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#include<stdio.h>

void stu_help(void);
int main(int argc,char *argv[])
{
	stu_help();

	while(1)
	{
		char cmd[32]="";
		printf(" Please input the operation instruction :");
		
		scanf("%s",cmd);
		if(strcmp(cmd,"help") == 0)
		{
			stu_help();
		}
		else if(strcmp(cmd,"insert") == 0)
		{
			printf("-----insert------\n");
		}
		else if(strcmp(cmd,"print") == 0)
		{
			printf("-----print------\n");
		}
		else if(strcmp(cmd,"search") == 0)
		{
			printf("-----search------\n");
		}
		else if(strcmp(cmd,"delete") == 0)
		{
			printf("-----delete------\n");
		}
		else if(strcmp(cmd,"free") == 0)
		{
			printf("-----free------\n");
		}
		else if(strcmp(cmd,"quit") == 0)
		{
			break;
		}
		
	}
	return 0;
}

void stu_help(void)
{
	printf("################################\n");
	printf("#help: Print help              #\n");
	printf("#insert: Insert linked list node            #\n");
	printf("#print: Traverse the linked list node information         #\n");
	printf("#search: Query linked list nodes            #\n");
	printf("#delete: Delete the linked list node            #\n");
	printf("#free: Release list                  #\n");
	printf("#quit: sign out                      #\n");
	printf("################################\n");
	return;
}

Linked list insertion node And Head Insert before

Case study ：

main.c

#include<stdio.h>
#include<string.h>
#include "link.h"
void stu_help(void);
int main(int argc,char *argv[])
{
	// Define a chain header   Be careful   Be sure to assign a value of NULL
	STU *head=NULL;

	stu_help();

	while(1)
	{
		char cmd[32]="";
		printf(" Please input the operation instruction :");
		
		scanf("%s",cmd);
		if(strcmp(cmd,"help") == 0)
		{
			stu_help();
		}
		else if(strcmp(cmd,"insert") == 0)
		{
			STU tmp;
			printf(" Please enter the data to be inserted :");
			scanf("%d %s %f",&tmp.num, tmp.name, &tmp.score);

			// take tmp data   Insert into head In the linked list pointed to 
			head = insert_link(head, tmp);
		}
		else if(strcmp(cmd,"print") == 0)
		{
			print_link(head);
		}
		else if(strcmp(cmd,"search") == 0)
		{
			printf("-----search------\n");
		}
		else if(strcmp(cmd,"delete") == 0)
		{
			printf("-----delete------\n");
		}
		else if(strcmp(cmd,"free") == 0)
		{
			printf("-----free------\n");
		}
		else if(strcmp(cmd,"quit") == 0)
		{
			break;
		}
		
	}
	return 0;
}

void stu_help(void)
{
	printf("################################\n");
	printf("#help: Print help              #\n");
	printf("#insert: Insert linked list node            #\n");
	printf("#print: Traverse the linked list node information         #\n");
	printf("#search: Query linked list nodes            #\n");
	printf("#delete: Delete the linked list node            #\n");
	printf("#free: Release list                  #\n");
	printf("#quit: sign out                      #\n");
	printf("################################\n");
	return;
}

link.c

#include<stdio.h>
#include<stdlib.h>//calloc
#include"link.h"
STU* insert_link(STU *head, STU tmp)
{
	
	//1、 Apply for a node space to be inserted from the heap 
	STU *pi = (STU *)calloc(1,sizeof(STU));
	if(pi == NULL)
	{
		perror("calloc");
		return head;
	}

	//2、 take tmp Value   assignment   to *pi
	*pi = tmp;
	pi->next = NULL;// Be careful 

	//3、 take pi Insert into the linked list 
	if(head == NULL)// The list does not exist 
	{
		head = pi;
		//return head;
	}
	else// The linked list exists （ Insert before the head ）
	{
		//1、 Give Way pi  Point to your head 
		pi->next = head;

		//2、head Point to the new head node 
		head = pi;

		//return head;
	}

	return head;
}

void print_link(STU *head)
{
	if(head == NULL)// The list does not exist 
	{
		printf("link not find\n");
		return;
	}
	else
	{
		STU *pb = head;
		while(pb != NULL)
		{
			printf("%d %s %f\n", pb->num, pb->name,pb->score);
			//pb Point to next node 
			pb = pb->next;
		}
		
	}

	return;
}

link.h

// Prevent header files from repeatedly containing 
#ifndef __LINK_H__
#define __LINK_H__
// Linked list node type   Definition 
typedef struct stu
{
	// Data fields 
	int num;
	char name[32];
	float score;

