Issue Initializing Double Stacked linked lists in C - c

Question

I am coding a data structure involving a set of two linked lists, stacked on top of each other. When trying to initialize the set in my test harness, I get a segmentation error. I've commented out all value setters to test to see if I could figure out the error myself, but I could not.
Prototype for init method:
Test Harness:
int
main( )
{
list the_list;
int used = 0;
int values[MAX_VALUES];
char input[LINE_LEN];
char command;
int argument;
int num_found;
bool result;
set_t lower;
set_t upper;
the_list->lower = lower;
the_list->upper = upper;
input[0] = '\0';
input[LINE_LEN-1] = '\0';
fgets( input, LINE_LEN, stdin );
while (*input != 'q') {
num_found = sscanf( input, "%c %d", &command, &argument );
if (num_found > 0) {
switch (command) {
case 'i':
printf ("Request to initialize the set\n");
if (num_found == 1) {
result = set_init( &the_list );
} else {
result = set_init( NULL );
}
printf ("Returned as %d\n", result);
break;
34,0-1 8%
Init method:
bool
set_init( list *the_list )
{
bool initialized = false;
if (the_list !=NULL ) {
/* We have space to initialize. */
the_list->lower->set_size = 0;
/* the_list->lower->head = NULL;
the_list->lower->tail = NULL;
the_list->lower->set_level = 1;
the_list->lower->ready = true;
the_list->upper->set_size = 0;
the_list->upper->head = NULL;
the_list->upper->tail = NULL;
the_list->upper->set_level = 2;
the_list->upper->ready = true;*/
initialized = true;
}
return initialized;
}
Also my struct definitions for my set, linked list, and node structs:
typedef struct _set_node_t {
test_type_t *data;
struct _set_node_t *next;
struct _set_node_t *below;
} set_node_t;
/* the set itself keeps track of the head and the tail of the linked list */
typedef struct {
int set_size;
bool ready;
set_node_t *head;
set_node_t *tail;
int set_level;
} set_t;
typedef struct {
set_t *lower;
set_t *upper;
}list;

Answer 1

The only thing that could be crashing here is this line:
the_list->lower->set_size = 0;
Either the_list or the_list->lower must be uninitialized or NULL or be pointing to invalid or inaccessible memory.
Edit: Yeah this line will crash because you don't initialize the_list.lower:
result = set_init( &the_list );
And this line will crash because you're passing NULL:
result = set_init( NULL );