c - Need Help Understanding Segmentation Faults -

i segfaults , causes them, question why pointer causing them? i'm trying write simple linked list adds on nodes containing 5 , segfault @ temp->x = 5;. thought malloc() should have allowed me access memory needs?

#include <stdio.h> #include <stdlib.h>  struct node{   int x;   struct node *next; };   void append(struct node *root){     struct node *temp, *right;    temp = (struct node *)malloc(sizeof(struct node));    temp->x = 5;    right = (struct node *)root;     while(right->next != null){        right = right->next;    }     right->next = temp;    right = temp; }  int main(){     struct node *root;     root = null;      int userinput;     printf("pick operation: ");    scanf("%d", &userinput);     if(userinput == 1){        append(root);    }   } 

your mistake here:

while(right->next != null){    right = right->next; } 

you trying check "right->next" "right" null.