Numbers

Dart's number types are int (whole numbers) and double (decimals). Both are subtypes of num.

Example

void main() {
  print(7 + 2);
  print(7 - 2);
  print(7 * 2);
  print(7 / 2);
  print(7 ~/ 2);
  print(7 % 2);
  print(6 / 2);
  print(10 / 3);
  print(-7 ~/ 2);
}

Expected output

9
5
14
3.5
3
1
3.0
3.3333333333333335
-3

Line by line:

• / always returns a double in Dart, even for 6 / 2.
• ~/ is integer division: it divides and drops the remainder, returning an int. -7 ~/ 2 is -3 — it rounds toward zero.
• % gives the remainder, handy for checking whether a number is even.
• Doubles are approximate: 10 / 3 shows the tiny rounding error built into how computers store decimals.

Useful number methods

import 'dart:math';

void main() {
  print((-5).abs());
  print(3.7.round());
  print(3.7.floor());
  print(3.2.ceil());
  print(3.99.toInt());
  print(3.14159.toStringAsFixed(2));
  print(17.clamp(1, 10));
  print(10.isEven);
  print(max(3, 9));
  print(pow(2, 10));
  print(sqrt(16));
}

5
4
3
4
3
3.14
10
true
9
1024
4.0

• toInt() truncates; round() rounds to the nearest whole number.
• toStringAsFixed(2) formats with two decimal places (it returns a String).
• max, pow, and sqrt come from dart:math, imported at the top.

Common mistakes

• Expecting 7 / 2 to be 3. Use ~/ for integer division.
• Using double for money. 0.1 + 0.2 is 0.30000000000000004. Store cents as int, or use a decimal package.

Practice

A pizza has 8 slices shared by 3 people. Print how many whole slices each person gets, how many are left over, and the exact share with two decimal places.

void main() {
  const slices = 8;
  const people = 3;
  print(slices ~/ people);
  print(slices % people);
  print((slices / people).toStringAsFixed(2));
}

2
2
2.67