Nullable Types

Part of the Fundamentals section of Coddy's Dart journey — lesson 78 of 94.

Nullable types in Dart are declared by adding a question mark (?) after the type name. This tells Dart that a variable can hold either a value of that type or null.

Declare nullable variables of different types:

String? name;
int? age;
bool? isActive;
double? price;

These variables can be assigned values or null:

name = 'Dart';
age = null;
isActive = true;
price = null;

print(name);
print(age);
print(isActive);
print(price);

After executing the above code, the output will be:

Dart
null
true
null

Challenge

Beginner

In this challenge, you'll practice working with nullable types in Dart. A nullable type is declared by adding a question mark (?) after the type name, allowing the variable to hold either a value or null.

Complete the code to check if the username variable is null. If it is, print "No username provided". If it's not null, print "Username: " followed by the username value.

Cheat sheet

Nullable types in Dart are declared by adding a question mark (?) after the type name, allowing variables to hold either a value of that type or null:

String? name;
int? age;
bool? isActive;
double? price;

Nullable variables can be assigned values or null:

name = 'Dart';
age = null;
isActive = true;
price = null;

Try it yourself

void main() {
  // This variable can be null because of the ? after String
  String? username = null;
  
  // TODO: Check if username is null
  // If it is null, print "No username provided"
  // If it's not null, print "Username: " followed by the username value
  
  // Later in the program, username gets a value
  username = "DartLearner";
  
  // TODO: Check username again using the same condition
}