Segfault and logic errors - c

Question

I am making a linked list program which utilizes several functions to simplify adding or removing nodes from the list. I believe that my logic is alright with allocating and adding a new node but I am still getting a seg fault. Could you look over my logic and explain what is causing the seg fault? I am very inexperienced with linked lists. Thank you!
This is my function declarations
#define SIMPLELL_H
#include<stdio.h>
#include<stdlib.h>
typedef struct Node
{
int data;
struct Node *next;
}node_t;
node_t* head;
void printList();
void append(int num);
void addFront(int num);
void deleteList();
void removeNode(int num);
int length();
#endif
This is the function definitions
void printList(){
// declare temp to traverse the LL and print each value
node_t *temporary = head;
while(temporary != NULL){
printf("%d, ", temporary->data);
temporary = temporary->next;
}
if (head == NULL){
printf("This list is empty.\n");
}
}
void append(int num){
//declare temporary pointer to traverse LL
node_t *tmp = head;
node_t *prev = NULL;
//malloc the new node
node_t *new = malloc(sizeof(node_t));
if(head == NULL){
//initialize the new node
new->data = num;
new->next = NULL;
head->next = new;
}
else{
//initialize the new node
new->data = num;
new->next = NULL;
//loop to traverse to the last value in the node
while(tmp != NULL){
prev = tmp;
tmp = tmp->next;
}
prev->next = new;
}
}
void addFront(int num){
//allocate memory for new node and allocate local variable equal to head
node_t *new = malloc(sizeof(node_t));
new->data = num;
new->next = head;
head = new;
}
void deleteList(){
node_t *tmp = head;
node_t *prev = NULL;
while(tmp != NULL){
prev = tmp;
tmp = tmp->next
free(prev);
}
}
void removeNode(int num){
//temp is used to traverse the ll until I find the node with the value
//then the previous value is linked to the next value removing the middle value.
node_t *temp = head;
node_t *prev = NULL;
if(head == NULL){
printf("List is not initialized\n");
return;
}
while(temp->data != num){
prev = temp;
temp = temp->next;
if (temp->data == num){
prev->next = temp->next;
free(prev);
}
else{
printf("Value is not in the list\n");
return;
}
}
int length(){
int length = 0;
node_t *temp = head;
while (temp != NULL){
length += 1;
temp = temp->next;
}
return length;
}
This is the driver function which I should not have to change
#include "SimpleLL.h"
#include "SimpleLL.c"
int main()
{
/*head is a global variable*/
head = NULL;
int size =0;
removeNode(1);
append(2);
append(3);
addFront(1);
append(4);
printList();
size = length();
printf("size now %d\n",size);
removeNode(8);
printList();
removeNode(1);
printList();
removeNode(4);
printList();
deleteList();
printList();
size = length();
printf("size after deletion %d\n",size);
return 0;
}

Answer 1

removeNode contains no test for reaching the end of the list. So if the value is not found in the list, it will dereference the NULL pointer at the end and crash.
This will be the case in the very first test, which attempts to remove a node when the list is empty, as well as for removeNode(8).
Your removeNode function also needs to free() the node it removed. Currently it is freeing the node that came after the one removed, which is still in the list and will cause undefined behavior when you access it later.