". Then print it to the screen with print("Welcome $name");. The output on a single line must be Welcome Alex.

Starter code

main.dart
// Declare name and print with interpolation

Sample solution

main.dart
String name = "Alex";
print("Welcome $name");

Expected output

Welcome Alex

Questions and answers

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

1 What is the output of this code?

main.dart
String name = "Alex";
print("Welcome $name");
  • Welcome name
  • Welcome Alex Correct answer
  • Welcome $name
  • Welcome ${name}

Explanation: $name is replaced by the value of name; the output is Welcome Alex.

2 Complete the interpolation

Question 
String name = "Alex";
print("Welcome ____");
Answer 
String name = "Alex";
print("Welcome $name");

Explanation: $name embeds the variable value into the string.

3 Match the expression to the form

Term Meaning
$name Simple variable
${name.length} Expression (method/property)
${a + b} Arithmetic expression
Welcome $name Variable embedding

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