Process finished with exit code instead of returning back to main function

I am creating an grocery store system as an assignment in C for a class I put off until my senior year. It uses a linked list to keep track of products in the store. I have gotten it mostly working, but for some reason each time I select a menu option, it will run until it tries to access a NULL memory location (Process finished with exit code -1073741819 (0xC0000005)) and exit with some random memory location that it tried to access instead of returning back to the main function.

I have tested out several different while loop conditionals, all of which lead to the process being terminated as it seems like NULL is accessed even if the conditional isn't met.

The program has two classes, both of which are below. I am trying to focus on the "showList" function for now, as I feel like if I'm able to figure one out, then I can correct the rest of them.

showList() is called by option 4 on the menu.

#include <stdio.h>
#include <stdlib.h>
#include "list.h"

void displayMenu()
{
puts("Welcome to the LinkedList grocery store.");
puts("Please let me know what you want to do by typing in one of the 
numbers.");
puts("============================================================");
puts("1: Add product to store           2: Purchase product from store");
puts("3: Check price of a product       4: Show products in store");
puts("5: Remove a product from store        6: Find product");
puts("7: Inventory       8: Done for today");

}

int main(int argc, char *argv[])
{
product * head = NULL, *p;
char temp[N];
float sales = 0.0, quantity;
int choice, done = 0;
//system("cls");

  head = load(head, "inventory.txt");
  while (!done) {
    displayMenu();
    puts("What do you want to do?");
    fflush(stdin);
    scanf("%d", &choice);
    fflush(stdin);

    switch (choice)
    {
        case 1:
            head = addProduct(head);
            break;
        case 2:
            fflush(stdin);
            printf("Please enter the name of a product: ");
            fflush(stdin);
            scanf("%s", temp);
            fflush(stdin);
            printf("Please enter the quantity: ");
            fflush(stdin);
            scanf("%f", &quantity);
            fflush(stdin);
            sales += purchase(head, temp, quantity);
            break;
        case 3:
            fflush(stdin);
            printf("Please enter the name of a product: ");
            fflush(stdin);
            scanf("%s", temp);
            fflush(stdin);
            checkPrice(head, temp);
            break;
        case 4:
            showList(head);
            break;
        case 5:
            fflush(stdin);
            printf("Please enter the name of a product: ");
            fflush(stdin);
            scanf("%s", temp);
            fflush(stdin);
            rmItem(head, temp);
            break;
        case 6:
            fflush(stdin);
            printf("Please enter the name of a product: ");
            fflush(stdin);
            scanf("%s", temp);
            fflush(stdin);
            findProduct(head, temp);
            break;
        case 7:
            puts("****INVENTORY****");
            fflush(stdin);
            printf("Total sales: %f\n", sales);
            fflush(stdin);
            display(head);
            break;
        case 8:
            doneToday(head, "inventory.txt");
            done = 1;
            break;
        default:
            puts("Wrong code. Please try again.");
            break;
        }
    }

    return 0;
}

List.c:

#include "list.h"

// load in data from a file appending to the list l, return it
product * load(product *l, char fn[])
{
char name[N], quantity_unit[N], price_unit[N];
float quantity_value, price_value;

int rt;
product * head = l;
FILE * fin = fopen(fn, "r");

if(fin == NULL) {
    printf("InLoad: File open failed (%s)\n", fn);
    return NULL;
}

while (1) {
    rt = fscanf(fin, "%s %f %s %f %s\n", name, &quantity_value,quantity_unit, 
&price_value, price_unit );
    if (rt < 5)
        break;
    if (head == NULL)
        head = buildNode(name, quantity_value, quantity_unit, price_value, 
price_unit);
    else
        append(head, buildNode(name, quantity_value, quantity_unit, 
price_value, price_unit));
}
fclose(fin);
return head;
}

void doneToday(product* l, char fn[])
{
FILE * fout = fopen(fn, "w");
if(fout == NULL) {
    printf("InSave: File open failed (%s)\n", fn);
    return;
}
product* current = l;
while(current != NULL){
    fprintf(fout, "%s %f %s %f %s\n", current->name, current- 
>quantity_value,current->quantity_unit, current->price_value, current- 
>price_unit);
    current = current->next;
}

fclose(fout);

