#include <stdio.h> void Nextday(int &year,int &month,int &day){ int arr[]{0,31,28,31,30,31,30,31,31,30,31,30,31}; bool isLeap=false; if(year%400==0||year%4==0&&year%100!=0){isLeap=true;} if(isLeap){arr[2]=29;} ++day; if(day>arr[month]){ day=1; ++month; } if(month>12){...