C :

#include<stdio.h>
struct time
{
	int year;
	int month;
	int day;
}t;
int main()
{
	int i, days = 0;
	int a[13] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
	scanf("%d%d%d", &t.year, &t.month, &t.day);
	if((t.year % 4 == 0 && t.year % 100 != 0) || t.year % 400 == 0)
		a[2] = 29;
	for(i = 1; i < t.month; i++)
		days += a[i];
	printf("%d\n", days + t.day);
	return 0;
}

C++ :

#include <iostream>
using namespace std;
int main()
{
    int month[12]= {31,28,31,30,31,30,31,31,30,31,30,31};
    int days=0,i;
    int mon,day,year;
    cin>>year>>mon>>day;
    if((year%4==0&&year%100!=0)||year%400==0)
        month[1]++;
    for(i=0; i<mon-1; i++)
        days+=month[i];
    cout<<days+day<<endl;
    return 0;
}