Structure and Enum in c#

Structure and Enum in c#

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  @ 2010 TataMcGraw-Hill Education 1 Education Structures and EnumerationsStructures and Enumerations
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  @ 2010 TataMcGraw-Hill Education 2 Education Introduction We have already seen that C# supports two kinds of value types, namely, predefined types and userdefined types. We have defined and used the predefined data types such as int and double throughout our earlier discussions. C# allows us to define our own complex value types (known as userdefined value types) based on these simple data types. There are two sorts of value types we can define in C#: Structures Enumerations As we know, value type variables store their data on the stack and therefore the structures and enumerations are stored on the stack. We shall discuss here briefl y how these data types are defined and used in programming.
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  @ 2010 TataMcGraw-Hill Education 3 Education STRUCTURES Structures (often referred to as structs) are similar to classes in C#. Although classes will be used to implement most objects, it is desirable to use structs whe re simple composite data types are required. Because they are value types sto red on the stack, they have the following advantages compared to class object s stored on the heap: They are created much more quickly than heap-allocated types. They are instantly and automatically deallocated once they go out of scope. It is easy to copy value type variables on the stack. The performance of programs may be enhanced by judicious use of structs. Defining a Struct A struct in C# provides a unique way of packing together data of different types. It is a convenient tool for handling a group of logically related data items. It creates a template that may be used to define its data properties
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  @ 2010 TataMcGraw-Hill Education 4 Education Assigning Values to Members Member variables can be accessed using the simple dot notation as follows: s1.Name = “John”; s1.RollNumber = 999 ; s1.TotalMarks = 575.50 ; We may also use the member variables in expressions on the right-hand side. Example: FinalMarks = s1.TotalMarks + 5.0 ; Copying Structs We can also copy values from one struct to another. Example: Student s2; // s2 is declared s2 = s1 ;
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  @ 2010 TataMcGraw-Hill Education 5 Education STRUCTS WITH METHODS We have seen that values may be assigned to the data members using struct objects and the dot operator. We can also assign values to the data members using what are known as constructors. A constructor is a method which is used to set values of data members at the time of declaration. Consider the code below: sruct Number { int number; // data member public Number ( int value ) // constructor { number = value; } }
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  @ 2010 TataMcGraw-Hill Education 6 Education NESTED STRUCTS C# permits declaration of structs nested inside other structs. The following code is valid: struct Employee { public string name; public int code; public struct Salary { public double basic; public double allowance; } }
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  @ 2010 TataMcGraw-Hill Education 7 Education DIFFERENCES BETWEEN CLASSES AND STRUCTS
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  @ 2010 TataMcGraw-Hill Education 8 Education ENUMERATIONS An enumeration is a user-defined integer type which provides a way for attaching names to numbers, thereby increasing the comprehensibility of the code. The enum keyword automatically enumerates a list of words by assigning them values 0, 1, 2 and so on. This facility provides an alternative means of creating ‘constant’ variable names. The syntax of an enum statement is illustrated below: enum Shape { Circle, //ends with comma Square, //ends with comma Triangle //no comma }
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  @ 2010 TataMcGraw-Hill Education 9 Education ENUMERATOR INITIALIZATION As mentioned earlier, by default, the value of the fi rst enum member is set to 0, and that of each subsequent member is incremented by one. However, we may assign specific values for different members, if we so desire. Example: enum Colour { Red = 1, Blue = 3, Green = 7, Yellow = 5 }
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  @ 2010 TataMcGraw-Hill Education 10 Education ENUMERATOR BASE TYPES By default, the type of an enum is int. However, we can declare explicitly a base type for each enum. The valid base types are: byte, sbyte, short, ushort, int, uint, long and ulong Examples: enum Position : byte { off, on } enum Shape : long { Circle, Square = 100, Triangle }
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  @ 2010 TataMcGraw-Hill Education 11 Education ENUMERATOR TYPE CONVERSION Enum types can be converted to their base type and back again with an explicit conversion using a cast. Example: enum Values { Value0, Value1, Value2, Value3 } . . . . . . . . Values u1 = (Values) 1; int a = (int ) u1; . . . . . . . . The exception to this is that the literal 0 can be converted to an enum type without a cast. That is Values u0 = 0;