C :

#include<stdio.h>
 
 
int main() {
    int year, month;
    // 平年各个月的天数
    int a[]={0,31,28,31,30,31,30,31,31,30,31,30,31};
    // 闰年各个月的天数
    int b[]={0,31,29,31,30,31,30,31,31,30,31,30,31};
    scanf("%d,%d", &year, &month);
    if (month < 1 || month > 12) {
        printf("Input error!\n");
    }else{
        // 闰年
        if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
            printf("%d days\n", b[month]);
        } else{
            printf("%d days\n", a[month]);
        }
    }
}