C :

#include<stdio.h>
int main()
{
    //freopen("111.txt","r",stdin);
    //freopen("111out.txt","w",stdout);
    int a[13] = {0, 31, 28, 31,30,31,30,31,31,30,31,30, 31};
    int year1, month1, day1, year2, month2, day2, i, sum;
    while(scanf("%d%d%d%d%d%d",&year1,&month1,&day1,&year2,&month2,&day2) != EOF)
    {
        sum = a[month1] - day1;
        for(i = month1 + 1; i <= 12; i++)
        {
            if(i == 2 && ((year1 % 4 == 0 && year1 % 100 != 0) || (year1 % 400 == 0)))
            {
                sum += 29;
                continue;
            }
            sum += a[i];
        }
        for(i = year1 + 1; i < year2; i++)
        {
            if((i % 4 == 0 && i % 100 != 0) || i % 400 == 0)
                sum += 366;
            else
                sum += 365;
        }
        sum += day2;
        for(i = 0; i < month2; i++)
        {
            if(i == 2 && ((year2 % 4 == 0 && year2 % 100 != 0) || (year2 % 400 == 0)))
            {
                sum += 29;
                continue;
            }
            sum += a[i];
        }
        printf("%d\n",sum);
    }
    return 0;
}

C++ :

#include<iostream>
#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<queue>
#include<math.h>
#define M(i,n,m) for(int i = n;i < m;i ++)
#define L(i,n,m) for(int i = n;i >= m;i --)
#define N(n,m) memset(n,m,sizeof(n));
const int MAX = 10010;

using namespace std;

int aa[13] = {0,31,28,31,30,31,30,31,31,30,31,30,31};

int is(int i)
{
    if((i%4 == 0 && i % 100 != 0)||(i % 400 == 0))
        return 1;
    return 0;
}

int main()
{
    int a,b,c,x,y,z;
    while(~scanf("%d%d%d%d%d%d",&a,&b,&c,&x,&y,&z))
    {
        int sum;
        sum = (x - a) * 365;
        for(int i = a; i < x; i ++)
            if(is(i))
                ++ sum;
        int t = c;
        for(int i = 1; i < b; i ++)
            t += aa[i];
        if(is(a) && b > 2)
            t ++;
        sum -= t;
        t = z;
        for(int i = 1; i < y; i ++)
            t += aa[i];
        if(is(x) && y > 2)
            t ++;
        sum += t;
        printf("%d\n",sum);
    }
    return 0;
}