我试图计算世纪之日，但在unix中遇到了以下错误： 我开始学习如何使用C++，并且现在试图计算一个世纪中的哪一天，以及它们在运行我的程序时提交的日期。我得到了一个错误，但当查找错误时，它表示没有任何输出。我在mac os中的终端应用程序上使用unix，所以我不确定这是否会影响什么。我已经用白板浏览了很多次我的程序，但仍然迷路。非常感谢您回顾我的问题

错误：

lab6.cpp: In function 'int day_of_century(int, int, int)':
lab6.cpp:80:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

代码：

#包括
//全局变量：
整月=0；
整年=0；
整日=0//此day变量用于获取日期的日期
整数天=0//此days变量用于计算天数
整数计数=1；
//职能：
整数长度（整数月，整数年）{
如果（月=1 |月=3 |月=5 |月=7 |月=8 |月=10 |月=12）{
cout我想你可能想重新组织你的世纪日函数。例如，如果你有year！=2000或year
世纪日
如果
year！=2000和
year，则不会返回任何内容。我将我的函数改成这样：
世纪日（int year，int month，int days）{if（year==2000）{return（年中之日（年、月、日）；}如果（年>2000）{返回（年中之日（年-1、12、31）+世纪之日（年-1、月、日）；}
注释不能很好地保存格式化代码。请使用该代码更新您的问题。我不会尝试在注释中阅读它。非常感谢您回答我的问题。我接受了您的建议，错误消失了，功能正常。非常感谢！！！没问题，先生：）
#include <library.h>
//global variables:

int month = 0;
int year = 0;
int day = 0; //this day variable is for getting the day for a date
int days = 0;//this days variable is for counting an amount of days
int count = 1;
//functions:

int length_of_month(int month, int year) {
 if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) {
  cout << "31 Days" << endl;
 }//31 day if
 if (month == 4 || month == 6 || month == 9 || month == 11) {
  cout << "30 Days" << endl;
 }//30 day if
 if (month == 2) {
  if (year % 400 == 0 && year % 100 == 0) {
   cout << "29 Days" << endl;
  }//29 day if 1
 else  if (year % 4 == 0 && year % 100 == 0) {
   cout << "28 days" << endl;
  } // 28 days 1
 else if (year % 4 == 0) {
   cout << "29 days" << endl;
  } // 29 days 2
  else {
   cout << "28 Days" << endl;
  }//28 day else
 }//february
 return(0);
}

int length_of_month_value(int month, int year) {
 if (month == 1 || month == 3 || month == 5 || month == 7 || month == 8 || month == 10 || month == 12) {
  days = 31;  
 }//31 day if
 if (month == 4 || month == 6 || month == 9 || month == 11) {
  days = 30;
 }//30 day if
 if (month == 2) {
  if (year % 400 == 0 && year % 100 == 0) {
   days = 29;
  }//29 day if 1
 else  if (year % 4 == 0 && year % 100 == 0) {
   days = 28;
  } // 28 days 1
 else if (year % 4 == 0) {
   days = 29;
  } // 29 days 2
  else {
   days = 28;
  }//28 day else
 }//february
 return(days);
}

int day_of_year(int year, int month, int days) {
 if (month == 1) {
  days = day;
 }//if
 else {
  while (count < month) {
  days = days + length_of_month_value(count, year);
  count = count + 1;
  }//while
// days = day + days;
 }//else
 return(days);
}


int day_of_century(int year, int month, int days) {
  if (year == 2000) {
  return(day_of_year(year, month, days));
 }
 else if (year > 0) {
  return(day_of_year(year - 1, 12, 31) + day_of_century(year - 1, month, days));
 }
}


int day_of_century(int year, int month, int days) {

}

//main function:
int main() {
//1: Length of Month:
 cout << "Please enter the month (numerically) with the year (numerically)  and this program will tell you how many days are in that month" << endl;
 cout << "Month: ";
 cin >> month;
 cout << endl << "Year: ";
 cin >> year;
 cout << endl;
 length_of_month(month, year);
 cout << endl;

//2: Day of the Year:
 year = 0;
 month = 0;
 days = 0;
 day = 0;
 cout << "Please enter the year, month, and day, and this program will tell you what day of the year that date is." << endl;
 cout << "Year: ";
 cin >> year;
 cout << endl << "Month: ";
 cin >> month;
 cout << endl << "Day: ";
 cin >> day;
 cout << "You are in day " <<  day_of_year(year, month, day) << " of the year." <<  endl;
// day_of_year(year, month, day);
// cout << days+day;
 cout << endl;

//3: Day of the Century:
 year = 0;
 month = 0;
 days = 0;
 day = 0;
 count = 1;
 cout << "Please enter the year, month, and day, and this program will tell you what day of the century that date is in. This program only stays in this current century so please pick a year between 2000 and 2099." << endl;
 cout << "Year: ";
 cin >> year;
 cout << endl << "Month: ";
 cin >> month;
 cout << endl << "Day: ";
 cin >> day;
 cout << "You are in day " <<  day_of_century(year, month, day) << " of the century." <<  endl;


return(0);
}