Вычислить количество дней, полных месяцев, и полных лет, прошедших между датами

int IntFromDMY(int day,  int month, int year )
{
  int m = (month - 14) / 12;
  return ((1461 * (year + 4800 + m)) / 4 + (367 * (month - 2 - 12 * m)) / 12 - (3 * ((year + 4900 + m) / 100)) / 4 + day - 32075) - 1757585;
}
//------
int d1 = IntFromDMY(1, 1, 2012);
int d2 = IntFromDMY(31, 12, 2012);
int ddif = d2 - d1;

#include <stdio.h>
#include <string.h>
 
char* difference(int day1,  int month1, int yea1r, int day2,  int month2, int year2);
 
int main()
{
    int d1,m1,y1,d2,m2,y2;
    printf("Enter first date (day month year): ");
    scanf("%d %d %d",&d1,&m1,&y1);//данные вводятся через пробел, например 10 6 2000
    printf("Enter second date (day month year): ");
    scanf("%d %d %d",&d2,&m2,&y2);
    printf("Date1 - Date2 = %s\n",difference(d1,m1,y1,d2,m2,y2));
    return 0;
}
 
int leap(int y)
{
    return (int)((y % 4 == 0 && y% 100 != 0) || y % 400);
}
 
int maxday(int month,int year)
{
    int days[12]= {31,28,31,30,31,30,31,31,30,31,30,31};
    if(leap(year))days[1]=29;
    return days[month-1];
}
 
char* difference(int day1,  int month1, int year1, int day2,  int month2, int year2)
{
    int d,m,y;
    char date[128];
    if(year1>=year2) {
        y=year1-year2;
        if(month1>month2) {
            m=month1-month2;
            d=day1+maxday(month2,year2)-day2;
            if(d>maxday(month2,year2))d-=maxday(month2,year2);
            else --m;
            --y;
        } else {
            m=12-month1+month2;
            d=day2+maxday(month1,year1)-day1;
            if(d>maxday(month1,year1))d-=maxday(month1,year1);
            else --m;
        }
    } else {
        y=year2-year1;
        if(month1>month2) {
            m=12-month1+month2;
            d=day1+maxday(month2,year2)-day2;
            if(d>maxday(month2,year2))d-=maxday(month2,year2);
            else --m;
            --y;
        } else {
            m=month2-month1;
            d=maxday(month1,year1)-day1+day2;
            if(d>maxday(month1,year1))d-=maxday(month1,year1);
            else --m;
        }
    }
    sprintf(date,"%d days, %d month, %d years\n",d,m,y);
    return date;
}

#include <stdio.h>
 
typedef struct{
  int Day, Month, Year;
}date;
 
int check(int i){
  static int mnth[]  = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
  return mnth[--i];
}
 
extern "C" int abs(int a);
 
void make_date(date *d, int nn, int mm, int yy){
  d->Day   = nn;
  d->Month = mm;
  d->Year  = yy;
}
 
int sub(date d1, date d2)
{
  int diff = 0, i;
  int from = d1.Month, to = d2.Month;
  int diffyear = abs(d2.Year - d1.Year);
  if(!diffyear)
    for(i = from; i < to; i++)
      diff += check(i);
    else{
    for(i = from; i <= 12; i++)
      diff += check(i);
    for(i = 1; i < to; i++)
      diff += check(i);
    }
    diff -= d1.Day;
    diff += d2.Day;
    diff += ((diffyear > 1)?(diffyear - 1):(0))*365;
    diff+=diffyear/4;
    for(i = d2.Year - diffyear; i <= d2.Year; i++){
      if(((i%4==0) && !(i%100==0))||(i%400==0))
        diff += 1; break;
    }
    return diff;
}
 
int main(){
  date d1, d2;
  make_date(&d1, 31, 12, 1999);
  make_date(&d2, 1, 1, 2000);
  printf("%d", sub(d1, d2));
  return 0;
}