CODEWITHSUNDEEP
cfunctionstructlinked-listparameter-passing
evangelia
evangelia

Reputation: 53

Linked Lists and Structures in C - Passing Linked List and Structures as Parameters in function (C)

I have the following code and I am trying to make it more dynamic and reusable. Well, I have a struct named Student and struct list, which contains all the added students. I have a function "int addStudent(Student b, list StudentList){", and I am trying to pass the structs Student and StudentList as parameters. But the problem is that I am doing something wrong and my list does not contains all the Students added. It contains only the last one. Can you help me?

NOTE: I have to create a body for the "int addStudent(Student b, list StudentList)". It is not permitted to change the declaration of this function ... this is very difficult for me and I need suggestions to work on ...

thank you in advance!

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

#define MAXSTRING 100
#define MAXLessonS 100

typedef  enum genders{
    female, 
    male
} genders;

typedef struct Student
{
    char name[MAXSTRING];
    char Surname[MAXSTRING];
    enum genders gender;
    int id;
    char Lessons[MAXLessonS][MAXSTRING];
} Student;


typedef struct list 
{
    struct list * next;
    struct Student * Student;
} list;

void printlist(list * StudentList) 
{
    list * current = StudentList;
    while (current != NULL) {
        printf("Student ID      = %d\n", current->Student->id);
        printf("Student name    = %s\n", current->Student->name);
        printf("Student Surname = %s\n", current->Student->Surname);
        printf("Student gender  = %d\n", current->Student->gender);
        printf("Student Lesson  = %s\n", current->Student->Lessons);     
        current = current->next;
    }
}


int main()
{
    Student b={"name 1","Surname 1",male,22,{"Lesson 1"}};  
    Student c={"name 2","Surname 2",female,32,{"Lesson 2"}};  

    list* StudentList = NULL;
    StudentList = malloc(sizeof(list));
    StudentList->next = NULL;
    //StudentList->next->next = NULL;

    int x=addStudent(b,StudentList);
    StudentList->next=NULL;
    int xx=addStudent(c,StudentList);

    printlist(StudentList);
    return 0;
}

int addStudent(Student b, list StudentList){
    //StudentList=malloc(sizeof(list));
    StudentList.Student = &b;
    //StudentList.next->next=NULL; 
    //free(StudentList);
    return 1;
}

Upvotes: 0

Views: 1573

Answers (3)

el furetto
el furetto

Reputation: 13

Use a while to go to the last element with a pointer, then create your new element in your list void addStudent(Student *b, list *StudentList) list *elem; elem = StudentList; while (elem->next) elem = elem->next; //now you can create your elem elem->next = malloc(sizeof(list)); elem->next->student = b; elem->next->next = NULL;

Upvotes: 1

4386427
4386427

Reputation: 44274

You have two problems:

1) You add the address of a local variable to the list

2) You never expand the list, i.e. it always contain a single element

To solve problem 1) change the addStudent function like:

int addStudent(Student* b, list* StudentList){
                     ^^^     ^^^
                   Use a pointer

    StudentList->Student = b;
                         ^^^
                       Save the pointer

    return 1;
}

and call it like:

int x=addStudent(&b, StudentList);
                 ^^

To solve problem 2):

You need to malloc a new list item and insert it into the current list.

However, your current code is a bit strange as you also allocate a list in main but puts nothing into it. Instead it would seem better to only allocate list items in the addStudent function.

A simple way to do that is:

// This function inserts new item in the front of the list
list*  addStudent(Student* b, list* StudentList){
    list* t;
    t = malloc(sizeof(list));
    if (!t) exit(1);
    t->next = StudentList;
    t->Student = b;
    return t;
}

int main()
{
    Student b={"name 1","Surname 1",male,22,{"Lesson 1"}};  
    Student c={"name 2","Surname 2",female,32,{"Lesson 2"}};  

    list* StudentList = NULL;

    StudentList = addStudent(&b, StudentList);
    StudentList = addStudent(&c, StudentList);

    printlist(StudentList);
    return 0;
}

Upvotes: 1

matt.robinson17
matt.robinson17

Reputation: 39

The addStudent method always overwrites previous nodes. So your list only ever contains 1 node. Also, to "store" a linked list, you would want to keep a pointer to the head (first element) of the list.

Upvotes: 1

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