Структура "Историческое событие". Найти интервал между двумя событиями в днях - C (СИ)

#include <stdio.h>
#include <malloc.h>
#include <math.h>
 
int mn[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
 
struct _event
{
int day;
int month;
int year;
char* event;
};
 
struct event_node
{
struct _event* ev;
struct event_node* next;
};
 
int is_leap_year(int year)
{
if (year%4 == 0)
return 1;
else
return 0;
}
 
// ввод
 
// аргумент функции нельзя передавать через одинарный указатель.
 
void enter_event(struct event_node** c)
{
struct event_node* iterator;
if (*c == 0)
{
*c = (struct event_node*) malloc( sizeof(struct event_node) );
if (*c != 0)
{
(*c)->next = 0;
(*c)->ev = 0;
(*c)->ev = (struct _event*) malloc( sizeof(struct _event) );
if ((*c)->ev != 0)
{
(*c)->ev->event = 0;
(*c)->ev->day = 18;
(*c)->ev->month = 3;
(*c)->ev->year = 2015;
(*c)->ev->event = (char*) malloc( 2 * sizeof(char) );
if ((*c)->ev->event != 0)
{
(*c)->ev->event[0] = 't';
(*c)->ev->event[1] = '\0';
}
}
}
}
else
{
iterator = *c;
while (iterator->next != 0)
iterator  = iterator ->next;
iterator->next = (struct event_node*) malloc( sizeof(struct event_node) );
if (iterator ->next != 0)
{
iterator->next->next = 0;
iterator->next->ev = (struct _event*) malloc( sizeof(struct _event) );
if (iterator ->next ->ev != 0)
{
iterator->next->ev->event = 0;
iterator->next->ev->day = 18;
iterator->next->ev->month = 3;
iterator->next->ev->year = 2015;
iterator->next->ev->event = (char*) malloc( 2 * sizeof(char) );
if (iterator->next->ev->event != 0)
{
iterator->next->ev->event[0] = 't';
iterator->next->ev->event[1] = '\0';
}
}
}
}
}
 
// вывод
 
void print_event_internal(struct _event* c)
{
if (c == 0) return;
printf("%d %d %d %s\n", c->day, c->month, c->year, c->event);
}
 
void print_event(struct event_node** c)
{
struct event_node* iterator = *c;
if (iterator == 0) return;
while (iterator->next != 0)
{
print_event_internal(iterator->ev);
iterator  = iterator ->next;
}
print_event_internal(iterator->ev);
}
 
 
 
// разность между датами (предполагается что год 1 события c больше года 2 события с1) 
// погрешность +-1
 
int diff_event_internal(struct _event* c, struct _event* c1)
{
int day;
int month;
int year;
int tday;
int tmonth;
int tyear;
int r;
 
if (c == 0) return -1;
 
day = c1->day;
month = c1->month;
year = c1->year;
 
if (year == c->year)
{
if (month == c->month) { return (abs(day - c->day)); }
else
{
r = c->day;
tmonth = c->month;
tmonth--;
while (tmonth != month && tmonth > 0)
{
r += mn[tmonth-1];
if (tmonth-1 == 1&& is_leap_year(c->year) ) r += 1;  
tmonth--;
}
tday = mn[tmonth-1];
if (tmonth-1 == 1 && is_leap_year(c->year)) tday += 1;
r += abs(tday - day);
return r;
}
}
else
{
//
 
r = c->day;
tmonth = c->month;
tmonth--;
while ( tmonth > 0 )
{
r += mn[tmonth-1]; 
tmonth--;
}
tyear = c->year;
tyear--;
while(tyear != year && tyear > 0)
{
r += 364;
if ( is_leap_year(tyear) == 1) r += 1;
tyear--;
}
//
tmonth = 12;
 
while (tmonth != month && tmonth > 0)
{
r += mn[tmonth-1];
if (tmonth-1 == 1 && is_leap_year(c->year) ) r += 1;
tmonth--;
}
tday = mn[tmonth-1];
if (tmonth-1 == 1 && is_leap_year(c->year)) tday += 1;
r += abs(tday - day);
 
return r;
//
}
 
return (-1);
}
 
int diff_event(struct event_node** c)
{
struct event_node* iterator = *c;
 
// событие, с которым происходит сравнение
struct _event c1;
c1.day = 18;
c1.month = 1;
c1.year = 2013;
 
if (iterator == 0) return;
while (iterator->next != 0)
{
printf("%d\n", diff_event_internal(iterator->ev, &c1));
iterator  = iterator ->next;
}
printf("%d\n", diff_event_internal(iterator->ev, &c1));
return 0;
}
 
 
// сборка мусора неавтоматическая (garbage collection unautomatic)
void free_event(struct event_node** c)
{
struct event_node* f;
struct event_node* iterator = *c;
if (iterator == 0) return;
while (iterator->next != 0)
{
f = iterator;
iterator  = iterator ->next;
if (f->ev->event  != 0) free(f->ev->event); f->ev->event = 0;
if (f->ev != 0) free(f->ev); f->ev = 0;
if (f != 0) free(f); f = 0;
}
if (iterator != 0) free(iterator); iterator = 0;
}
 
 
 
 
int main(int argc, char* argv[])
{
struct event_node* first;
first = 0;
enter_event(&first);
enter_event(&first);
enter_event(&first);
print_event(&first);
diff_event(&first);
free_event(&first);
return 0;
}