Dart Lesson 10 of 102 2 min read

Operators in Dart: Arithmetic, Comparison, Logical and More

Every operator in Dart explained with examples: arithmetic, assignment, comparison, logical, type test, cascade and null-aware.

An operator is a symbol that works on one or more values. You have already used + and ==. This lesson collects all the common ones in one place.

Arithmetic #

Assignment #

void main() {
  var x = 10;
  x += 5;  // x = x + 5
  print(x);
  x -= 3;
  print(x);
  x *= 2;
  print(x);
  x ~/= 5;
  print(x);
}

15
12
24
4

Increment and decrement #

++ adds one and -- subtracts one. Placed before the name, the change happens first. Placed after, the old value is used first.

void main() {
  var a = 5;
  print(a++); // prints 5, then a becomes 6
  print(++a); // a becomes 7, then prints 7
  print(a--); // prints 7, then a becomes 6
  print(a);
}

5
7
7
6

Comparison #

All of these give a bool.

void main() {
  print(5 == 5);
  print(5 != 3);
  print(5 > 3);
  print(5 < 3);
  print(5 >= 5);
  print(5 <= 4);
}

true
true
true
false
true
false

Logical #

&& (and), || (or) and ! (not) are covered in booleans.

Type test and cast #

void main() {
  Object value = 'hello';

  print(value is String);
  print(value is! int);

  var text = value as String; // cast: throws if the type is wrong
  print(text.length);
}

true
true
5

Prefer is in an if over as. After an is check Dart treats the variable as that type automatically.

Conditional operators #

void main() {
  var age = 15;
  var label = age >= 18 ? 'adult' : 'minor';
  print(label);

  String? nickname;
  print(nickname ?? 'no nickname');
}

minor
no nickname

The ? : form is the ternary operator. ?? and its relatives are explained in null-aware operators.

The cascade operator #

.. lets you make several calls on the same object without repeating its name.

void main() {
  var numbers = <int>[]
    ..add(3)
    ..add(1)
    ..add(2)
    ..sort();

  print(numbers);
}

[1, 2, 3]

Precedence #

Multiplication and division happen before addition and subtraction, and comparisons happen before && and ||. When in doubt, add brackets. They cost nothing and make the intent obvious.

void main() {
  print(2 + 3 * 4);
  print((2 + 3) * 4);
}

14
20

Try it yourself #

Start with var balance = 1000;. Use compound assignment to add 250, take away 400, then double what is left. Print true if the final balance is more than 1500.