[C language - zero foundation lesson 11] rotate the pointer of the big turntable

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This issue is about the pointer of rotating the turntable , If there is any mistake, please point out thank you ！

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Catalog

What is the pointer ？

Definition of pointer

Assignment of pointer

Pointer operation

Reference to pointer

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What is the pointer ？

In life, we should have played the game of spinning the big wheel , I will take away the object that the pointer points to , This is the pointer . In real life, did you win the prize by playing the game of rotating the turntable ？ Another is our house number. We can think of it as a pointer , As long as we tell others our house number, he can follow it to find you , And in us C There are also pointers in languages .

Pointer definition

To make it clear what a pointer is , We must first find out how the data is stored in memory , How to store and read . If a variable is defined in the program , When compiling a program , The system allocates memory units to this variable . The compilation system is based on the variable types defined in the system , Assign a certain length . Each byte of the memory area has a number , This is it. “ Address ”, It is equivalent to the house number in the hotel . The data stored in the memory unit marked by the address is equivalent to the passengers living in the hotel room .

Because the variable unit can be found through the address , so to speak , The address points to the variable unit . For example, the door of a room is hung 201 room , This is the address of the room . Or say ,201“ Point to ” The room . therefore , Visualize the address as “ The pointer ”. Through it, you can find the memory unit with its address .

Pointer is address , The pointer to a variable is the address of the variable .

Definition of pointer

The general form of defining a pointer variable is ： Base address * Pointer to the variable

* Indicate symbols for pointers

int *p;

Assignment of pointer

1. By taking the address operator ：&

int a,*b;
b=&a;

2. Through another address

int a,*q,*p;
q=&a;
p=q;

3. Definition of null pointer

int *p=NULL;

explain

1. NULL Said empty , Its value is 0

2. Null pointer cannot be referenced after definition

Pointer operation

&： Fetch address operator Only address the content

*： Take the content operator You can only get the content from the address

#include<stdio.h>
int main(){
	int a=5,b,*p;
	p=&a;
	b=*p;

		printf("%d\n",b);


}

  result ：5

Reference to pointer

Input two values to exchange their values, and then output

	int a,b,*p,*q;
	q=&a;
	p=&b;
	scanf("%d%d",q,p);
    printf("%d,%d\n",a,b);//5,5
    printf("%d,%d\n",*q,*p);//5,5
    *q=3;
    *p=2;
      printf("%d,%d\n",a,b);//3,2

Address passing between functions

#include<stdio.h>
void fun(int *q,int *p){
    *q+=*p;   
	*p+=*q;	
}
int main(){
	int a=5,b=2;
	fun(&a,&b);
      printf("%d,%d\n",a,b);//3,2
}

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