	// Pointer to the domain 
	struct stu *next;
}STU;

extern STU* insert_link(STU *head, STU tmp);
extern void print_link(STU *head);
#endif

Knowledge point 2【 Insertion of linked list 】

1、 Insert... At the end of the linked list

// The tail of the linked list is inserted 
STU* insert_link(STU *head, STU tmp)
{
	//1、 Apply for the node to be inserted 
	STU *pi = (STU *)calloc(1,sizeof(STU));
	if(pi == NULL)
	{
		perror(calloc);
		return head;
	}

	//2、 take tmp The data of   Assign values to the  *pi
	*pi = tmp;
	pi->next = NULL;

	//3、 Insert the node into the end of the linked list 
	if(head == NULL)// The list does not exist 
	{
		head = pi;
		return head;
	}
	else// The linked list exists 
	{
		//a、 Find the tail node of the linked list 
		STU *pb = head;
		while(pb->next != NULL)// If it's not the tail node 
			pb = pb->next;//pb Just point to the next node 

		//b、 Use the tail node  pb  On link   Inserted nodes pi
		pb->next = pi;
		return head;
	}

	return head;
}

2、 Orderly insertion of linked list （ difficulty ）

// Orderly insertion of linked list   With num The order of （ Small ---> Big ）
STU* insert_link(STU *head, STU tmp)
{
	//1、 To the node to be inserted pi  apply   Heap space 
	STU *pi = (STU *)calloc(1,sizeof(STU));
	if(pi == NULL)
	{
		perror("calloc");
		return head;
	}

	//2、 take tmp The content of   Assign a value to  *pi
	*pi = tmp;
	pi->next = NULL;

	//3、 List nodes pi Insertion 
	if(head == NULL)// The list does not exist 
	{
		head = pi;
		return head;
	}
	else// There is 
	{
		//a、 Look for the insertion point 
		STU *pb = head, *pf = head;
		while(pb->num < pi->num && pb->next != NULL)
		{
			pf = pb;
			pb = pb->next;
		}

		//b、 Judgment of insertion point 
		if(pb->num >= pi->num)// Head   Middle insert 
		{
			if(pb == head)// Insert before the head 
			{
				pi->next = head;
				head = pi;
				return head;
			}
			else// Middle insert 
			{
				pf->next = pi;
				pi->next = pb;
				return head;
			}
		}
		else// Tail insertion 
		{
			pb->next = pi;
			return head;
		}
	}
	return head;
}

Knowledge point 2【 The linked list queries a node 】 By name lookup

STU* search_link(STU *head, char *name)
{
	//1、 Determine whether the linked list exists 
	if(head == NULL)// non-existent 
	{
		printf("link not found\n");
		return NULL;
	}
	else// The linked list exists 
	{
		STU *pb = head;

		// One by one name  and  name Compare   If it's not equal  pb=pb->next
		while(strcmp(pb->name,name)!=0 && pb->next != NULL)
			pb = pb->next;

		// Determine if it is found 
		if(strcmp(pb->name,name)==0)// find 
			return pb;
		else// Did not find 
			return NULL;
	}

	return NULL;
}

Knowledge point 3【 Delete the specified node in the linked list 】

STU* detele_link(STU *head,char *name)
{
	//1、 Determine whether the linked list exists 
	if(head == NULL)// non-existent 
	{
		printf("link not found\n");
		return head;
	}
	else// There is 
	{
		//2、 Look for deletion points 
		STU *pf=head, *pb = head;
		while(strcmp(pb->name,name)!=0 && pb->next != NULL)
		{
			pf = pb;
			pb = pb->next;
		}

		//3、 Find the deletion point 
		if(strcmp(pb->name,name)==0)// Find the deletion point 
		{
			//4、 Determine the location of deletion 
			if(pb == head)// Delete header node 
			{
				head = pb->next;
				free(pb);
				
			}
			else// In the middle   or   The tail node 
			{
				pf->next = pb->next;
				free(pb);
			}
			printf(" Successfully deleted %s Related nodes of \n",name);
			return head;
		}
		else// No deletion point found 
		{
			printf(" Not in the linked list %s Relevant data node information \n",name);
		}
	}
	return head;
}

Knowledge point 4【 Release of linked list 】

STU* free_link(STU *head)
{
	// Determine whether the linked list exists 
	if(head == NULL)
	{
		printf("link not found\n");
		return head;
	}
	else// The linked list exists 
	{
		STU *pb = head;

