Booleans & Conditions

Real-world analogy

What is it?

Booleans are true/false values used for decision-making. Comparison operators (==, !=, >, =, <=) produce booleans. if/else and switch statements let your code choose different paths based on conditions. Logical operators (&&, ||, !) combine conditions. The ternary operator (? :) is a concise if/else for simple decisions.

Real-world relevance

Every app is full of decisions. Is the user logged in? Show the dashboard or the login screen. Is the cart empty? Show products or a message. Is the password valid? Allow login or show an error. Conditions are the logic that makes apps intelligent.

Key points

• Boolean Values — A bool in Dart can only be 'true' or 'false'. That is it -- two options. Booleans are the foundation of all decision-making in code. Every time your app decides what to show or what to do, a boolean is involved.
• Comparison Operators — Dart has 6 comparison operators: == (equal), != (not equal), > (greater), = (greater or equal), <= (less or equal). Each returns a bool -- true or false.
• if / else - Basic Decisions — 'if' checks a condition. If it is true, the code inside runs. 'else' runs when the condition is false. 'else if' adds more conditions in between. This is the most fundamental control flow in any programming language.
• Logical Operators: &&, ||, ! — && means AND (both must be true). || means OR (at least one true). ! means NOT (flips true to false). These let you combine multiple conditions into one decision.
• Ternary Operator ?: — The ternary operator is a shortcut for simple if/else. Syntax: condition ? valueIfTrue : valueIfFalse. It fits on one line and is great for assigning values based on a condition.
• switch Statement — switch checks a value against multiple cases. It is cleaner than many if/else chains when checking one variable against specific values. Each case needs a break (or return) to stop. 'default' handles unmatched cases.
• Dart 3 Switch Expressions — Dart 3 introduced switch expressions -- a modern, concise way to use switch that returns a value directly. No break needed! Use the => arrow syntax for each case.
• Null-Aware Conditions — Dart's null safety means a variable can be nullable (might be null). Use the ? operator to mark nullable types, ?? to provide a fallback, and ?. to safely access properties on nullable values.
• Assert - Debug-Time Checks — assert() checks a condition during development. If the condition is false, the app pauses with an error message. Asserts are removed in production builds, so they have zero cost. Great for catching bugs early.

Code example

void main() {
  int age = 15;
  bool hasPermission = true;
  String role = 'student';

  // if / else if / else
  if (age >= 18) {
    print('You are an adult');
  } else if (age >= 13) {
    print('You are a teenager');
  } else {
    print('You are a child');
  }

  // Logical operators
  if (age >= 13 && hasPermission) {
    print('Access granted!');
  }

  if (age < 5 || age > 65) {
    print('Free entry!');
  }

  // Ternary operator
  var status = age >= 18 ? 'Adult' : 'Minor';
  print('Status: $status');

  // switch expression (Dart 3)
  var greeting = switch (role) {
    'admin' => 'Welcome, Admin!',
    'teacher' => 'Hello, Teacher!',
    'student' => 'Hi, Student!',
    _ => 'Hello, Guest!',
  };
  print(greeting);

  // Null safety
  String? nickname;
  print('Nickname: ${nickname ?? "No nickname"}');

  // Chained conditions
  bool canDrive = age >= 16 && hasPermission && !false;
  print('Can drive: $canDrive');
}

Line-by-line walkthrough

1. 1. The main function starts
2. 2. Declaring age as 15
3. 3. Declaring hasPermission as true
4. 4. Declaring role as 'student'
5. 5.
6. 6. A comment for if/else if/else
7. 7. Checking if age is 18 or more
8. 8. If true, print 'You are an adult'
9. 9. else if checks if age is 13 or more
10. 10. If true, print 'You are a teenager' -- this runs for age 15
11. 11. The else catches everything else
12. 12. If neither condition above was true, print 'You are a child'
13. 13.
14. 14. A comment for logical operators
15. 15. AND: both age >= 13 AND hasPermission must be true
16. 16. Both are true, so 'Access granted!' prints
17. 17.
18. 18. OR: age 65 -- either one being true is enough
19. 19. Age is 15, so neither is true -- this does not print
20. 20.
21. 21. A comment for ternary operator
22. 22. If age >= 18, status is 'Adult', otherwise 'Minor'
23. 23. Printing the status (will be 'Minor' since age is 15)
24. 24.
25. 25. A comment for switch expression
26. 26. Using switch on the role variable
27. 27. If role is 'admin', returns 'Welcome, Admin!'
28. 28. If role is 'teacher', returns 'Hello, Teacher!'
29. 29. If role is 'student', returns 'Hi, Student!' -- this matches!
30. 30. The _ wildcard matches anything else (default)
31. 31. Closing the switch expression with a semicolon
32. 32. Printing the greeting
33. 33.
34. 34. A comment for null safety
35. 35. Declaring nickname as nullable String, currently null
36. 36. Using ?? to print 'No nickname' because nickname is null
37. 37.
38. 38. A comment for chained conditions
39. 39. Combining three conditions with && to check if canDrive
40. 40. Printing the result

Spot the bug

void main() {
  int score = 85;

  if score >= 90 {
    print('A');
  } else if (score >= 80)
    print('B');
    print('Good job!');
  } else {
    print('C');
  }
}

Explain like I'm 5

Fun fact

Hands-on challenge

More resources

• Dart Branches (if/else, switch) (Dart Official)
• Dart Operators (Dart Official)
• Dart Patterns and Switch (Dart Official)