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Logical operators

Learn boolean logic with &&, || and !.

Logical operators

Logical operators combine bool values: && (and), || (or), ! (not).

&& gives true only when both sides are true. || gives true when at least one side is true. ! flips the value: !true = false.

Example: if (age >= 18 && hasTicket) — passes only if age is right and there is a ticket. These operators are the basic way to combine conditions.

Short-circuit evaluation

The && and || operators short-circuit: once the result is known, they skip the rest.

For example in false && expensiveCall() the left side is false, so the right side is not called; the result is false. This avoids unnecessary work.

Similarly in true || expensiveCall() the left side is true, so the right side is not called. This feature is used to safely guard side effects.

Practice Logical operations

Write print(true && false), print(true || false) and print(!true) inside void main().

Starter code

main.dart
// Logical operations

Sample solution

main.dart
void main() {
  print(true && false);
  print(true || false);
  print(!true);
}

Expected output

false
true
false

Questions and answers

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

1 What is the result of true && false?

  • true
  • false Correct answer
  • 1
  • Throws an error

Explanation: && requires both sides to be true.

2 And operator

Question 
if (a > 0 ____ a < 10) { print('in range'); }
Answer 
if (a > 0 && a < 10) { print('in range'); }

Explanation: && requires both conditions together.

3 Logical operators

Term Meaning
&& And
|| Or
! Not
true True

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
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20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together