Numbers and Math

Double Methods

double exposes useful methods to round a value to a nearby integer (.floor(), .ceil(), .round()), keep a value inside a range with .clamp(), and format fixed-decimal text with .toStringAsFixed(). Each rounding method returns an int; clamp keeps a double receiver as double; toStringAsFixed returns a String.

Program

Play the program to round 3.7 three different ways, clamp it into a range, and format it with two fixed decimals.

double_methods.dart
Replay: real traced execution (multi-file project)
void main() {
  double value = 3.7;
  var down = value.floor();
  var up = value.ceil();
  var near = value.round();
  var bounded = value.clamp(0.0, 3.0);
  var fixed = value.toStringAsFixed(2);
  print('$down $up $near $bounded $fixed');
}

  1. value ← 3.7 (double)

    1void main() {2  double value = 3.7;3  var down = value.floor();
    values this step3.7 (double)value

  2. down ← 3 (int)

    2double value = 3.7;3var down = value.floor();4var up = value.ceil();
    values this step3 (int)down3.7value

  3. up ← 4 (int)

    3var down = value.floor();4var up = value.ceil();5var near = value.round();
    values this step4 (int)up3.7value

  4. near ← 4 (int)

    4var up = value.ceil();5var near = value.round();6var bounded = value.clamp(0.0, 3.0);
    values this step4 (int)near3.7value

  5. bounded ← 3.0 (double, clamped)

    5var near = value.round();6var bounded = value.clamp(0.0, 3.0);7var fixed = value.toStringAsFixed(2);
    values this step3.0 (double, clamped)bounded3.7value

  6. fixed ← 3.70 (String)

    6var bounded = value.clamp(0.0, 3.0);7var fixed = value.toStringAsFixed(2);8print('$down $up $near $bounded $fixed');
    values this step3.70 (String)fixed3.7value

  7. print('$down $up $near $bounded $fixed');

    7  var fixed = value.toStringAsFixed(2);8  print('$down $up $near $bounded $fixed');9}
    output3 4 4 3.0 3.70
    values this step3down4up4near3.0bounded3.70fixed

Follow the Values

  1. value starts as 3.7.
  2. floor gives 3, ceil gives 4, and round gives 4.
  3. clamp keeps the shown value at 3.0.
  4. toStringAsFixed(2) gives 3.70.
  5. The program prints 3 4 4 3.0 3.70. | result name | value | | --- | --- | | down | 3 | | up | 4 | | near | 4 | | bounded | 3.0 | | fixed | 3.70 |
floor and ceil `.floor()` rounds toward negative infinity; `.ceil()` rounds toward positive infinity. Both return `int`.
round `.round()` rounds halfway cases away from zero and returns an `int`. `3.7.round()` is `4`.
clamp `.clamp(lo, hi)` keeps a value inside a range. With a `double` receiver, the result is a `double`; here `3.7` is capped to `3.0`.
toStringAsFixed `.toStringAsFixed(n)` formats a `double` with exactly `n` digits after the decimal point and returns a `String`.

Exercise: double_methods.dart

Reproduce 3 4 4 3.0 3.70, then identify which result is formatted text with two decimal places.