C language - Introduction - Foundation - syntax - data type (4)

What is data ？

Dealing with data all the time in life

• for example : People's weight 、 height 、 income 、 Gender and other data
• In the process of using computers , Will also be exposed to a variety of data
• for example : Document data 、 Picture data 、 Video data, etc

data classification

Static data

• Static data refers to some permanent data , It's usually stored on a hard disk . The storage space of hard disk is generally large , Now the hard disk of ordinary computer has 500G about , Therefore, some large files can be stored in the hard disk
• The length of storage ： Turn on the computer after it is turned off , The data is still there , As long as you don't take the initiative to delete or the hard disk is not broken , The data will always be
• Which are static data ： Static data is usually stored on the hard disk in the form of files , Like documents 、 Photo 、 Video etc. .

Dynamic data

• Dynamic data refers to the process of running a program , Temporary data generated dynamically , Generally stored in memory . The memory space is generally small , Now the memory of ordinary computer is only 8G about , So use memory with caution , Don't occupy too much space
  Storage space
• The length of storage ： After the computer is turned off , These temporary data will be cleared
• Which are dynamic data ： When running a program （ Software ） when , The whole program will be loaded into memory , While the program is running , All kinds of temporary data are generated , These temporary data are stored in memory . When a program stops running or the computer is forced to shut down , All temporary data generated by this program will be cleared .

Since the hard disk has so much storage space , Why not load all the applications into the hard disk to execute ？

• The main reason is that the access speed of memory is faster than that of hard disk N times

• Conversion between static data and dynamic data , That is, load from disk to memory
• Conversion between dynamic data and static data , That is, save from memory to disk

As a programmer , What we care about most is the dynamic data in memory , Because the program we write runs in memory , All kinds of temporary data will be generated during the operation of the program , In order to facilitate the calculation and operation of data , C Language classifies these data , Provides a wealth of data types

Data type introduction

C The data types of languages are ： Basic types 、 Empty type 、 Construct type and pointer type . The construction type includes the common body 、 Array 、 There are three types of structures . Basic types also include integers 、 floating-point 、 There are four types of characters and enumerations .

stay C In language , Numbers or Chinese characters that carry a series of information are data types , Computers cannot directly recognize different types , Therefore, when using a variable, you need to specify its data type in the declaration statement .C The data type of the language , Popular understanding is to put different items in different boxes , For example, decimals are stored in floating point 、 Integers are stored in integer 、 Characters are stored in character type and so on , Writing C The language needs to be different according to the stored data , Define different types of variables .

for example ：int Integers are generally allocated 4 Bytes of storage space ,double Double precision floating-point allocation 8 Bytes of storage space ; The data type of a variable also determines what values the variable can take and what operations it can perform . For example, integer type can only be rounded , Decimal type can represent decimal , Integers and decimals can be added, subtracted, multiplied and divided .

Basic data type

C The most basic data type of a language is arithmetic , Including integer type and floating point number type . Character type 、 Enumeration types are also integer types in nature ; Integer type subdivides signed and unsigned integers 、 Long and short integers ; The difference between different integer types is that the storage length is different 、 The value range is different ; Floating point number type is relatively simple , It's all symbolic , It is divided into single precision and double precision floating-point numbers .

Integer types and declaration keywords include ：

• Character type ：char （ Whether it is signed or unsigned is customized by the compiler ）
• Signed character type ：signed char
• The unsigned character type ：unsigned char
• Signed short integers ：short, signed short, short int, signed short int
• Unsigned short ：unsigned short, unsigned short int
• signed int ：int, signed, signed int
• Unsigned integer ：unsigned, unsigned int
• Signed long integer ：long, signed long, long int, signed long int
• Unsigned long ：unsigned long, unsigned long int

Floating point type declarations include ：

• Single precision floating point ：float
• Double precision floating point ：double
• Long double precision floating point ：long double

Common basic data type size

char 1 byte ,int 4 byte , long 8 byte ,float 4 byte ,double 8 byte ; Storage space size of each type , Number of bytes taken , It is related to the number of digits in the computer , Different machine data types have different sizes , Can pass sizeof() Keyword to calculate the size of each type , Determine the storage space and value range .

Get the variable size of the current machine

#include<stdio.h>
int main()
{
    
        printf("int = %d\n",sizeof(int));
        printf("short = %d\n",sizeof(short));
        printf("long int = %d\n",sizeof(long int));
        printf("long long int = %d\n",sizeof(long long int));
        printf("char = %d\n",sizeof(char));
        printf("_Bool = %d\n",sizeof(_Bool));
        printf("float = %d\n",sizeof(float));
        printf("double = %d\n",sizeof(double));
        printf("long double = %d\n",sizeof(long double));
}

32 Bit compiler and 64 Bit compiler differences

32 Bit compiler

• char ：1 Bytes
• char*（ That is, pointer variable ）: 4 Bytes （32 The addressing space of bits is 2^32, namely 32 individual bit, That is to say 4 Bytes ）
• short int : 2 Bytes
• int： 4 Bytes
• unsigned int : 4 Bytes
• float: 4 Bytes
• double: 8 Bytes
• long: 4 Bytes
• long long: 8 Bytes
• unsigned long: 4 Bytes

64 Bit compiler ( At present, they are basically 64 Of course. )

• char ：1 Bytes
• char*( That is, pointer variable ): 8 Bytes
• short int : 2 Bytes
• int： 4 Bytes
• unsigned int : 4 Bytes
• float: 4 Bytes
• double: 8 Bytes
• long: 8 Bytes
• long long: 8 Bytes
• unsigned long: 8 Bytes

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