1. Enumerations
CS Fall 1999
Enumerations

2. C++ Simple Data Types Simple types Integral Floating
char short int long enum float double long double
unsigned

3. Short Comings
In many programming situations, the primitive data types int, char, and float are inadequate to provide the desired degree of program readability.
In some situations, the variables can only take values from a finite set of possibilities.
For examples: Days of the week, Months of the year, College classification, Colors
CS Fall 1999
Enumerations

4. Enumeration Types C++ Syntax Examples:
Enumeration type is a type with a list of descriptive values.
C++ Syntax
enume numeration-type {enumerator-list};
Examples:
enum Seasons {Winter, Spring, Summer, Fall};
enum Color {red, white, green, bule};
enum Days {Sunday, Monday, Tuesday, Wednesday,
Thursday, Friday, Saturdays};
CS Fall 1999
Enumerations

5. Value of Enumerators
Enumeration type associates names (enumerator) with integer values. By default, the first enumerator has the value of 0 and the value increases by 1 for the next enumerator. Therefore, example 1 can be defined as
enum Seasons {Winter=0, Spring=1, Summer=2, Fall=3};
CS Fall 1999
Enumerations

6. Redefined Values of Enumerators
The values of enumerators can be redefined in the same manner as constant variables. In example 3, Sunday can be redefined to be 1 instead of 0.
enum day {Sunday=1, Monday, Tuesday, Wednesday, Thursday, Friday,Saturdays};
CS Fall 1999
Enumerations

7. More Example
The values of enumerators can be defined in manner as required.
enum MonthLength {Jan=31, Feb=28, Mar=31, Apr=30, May, June=30, July, Aug=31, Sep=Feb+2, Oct, Nov=30, Dec};
CS Fall 1999
Enumerations

8. More Example Enumerator values can be characters.
enum EscapeChar {Backspace='\b', Bell='\a', Newline='\n', Return='\r'};
CS Fall 1999
Enumerations

9. Operations on Enumerations
Assignment
enum day {Sunday=1, Monday, Tuesday, Wednesday,
Thursday, Friday, Saturdays};
day Days, Weekday, Weekend;
int SomeInt;
Weekday = Thursday; // valid
Weekend = Sunday; // valid
Weekday = 5; // invalid
SomeInt = Thursday; // valid
CS Fall 1999
Enumerations

10. Incrementation Weekday = Weekday + 1; // invalid
Weekday = day(Weekday + 1); //valid
for (Days = Sunday; Days <= Saturday;
Days = day(Days + 1)) {  }
CS Fall 1999
Enumerations

11. Comparison Weekday <= Thursday; Switch (Weekday)
This statement is true if the value of Weekday is either Sunday, Monday, Tuesday, Wednesday, or Thursday.
Switch (Weekday) {
case Monday:  ;
case Tuesday:  ;
case Wednesday:  ;
case Thursday:  ;
case Friday:  ; }
CS Fall 1999
Enumerations

12. Input / Output
Stream I/O is defined only for the primitive data types not for enumeration types.
Switch (Weekday) {
case Monday: cout << "Monday"; break;
case Tuesday: cout << "Tuesday"; break;
case Wednesday: cout << "Wednesday"; break;
case Thursday: cout << "Thursday"; break;
case Friday: cout << "Friday"; break; }
CS Fall 1999
Enumerations

13. Function Return Enumeration Type
enum SchoolType {PRE_SCHOOL, ELEM_SCHOOL,
MIDDLE_SCHOOL, HIGH_SCHOOL, COLLEGE } ; .
SchoolType GetSchoolData ( void )
// Obtains information from keyboard to determine school level
// Postcondition: Function value == personal school level {
SchoolType SchoolLevel;
int Age;
int LastGrade;
cout <<“Enter Age : ";// prompt for information
cin >> Age;
if ( Age < 6 )
SchoolLevel = PRE_SCHOOL;
else
cout << “Enter last grade completed in
school: “;
cin >> LastGrade;
if ( LastGrade < 5 )
SchoolLevel = ELEM_SCHOOL;
else if ( LastGrade < 8 )
SchoolLevel = MIDDLE_SCHOOL;
else if ( LastGrade < 12 )
SchoolLevel = HIGH_SCHOOL;
else SchoolLevel = COLLEGE; }
return SchoolLevel; // return enum type value
CS Fall 1999
Enumerations

14. Overloading Output Operator
ostream& operator<< (ostream& Out, Day DayVal) {
const char ErrorMsg[] = "*** invalid Day value
***";
switch (DayVal)
case Sunday: Out << "Sunday"; break;
case Monday: Out << "Monday"; break;
case Tuesday: Out << "Tuesday"; break;
case Wednesday: Out << "Wednesday"; break;
case Thursday: Out << "Thursday"; break;
case Friday: Out << "Friday"; break;
case Saturday: Out << "Saturday"; break;
default: cerr << ErrorMsg; }
return Out;
CS Fall 1999
Enumerations