Little white battle pointer (Part 1)

One 、 Getting to know the pointer

1. Pointer overview ：
The pointer ： An address in memory .
Pointer to the variable ： Dedicated to Storage variable address The variable of .

1.1  Definition             Format ： Type specification  * Variable name 
	eg：int *p
	  （ Type specification ： Determined by the data type pointed to by the pointer variable .  *--- Indicates that the variable is a pointer variable ） 

1.2  assignment             Format ：（&  Variable name ）
	a.int a; int *p=&a            [ Assign values while defining ] 
	b.int a; int *p; p=&a;        [ Define before assign     ！！！ Do not add "*"] 
	 You must assign a value before using a pointer variable , And assigning a value to a pointer variable can only assign an address . 
3. A reference to a variable pointer       Format ：*  Pointer to the variable 
     Its meaning is to refer to the value pointed to by the pointer variable . 

#include<stdio.h>
int main()
{
    
	int a,b;             
	printf(" Yes, please. a、b Assign initial value to ：\n");
	scanf("%d%d",&a,&b);
	//int *p,*q;  Defining pointer variables p,q.
	 
	 int *p=&a,*q=&b;   // Assign values while defining pointer variables  

	//p=&a,q=&b;  Assign values to pointer variables  
	printf("a=%d,b=%d",*p,*q);   // Reference pointer variables  
	return 0;
}

---

2."&" and “*”

&: Fetch address , A unary operator that returns the address of an operand ;
*： Pointer operator , Returns the value of the variable in the specified address ;

" &* “ and " * & " （”&“ and ”*" Operators have the same precedence , associativity ： From right to left .)

With int num , *p ; p = &num ; For example
1. &*p = &(*p) =p 【 Take variables num Address 】
2. *&num = *(&num)=num 【 Take variables num Value 】

#include<stdio.h>
int main() {
    
	long i;
	long *p;
	printf("please input the number:\n");
	scanf("%ld",&i);
	p=&i;
	printf("the r1 is:%d\n",&*p);    /*  Output variables i The address of */ 
	printf("the r2 is:%d\n",&i);     /*  Output variables i The address of */ 
	printf("the r3 is:%d\n",*&i);    /*  Output variables i Value */
	printf("the r4 is:%d\n",i);	     /*  Output variables i Value */
	printf("the r5 is:%d\n",*p);	 /*  Output variables as pointers i Value */
}

---

3. Pointer self increment and self decrement operation

The self increasing and self decreasing operation of the pointer is Increase or decrease by the direct length of the data type it points to .

Example：

	short i=4;
	short *p=&i;
	p++;             //short- Occupy 2 Bytes ,p The value of the increase 2(2 Bytes ) 

#include<stdio.h>
int main(){
    
	int i;
	int *p;
	printf("please input the number:\n");
	scanf("%d",&i);
	p=&i;
	printf("the result1 is %d\n",p);
	p++;                                // Point to the next store int Address of type number ,p The value of the increase 4(4 Bytes ) 
	printf("the result2 is %d\n",p);
	
} 

---

Two 、 One dimensional arrays and pointers

1. When defining a one-dimensional array , The system will allocate storage space for the array in memory , The array name is the first address of the array .

1. When defining a pointer variable , And pass the first address of the array to the pointer variable , Then the pointer points to the one-dimensional array .

eg：int *p,a[5];
	p=a || p&a[0];      // Will array a First address assigned to p 

2. Reference a one-dimensional array through a pointer

eg：        *(p+i) || *(a+i))              //i: Is a cyclic variable , Print array elements by moving the pointer with a loop statement  
     Optimize ： printf("%d\t",*p++)                 // Indicates that the pointer movement can use "++" or "--" Operator  

#include<stdio.h>
int main() {
    
	int *p,*q,a[5],b[5];
	p=&a[0];
	q=b;
	printf("please input array a:\n");
	for(int i=0; i<5; i++) {
    
		scanf("%d",&a[i]);
	}
	printf("please input array b:\n");
	for(int i=0; i<5; i++) {
    
		scanf("%d",&b[i]);
	}
	printf("array a is:\n");
	for(int i=0; i<5; i++)
		printf("%-5d",*p++);		 // use p++ Control pointer movement  
	printf("\n");
	printf("array b is:\n");
	for(int i=0; i<5; i++)
		printf("%5d",*(b+i));        // Output array elements ,*(q+i)  or  *(b+i) 
	printf("\n");
}

Case optimization ：

 When an array is assigned ： use (p++) Enter the next address to store the basic integer .
	  @！！！ If... Is used for output at this time *p++, Then reset the pointer variable p Pointing to the array a The first address . 
Example：for(int i=1;i<5;i++)
			scanf("%d", p++ || &a[i]);

#include<stdio.h>
int main(){
    
	int *p,*q,a[5],b[5];
	p=&a[0];
	q=b;
	printf("please input array a:\n");
	for(int i=0; i<5; i++) {
    
		scanf("%d",p++);           //p++: Point to the next address to store the basic integer . 
	}
	printf("please input array b:\n");
	for(int i=0; i<5; i++) {
    
		scanf("%d",q++);
	}
	q=a;     /*@ At this time must be ： Put the pointer variable p、q Relocate to array a、b Starting position */ 
	q=b;
	printf("array a is:\n");
	for(int i=0; i<5; i++)
		printf("%-5d",*p++);		 // use *p++ Control pointer movement  
	printf("\n");
	printf("array b is:\n");
	for(int i=0; i<5; i++)
		printf("%5d",*q++);        // Output array elements ,*(q+i)  or  *(b+i) 
	printf("\n");
}

	![Demo](https://img-blog.csdnimg.cn/20200228194028424.jpg?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L01JRE85NA==,size_16,color_FFFFFF,t_70)