Segmentation fault while doing malloc for a struct pointer - c

Question

I trying to write basic Linked list code. I have two functions to add data to beginning of list and end of the list. Function to add data in the beginning works fine every time.
I am facing segmentation fault in insert_end function always.
I am getting the error while trying to access temp1 pointer to structure after doing malloc to it. But this is the same exact thing I am doing even in the insert_first function, but works every time. I tried googling it and tried in forums, no answer. Please help.
This link is my exact kinda problem.. but i dont understand the solution fully
Segmentation fault in C with malloc
I am getting error particularly on this block
struct node *temp1,*trav;
temp1 = (struct node *)malloc(sizeof(struct node));
trav = (struct node *)malloc(sizeof(struct node));
if (temp1 != NULL) { //******************Segmentation fault at this line**********
temp1->data = input;
}
#include<stdio.h>
#include<stdlib.h>
//*******Structure to hold linked list*********//
struct node {
int data;
struct node *next;
}*head,*temp;
//***********Function to Display everything**********//
void display(struct node *head) {
struct node *trav;
trav= (struct node *)malloc(sizeof(struct node));
printf("Entering into Display\n");
if (head == NULL) {
printf("Oh My God, the list is empty\n");
}
else {
trav = head;
while (trav != NULL) {
printf("Value stored in [%p] is [%d]\n",trav,trav->data);
trav = trav->next;
}
}
}
//***********Function to Insert at beginning*********//
struct node *insert_first(struct node *head,int input) {
temp = (struct node *)malloc(sizeof(struct node));
temp->data = input;
printf("\nEntering insert first");
if (head == NULL) {
head = temp;
head->next = NULL;
}
else {
temp->next = head;
head = temp;
}
return head;
}
//**************Function to Insert at End******************//
struct node *insert_last(struct node *head,int input) {
struct node *temp1,*trav;
temp1 = (struct node *)malloc(sizeof(struct node));
trav = (struct node *)malloc(sizeof(struct node));
if (temp1 != NULL) {
temp1->data = input;
}
else {
printf("empty");
}
printf("\nEntering insert last");
if (head == NULL) {
head = temp1;
head->next = NULL;
}
else {
trav = head;
while (trav != NULL) {
trav = trav->next;
}
trav->next = temp1;
}
return head;
}
//*************Main Fucntion***********//
int main() {
int choice,value;
head = NULL;
while(1) {
printf("\n******Please Enter your choice****\n1. To insert at beginning\n2. To insert at End\n3. To Insert middle\n4. To delete\n5. To display\n0. To Exit\n");
scanf("%d",&choice);
switch(choice){
case 1:
printf("Please Enter the value to be added\n");
scanf("%d",&value);
head = insert_first(head,value);
break;
case 2:
printf("Please Enter the value to be added\n");
scanf("%d",&value);
head = insert_last(head,value);
break;
case 5:
display(head);
break;
case 0:
return 0;
default:
printf("Thats a wrong choice\n");
break;
}
}
}

Answer 1

This is the problematic block.
else {
trav = head;
while (trav != NULL) {
trav = trav->next;
}
trav->next = temp1;
When you come out of the while loop trav is NULL. That makes the line
trav->next = temp1;
fail with segmentation violation.
Change that block to:
else {
trav = head;
while (trav->next != NULL) {
trav = trav->next;
}
trav->next = temp1;