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3.2   Basic Data Types

When we talk about data in computers, we think of various forms such as text, images, videos, audio, 3D models, and more. Although these data are organized in different ways, they are all composed of various basic data types.

Basic data types are types that the CPU can directly operate on, and they are directly used in algorithms, mainly including the following.

  • Integer types byte, short, int, long.
  • Floating-point types float, double, used to represent decimal numbers.
  • Character type char, used to represent letters, punctuation marks, and even emojis in various languages.
  • Boolean type bool, used to represent "yes" and "no" judgments.

Basic data types are stored in binary form in computers. One binary bit is \(1\) bit. In most modern operating systems, \(1\) byte consists of \(8\) bits.

The range of values for basic data types depends on the size of the space they occupy. Below is an example using Java.

  • Integer type byte occupies \(1\) byte = \(8\) bits, and can represent \(2^{8}\) numbers.
  • Integer type int occupies \(4\) bytes = \(32\) bits, and can represent \(2^{32}\) numbers.

The following table lists the space occupied, value ranges, and default values of various basic data types in Java. You don't need to memorize this table; a general understanding is sufficient, and you can refer to it when needed.

Table 3-1   Space occupied and value ranges of basic data types

Type Symbol Space Occupied Minimum Value Maximum Value Default Value
Integer byte 1 byte \(-2^7\) (\(-128\)) \(2^7 - 1\) (\(127\)) \(0\)
short 2 bytes \(-2^{15}\) \(2^{15} - 1\) \(0\)
int 4 bytes \(-2^{31}\) \(2^{31} - 1\) \(0\)
long 8 bytes \(-2^{63}\) \(2^{63} - 1\) \(0\)
Float float 4 bytes \(1.175 \times 10^{-38}\) \(3.403 \times 10^{38}\) \(0.0\text{f}\)
double 8 bytes \(2.225 \times 10^{-308}\) \(1.798 \times 10^{308}\) \(0.0\)
Character char 2 bytes \(0\) \(2^{16} - 1\) \(0\)
Boolean bool 1 byte \(\text{false}\) \(\text{true}\) \(\text{false}\)

Please note that the above table is specific to Java's basic data types. Each programming language has its own data type definitions, and their space occupied, value ranges, and default values may vary.

  • In Python, the integer type int can be of any size, limited only by available memory; the floating-point type float is double-precision 64-bit; there is no char type, a single character is actually a string str of length 1.
  • C and C++ do not explicitly specify the size of basic data types, which varies by implementation and platform. The above table follows the LP64 data model, which is used in Unix 64-bit operating systems including Linux and macOS.
  • The size of character char is 1 byte in C and C++, and in most programming languages it depends on the specific character encoding method, as detailed in the "Character Encoding" section.
  • Even though representing a boolean value requires only 1 bit (\(0\) or \(1\)), it is usually stored as 1 byte in memory. This is because modern computer CPUs typically use 1 byte as the minimum addressable memory unit.

So, what is the relationship between basic data types and data structures? We know that data structures are ways of organizing and storing data in computers. The subject of this statement is "structure", not "data".

If we want to represent "a row of numbers", we naturally think of using an array. This is because the linear structure of an array can represent the adjacency and order relationships of numbers, but the content stored—whether integer int, floating-point float, or character char—is unrelated to the "data structure".

In other words, basic data types provide the "content type" of data, while data structures provide the "organization method" of data. For example, in the following code, we use the same data structure (array) to store and represent different basic data types, including int, float, char, bool, etc.

# Initialize arrays using various basic data types
numbers: list[int] = [0] * 5
decimals: list[float] = [0.0] * 5
# In Python, characters are actually strings of length 1
characters: list[str] = ['0'] * 5
bools: list[bool] = [False] * 5
# Python lists can freely store various basic data types and object references
data = [0, 0.0, 'a', False, ListNode(0)]

// Initialize arrays using various basic data types
int numbers[5];
float decimals[5];
char characters[5];
bool bools[5];

// Initialize arrays using various basic data types
int[] numbers = new int[5];
float[] decimals = new float[5];
char[] characters = new char[5];
boolean[] bools = new boolean[5];

// Initialize arrays using various basic data types
int[] numbers = new int[5];
float[] decimals = new float[5];
char[] characters = new char[5];
bool[] bools = new bool[5];

// Initialize arrays using various basic data types
var numbers = [5]int{}
var decimals = [5]float64{}
var characters = [5]byte{}
var bools = [5]bool{}

// Initialize arrays using various basic data types
let numbers = Array(repeating: 0, count: 5)
let decimals = Array(repeating: 0.0, count: 5)
let characters: [Character] = Array(repeating: "a", count: 5)
let bools = Array(repeating: false, count: 5)

// JavaScript arrays can freely store various basic data types and objects
const array = [0, 0.0, 'a', false];

// Initialize arrays using various basic data types
const numbers: number[] = [];
const characters: string[] = [];
const bools: boolean[] = [];

// Initialize arrays using various basic data types
List<int> numbers = List.filled(5, 0);
List<double> decimals = List.filled(5, 0.0);
List<String> characters = List.filled(5, 'a');
List<bool> bools = List.filled(5, false);

// Initialize arrays using various basic data types
let numbers: Vec<i32> = vec![0; 5];
let decimals: Vec<f32> = vec![0.0; 5];
let characters: Vec<char> = vec!['0'; 5];
let bools: Vec<bool> = vec![false; 5];

// Initialize arrays using various basic data types
int numbers[10];
float decimals[10];
char characters[10];
bool bools[10];

// Initialize arrays using various basic data types
val numbers = IntArray(5)
val decinals = FloatArray(5)
val characters = CharArray(5)
val bools = BooleanArray(5)

# Ruby lists can freely store various basic data types and object references
data = [0, 0.0, 'a', false, ListNode(0)]
Visualized Execution

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