Pointers and Linked List in C
c, pointers, singly-linked-list
Solution
In your `pop` function you want to modify your `head` variable. Since C is passing parameters per value, you must give the address of `head` variable in order to modify its value. The same thing applies for `tail`.
Thus change your pop function from:
int pop(struct pointer *head, struct pointer *tail)
to:
int pop(struct pointer **head, struct pointer **tail)
And when calling this function, use `pop(&head, &tail);`
Problem
I starting study pointers and linked list in C but i have a problem: ``` struct pointer { int id; struct pointer *next; }; int pop(struct pointer *head, struct pointer *tail); main() { struct pointer *head = NULL; head = (struct pointer*)malloc(sizeof(struct pointer)); head->id=1; struct pointer *tail = head; tail->next=NULL; pop(head,tail); if (head==NULL) printf ("In main, head is NULL"); else printf ("In main, head is NOT NULL"); } int pop(struct pointer *head, struct pointer *tail) { int toReturn; struct pointer *toFree; if (head!=NULL) { toReturn = head->id; toFree = head; head = head->next; free(toFree); if (head==NULL) tail = head; } else toReturn = -1; if (head==NULL) printf ("In function, head is NULL\n"); else printf ("In function, head is NOT NULL\n"); return toReturn; } ``` why is the output: ``` In function, head is NULL In main, head is NOT NULL ``` I expect this: In function, head is NULL In main, head is NULL This is my first experience with pointers in C and can't understand what i wrong