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else and else if

Learn else and else if chains for alternative cases.

else and else if

To run another block when the if condition is false you use else. In if (cond) { A } else { B } A runs when the condition is true; B when it is false.

To check several conditions in order you build an else if chain: if (a) { ... } else if (b) { ... } else { ... }. Dart checks top to bottom; it runs the first true block and skips the rest.

else if chain

To separate three or more cases you use else if. For example computing a grade: if (score >= 90) { print("A"); } else if (score >= 80) { print("B"); } else { print("C"); }.

Dart checks top to bottom; it runs the first true block and skips the rest of the chain. So putting the strictest condition first is efficient. The else block is optional; if no condition is true it is skipped.

Practice Print the grade letter

Declare an int variable score with the value 75. If score >= 90 print print("A");, else if score >= 70 print print("B");, in the else block print print("C");. The output on a single line must be B.

Starter code

main.dart
// Declare score, print grade letter with if/else if/else

Sample solution

main.dart
int score = 75;
if (score >= 90) {
  print("A");
} else if (score >= 70) {
  print("B");
} else {
  print("C");
}

Expected output

B

Questions and answers

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

1 Write the else keyword

Question 
int score = 40;
if (score >= 50) {
  print("passed");
} ____ {
  print("failed");
}
Answer 
int score = 40;
if (score >= 50) {
  print("passed");
} else {
  print("failed");
}

Explanation: else runs when the if condition is false.

2 When does the else block run?

main.dart
if (cond) { A } else { B }
  • when cond is always true
  • when cond is true
  • never
  • when cond is false Correct answer

Explanation: The else block runs when the if condition is false.

3 Match each part to its job

Term Meaning
if (a) First condition
else if (b) Second condition
else If none match
{ ... } Block

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