如何在另一个函数中访问一个函数中的变量

您的函数具有返回类型 int，但实际上不返回任何值。返回 z ，然后将其作为参数传递给下一个函数。

另一个观察结果是，这个函数int dayofthemonth (int year, int month)没有调用者。

也许你应该改变为，

r = (day - z) + 14;至

r = (day - dayofthemonth(year, month)) + 14;//前提是此函数返回z 。

如果你想要一种简单的方法来在代码的所有作用域中使用一个变量，你可以在main函数之前和"#include <...>"s和"using namespace..."之后声明它。但是当你使用这种方式时要小心，因为如果你在代码中使用变量 2 或更多时间并且不将其设为 0，你会看到错误的答案。最后，我在代码中使用了"cin.get（）"而不是"system（"pause"）"，因为如果你想在Linux中编译你的代码，"system（"pause"）"会给你一个错误。

#include <iostream>
#include <string>
using namespace std;
int z;
void dayofthemonth (int year, int month)
{
    z = 0;
    if ((year % 400 == 0 || year % 100 !=0) && (year % 4 == 0)){  //reference day of   the month for leap years
    cout << year << " is a leap year." << endl;
    if (month == 1){
       cout << "The doomsday for month " << month << " is 4." << endl;
       z = 4;
    }
    if (month == 2){
       cout << "The doomsday for month " << month << " is 1." << endl;
       z = 1;
    }
    if (month == 3){
       cout << "The doomsday for month " << month << " is 0." << endl;
       z = 0;
    }
    if (month == 4){
       cout << "The doomsday for month " << month << " is 4." << endl;
       z = 4;
    }
    if (month == 5){
       cout << "The doomsday for month " << month << " is 9." << endl;
       z = 9;
    }
    if (month == 6){
       cout << "The doomsday for month " << month << " is 6." << endl;
       z = 6;
    }
    if (month == 7){
       cout << "The doomsday for month " << month << " is 11." << endl;
       z = 11;
    }
    if (month == 8){
       cout << "The doomsday for month " << month << " is 8." << endl;
       z = 8;
    }
        if (month == 9){
       cout << "The doomsday for month " << month << " is 5." << endl;
       z = 5;
    }
    if (month == 10){
       cout << "The doomsday for month " << month << " is 10." << endl;
       z = 10;
    }
    if (month == 11){
       cout << "The doomsday for month " << month << " is 7." << endl;
       z = 7;
    }
    if (month == 12){
       cout << "The doomsday for month " << month << " is 12." << endl;
       z = 12;
    }
 }
 else{                                                       //reference day of the month for non-leap years
    cout << year << " is not a leap year." << endl;
    if (month == 1){
       cout << "The doomsday for month " << month << " is 3." << endl;
       z = 3;
    }
    if(month == 2){
       cout << "The doomsday for month " << month << " is 0." << endl;
   z = 0;
    }
    if (month == 3){
       cout << "The doomsday for month " << month << " is 0." << endl;
       z = 0;
    }
    if (month == 4){
       cout << "The doomsday for month " << month << " is 4." << endl;
       z = 4;
    }
    if (month == 5){
       cout << "The doomsday for month " << month << " is 9." << endl;
       z = 9;
    }
    if (month == 6){
       cout << "The doomsday for month " << month << " is 6." << endl;
       z = 6;
    }
    if (month == 7){
       cout << "The doomsday for month " << month << " is 11." << endl;
       z = 11;
    }
    if (month == 8){
       cout << "The doomsday for month " << month << " is 8." << endl;
       z = 8;
    }
    if (month == 9){
       cout << "The doomsday for month " << month << " is 5." << endl;
       z = 5;
    }
    if (month == 10){
       cout << "The doomsday for month " << month << " is 10." << endl;
       z = 10;
    }
    if (month == 11){
       cout << "The doomsday for month " << month << " is 7." << endl;
       z = 7;
    }
    if (month == 12){
       cout << "The doomsday for month " << month << " is 12." << endl;
       z = 12;
    }
 }

}
void doomsday (int year)
{         //reference day of the week
  int a, b, c , d, e, x;

  a = ((year/100) % 4);
  b = (year % 100);
  c = (b/12);
  d = (b % 12);
  e = (d/4);
  x = ((c + d + e + (5*a) + 2) % 7);
  if (x == 0)
    cout << "The doomsday for " << year << " is Sunday." << endl;
  else if (x == 1)
    cout << "The doomsday for " << year << " is Monday." << endl;
  else if (x == 2)
    cout << "The doomsday for " << year << " is Tuesday." << endl;
  else if (x == 3)
    cout << "The doomsday for " << year << " is Wednesday." << endl;
  else if (x == 4)
    cout << "The doomsday for " << year << " is Thursday." << endl;
  else if (x == 5)
    cout << "The doomsday for " << year << " is Friday." << endl;
  else if (x == 6)
    cout << "The doomsday for " << year << " is Saturday." << endl;
}
void dayoftheweek(int month, int day, int year)
{
 int r;
 cout << "You want to find out what day of the week " << month << "/" << day << "/" << year << " lies on." << endl;
 doomsday(year);
 r = (day - z) + 14;          //offset between the given day and the result of     dayofthemonth function.
 cout << r << endl;
}

int main(){
int year, month, day;

cout << "Enter the year." << endl;
cin >> year;
cout << "Enter the month using numbers 1-12." << endl;
cin >> month;
cout << "Enter the day." << endl;
cin >> day;
dayoftheweek(month, day, year);

cin.get();
return 0;

}