## ChapterÂ 3.Â A Tour of the Dart Libraries

This chapter shows you how to use the major features in Dartâs libraries. Itâs just an overview, and by no means comprehensive. Whenever you need more details about a class, consult the Dart API reference.

## dart:coreâNumbers, Collections, Strings, and More

The Dart core library provides a small but critical set of built-in functionality. This library is automatically imported into every Dart program.

### Numbers

The dart:core library defines the num, int, and double classes, which have some basic utilities for working with numbers.

You can convert a string into an integer or double with the `parse()` methods of int and double, respectively:

```assert(int.parse('42') == 42);
assert(int.parse('0x42') == 66);
assert(double.parse('0.50') == 0.5);```

Or use the parse() method of num, which creates an integer if possible and otherwise a double:

```assert(num.parse('42') is int);
assert(num.parse('0x42') is int);
assert(num.parse('0.50') is double);```

To specify the base of an integer, add a `radix` parameter:

`assert(int.parse('42', radix: 16) == 66);`

Use the `toString()` method (defined by Object) to convert an int or double to a string. To specify the number of digits to the right of the decimal, use `toStringAsFixed()` (defined by num). To specify the number of significant digits in the string, use `toStringAsPrecision()` (also in num):

`// Convert an int to a string. assert(42.toString() == '42'); // Convert a double to a string. assert(123.456.toString() == '123.456'); // ...`

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