Linked List in C (1)

#include<stdio.h>
#include<stdlib.h>

typedef struct _Node
{
    int data;
    struct _Node *next;
}Node;

Node *newList();
Node *insertNode(Node *head, int data);
void printList(Node *head);
Node* insert_at_tail(Node *tail, int data);
void deleteList(Node *head);
int getMax(Node *head);

int getMax(Node *head)
{
    Node *temp = head;
    int maxVal = head->data;
    while(temp != NULL)
    {
        if(maxVal < temp->data)
        {
            maxVal = temp->data;
        }
        temp = temp->next;            
    }
    return retVal;
}

Node *insertNode(Node *head, int data)
{
    Node *newNode = malloc(sizeof(Node));
    if(newNode == NULL)
    {
        printf("newNode is NULL!\n");
        exit(-1);
    }
    Node *temp = head;
    while( temp->next != NULL)
    {
        temp = temp->next;
    }
    newNode->data = data;
    newNode->next = temp->next;
    temp->next = newNode;

    return newNode;
}

/* Make a new list. Create a dummy head node to represent an empty list, and it returns a head of a new empty list*/
Node *newList()
{
    Node *dummyNode = malloc(sizeof(Node));
    if(dummyNode == NULL)
    {
        printf("dummyNode is NULL! \n");
        exit(-1);
    }
    return dummyNode;    
}

/* Insert at tail */
Node *insert_at_tail(Node *tail, int data)
{
    Node *newNode = malloc(sizeof(Node));
    if(newNode == NULL)
    {
        printf("newNode is NULL!\n");
        exit(-1);
    }
    newNode->data = data;
    newNode->next = NULL;
    tail->next = newNode;
    return newNode;            
}

/* Delete an entire list */
void deleteList(Node *head)
{    
    ListNode *temp = head;
    ListNode *delNode;

    while(temp != NULL)
    {    
        delNode = temp;
        temp = temp->next;
        delNode->next = NULL;
        free(delNode);
    }
    free(temp);
}

void printList(Node *head)
{
    Node *temp = head;
    while(temp != NULL)
    {
        printf("%d  \n",temp->data);
        temp = temp->next;        
    }    
}