如何在另一个函数中访问一个函数中的变量？ [复制]

Question

我正在尝试编写一个 C++ 代码，其中用户输入日期并使用 John Conway 的世界末日算法输出日期所在的星期几。

我正在尝试访问在函数 dayofthemonth 中声明和定义的变量 z，并在名为 dayoftheweek 的函数中使用它。请记住，我对 C++ 很陌生，所以如果你能尽可能简单地回答，那将有很大帮助。代码如下：

#include <iostream>
#include <string>
using namespace std;



int dayofthemonth (int year, int month){          
    int z;

    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;
    }       

 }     



}

int 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);



system ("PAUSE");
return 0;


}

Answer 1

您的函数有返回类型int，但实际上并没有返回任何值。返回z，然后将其作为参数传递给下一个函数。

Answer 2

另一个观察，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;到

r = (day - dayofthemonth(year, month)) + 14; //如果这个函数返回z.

Answer 3

如果您想要一种在代码的所有范围内使用一个变量的简单方法，您可以在 main 函数之前和“#include <...>”s 和“using namespace ...”之后声明它。 但是在使用这种方式时要小心，因为如果您在代码中使用该变量 2 次或更多时间并且不将其设为 0，您将看到错误的答案。 最后我在我的代码中使用了“cin.get()”，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;


}