Enumerated Data Type

Enumerated Data Type

    This is one of the user defined datatypes. The use of this

datatype is to make programs more readable.It allows you to create your own datatype with predefined values. Though its form is like that of a structure, the values mentioned within
its braces do not indicate variables but infact are constant values that are enum can take.



Syntax:

enum identifier
{
value 1;
value 2
.
.
.
.
.
value n;
};

   The identifier can be used to declare variables that can have one of the values enclosed within the braces (known as  enumerated constants) After this definition, we can declare variables to be of this 'new' type as below.

Enum identifier  v1,v2,v3.....vn;
    The enumerated variables v1,v2,.......vn have only values
among value1,value2........valuen
The assignments of the following types are valid

v1=value5;
v5=value3;
Ex:
enum rail
{
firstclass;
secondclass;
ac
};
enum rail person1,person2;

  Here firstclass , secondclass , ac are called enumerators, which are the values that the variable of the type enum rail can take. The next statement declares that person1, person2  are variables of the type enum rail. These variable cannot take values other than firstclass, secondclass and ac. Internally, these values are treated as integers by compiler. Hence, firstclass is interpreted as value 0, secondclass as
value1 and a as 2. we can override these values by saying in the declaration.

Enum rail
{
firstclass=20;
secondclass=30;
ac=40;
};

 or any numbers we can  assign. The enumerated variables suffer from one minor weakness. The enumerated values cannot be used directly in input/output functions like printf() and scanf(). This is because these functions are not smart enough  to understand that by 20 you mean firstclass or vicevera.

Ex:

main()
{
enum code.m{
odd,delete
modify, unchanged
};
typedef enum code CODE
CODE c, d;
c=add;
d=modify;
printf("c=%d \t d=%d", c, d);
}

Output: c=0, d=2
Explanation: the enumerated datatype code is declared to be capable of taking values odd,delete,modify,unchanged using the typedef statement. Two variables of this type c and d are
declared and initialized. Cis assigned the value odd and d, the value modify. The printf() then prints out the values of  c and d. When values are defined for enum, they are interpreted as integer values 0,1,2 etc by default.So odd is assigned 0 and delete-1, modify-2. Hence the output is 0,2.

main()
{
enum status { low,medium,high};
enum status rain;
rain=0;
if(rain==low)
printf("rain=%d",rain);
}

output: rain=0
   rain is a variable of the type enum status, which is declared to be able to take values low,medium,high.In an enum,the values are interpreted as 0,1,2 in that order. Hence assigning 0 to rain is same as assigning low to rain. The if condition is therefore satisfied & hence output rain=0.