Enums part 1

• Enumerated types allow a user to declare a simple "type"
• There are two types, we will look at both.
• Reference:
  • Book starting on page 467
  • cppreference.com's Enumeration Declaration
• There are minor differences between the two methods but
  • In our last program some people used

    const int ADD=10;
    const int SUB=11;
    const int MUL=12;
    const int DIV=13;
    ...
    	

  • This is nice but there is no reason to assign a 10 to ADD
  • And there is no protection from a copy paste error giving two different operators the same value.
• C++ has an answer to this type of problem, Enumerated types.
• To declare the type
  • enum identifier {IDENTIFIER[=int], }

  • enum DayT {MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY}
    
    enum MonthT{JAN=1, FEB=2, MAR=3, APR=4, MAY=5, JUN=6, JUL=7, AUG=8, SEP=9, OCT=10, NOV=11, DEC=12}
    
    enum SeasonT {SPRING=0, SUMMER, FALL, WINTER}
           

  • I prefer the first.
  • I do not like the second or third, but you see them.
• The compiler is allowed to pick the internal representation for the type.
  • This is probably an int unless something bigger is needed.
  • If no value is assigned, the value of the first is 0.
  • If no value is assigned, the value of each is greater than the proceeding.
• SPRING, SUMMER, ... are called enumerators
  • By convention we use all upper case for enumerators.
  • In this usage enumerators must be unique.
• Operations are, and should be limited.
  • You can add, but be careful, you might go out of range.
  • I/O as integers.
  • Can pass as value or reference parameter
  • Can be a return value.
• examples

  DayT today  = MONDAY;
  
  void PrintDay(DayT day) {
      switch(day) {
         case MONDAY: cout << "Monday " << endl;
              break;
  	    ...
      }
  }
  
  DayT RandomDayT(void) {
      DayT rv;
      ...
  
      return rv;
  }
  
      

• In C++11 and beyond the scoped or strong enumerated type was introduced
  • enum struct|class identifier[:type] {enumerator list};

  • enum struct DirectionT:char {NORTH, SOUTH, EAST, WEST};
    
    enum class ColorT:short {RED, GREEN, BLUE};
    
    enum class MoodT:char {HAPPY, SAD, BLUE};
    
           

• The use is slightly different.
  • The enumerators are not in the global scope but in the scope of the enumerator.
  • So the scope reference operator must be used.
  • But you can have two versions of BLUE

  • MoodT mood = MoodT::BLUE;
    ColorT skyColor = ColorT::BLUE;
    	

• You really should treat these like an ADT (what is an ADT?)
  • Domain: the enumerators + UNKNOWN
  • Operations: depends on what you are doing but
    • I at least want
      • StringToType
      • TypeToString
      • FIRST_TYPE
      • LAST_TYPE
    • And probably
      • NextType
      • PrevType
    • And possibly
      • RandomType()
• Lets look at animals.h and animals.C.
• And animalTest.C and game.C.
• You should study the enumerated type used in PalRoutines.h and PalRoutines.C.