Phone book Linked list - c

Question

I have a problem with linked list when I add the contacts to the list and print it out it prints out the first list twice rather than the first and the second list. Please let me know what I am doing wrong.
Thanks.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#define true 1
#define false 0
typedef int boolean;
typedef int Position;
typedef int Count;
typedef struct node_def {
int area_code;
char name[30];
char phone_number[8];
struct mode_def *next;
} Node;
typedef struct {
Position currentPos;
Count nodeCount;
Node *head;
Node *current;
Node *tail;
} ListADT;
void initList(ListADT*);
boolean checkEmpty(ListADT*);
void addList(ListADT*, int, char*, char*);
void printList(ListADT*);
int main(void) {
ListADT phoneList;
initList(&phoneList);
Node *firstNode;
addList(&phoneList, 416, "Sam", "1234567");
addList(&phoneList, 416, "Bob", "7654321");
firstNode-> next;
printList(&phoneList);
printList(&phoneList);
return 0;
}
void initList(ListADT* list){
list->currentPos = -1;
list->nodeCount = 0;
list->head = NULL;
list->tail = NULL;
}
boolean checkEmpty(ListADT* list){
return list->nodeCount == 0 ? true : false;
}
void addList(ListADT* list, int areaCode, char* name, char* phoneNum){
Node* newNode = malloc(sizeof(Node));
assert(newNode);
newNode->area_code = areaCode;
strcpy(newNode->name, name);
strcpy(newNode->phone_number, phoneNum);
newNode->next = NULL;
if(list->nodeCount == 0) {
list->head = newNode;
list->tail = newNode;
list->currentPos = 0;
list->nodeCount = 1;
}
else {
list->tail = newNode;
list->current = list->tail;
list->nodeCount++;
list->currentPos = list->nodeCount -1;
}
}
void printList(ListADT* list){
if(!checkEmpty(list)){
Node* newNode = list->head;
printf("The name is %s\n",newNode->name);
printf("The phone number is %i-%s\n",newNode->area_code,newNode->phone_number);
}else
printf("The list is empty.\n");
}

Answer 1

Mean no harm, but based on your question concerning the current code, I suppose you have to get some more experience in programming, particularly in programming in C++, before writing your own abstract data types.
There are a lot of things done only to the half, and actually you are asking "why does my function, which does nothing else than printing out exactly the first element, print the same element twice if I call this function twice.".
Anyway, some hints:
Typo in struct mode_def *next, should be struct node_def *next.
Make sure that next is actually set somewhere, e.g. else {
list->tail->next = newNode; otherwise you won't get a linked list but unlinked nodes
When printing, traverse the nodes through next, i.e something like while(node!=NULL) { ...; node=node->next; }
firstNode-> next; does simply nothing