Adding node to singly linked list not working properly - c

Question

I have a singly linked list struct and a local Node declared in main with my addToList() function, but every time addToList() executes it runs the case (head == NULL). Even when I already added values to the list. I am sure there is a small bug in my code, I just can't find it.
typedef struct node{
char* name;
int groupSize;
int status;
struct node* next;
}Node;
void addToList(char* name, Node* head, int groupSize, int status){
if(head == NULL){
head =(Node*)malloc(sizeof(Node));
head->name = (char*) malloc(sizeof(char)*30);
strcpy(head->name, name);
head->groupSize = groupSize;
head->status = status;
head->next = NULL;
printf("Name is %s\n\n", head->name);
}
else {
printf("entered else\n");
Node *tmp = head;
if(tmp->next!=NULL){
tmp = tmp->next;
}
tmp->next = (Node*) malloc(sizeof(Node));
tmp->next->name = (char*) malloc(sizeof(char)*30);
strcpy(tmp->next->name, name);
tmp->next->groupSize = groupSize;
tmp->next->status = status;
tmp->next->next = NULL;
}
}
int main(){
Node* head = NULL;
//TESTNG SECTION
addToList("Julio", head, 5, 7);
addToList("Francisco", head, 5, 7);
addToList("Jorge", head, 5, 7);
}

Answer 1

The cause of your problem is the call by value of every C function call.
At the first call of addToList(), head of the main() points to NULL.
Inside the addToList() you change the parameter head to point to a newly allocated memory region. Unfortunately, by the time addToList() returns the scope of the parameter head does not exist any more. So the head variable at the main, has exactly the same value prior the addToList() call.
The solution to this problem would be the use of double pointer for the head, or return and assign at every call the head of the list. So because previous answer covered the one solution, I will provide the other.
Node* addToList(char* name, Node* head, int groupSize, int status){
if(head == NULL){
head =(Node*)malloc(sizeof(Node));
head->name = (char*) malloc(sizeof(char)*30);
strcpy(head->name, name);
head->groupSize = groupSize;
head->status = status;
head->next = NULL;
printf("Name is %s\n\n", head->name);
}
else {
printf("entered else\n");
Node *tmp = head;
if(tmp->next!=NULL){
tmp = tmp->next;
}
tmp->next = (Node*) malloc(sizeof(Node));
tmp->next->name = (char*) malloc(sizeof(char)*30);
strcpy(tmp->next->name, name);
tmp->next->groupSize = groupSize;
tmp->next->status = status;
tmp->next->next = NULL;
}
return head;
}
int main(){
Node* head = NULL;
//TESTNG SECTION
head = addToList("Julio", head, 5, 7);
head = addToList("Francisco", head, 5, 7);
head = addToList("Jorge", head, 5, 7);
}

Answer 2

The head parameter will be initialized inside the function, you have to pass a pointer to a Node pointer :
void addToList(char* name, Node** head, int groupSize, int status);
Then :
*head =(Node*)malloc(sizeof(Node));
Explanations by Manos.

Answer 3

There are a few small problems that I see with your code.
First, I would use different names when passing in the head pointer. It might be confusing the compiler on where to look. Also, when you pass in a node pointer in addToList, you need to dereference it, so instead pass in Node**, and initialize a pointer within the method.
Second, in your addToList method, you have the following condition:
if(tmp->next!=NULL){
tmp = tmp->next;
}
this will only work when you have 2 elements in your list. Instead, make it a while loop, like so:
while(tmp->next!=NULL){
tmp = tmp->next;
}
This will correctly place the tmp pointer at the end of your list.
Hopefully this will fix some bugs,