CSci 162

Lecture 2

Martin van Bommel

Enumeration

• Enumeration– process of listing all of the elements in the

domain of a type• Enumerated type

– type defined via enumeration• Representation of enumerated type

– give each element a number e.g. 0, 1, 2, 3, ...

Enumeration via constants• One method to use enumerated type#define Sunday 0#define Monday 1#define Tuesday 2#define Wednesday 3#define Thursday 4#define Friday 5#define Saturday 6

• Then can useif (day == Sunday) cout << ”Rest today\n”;

Defining Enumerated Types

• Better to use explicit type definition• Why?

– Compiler chooses integer codes– Programs easier to read with separate, meaningful

type name– Easier to debug the program

Enumerated Type Definitionenum typename { list of elements};

• Exampleenum weekdayT { Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday};

Enumerated types• Values corresponding to elements of types are by default assigned

sequentially from zero• Can change this behavior:enum yearT {Freshman = 1, Sophmore = 2,Junior = 3, Senior = 4 };

• Values assigned sequentially from previousenum yearT{Freshman=1,Sophmore,Junior,Senior

};

Operations of Enumerated Types

• Values of enumerated type is implicitly converted to integer

• Integer not implicitly converted to enumweekdayT day = Monday;int d;d = (day + 1) % 7;day = (weekdayT) d;day = (weekdayT) ( (day + 1) % 7 );

Displaying value of type

• Use function to display value of typevoid PrintDay(weekdayT day){switch(day) { case Sunday: cout << ”Sunday”;break;

case Monday: cout << ”Monday”;break;etc.}

}

Another Way to Display Value

void PrintDay(weekdayT day){ string name[] = {”Sunday”,”Monday”,…}; cout << name[day];}

Characters

• Characters are internally defined almost like an enumerated type

enum char {…,’0’,’1’,…,’9’,’:’,’;’,…,’@’,’A’,’B’,

…,’Z’,’[’,…,’`’,’a’,…,’z’,…};

Boolean Values

• The bool type is an enumerated type

enum bool {false, true};

• Functions with return type “bool” can return “false” or “true” and still be used in “if”

Array Indexed by enum• Since values of enumerated type are

implicitly converted to integer, can use as indices to arrayint sales[7], i, total = 0;

sales[Monday] = 10000;

for (i=Sunday; i<=Saturday; i++) {total += sales[i];}