[C language] a brief introduction to the first C language program and data type

The compiler I use is vs2019, After we create the project and create the source file , You can write code happily , Next we will write the first C Language program .

ordinary C Language program

First , To write the main function （main function ）.

#include<stdio.h>

int main()
{
   printf("hello, world!")

   return 0;
}

main A function is a function of a program entrance ,C The language code starts from the first line of the main function . There can be more than one in a program .c file , But many ,c In file There can only be one main function .

printf It's a library function , It's a print function , Role is Print information on the screen .

The use of library functions should Header file in source file （printf The header file for is stdio.h）.

Let's write the first simple C Language program , Next, let's look at data types .

Get to know the data type

There are differences between different data types , Some data types represent Numbers , Some indications character .C Identify and use these data types through some basic data types . The data types are as follows ：

char       // Character data type 
short      // Short 
int        // integer 
long       // Long integer 
long long  // Longer plastic surgery 
float      // Single-precision floating-point 
double     // Double precision floating point 

• int Keywords can represent the most basic Integer types .
• short、long、long long All are Variant of integer type .
• char Keywords can Specify letters and other characters , It's fine too Represents a smaller integer .
• float、double Express Number with decimal point , The difference is that double More accurate .

Types created by these keywords , Computer storage methods can be divided into these two basic types  ： Integer types and Floating point type .

Next, let's introduce the Company

1. bit - bits （ It's in the computer Minimum Company , Used to store a binary bit ）
2. byte - byte —>1 byte = 8 bit
3. kb = 1024 byte
4. mb = 1024 kb 
5. gb = 1024 mb
6. tb = 1024 gb 
7. pb = 1024 tb

sizeof  --- keyword ---- The operator --- Be able to calculate the space occupied by types or variables  

In this way, you can visually see the space occupied by different data types , The unit is byte .