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  1. #include <iostream>
  2. #include<string>
  3. #include <cctype>
  4. #include <stdexcept>
  5.  
  6. struct day_type
  7. {
  8.     enum weekday { SUN, MON, TUE, WED, THU, FRI, SAT };
  9.  
  10.     day_type(weekday day) : _day(day) {}
  11.     day_type(std::string day);
  12.  
  13.     day_type prev() const { return dec(_day); }
  14.     day_type next() const { return inc(_day); }
  15.  
  16.     day_type operator+(unsigned n_days) { return weekday((_day + n_days) % 7); }
  17.     day_type operator-(unsigned n_days) { return *this; /* I leave this to you! */ }
  18.  
  19.     operator std::string() const;
  20.  
  21. private:
  22.     weekday _day;
  23.  
  24.     static weekday dec(weekday d) { return d == 0 ? weekday(6) : weekday(d-1); }
  25.     static weekday inc(weekday d) { return weekday((d + 1) % 7);}
  26. };
  27.  
  28. std::string to_string(day_type::weekday day)
  29. {
  30.     static const char* days [] =
  31.     {
  32.         "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
  33.     };
  34.  
  35.     return days[day];
  36. }
  37.  
  38. void to_lower(std::string& str)
  39. {
  40.     for (auto&ch : str)
  41.         ch = std::tolower(ch);
  42. }
  43.  
  44. day_type::operator std::string() const
  45. {
  46.     return to_string(_day);
  47. }
  48.  
  49. day_type::day_type(std::string day)
  50. {
  51.     static const std::string days [] = 
  52.     { 
  53.         "sunday", "monday", "tuesday", "wednesday", "thursday", "friday", "saturday" 
  54.     };
  55.  
  56.     unsigned matches = 0;
  57.     unsigned match_index;
  58.  
  59.     to_lower(day);
  60.  
  61.     for (unsigned index=0; index != 7 && matches <= 1; ++index)
  62.     {
  63.         if (days[index].find(day) != std::string::npos)
  64.         {
  65.             match_index = index;
  66.             ++matches;
  67.         }
  68.     }
  69.  
  70.     if (matches != 1)
  71.         throw std::invalid_argument("\"" + day + "\" is not a valid day");
  72.  
  73.     _day = weekday(match_index);
  74. }
  75.  
  76. int main()
  77. {
  78.     const char* day_prompt = "Enter a day of the week (quit to stop):\n";
  79.     std::string today;
  80.  
  81.     while (std::cout << day_prompt && std::cin >> today && today != "quit")
  82.     {
  83.         try 
  84.         {
  85.             day_type day(today);
  86.  
  87. 			std::cout << "Day is " << std::string(day) << ".\n";
  88.             std::cout << "Previous day was " << std::string(day.prev()) << ".\n";
  89.             std::cout << "Next day is " << std::string(day.next()) << ".\n";
  90.  
  91.  
  92.             std::cout << "How many days would you like to add?\n";
  93.             unsigned to_add;
  94.             std::cin >> to_add;
  95.  
  96.             std::cout << "In " << to_add << " days it will be " ;
  97.             std::cout << std::string(day + to_add) << ".\n\n";
  98.         }
  99.  
  100.         catch (std::exception & ex)
  101.         {
  102.             std::cout << "ERROR: " << ex.what() << "\n\n";
  103.         }
  104.     }
  105. }
Success #stdin #stdout 0s 3436KB
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stdin
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Tuesday
7
tuesday
8
mon
10
T
9
F
31
quit
stdout
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Enter a day of the week (quit to stop):
Day is Tuesday.
Previous day was Monday.
Next day is Wednesday.
How many days would you like to add?
In 7 days it will be Tuesday.

Enter a day of the week (quit to stop):
Day is Tuesday.
Previous day was Monday.
Next day is Wednesday.
How many days would you like to add?
In 8 days it will be Wednesday.

Enter a day of the week (quit to stop):
Day is Monday.
Previous day was Sunday.
Next day is Tuesday.
How many days would you like to add?
In 10 days it will be Thursday.

Enter a day of the week (quit to stop):
ERROR: "t" is not a valid day

Enter a day of the week (quit to stop):
ERROR: "9" is not a valid day

Enter a day of the week (quit to stop):
Day is Friday.
Previous day was Thursday.
Next day is Saturday.
How many days would you like to add?
In 31 days it will be Monday.

Enter a day of the week (quit to stop):
https://ideone.com/SV7gyl
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
secret

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