Best way to insert a node into this linked list? - c

Question

So this is my code for the a linked list program. I know it's not that great, but it works. I want to change the ins() function so that new elements are inserted to the list by magnitude.. i.e., the last node on the list will contain the greatest integer, and the smallest the first. The integers are read in from a text file, and as you can see in main(), the INSERT and REMOVE commands in the text file are interpreted as commands to either insert (the following integer on the next line) into the list, or remove an element from the list. How can I do this with my existing code? I tried modifying my ins() function, but was unable to get my list ordered properly.
#include <stdio.h>
#include <stdlib.h>
struct node {
int number;
struct node *next;
};
/* prototypes */
void ins(struct node *llist, int number);
void rem(struct node *llist);
void sho(struct node *llist);
int main(void)
{
int number;
char command[6];
struct node *llist;
struct node *root;
llist = (struct node *)malloc(sizeof(struct node));
llist->number = 0;
llist->next = NULL;
root = llist;
printf("addr: \n\n%p,%p\n\n", &llist, &root);
FILE *file;
file = fopen("a3data.txt", "r");
if (file == NULL)
{
printf("\n----------------------------------------\n");
printf("| Error. Did not read file. Exiting. |\n");
printf("----------------------------------------\n\n");
exit(1);
}
else
{
while ((fscanf(file, "%s", command)) != EOF)
{
if((strcmp(command, "INSERT"))==0)
{
fscanf(file, "%d", &number);
printf("\nINSERT ", number);
ins(llist, number);
sho(llist);
}
else if((strcmp(command, "REMOVE"))==0)
{
printf("\n REMOVE ");
rem(llist);
sho(llist);
}
}
}
printf("\n");
free(llist);
return(0);
}
void ins(struct node *llist, int number)
{
while(llist->next != NULL)
{
llist = llist->next;
}
llist->next = (struct node *)malloc(sizeof(struct node));
llist->next->number = number;
llist->next->next = NULL;
}
void rem(struct node *llist)
{
while(llist->next->next != NULL)
{
llist = llist->next;
}
llist->next = NULL;
}
void sho(struct node *llist)
{
while(llist->next != NULL)
{
printf("%d ", llist->number);
llist = llist->next;
}
printf("%d", llist->number);
}

Answer 1

Modified function in your case
void ins(struct node *llist, int number)
{
struct node *llist1;
while(llist->next != NULL)
{
if (llist->next->number > number)
break;
llist = llist->next;
}
llist1 = (struct node *)malloc(sizeof(struct node));
llist1->number = number;
llist1->next = llist->next;
llist->next = llist1;
}

Answer 2

Your insert is simply adding the element in the tail. You have to write code to compare the present value of node(list->number) against the number to be inserted. If the current value is greater than the number to be inserted, then the number has to be inserted before the current node. For this, you will have to keep previous pointer also. The code, I have written, is just to understand the logic, Didn't check for correctness.
if(llist->number > innumber) {
node *newNode = (struct node *)malloc(sizeof(struct node);
newNode->number = innumber;
prevPointer->next = newNode;
newNode->next = llist;
}

Answer 3

in ins() function, instead of
while(llist->next != NULL)
use
while((llist->next != NULL) && (llist->number < number))
This will help you to sort while inserting itself.
Also in rem() function, you have to free the memory that you dynamically allocate.