C program not recognizing null pointer - c

Question

I'm trying to recurvisely implement an insert function in C, but I'm having all sorts of issues. I'm in an intro CS class and they started throwing C labs at us before we had ever worked with it before. Part of the issue is that the list pointer is not being recognized as NULL and I'm also pretty sure that I'm using malloc improperly.
#include <stdio.h>
#include <stdlib.h>
#define True 1
#define False 0
typedef int BOOLEAN;
struct Node{
int value;
struct Node *next;
};
void insert(int x, struct Node **pL){
printf("insert\n");
if(*pL == NULL){
printf("inside if\n");
struct Node *pN;
pN = (struct Node*) malloc(sizeof(struct Node));
(*pN).value = x;
(*pN).next = NULL;
return;
}
if (*pL != NULL){
printf("inside else\n");
insert(x, &(((*pL)->next)));
}
printf("end insert\n");
};
void printList(struct Node *L){
while (L != NULL){
printf("%d", (*L).value);
printList((*L).next);
}
return;
};
main(){
printf("main\n");
struct Node* L;
//L).next = NULL;
int i;
printf("for loop\n");
for (i = 3; i < 20; i+=2){
printf("%d\n", i);
insert(i, &L);
}
printList(L);
};

Answer 1

First of all, in main you need to initialise L:
struct Node* L = NULL;
Second, in insert when you allocate the new node pN, you are not assigning it to the pL, i.e., it doesn't get inserted. Put this right before the return; in insert:
*pL = pN;
(Also you could remove the return and change if (*pL != NULL) into else.)
Then, in printList you are both iterating with a while loop, and with recursion. Choose one, not both, e.g.,:
while (L) {
printf("%d\n", L->value);
L = L->next;
}
Also, throughout your code you can replace (*pointer_to_struct).field with pointer_to_struct->field for better style.