An enumeration is a set of named integer constants.
The keyword enum declares an enumerated type.
The general form for an enumeration is
enum name {
enumeration list
};
name specifies the enumeration type name.
enumeration list is a comma-separated list of identifiers.
Each of the symbols stands for an integer value.
Each of the symbols has a value one greater than the symbol that precedes it.
By default, the value of the first enumeration symbol is 0.