Linked List - Error

Good day!

Our teacher asked us to make a student list using a linked list. His condition is to add new student info into a list in a way that it will be sorted according to the grades of the student in descending order. An error occurs every time i run the program. My code is as follows. Am i on the right path or am i missing something important? What causes the error? Your reply would be highly appreciated. Thank you in advance.

typedef struct student{
       char name[11];
       unsigned int grade;
       str开发者_如何学运维uct student* next;       
    }NODE;

int main (void){
    NODE *head, *std;
    std = new_student();
}

I think the bug is probably that you don't initialize head to NULL in main before passing it to add_student, but there are some other issues:

• gets can overrun the buffer if you enter too many characters of input for the name.
• as yurib says, the loop in add_student always returns on the first attempt
• you don't check the return from malloc, but that's not going to be the problem.
• you haven't forward-declared the functions you call.
• you haven't included <stdlib.h> (for malloc) or <stdio.h> (for printf).

The return in the while loop looks very suspicious, since that means the code after the loop can never be reached.

Also, dangerous to use plain gets() into a 11-char array; very easy to get overflow. Use fgets().

NODE *head, *std;
head = null;
std = null    
std = new_student();
head = add_student(head, std);   

Try that. You dont initialize head, and when

if (head == NULL) return to_add;

on add_student, head containts garbage value.

Edit1: Also keep in mind

NODE *curr_std, *prev_std = NULL;

is NOT equivalent to

NODE * curr_std = NULL;
NODE * prev_std = NULL:

if thats what you wanted to write then you should:

NODE *curr_std = NULL, *prev_std = NULL;

but the way you did it does not affect your program.

Edit2:

while (curr_std != NULL && to_add->grade < curr_std->grade){
    prev_std = curr_std;
    curr_std = curr_std->next;
}
prev_std->next = to_add;
to_add->next = curr_std;
return head;

is a bit weird. That return head; shouldn't really be there. You don't "refresh" your LL that way.

First error everyone makes, forgot to init vars:

NODE *head=NULL, *std=NULL;

The compiler should tell you about some errors before we do. This is the important warning gcc gave me:

1209.c:18:10: warning: 'head' is used uninitialized in this function