}

// build a product Node
product * buildNode(char name[], float quantity_value, char quantity_unit[], 
float price_value, char price_unit[])
{
product * p =  (product *) malloc(sizeof(product));
if(p == NULL) {
    puts("InBuildNode: Memory Allocation Failed!");
    return NULL;
}

strcpy(p->name, name);
p->quantity_value = quantity_value;
strcpy(p->quantity_unit, quantity_unit);
p-> price_value = price_value;
strcpy(p->price_unit, price_unit);

return p;
}

//shows the current product list
void showList(product *l)
{
product* cursor = l;
puts("************ Product List ******************");
printf("Name\tQuantity\tUnit\tPrice\t\tUnit\n\n");


    while(cursor != NULL){
        printf("%s\t%f\t%s\t%f\t%s\n", cursor->name, cursor->quantity_value, 
cursor->quantity_unit, cursor->price_value, cursor->price_unit);
        cursor = cursor->next;
    }


}

//adds a product to the list if it's not already
product * addProduct(product* l)
{
product* cursor = l;
product* result = l;
char name[N];
float quantity_value;
char quantity_unit[N];
float price_value;
char price_unit[N];

puts("Please enter the name of a product: ");
scanf("%s", name);
puts("Please enter the quantity value of a product: ");
scanf("%f", &quantity_value);
puts("Please enter the quantity unit of a product: ");
scanf("%s", quantity_unit);
puts("Please enter the price value of a product: ");
scanf("%f", &price_value);
puts("Please enter the price unit of a product: ");
scanf("%s", price_unit);

while(cursor != NULL){
    if(name == cursor->name){
        cursor->quantity_value += quantity_value;
        printf("The product with name **%s** already exists.", name);
        printf("The quantity was updated. New quantity is: %f", cursor- 
>quantity_value);
        return result;

    }
    cursor = cursor->next;

}

if(!cursor){
    result = append(l, buildNode(name, quantity_value, quantity_unit, 
price_value, price_unit));
    puts("New product added successfully!");
}

return result;

}

product * append(product *l, product * p)
{

product* cursor = l;

if(cursor == NULL){
    return p;

} else {

    while(cursor->next != NULL){
        cursor = cursor->next;
    }

    cursor->next = p;
    return l;
    }

}

void checkPrice(product* l, char p[])
{
product* cursor = l;

while(cursor->next != NULL){
    if(strcmp(cursor->name, p) == 0 ){
        printf("The current price of %s is %f %s", p, cursor->price_value, 
cursor->price_unit);
    }
    cursor = cursor->next;
    }
}

void findProduct(product* l, char p[])
{
product* cursor = l;

while(cursor->next != NULL){
    if(strcmp(cursor->name, p) == 0){
        printf("Product Found: %s %f %s %f %s", cursor->name, cursor- 
 >quantity_value, cursor->quantity_unit, cursor->price_value, cursor- 
 >price_unit);
        return;
    }
    cursor = cursor->next;
}

printf("The requested product was not found.");
}

void display(product *l)
{
product* cursor = l;

printf("Product: \n");
    while(cursor){
        printf("%s %f %s %f %s\n", cursor->name, cursor->quantity_value, 
cursor->quantity_unit, cursor->price_value, cursor->price_unit);
        cursor = cursor->next;

    }

}

float purchase(product* l, char p[], float q){
product* cursor = l;
float dollars = 0.0;

while(cursor->next != NULL){
    if(strcmp(cursor->name, p) == 0){
       if(cursor->quantity_value > q){
           dollars = cursor->price_value * q;
           cursor->quantity_value -= q;
           printf("Sale Completed, dollars made: %f\n", dollars);
           return dollars;
       } else if(cursor->quantity_value < q){
           dollars = cursor->price_value * cursor->quantity_value;
           printf("Sale partially completed, dollars made: %f\n", dollars);
           rmItem(l, cursor);
           return dollars;
       }
    }
}

printf("The sale was not completed, maybe the product doesn't exist.");
return dollars;

}

void rmItem(product* l, char p[])
{
product * current = l;
product * previous = current;
while(current != NULL) {
    if (strcmp(current->name, p) == 0) {
        if(previous == current)  // the first node
            l = (current->next);
        else // not the first one
            previous->next = current->next;

        free (current);
        return;
    }
    previous = current;
    current = current->next;
    }
}

list.h:

    #ifndef PROJECT3_LIST_H
#define PROJECT3_LIST_H
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define N 20

struct product
{
    char name[N];
    float quantity_value;
    char quantity_unit[N];
    float price_value;
    char price_unit[N];
    struct product *next;
};

typedef struct product product;

product * load(product *l, char fn[]);
product * buildNode(char name[], float quantity_value, char quantity_unit[], 
float price_value, char price_unit[]);
void showList(product *l);
product * addProduct(product* l);
product * append(product *l, product * p);
void checkPrice(product* l, char p[]);
void findProduct(product* l, char p[]);
void display(product *l);
float purchase(product* l, char product[], float q);
void rmItem(product* l, char p[]);
void doneToday(product* l, char fn[]);




#endif //PROJECT3_LIST_H