Booleans in Dart

What is a Boolean?

A Boolean is a data type with only two possible values: true or false. Booleans are the foundation of conditional logic — every if statement, loop condition, and logical expression evaluates to a boolean.

Declaring Booleans

bool isLoggedIn = true;
bool hasErrors = false;
bool isAdult = true;

var isDarkMode = false;   // type inferred as bool

Boolean Operators

bool a = true;
bool b = false;

print(a && b);   // false (both must be true)
print(a || b);   // true  (at least one must be true)
print(!a);       // false (NOT true = false)
print(!b);       // true  (NOT false = true)

Comparison Results

Comparison operators always return a boolean:

print(5 > 3);    // true
print(5 < 3);    // false
print(5 == 5);   // true
print(5 != 3);   // true
print(5 >= 5);   // true
print(5 <= 4);   // false

Example

void main() {
  int age = 20;
  bool hasID = true;
  double balance = 50.0;

  bool canEnter = age >= 18 && hasID;
  bool canAfford = balance >= 30.0;

  print('Can enter: $canEnter');          // true
  print('Can afford ticket: $canAfford'); // true
  print('All good: $${canEnter && canAfford}'); // true

  // Negation
  bool isMinor = !(age >= 18);
  print('Is minor: $isMinor');            // false
}

Can enter: true
Can afford ticket: true
All good: true
Is minor: false

⚠️ Common Mistakes

• Using = (assignment) instead of == (comparison): if (x = 5) is invalid in Dart.
• Treating non-zero integers as truthy — Dart does NOT allow if (1). You must use an actual bool.
• Confusing && with & — use && for logical AND in conditions.

🧠 Quiz

Summary

Booleans in Dart hold only true or false. Use && (AND), || (OR), and ! (NOT) for boolean logic. Comparison operators return booleans. Dart requires actual boolean values in conditions — non-zero integers are NOT truthy.