2 data types

C++ stipulates that when creating a variable or constant, the corresponding data type must be specified, otherwise memory cannot be allocated to the variable.

The meaning of the existence of the data type: to allocate the appropriate memory space to the variable.

2.1 Integer

**Function:** Integer variables represent data of integer type.

There are several ways to represent integer types in C++, the difference lies in the different memory space occupied.

type of data	take up space	Ranges
short (short integer)	2 bytes	(-215~215-1)
int (integer)	4 bytes	(-231~231-1)
long (long integer)	Window is 4 bytes; Linux is 4 bytes (32-bit), 8 bytes (64-bit)	(-231~231-1)
long long	8 bytes	(-263~263-1)

#include <iostream>
using namespace std;

int main()
{
	//1. Short integer (-32768~32767)
	short num1 = 32768;
	//2. Integer
	int num2 = 10;
	//3. Long integer
	long num3 = 10;
	//4, long integer
	long long num4 = 10;

	cout << "num1 = " << num1 << endl;
	cout << "num2 = " << num2 << endl;
	cout << "num3 = " << num3 << endl;
	cout << "num4 = " << num4 << endl;

	system("pause");

	return 0;
}

2.2 sizeof keyword

**Function:** Use the sizeof keyword to count the memory size occupied by the data type.

Syntax: sizeof( datatype/variable)

Example:

int main()
{
	//You can use sizeof to find the memory size of the data type
	//Syntax: sizeof( datatype/variable)

	short num1 = 10;

	cout << "short Occupied space memory:" << sizeof(short) << endl;

	int num2 = 10;

	cout << "int Occupied space memory:" << sizeof(int) << endl;

	cout << "long Occupied space memory:" << sizeof(long) << endl;

	cout << "long long Occupied space memory:" << sizeof(long long) << endl;

	system("pause");

	return 0;
}

Integer size comparison:

short < int <= long <= long long

2.3 Real (float)

**Function:** is used to represent decimals.

There are two types of floating-point variables:

1. single precision float
2. double precision double

The difference between the two is the range of significant digits represented.

type of data	take up space	valid number range
float	4 bytes	7 significant digits
double	8 bytes	15~16 significant digits

Example:

int main()
{
	//1. Single precision float
	//2. Double precision double

	float f1 = 3.1415926f;

	cout << "f1 = " << f1 << endl;

	double d1 = 3.1415926;

	cout << "d1 = " << d1 << endl;
	
	//Statistics float and double occupy memory space
	cout << "float Occupy memory space:" << sizeof(float) << endl;

	cout << "double Occupy memory space:" << sizeof(double) << endl;

	//Scientific notation
	float f2 = 3e2; // 3 * 10 ^ 2

	cout << "f2 = " << f2 << endl;

	float f3 = 3e-2;

	cout << "f3 = " << f3 << endl;

	system("pause");

	return 0;
}

In c++, whether it is single precision or double precision, output a decimal and display up to 6 significant figures.

Output result:

f1 = 3.14159
d1 = 3.14159
float Occupied memory space: 4
double Occupied memory space: 8

2.4 Character type

**Function:** The character variable is used to display a single character.

Syntax: char ch = 'a'

Note 1: When displaying character variables, enclose the characters in single quotes, not double quotes

Note 2: There can only be one character in single quotes, not a string

Character variables in C++ and C occupy only one byte.

Character variables do not store the character itself in memory, but store the corresponding ASCII code into the storage unit.

Example:

int main()
{
	//1. How to create a character variable
	char ch = 'a';
	cout << ch << endl;

	//2. The size of the memory occupied by the character variable
	cout << sizeof(char) << endl;

	//3. Common errors of character variables
	//char ch2 = "b"; //When creating a character variable, use single quotes
	//char ch2 = 'abcdef'; //When creating a character variable, there can only be one character in the single quote

	//4. Character variables correspond to ASCII encoding
	// a - 97
	// A - 65
	cout << (int)ch << endl;

	system("pause");

	return 0;
}

2.5 Escape characters

**Function:** Used to represent some ASCII characters that cannot be displayed.

At this stage, our commonly used escape characters are: \n \ \t

escape character	meaning	ASCII code value (decimal)
\a	alarm	007
\b	Backspace (BS) moves the current position to the previous column	008
\f	Form feed, move the current position to the beginning of the next page	012
\n	newline, move the current position to the beginning of the next line	010
\r	Enter, move the current position to the beginning of this line	013
\t	Horizontal tab (skip to next TAB position)	009
\v	vertical tabulation	011
\\	Represents a backslash character "\"	092

int main()
{
	//escape character

	//newline character \n
	cout << "Hello World\n" << endl;
	//backslash "\"
	cout << "\\" << endl;
	//The horizontal tab character \t function: the data can be output neatly
	cout << "aaa\tbbb" << endl;
	cout << "aa\tbbb" << endl;

	system("pause");

	return 0;
}

It can be seen that both \n and endl are used for line breaks. When both are used, two line breaks appear.

2.6 String type

**Function:** Used to represent a string of characters

two styles

1. C-style strings

char variablename[] = "string value"

Example:

int main()
{
	//1. C-style strings
	char str[] = "Hello World";
	cout << str << endl;

	system("pause");
	return 0;
}

Notice:

• C-style strings are enclosed in double quotes.
• To add square brackets char str[] = "Hello World";

2. C++ style strings

string variable name = "string value"

Example:

int main()
{
	//1. C-style strings
	char str[] = "Hello World";
	cout << str << endl;

	//2. C++ style strings
	string str2 = "Hello C++";
	cout << str2 << endl;

	system("pause");
	return 0;
}

Notice:

• When using string here, you need to introduce the header file #include <string>, but the 2019 version and later do not need to add

2.7 Boolean type bool

Role: Boolean data type represents a true or false value

The bool type has only two values:

• true - true (essentially 1)
• false - false (essentially 0)

The bool type occupies one byte.

Example:

int main()
{
	//1. Create bool data type
	bool flag = true;
	cout << flag << endl;

	bool flag2 = false;
	cout << flag2 << endl;

	//2. View the memory size occupied by bool
	cout << "bool Types occupy memory space:" << sizeof(bool) << endl;

	system("pause");

	return 0;
}

2.8 Data input

Role: used to get data from the keyboard

keyword: cin

Syntax: cin >> variable

Example:

int main()
{
	//1. Integer
	int a = 0;
	cout << "Please give integer variable a Assignment:" << endl;
	cin >> a;
	cout << "Integer variable a = " << a << endl;
	//2. Floating point
	float f = 3.14f;
	cout << "Please give float variable f Assignment:" << endl;
	cin >> f;
	cout << "floating point variable f = " << f << endl;
	//3. Character type
	char ch = 'a';
	cout << "Please give character variable ch Assignment:" << endl;
	cin >> ch;
	cout << "character variable ch = " << ch << endl;
	//4. String type
	string str = "kevin";
	cout << "Please give string variable str Assignment:" << endl;
	cin >> str;
	cout << "string variable str = " << str << endl;
	//5. Boolean type
	bool flag = false;
	cout << "Please give boolean type variable flag Assignment:" << endl;
	cin >> flag;
	cout << "boolean variable flag = " << flag << endl;
	//system("pause");

	return 0;
}