#define _CRT_SECURE_NO_WARNINGS #include <stdio.h> using namespace std; void Nextday(int& year, int& month1, int& day1) { 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 (i...