Ternary & Conditional Expressions

Sometimes an if-else block feels like overkill for a simple choice between two values. Dart gives you the ternary operator — a compact, expressive way to write conditional logic in a single line.

🔹 The Ternary Operator

Syntax:

dart
condition ? valueIfTrue : valueIfFalse

It reads like a question: "If condition is true, give me valueIfTrue; otherwise give me valueIfFalse."

dart
void main() {
  int age = 20;

  // Using if-else
  String result1;
  if (age >= 18) {
    result1 = 'Adult';
  } else {
    result1 = 'Minor';
  }

  // Using ternary — same logic, one line
  String result2 = age >= 18 ? 'Adult' : 'Minor';

  print(result1);  // Adult
  print(result2);  // Adult
}

Both produce the same result. The ternary version is shorter and reads naturally once you are familiar with it.

🔹 When to Use Ternary vs if-else

Good Use of Ternary

dart
void main() {
  int number = 7;

  // Concise, readable
  String parity = number % 2 == 0 ? 'Even' : 'Odd';
  print(parity);  // Odd

  // Works great inside string interpolation
  print('The number $number is ${number % 2 == 0 ? "even" : "odd"}.');
}

When if-else Is Better

dart
void main() {
  bool isLoggedIn = false;

  // Too many side effects — use if-else
  if (isLoggedIn) {
    print('Loading dashboard...');
    fetchUserData();
    setupNotifications();
  } else {
    print('Redirecting to login...');
    clearSession();
  }
}

🔹 Nested Ternary (and Why to Avoid It)

Technically, you can nest ternary operators:

dart
void main() {
  int score = 72;

  // Nested ternary — technically valid
  String grade = score >= 90
      ? 'A'
      : score >= 80
          ? 'B'
          : score >= 70
              ? 'C'
              : 'F';

  print(grade);  // C
}

🔹 Ternary with Null Safety

Dart's null safety pairs beautifully with ternary for concise null handling:

dart
void main() {
  String? name; // nullable

  // Check and provide a fallback
  String displayName = name != null ? name : 'Guest';
  print(displayName);  // Guest

  String? city = 'Kolkata';
  String location = city != null ? city : 'Unknown';
  print(location);  // Kolkata
}

dart
String displayName = name ?? 'Guest';

🔹 Dart-Specific: Conditional Expressions in Flutter

One of the places ternary truly shines in Dart is inside Flutter widget trees. Because Flutter UIs are built by composing expressions, ternary fits perfectly:

dart
// Flutter preview (requires Flutter SDK)
Widget build(BuildContext context) {
  bool isLoggedIn = false;

  return Scaffold(
    body: Center(
      // Ternary picks the right widget based on state
      child: isLoggedIn
          ? const Text('Welcome back, Alice!')
          : const Text('Please log in.'),
    ),
  );
}

Without ternary, you would need an if-else block outside the widget tree and a variable to hold the widget — much more verbose.

Another common Flutter pattern:

dart
Widget build(BuildContext context) {
  bool isDarkMode = true;

  return Container(
    color: isDarkMode ? Colors.black : Colors.white,
    padding: const EdgeInsets.all(16),
    child: Text(
      isDarkMode ? 'Dark Mode Active' : 'Light Mode Active',
      style: TextStyle(
        color: isDarkMode ? Colors.white : Colors.black,
        fontSize: 18,
      ),
    ),
  );
}

🔹 Practical Examples

Example 1: Maximum of Two Numbers

dart
int max(int a, int b) => a > b ? a : b;

void main() {
  print(max(10, 20));  // 20
  print(max(50, 30));  // 50
  print(max(7, 7));    // 7
}

Example 2: Odd or Even Check

dart
String oddOrEven(int n) => n % 2 == 0 ? 'Even' : 'Odd';

void main() {
  for (int i = 1; i <= 6; i++) {
    print('$i is ${oddOrEven(i)}');
  }
}

Output:

1 is Odd
2 is Even
3 is Odd
4 is Even
5 is Odd
6 is Even

Example 3: Display Name

dart
String getDisplayName(String? firstName, String? lastName) {
  String first = firstName ?? 'Unknown';
  String last = lastName ?? '';
  return last.isNotEmpty ? '$first $last' : first;
}

void main() {
  print(getDisplayName('Alice', 'Smith'));  // Alice Smith
  print(getDisplayName('Bob', null));       // Bob
  print(getDisplayName(null, null));        // Unknown
}

Example 4: Absolute Value

dart
int absolute(int n) => n < 0 ? -n : n;

void main() {
  print(absolute(-42));  // 42
  print(absolute(15));   // 15
  print(absolute(0));    // 0
}

🔹 Quick Reference: Conditional Operators in Dart

Summary

• The ternary operator condition ? trueValue : falseValue is a concise alternative to simple if-else assignments.
• Use it for single-expression decisions — avoid it when logic is complex or multi-step.
• Avoid nesting ternaries; switch to if-else if or switch expressions for multiple branches.
• In null safety, prefer ?? over value != null ? value : fallback for cleaner code.
• Ternary is especially powerful inside Flutter widget trees where everything is an expression.

In the next lesson, we'll explore one of Dart's most unique features: collection if and collection for operators!