		// Release... Node by node 
		while(pb != NULL)
		{
			//head Save the location of the next node 
			head = pb->next;
			// Release pb Node to 
			free(pb);
			//pb  Point to  head
			pb = head;
		}

		printf(" The linked list has been released \n");
		return head;
	}

	return head;
}

Knowledge point 5【 Take a look back. 】

Insertion of linked list ： Insert before the head Tail insertion To insert in order

1、 For the inserted node pi To apply for space

2、 take tmp The value of is assigned to *pi *pi = tmp

3、 Determine whether the linked list There is

3-1： non-existent head = pi

3-2: There is （ Tail insertion To insert in order ） Look for the insertion point Specific installation location Insert node

Traversal of the list ：

1、 Determine whether the linked list exists

1-1： non-existent Do nothing

1-2： There is Traverse node by node Be careful Don't cross the line .

Query of linked list ：

1、 Determine whether the linked list exists

1-1： non-existent Do nothing

1-2： There is Compare node by node Return to the location successfully Be careful Don't cross the line .

Deletion of linked list nodes ：

1、 Determine whether the linked list exists

1-1： non-existent Do nothing

1-2： There is Compare node by node Delete the specified node Be careful Don't cross the line .

Release list ：

1、 Determine whether the linked list exists

1-1： non-existent Do nothing

1-2： There is Release node by node Be careful Don't cross the line

Knowledge point 6【 The reverse order of the linked list 】

STU* reverse_link(STU *head)
{
	// Determine whether the linked list exists 
	if(head == NULL)
	{
		printf("link not founf\n");
		return head;
	}
	else// The linked list exists 
	{
		//int *p,num;//p by int * , num by int
		STU *pb,*pr;//pb by STU * , pr by STU *

		//pb preservation head->next（ reason head->next I'll set NULL）
		pb = head->next;
		// take head->next Set up NULL   （ reason ： Head node becomes tail node ）
		head->next = NULL;

		while(pb != NULL)
		{
			//pr preservation pb->next  ( reason :pb->next Will point to head)
			pr = pb->next;

			//pb->next  Point to  head （ reason ： reverse direction  ）
			pb->next = head;

			// preservation   Reverse the direction of the code   Can be repeated   perform 
			head = pb;
			pb = pr;
		}

		return head;
	}
	return head;
}

Knowledge point 7【 Sorting of linked lists 】

Sorting by selection ：（ Implemented as an array ）

#include<stdio.h>
int main()
{
	int arr[10]={0};
	int n = sizeof(arr)/sizeof(arr[0]);
	int i=0,j=0,min=0;
	
	printf(" Please enter %d individual int data \n",n);
	for(i=0;i<n;i++)
	{
		scanf("%d",arr+i);
	}
	
	// Sorting by selection 
	for(i=0;i<n-1; i++)
	{
		for(min=i,j=min+1; j<n;j++)
		{
			if(arr[min] > arr[j])
				min = j;
		}
		
		if(min != i)
		{
			int tmp = 0;
			tmp = arr[i];
			arr[i]=arr[min];
			arr[min]=tmp;
		}

	}

	for(i=0;i<n;i++)
	{
		printf("%d ",arr[i]);
	}
	printf("\n");

	return 0;
}

Running results ：

Knowledge point 7【 Sorting of linked lists （ Selection method ）】

void sort_link(STU *head)
{
	//1、 Determine whether the linked list exists 
	if(NULL == head)
	{
		printf("link not found\n");
		return;
	}
	else
	{
		STU *p_i = head;//i=0 
		while(p_i->next != NULL)//i<n-1   The outer loop 
		{
			STU *p_min = p_i;//min = i;
			STU *p_j = p_min->next;//j = min+1
			while(p_j != NULL)//j<n   Inner circulation 
			{
				
				// Looking for members num The minimum   node 
				if(p_min->num > p_j->num)//if(arr[min] > arr[j])
					p_min = p_j;//min = j
				p_j = p_j->next;//j++
			
			}

			if(p_min != p_i)//min != i
			{
				// Exchange only data fields （1、 Overall exchange of node content    2、 Only exchange pointer fields ）
				//1、 Overall exchange of node content ( Data domain exchange 1 Time     Pointer field Exchange 1 Time )
				STU tmp;
				tmp = *p_i;
				*p_i = *p_min;
				*p_min = tmp;

				//2、 Only exchange pointer fields ( Pointer field Exchange 2 Time )
				tmp.next = p_i->next;
				p_i->next = p_min->next;
				p_min->next = tmp.next;
			}


			p_i = p_i->next;//i++
		}
		
	}
	
}

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