Insertion into linked list - c

Question

I wrote a program that inserts nodes into a linked list in descending order.But whenever I test my code with numbers 12,14,13,19,7 in this order.Whenever I entered 7 I took 7 is already in the list.But as easily seen 7 is not in the list before I inserted.After give this error,if I choose print option by typing 2 my program entered in an infinite loop.I can not see my mistake and I am very confused.
#include <stdio.h>
#include <stdlib.h>
struct node {
int content;
struct node* nextLink;
};
typedef struct node NODE;
void print (NODE*);
int insertNode (NODE** head, int x);
int main (void)
{
int num, choice;
NODE* head;
head = NULL;
do {
printf("\nPlease press 1 to insert or press 2 to print or press 0 to exit\n");
scanf("%d", &choice);
switch (choice) {
case 0:
return 0;
break;
case 1:
printf("Enter an integer to insert into the linkedlist: ");
printf("\n");
scanf("%d", &num);
insertNode(&head, num);
break;
case 2:
print(head);
break;
default:
printf("You entered an invalid number\n");
return 0;
break;
}
} while (choice == 1 || choice == 2);
return 0;
}
int insertNode (NODE** head, int i)
{
NODE* newNode;
newNode = (NODE*)malloc(sizeof(NODE));
newNode->content = i;
NODE* temporary = *head;
newNode->nextLink = NULL;
if ((*head == NULL) || ((*head)->content) < i) {
*head = newNode;
(*head)->nextLink = temporary;
}
else {
do {
if (((temporary->content) > i) && ((temporary->nextLink->content) < i)) {
newNode->nextLink = temporary->nextLink;
temporary->nextLink = newNode;
return;
}
else if (temporary->content == i) {
printf("To be inserted value is already in the list\n");
return;
}
temporary = temporary->nextLink;
} while (temporary->nextLink != NULL);
if (temporary->content == i) {
printf("To be inserted value is already in the list\n");
return;
}
temporary->nextLink = newNode;
}
return 0;
}
void print (NODE* head)
{
if (head == NULL) {
printf("\nLinkedList is empty \n");
}
while (head != NULL) {
printf("%d ", head->content);
head = head->nextLink;
}
}

Answer 1

I compiled it and ran it and it seemed to work fine except for one thing. insertNode is defined to return an int, yet 3 of the return statements are void returns. To get it to compile, I changed them to return 0;. If you were able to compile and run it as is, then it could be the stack was getting destroyed by the inconsistent returns.

Answer 2

Your code won't work, if the first two values to be inserted are in descending order. It would give segmentation fault.
For the insertion of 2nd element you need to be careful
So after if condition
else if (temporary->content > i && temporary->nextLink==NULL)
(*head)->nextLink = newNode;

Answer 3

Your code is doing too much. If you code it differently, there are no special cases (such as insert at the top, insert at the tail of the list).
int insertNode (NODE **head, int val)
{
NODE *newnode;
for ( ; *head; head = &(*head)->nextLink) {
if ( (*head)->content == val) {
printf("To be inserted value (%d)is already in the list\n", val);
return 0;
}
if ( (*head)->content > val) break;
}
newnode = malloc(sizeof *newnode); // Maybe check return here ;-)
newnode->content = val;
newnode->nextLink = *head;
*head = newnode;
return 1;
}