C++ 格式化输入与格式化输出的处理

#include 
#include
#include
#include  //atoi
using namespace std;
int GetMonthDay(int year, int month)
{
	static int days[13] = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
	int day = days[month];
	if (month == 2)
		if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0)
		{
			day += 1;
		}
	return day;
}

int main()
{
	int a[3],i=0;
	int year, month, day;
	
	char sentence[20];
	
	const char *d="-";
	cin.getline(sentence, 20);//2017-12-31
	char *p;
	p = strtok(sentence,d);
	
    while(p)
    {
    	a[i++]=atoi(p);        
        p=strtok(NULL,d);
    }
    
    year=a[0];
    month=a[1];
    day=a[2];
    
	day += 1;

	while (day > GetMonthDay(year, month))
	{
		day -= GetMonthDay(year, month);
		month++;
		if (month == 13)
		{
			year++;
			month = 1;
		}
	}
	
	cout<