#include <stdio.h>
#include <stdlib.h>
#define N 10

typedef struct music_student *StudentPtr;
typedef struct music_student
{
    int student_ID;
    double hw_average;
    int exam_grade;
    int final_grade;
    StudentPtr next;
} Music_student;
StudentPtr creatnew(int id,double hw,int exam);
StudentPtr Del(int id,StudentPtr list);
StudentPtr insert(int id,double hw,int exam,StudentPtr list);
void Proportion(float prop,StudentPtr list);
int main()
{
    int req,id,exam;
    double avg;
    float prop;
    StudentPtr list=NULL;
    printf("Course Management Menu\nPlease choose among the following:\n");
    printf("***\n");
    printf("0: Quit.\n1: Insert student at first place on the list.\n2: Delete by ID.\n3: Find lucky student.\n4: Change homework exam ratio.\n5: Print List.\n");
    while (N<15)
    {
        if(scanf("%d",&req)!=1)
        {
            printf("Input Error!");
            return 1;
        }
        while(req>6||req<0)
        {
            printf("Invalid Selection\n");
            if(scanf("%d",&req)!=1)
            {
                printf("Input Error!");
                return 1;
            }
        }
        switch (req)
        {
        case 1:
            printf("insert student ID\n");
            scanf("%d",&id);
            while(id<10000||id>99999)
            {
                printf("Invalid student id try_again: value between 10,000 and 99,999\n");
                scanf("%d",&id);
            }
            printf("insert hw grade\n");
            scanf("%lf",&avg);
            while(avg>100||avg<0)
            {
                printf("Invalid hw grade: value between 0 and 100\n");
                scanf("%lf",&avg);
            }
            printf("insert exam grade\n");
            scanf("%d",&exam);
            while(exam>100||exam<0)
            {
                printf("Invalid exam grade: value between 0 and 100\n");
                scanf("%d",&exam);
            }
            list=insert(id,avg,exam,list);
            break;
        case 2:
            printf("Enter student to expunge from records:\n");
            scanf("%d",&id);
            Del(id,list);
            break;
        case 3:
            Lucky(list);
            break;
case 5:
            lilPrint(list);
            break;
        case 0:
            printf ("bye bye!");
            return 0;
        }
    }
}
void lilPrint(StudentPtr list)
{
    StudentPtr temp = list;
    if(list==NULL)
        return;
    while (temp != NULL)
    {
        printf("Student Id: %d\nFinal Grade: %d\n",temp->student_ID,temp->final_grade);
        temp = temp->next;
    }
    return;
}
StudentPtr Del(int id, StudentPtr list)
{
    StudentPtr curr = list, prev = NULL;
    if(curr->student_ID==id)
    {
        list=list->next;
        free(curr);
        curr=list;
    }
    while (curr != NULL)
    {
        if (curr->student_ID == id)
            {
            if (prev == NULL)
                {
                list = curr->next;
                }
            else
            {
                prev->next = curr->next;
            }
            free(curr);
            return list;
            }
        prev = curr;
        curr = curr->next;
    }
    return list;
}
StudentPtr insert(int id,double hw,int exam,StudentPtr list)
{
    StudentPtr cell=creatnew(id,hw,exam);
    if(cell==NULL)
    {
        free(list);
        exit(1);
    }
    cell->next=list;
    list=cell;
    return list;
}
StudentPtr creatnew(int id,double hw,int exam)
{
    StudentPtr cell=(StudentPtr)malloc(sizeof(Music_student));
    if(cell == NULL)
    {
        printf("Allocation failed!");
        return NULL;
    }
    cell->exam_grade=exam;
    cell->student_ID=id;
    cell->hw_average=hw;
    cell->final_grade=(my_round(0.7*cell->exam_grade) my_round(cell->hw_average*0.3));
    cell->next=NULL;
    return cell;
}

im trying to enter 4 or 5 nodes in it and the use lilprint to print some info about the linked list. when i enter some nodes and then delete the firstnode(only delting the first one does this problem) the program doesnt delete it fully so it only delets the student_id in that node and returns the rest. so when i print it it prints normally but the student_id is trash value .

CodePudding user response：

This definition and using of N with the magic number 10 along with another magic number 15

#define N 10
//...

while (N<15)
//... 

makes your code unclear.

Also this typedef declaration for a pointer

typedef struct music_student *StudentPtr;

is a bad idea. For example if you will write const StudentPtr then it will be equivalent to struct music_student * const instead of const struct music_student * and the last type specification should be used in the function lilPrint because within the function the list is not changed.

void lilPrint( const struct music_student *list);

And by the way you forgot to place the function declaration before main.

In the function insert this statement

free(list);

does not make sense because it does not free all the allocated memory.

The function Del can invoke undefined when the list is empty due to using a null pointer accessing memory as for example in this statement

if(curr->student_ID==id)

Also it seems the list should store nodes with unique student_ID but the function Del is designed such a way that it deletes at most two nodes with the same student_ID due to the following while loop after the first if statement

if(curr->student_ID==id)
{
    list=list->next;
    free(curr);
    curr=list;
}
while (curr != NULL)
{
    if (curr->student_ID == id)
        {
        if (prev == NULL)
            {
            list = curr->next;
            }
        else
        {
            prev->next = curr->next;
        }
        free(curr);
        return list;
        }
        //...

That is the function should delete either all nodes with the same student_ID or only one node with the given id.

And in main you forgot to assign the returned pointer to the pointer list

Del(id,list);

Instead you need to write

list = Del(id,list);