用c++怎么写哎，求解答

编写程序，输入年份和月份，输出该月有多少天(考虑闰年)

#include <iostream>
#include <math.h>
 
int main()
{
    int y,m;
    cin >> y >> m;
    switch(m)
    {
    case 1:
    case 3:
    case 5:
    case 7:
    case 8:
    case 10:
    case 12:
        cout << "本月31天"
        break;
    case 4:
    case 6:
    case 9:
    case 11:
        cout << "本月30天";
        break;
    case 2:
    {
        if(y%4==0&&y%100!=0||y%400==0)
        {
            cout << "本月有29天";
        }
        else
        {
            cout << "本月有28天";
        }
    }
    }
    return 0;
}