Linked List Assistance [closed] - c

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I'm working on a linked list in C with insert and print functions. However, I am getting a segmentation fault from the insert, and when I try to fix this I end up with one from the print function. Any help would be greatly appreciated.
typedef struct node
{
struct node *next;
double value;
} NodeT, *NodeTP;
int listSize = 0;
int insert(NodeT *firstEle, int value)
{
NodeTP temp;
if((temp = (NodeTP)malloc(sizeof(NodeT))) == NULL)
{
return 0;
}
// first node in the list.
if(listSize == 0)
{
firstEle->value = value;
firstEle->next = NULL;
}
// finds the end node and adds the new node to the list.
else
{
while(temp != NULL)
{
temp = temp->next;
}
temp->value = value;
temp->next = firstEle;
firstEle = temp;
}
listSize++;
return 1;
}
int print(NodeT List)
{
printf("Element: %.2f\n", List.value);
return 1;
}
int main(int argc, char* argv[])
{
// creates the list.
NodeTP list;
if((list = (NodeTP)malloc(sizeof(NodeT))) == NULL)
{
return 0;
}
list = NULL;
insert(list, 5);
print(list[0]);
insert(list, 15);
print(list[1]);
return EXIT_SUCCESS;
}

Answer 1

Print Issue
When it comes to the print statements, you are using an invalid syntax. You created a single pointer and allocated enough memory for that pointer and what it points to. You did not create an array of NodeT elements. As such, the list[x] will not work.
You will need to generate a function that will locate the 'x' element in the list you are making. You could include that in the print function you write. Just change it up to take the int of the element you want:
int print(NodeT head, int element) {}
Don't forget to check your bounds in case the element asked for is outside of your current range.
All you really need to do then is step through the elements to the desired one.
Insert Issue
In your if/else statement, why are you trying to iterate through 'temp'? 'temp' was created in this function and should have no other elements attached to it. You should be iterating through 'firstEle'. You also don't want to set firstEle = temp; as that will over write what was there before and you are now pointing to something else.
One way to simplify this code is to use a head and tail. The head never changes but the tail moves as elements get added. You can have 'insert' return the tail and when you insert a new element, just provide the tail and the new element will be added there, no iteration needed.
Memory Issue
While this will not be major for this program, I would adjust where I malloc my new node till after I have insured that it isn't the first element. Else, you have a block allocated that is never used. Or, if this is the first element to be added, free the block.
And Fred makes a good point. That will cause issues.

Answer 2

Multiple issues (the list is far from complete):
You're missing the include files for malloc() and printf().
You allocate memory in main(), but don't use it.
If you want to modify the list head in insert(), you have to pass a pointer to it.
You check if the memory allocation in insert() succeeds, but don't handle the case that it doesn't - so you can as well just get rid of it.
As you ignore the return values of both insert() and print() you could as well change their return types to void.
While searching for the last element of the list, you overwrite the pointer (temp) to the memory you just allocated.
When you think you've found the last element, you actually make the new element's next point to it and set the first element to point to the new element, which would make it effectively the first and not the last element (if all the other stuff would work...).
You're trying to use array style access with [] for the list. You have to use pointers.
This is a version where I fixed at least the most basic errors in order to make it compile and at least work. It's still far from perfect (or even acceptable), but I tried change as little as possible to make it easier for you to spot the differences and learn what you did wrong and further improve it from there.
#include <stdlib.h>
#include <stdio.h>
typedef struct node
{
struct node *next;
double value;
} NodeT, *NodeTP;
int listSize = 0;
int insert(NodeT **firstEle, int value)
{
NodeTP temp, lastEle;
temp = (NodeTP)malloc(sizeof(NodeT));
// first node in the list.
if(listSize == 0)
{
temp->value = value;
temp->next = NULL;
*firstEle = temp;
}
// finds the end node and adds the new node to the list.
else
{
for (lastEle = *firstEle;lastEle->next != NULL;lastEle = lastEle->next);
temp->value = value;
temp->next = NULL;
lastEle->next = temp;
}
listSize++;
return 1;
}
int print(NodeT List)
{
printf("Element: %.2f\n", List.value);
return 1;
}
int main(int argc, char* argv[])
{
// creates the list.
NodeTP list;
list = NULL;
insert(&list, 5);
print(*list);
insert(&list, 15);
print(*list->next);
return EXIT_SUCCESS;
}