type of data
The meaning of data type existence: allocate appropriate memory space to variables
There are several ways to represent integer types in C++, the difference is that the memory space occupied is different:
short (short integer) Occupied space: 2 bytes
int (integer) Occupied space: 4 bytes
long (long integer) Occupied space: 4 bytes (windows)
long long (long long integer) Occupied space: 8 bytes
sizeof keyword
The sizeof operator can be used to obtain the size of classes, structures, unions, and other user-defined data types.
The syntax for using sizeof is as follows:
sizeof (data type)
#include<iostream>
using namespace std;
int main() {
cout << "short The memory space occupied by the type is: " << sizeof(short) << endl;
cout << "int The memory space occupied by the type is: " << sizeof(int) << endl;
cout << "long The memory space occupied by the type is: " << sizeof(long) << endl;
cout << "long long The memory space occupied by the type is: " << sizeof(long long) << endl;
system("pause");
return 0;
}
There are two types of floating-point variables:
1. Single-precision float takes up space: 4 bytes, 7 significant figures
2. Double-precision double takes up space: 8 bytes with 15-16 significant digits
The number of significant digits displayed for floating-point values can be controlled by using the setprecision operator
int main()
{
float a = 12.257902012398877;
double b = 12.257902012398877;
const float PI = 3.1415926; // constant definition
cout << setprecision(15) << a << endl; // There are only 6-7 significant digits, and the following ones are imprecise
cout << setprecision(15) << b << endl; // has 15-16 significant figures, so exactly
cout << setprecision(15) << PI << endl;
return 0;
}
Character variables are used to display a single character
Syntax: `char ch = 'a';
> Note 1: When displaying character variables, enclose the characters in single quotes instead of double quotes
> Note 2: There can only be one character in single quotes, not a string
- Character variables in C and C++ only occupy 1 byte.
- The character variable does not store the character itself in the memory, but puts the corresponding ASCII code into the storage unit
int main() {
char ch = 'b';
cout << ch << endl;
cout << sizeof(char) << endl;
//ch = "abcde"; //Error, double quotes are not allowed
//ch = 'abcde'; // error, only one character can be quoted in single quotes
cout << (int)ch << endl; //View the ASCII code corresponding to the character a
ch = 98; //You can directly use ASCII to assign values to character variables
cout << ch << endl;
system("pause");
return 0;
}
escape character
Function: used to represent some ASCII characters that == cannot be displayed
Examples of escape characters "\", "\t", "\n"
int main() {
cout << "\\" << endl;
cout << "hi\tHello" << endl;
cout << "aaaa\n" ;
system("pause");
return 0;
}If there is no \n here, the words "please press any key to continue" will be on the same line as aaaa
string type
Role: used to represent a string of characters
You can use these two ways of writing
1. C-style string: `char variable name[] = "string value"`
int main() {
char str1[] = "hello world";
cout << str1 << endl;
system("pause");
return 0;
}2. C++ style string: `string variable name = "string value"`
int main() {
string str = "hello world";
cout << str << endl;
system("pause");
return 0;
}For example, these two ways of writing are output hello world (note: C++ style string, you need to add the header file #include\<string>)
Boolean type bool
Role: Boolean data type represents true or false value
The bool type has only two values:
true --- true (essentially 1)
false --- false (essentially 0)
int main() {
bool flag = true;
cout << flag << endl; // 1
flag = false;
cout << flag << endl; // 0
system("pause");
return 0;
}