1. Problem description

         Build a 4 A student's information registration form , Each student's information includes ： Student number , full name , and 3 Results of courses Python,C++,Java）.

         When the program runs, it displays a simple menu , for example ：

        （1）： Information input （INPUT）

        （2）： Total score statistics （COUNT）

        （3）： Total score sorting （SORT）

        （4）： Inquire about (QUERY）

        among ：（1） Yes 4 Input the information of students

                   （2） For each student 3 Statistical total score of courses

                   （3） Yes 4 The total scores of students are sorted in descending order and displayed

                   （4） Query and enter a student number , Display information about the student

        data structure ：

struct student
{
    int num;            // Student number 
    char name[20];      // full name 
    int javascore;      //java achievement 
    int cscore;         //C++ Language 
    int pythonscore;    //python achievement 
    struct student *next;
};

2. Outline design

     This program contains 7 A function , Its function definition and function are ：

  （1）void menu()： Show menu .

  （2）void input(stuNode* list)： Get the student information entered by the user , Create a new node and insert it into the list .

  （3）void count(stuNode* list)： Traverse each data node of the linked list , Calculate the sum of the three grades and assign it to... In the data field of the node count Variable .

  （4）void sort(stuNode* list)： Use the selective sorting method to sort the linked list in descending order according to the total score . Find the node with the highest total score among the unordered nodes , Put it in the position of the first data node , Then continue to find the node with the highest total score from the remaining unordered nodes , Put it at the second data node , So circular , Until all nodes are sorted .

  （5）void query(stuNode* list)： User input student number , Query the student information corresponding to the student number and print it out ; If there is no student number in the linked list , It will prompt that the student does not exist .

  （6）void delete(stuNode* list)： Delete the student information of the specified student number .

  （7）void show(stuNode* list)： Show all student information .

3. Program realization

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct student
{
    int num;// Student number 
    char name[20];// full name 
    int javascore;//java achievement 
    int cscore;//c++ Language 
    int pythonscore;//python achievement 
    int count;// Total score 
    struct student* next;// Point to the next student 
};

typedef struct student stuNode;

//  Information input 
void input(stuNode* list)
{
	//  Request memory space for nodes  
    stuNode* stu = (stuNode*)malloc(sizeof(stuNode));
    //  Application failed 
    if (stu==NULL)
	{
		printf("\n Out of memory , Add failure ！\n\n");
		return ;	
	} 
    printf(" Student number ：");
    scanf("%d",&stu->num);
    printf(" full name ：");
    scanf("%s",stu->name);
    printf("Java achievement ：");
    scanf("%d",&stu->javascore);
    printf("C++ achievement ：");
    scanf("%d",&stu->cscore);
    printf("Python achievement ：");
    scanf("%d",&stu->pythonscore);
     
    //  Insert the new node into the head node  
    stu->next=list->next;
    list->next=stu;
    printf("\n Add success ！\n\n");
}

//  Total score statistics 
void count(stuNode* list)
{
    stuNode* p = list->next;
    if(list==NULL||list->next==NULL)
    {
        printf("\n No student information , Unable to statistics ！\n\n");
        return ;
    }
    //  Traverse the entire list , Calculate the total score of each student  
    while(p!=NULL)
    { 
        int count = p->pythonscore+p->javascore+p->cscore;
        p->count = count;
        p=p->next;
    }
}

//  Total score sorting 
void sort(stuNode* list)
{
    stuNode *p,*q,temp;
    //  If the linked list is empty or has only the head node , It's out of order  
    if(list==NULL||list->next==NULL)
    {
        printf("\n No student information , Unable to sort ！\n\n");
        return ;
    }
    for(p=list->next;p->next!=NULL;p=p->next)
    {
        for (q=p->next;q!=NULL;q=q->next)
        {
            if (q->count>p->count)
            {
            	//  Exchange the values of two nodes  
                temp = *p;
                *p=*q;
                *q=temp;
                temp.next=p->next;
                p->next=q->next;
                q->next=temp.next;
            }
        }
    }
}

//  Inquire about 
void query(stuNode* list)
{
    stuNode *p=list;
    int num;
    if(list==NULL||list->next==NULL)
    {
        printf("\n No student information , Can't query ！\n\n");
        return ;
    }
    printf(" Student number ：");
    scanf("%d",&num);
    p=p->next;
    while(p!=NULL)
    {
        if (p->num == num)
        {
        	printf("\n Student number \t full name \t\tJava\tC++\tPython\t\t Total score \n");
            printf("%d\t%-10s\t%d\t%d\t%d\t\t%d\n\n",p->num,p->name,p->javascore,p->cscore,p->pythonscore,p->count);
            return ;
        }
        p=p->next;
    }
    printf("\n There is no information about the student ！\n\n");
}

//  Delete 
void delete(stuNode* list)
{
    stuNode *p,*q;
    int num;
    if(list==NULL||list->next==NULL)
    {
        printf("\n No student information , Cannot delete ！\n\n");
        return ;
    }
    printf(" Student number ：");
    scanf("%d",&num);
    p=list;
    while(p->next!=NULL)
    {
    	//  If you find it , Let the of the previous node first next Point to the successor node , Then release the current node  
        if (p->next->num == num)
        {
            q=p->next;
            p->next = p->next->next;
            free(q);
            printf("\n Delete successful ！\n\n");
            return ;
        }
        p=p->next;
    }
    printf("\n There is no information about the student , Cannot delete ！\n\n");
}

//  Show all 
void show(stuNode* list)
{
    stuNode* p = list;
    if (list==NULL || list->next==NULL)
    {
        printf("\n No student information ！\n\n");
        return ;
    }
    p=list->next;
    printf(" Student number \t full name \t\tJava\tC++\tPython\t\t Total score \n");
    while(p!=NULL)
    {
        printf("%d\t%-10s\t%d\t%d\t%d\t\t%d\n",p->num,p->name,p->javascore,p->cscore,p->pythonscore,p->count);
        p=p->next;
    }
    printf("\n\n");
}


//  menu 
void menu()
{
    printf("************ Student achievement management system *************\n");
    printf("*           1: Add student information               *\n");
    printf("*           2: Total statistical score                   *\n");
    printf("*           3: In descending order of total score             *\n");
    printf("*           4: Search student information by student number         *\n");
    printf("*           5: Delete student information               *\n");
    printf("*           6: Show all student information           *\n");
    printf("*           0: Exit procedure                   *\n");
    printf("*****************************************\n\n");
}

int main()
{
    int code;//  Option code 
    char over = 'Y';// Continue to add student logo  
    //  Initialize linked list  
    stuNode* list = (stuNode*)malloc(sizeof(stuNode));
    if (list == NULL)
    {
        printf("\n Out of memory , Program error ！\n");
        return -1;
    }
    list->count=0;
    list->next=NULL;

    menu();

    do{
        printf(" Please enter the option code （0-6）：");
        scanf("%d",&code);
        printf("\n"); 
        switch(code)
        {
        	case 0:
                return 0;
            case 1:
                do{
                    input(list);
                    printf(" Continue to add ?(Y or N):");
                    getchar();
                    over=getchar();
                    printf("\n"); 
                }while(over!='N');
                break;
            case 2:
                count(list);
                show(list);
                break;
            case 3:
                sort(list);
                show(list);
                break;
            case 4:
                query(list);
                break;
            case 5:
                delete(list);
                break;
            case 6:
                show(list);
                break;
            default:
                printf("\n Input error , Please re-enter ！\n\n");
                break;
        }
    }while(code!=0);
    return 0;
}

4. Implementation interface