运算符重载C++

我正在试图创建一个程序，要求用户输入一个月的输入。然后程序会显示月份，接下来的月份，前一个月份，之后的第五个月份以及之前的第七个月份。我无法让程序减去一个月，或其他下面的操作。我只能得到它来添加下个月。有什么想法吗？运算符重载C++

#include <iostream> 
#include <string> 

using namespace std; 

enum Month { JAN = 1, FEB, MAR, APR, MAY, JUN, JUL, AUG, SEP, OCT, NOV, DEC }; 

Month& operator++(Month& theMonth) 
{ 
if (theMonth == DEC) 
    theMonth = JAN; 
else 
    theMonth = static_cast<Month>(theMonth + 1); 

return theMonth; 
} 

Month& operator--(Month& theMonth) 
{ 

if (theMonth == JAN) 
    theMonth = DEC; 
else 
    theMonth = static_cast<Month>(theMonth - 1); 

return theMonth; 
} 

    ostream &operator<<(ostream &output, Month &theMonth) 
{ 
switch (theMonth){ 
case JAN: output << "January"; 
    break; 
case FEB: output << "February"; 
    break; 
case MAR: output << "March"; 
    break; 
case APR: output << "April"; 
    break; 
case MAY: output << "May"; 
    break; 
case JUN: output << "June"; 
    break; 
case JUL: output << "July"; 
    break; 
case AUG: output << "Augest"; 
    break; 
case SEP: output << "September"; 
    break; 
case OCT: output << "October"; 
    break; 
case NOV: output << "November"; 
    break; 
case DEC: output << "December"; 
    break; 
} 
return output; 
} 
istream &operator>>(istream &input, Month &theMonth) 
{ 
int value; 
input >> value; 
theMonth = static_cast<Month>(value); 
return input; 
} 




#include<iostream> 
#include<string> 
#include "Month.h" 

using namespace std; 

int main() 
{ 
Month myMonth; 

cout << "Enter Month (1-12): "; 
cin >> myMonth; 
cout << "You selected month, " << myMonth << " \n" << endl; 
cout << "The next month after the month you entered is " << myMonth++ <<  "\n" << endl; 
cout << "The month before the month you entered is " << myMonth-- << "\n" << endl; 
cout << "Five months after the month you entered is " << myMonth+= << "\n" << endl; 
cout << "Seven months before the month you entered is " << myMonth-= << "\n" << endl; 

cin.ignore(); 
cin.get(); 

return 0; 
}

来源

2016-02-26 Trent Freguson

'myMonth + = <<'和'myMonth- = <<'显然是错误的语法。 – MikeCAT

你重载了前缀运算符，但是'main'中的代码试图调用后缀版本 –

而不是使用一个枚举值的，我会建议不同的类，它包装一个int：

class Month { 
    int month_num; // Month, 0-11. (0-January, 1-February, etc...) 

public: 

    // ... 
};

然后，所有月份的操作，例如加，减，加n个月，减n个月等 - 它们都变成微不足道的模12算术。

显示月份的名称也变得简单，因为它可能可以：

static const char * const months[] = { 
    "January", 
    "February", 

    // etc... I'm too lazy to type 

    "December" 
};

因此，实现您std::ostreamoperator<<过载时，你猜怎么着“月[month_num]”会为你做什么？

运营++变成：

month_num=(month_num+1) % 12;

operator--成为

month_num=(month_num+11) % 12; // Yes, I just can't wrap negative values and modulo inside my brain, this is easier to grok...

运营商+ =，以n添加到月份数，成为

month_num=(month_num+n) % 12;

等等

来源

2016-02-26 01:13:34

感谢所有的帮助！我不会说谎，我是新手，但我对此很感兴趣。我感谢支持！ –

运算符重载C++

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