c++ Linked list inserts a false node at start - c++

Question

I've been writing a program using a linked list, but for some reason my program is making a false node at the start of the program that is messing with everything else
this file controls the functions in the header file
Node *createNode() {
Node *newNode = new Node;
cout << "Enter in Students last Name" << endl;
cin >> newNode->lastName;
cout << "Enter in Students first Name" << endl;
cin >> newNode->firstName;
cout << "Enter in Students id" << endl;
cin >> newNode->idNumber;
return newNode;
}
Node *insertNode(Node *ptr) {
Node *newNode = createNode();
if( ptr == NULL ) {
ptr = newNode;
} else if ( ptr->idNumber > newNode->idNumber ) {
newNode->next = ptr;
ptr = newNode;
} else {
Node *temp = ptr;
while( temp->next != NULL &&
temp->next->idNumber < newNode->idNumber )
temp = temp->next;
if( temp->next == NULL ) {
temp->next = newNode;
} else {
newNode->next = temp->next;
temp->next = newNode;
}
}
return ptr;
}
Node *searchNode(Node *ptr, int id) {
Node *temp;
Node *found;
bool isfound = false;
temp = ptr;
if(temp == NULL) {
cout << "There are no students in the list" << endl;
isfound = true;
}
while( isfound != true && temp->next != NULL ) {
if( temp->idNumber == id ) {
found = temp;
isfound = true;
cout << found->lastName << ", " << found->firstName
<< ": " << found->idNumber << endl;
} else {
temp = temp->next;
}
}
return found;
}
void printList( Node *ptr ){
Node *temp = ptr;
while( temp != NULL ) {
cout << temp->lastName << ", "
<< temp->firstName<< ": "
<< temp->idNumber << endl;
temp = temp->next;
}
}
and this is the main file where the program is executed
int main() {
Node *list = new Node();
displayList(list);
return 0;
}
void displayList( Node *node ) {
int option = -1;
cout << node->idNumber << endl;
while( option != 5 ) {
cout << endl;
cout << "What do you want to do?" << endl;
cout << "1: Add a student" << endl;
cout << "2: Search for student" << endl;
cout << "3: Delete Student" << endl;
cout << "4: Print Student List" << endl;
cout << "5: Exit" << endl;
cout << "Enter a number for the choice: ";
cin >> option;
if( cin.fail() || option > 5 || option < 0 ) {
cin.clear();
cin.ignore();
option = -1;
}
switch( option ) {
case 1:{
insertNode(node);
}
break;
case 2:{
if(node != NULL){
cout<<"Enter the id you want to find: ";
int sid;
cin >> sid;
searchNode(node, sid);
} else {
cout<<"No Ids in the list"<<endl;
}
}
break;
case 4: printList(node);
break;
case 5: cout<<"GoodBye."<<endl ;
break;
default: cout<<"you have entered a invalid character"<<endl;
}
}
}
this is what is being created before a new node is even created
What do you want to do?
1: Add a student
2: Search for student
3: Delete Student
4: Print Student List
5: Exit
Enter a number for the choice: 4
, : 0

Answer 1

Node *list = new Node(); since you created a new Node in main and passing a valid Node address to displayList( Node *node ); and then to printList( Node *ptr ), its printing the zero initialized Node data.
You can change Node *list = new Node(); to Node *list = NULL in main()
Remove cout << node->idNumber << endl; in displayList( Node *node ); otherwise you will be getting segmentation fault or null dereferencing.
In Node *createNode(), add newNode->next = 0; you must set the next pointer of newly created Node to NULL.
In Node *searchNode(Node *ptr, int id) change while( isfound != true && temp->next != NULL ) into while( isfound != true && temp != NULL ), otherwise it will not search the last node.
Store the return value of insertNode(node) to node in displayList( Node *node ); as node = insertNode(node) otherwise you are loosing the newly added node for both the if and else if cases of insertNode