How to add & delete node in Double Linked List with C Language?

Question

I have 3 struct Node :

struct Student{
    char id[255];
    char name[255];
    float gpa;
};
struct Elemen{
    struct Student *mhs;
    struct Elemen *next;
};
struct List{
    struct Elemen *first;
};

If I add data to the student node, the data that has been added can't be more with the code as below :

int main() 
{ 
    head = (struct List*)malloc(sizeof(struct List));   
    after = (struct List*)malloc(sizeof(struct List));  
    last = (struct List*)malloc(sizeof(struct List));
    
    after->first = (struct Elemen*)malloc(sizeof(struct Elemen));
    head->first = (struct Elemen*)malloc(sizeof(struct Elemen));
    last->first = (struct Elemen*)malloc(sizeof(struct Elemen));
  
    after->first->next = (struct Elemen*)malloc(sizeof(struct Elemen));
    head->first->next = (struct Elemen*)malloc(sizeof(struct Elemen));
    last->first->next = (struct Elemen*)malloc(sizeof(struct Elemen));
  
    after->first->mhs = (struct Student*)malloc(sizeof(struct Student));
    head->first->mhs = (struct Student*)malloc(sizeof(struct Student));
    last->first->mhs = (struct Student*)malloc(sizeof(struct Student));
    
    strcpy(head->first->mhs->id, "1"); 
    strcpy(head->first->mhs->name, "Student 1"); 
    head->first->mhs->gpa = 4;
    head->first->next = after->first;
    
    strcpy(after->first->mhs->id, "2"); 
    strcpy(after->first->mhs->name, "Student 2");
    after->first->mhs->gpa = 5;
    after->first->next = last->first;
    
    strcpy(last->first->mhs->id, "3"); 
    strcpy(last->first->mhs->name, "Student 3");
    last->first->mhs->gpa = 6;
    last->first->next = NULL;
    
    printAllElemen(head);
    return 0; 
}

void printAllElemen(struct List *e){
    printf("ID\t|Name\t|GPA\n");
    while(e->first != NULL)
    {
        printf("%s\t|%s\t|%.2f\n", e->first->mhs->id, e->first->mhs->name, e->first->mhs->gpa);
        e->first = e->first->next;
    }
}

examples of procedures like this :

void addFirst(char id[], char name[], float gpa, struct List *e);
void addAfter(struct Elemen *prev, char id[], char name[], float gpa, struct List *e);
void addLast(char id[], char name[], float gpa, struct List *e);
void deleteFirst(struct List *e);
void deleteAfter(struct Elemen *prev, struct List *e);
void deleteLast(struct List *e);

My problem is how to add data nodes functionally and the data can be more than 1 in the node list?

Thanks

Answer 1

Rewrite code here.

    void addFirst(const char *id, const char *name, float gpa, struct List *e);
        void addAfter(struct Elemen *prev, const char *id, const char *name, float gpa, struct List *e);
        void addLast(const char *id, const char *name, float gpa, struct List *e);
        void deleteFirst(struct List *e);
        void deleteAfter(struct Elemen *prev, struct List *e);
        void deleteLast(struct List *e);
        
        
        void addFirst(const char *id, const char *name, float gpa, struct List *e){
            struct Elemen*newE = (struct Elemen*)malloc(sizeof(struct Elemen));
            newE->mhs = (struct Student*)malloc(sizeof(struct Student));
            strcpy(newE->mhs->id, id);
            strcpy(newE->mhs->name,name);
            newE->mhs->gpa = gpa;
            newE->next = e->first->next;
            e->first = newE;
        }
        void addAfter(struct Elemen *prev, const char *id, const char *name, float gpa, struct List *e){
            struct Elemen*newE = (struct Elemen*)malloc(sizeof(struct Elemen));
            newE->mhs = (struct Student*)malloc(sizeof(struct Student));
            strcpy(newE->mhs->id, id);
            strcpy(newE->mhs->name,name);
            newE->mhs->gpa = gpa;
            newE->next = 0;
            struct Elemen*ptr = e->first;
            if(ptr == 0){ // emptry list
                e->first = newE;
                return;
            }
            while(ptr != prev) ptr = ptr->next;
            newE->next = ptr->next;
            ptr->next = newE;
        }
        
        void addLast(const char *id, const char *name, float gpa, struct List *e){
            struct Elemen*newE = (struct Elemen*)malloc(sizeof(struct Elemen));
            newE->mhs = (struct Student*)malloc(sizeof(struct Student));
            strcpy(newE->mhs->id, id);
            strcpy(newE->mhs->name,name);
            newE->mhs->gpa = gpa;
            newE->next = 0;
            // insert new node
            struct Elemen *ptr = e->first;
            if(ptr == 0){ // there are no nodes in list.
                e->first = newE;
            }else{
                while(ptr->next != 0) ptr = ptr->next; // find last node
                ptr->next = newE;
            }
        }
        void deleteFirst(struct List *e){
            if(e->first == 0) return; // empty list
            struct Elemen*firptr = e->first;
            e->first = e->first->next;
            free(firptr);
        }
        void deleteAfter(struct Elemen *prev, struct List *e){
            struct Elemen*ptr = e->first;
            if(ptr == 0){ // emptry list
                return;
            }
            while((ptr != prev) && ptr->next != 0) ptr = ptr->next;
            
            Elemen*ptr1 = ptr->next;
            ptr->next = ptr->next->next;
            free(ptr1);
        }
        void deleteLast(struct List *e){
            struct Elemen*ptr = e->first;
            struct Elemen*prev = ptr;
            if(ptr == 0){ // emptry list
                return;
            }
            if(ptr->next == 0) {
free(e->first);e->first = 0;return;
} // only first node exists.
            while((ptr->next != 0) { prev = ptr;ptr = ptr->next;}
            free(ptr);
            prev->next = 0;
            
        }
        
        void printAllElemen(struct List *e){
            printf("ID\t|Name\t|GPA\n");
            struct Elemen*ptr = e->first;
            while(ptr != 0)
            {
                printf("%s\t|%s\t|%.2f\n", ptr->mhs->id, ptr->mhs->name, ptr->mhs->gpa);
               ptr = ptr->next;
            }
        }
        
        
        
        
        int main(){
        struct List*mList = (struct List*)malloc(sizeof(struct List));
        mList->first = 0;
        addFirst("1", "stud1", 4, mList);
        addLast("2", "std2", 5, mList);
        addLast("3", "std3", 6, mList);
        printAllElemen(head);
        return 0; 
        }