Value Types and Reference Types Enumerations and Structures

1. Value Types and Reference Types Enumerations and Structures

2. Introduction to Value types and Reference types • Simply put • Reference types store data in the memory address of the variable itself • Reference types store a 32 bit (or 64 bit) pointer to another object • The variable references the object, in other words • Value types are stored in the program stack

3. Value Types • Most intrinsic data types are value types • bool, byte, decimal, double, float, int, long • They all derive from System.ValueType

4. Value Type (Illustration)

5. Value Type (Example) • Note that Int32 type has constant members named minValue and MaxValue txtMinValue.Text = System.Int32.MinValue.ToString(); txtMaxValue.Text = System.Int32.MaxValue.ToString();

6. ValueType (Illustration) inti = 42; int j = 43; Program Stack i 42 j 43

7. Reference types (Introduction) • Reference types do not store data • They store a memory address. That memory address, in turn, contains the data • Data (memory) is obtained from the managed heap • Arrays are reference types • Most everything else is too (text boxes, buttons, etc…)

8. Reference Type (null reference) int[] i; Program Stack Heap i null

9. Reference Type (Initialized) Program Stack Heap i 1,2,3 @ int[] i = new int[] {1,2,3};

10. Reference Type (Assignment) • Both “i” and “j” point to the same array int[] i = new int[] { 1, 2, 3, 4, 5, 6, 7 }; int[] j; i[0] = 3; j = i;

11. Enumerations (Introduction) • Simply put, enumerations give mnemonic names to integral values • Their only real purpose is to improve code readability • Use the enum statement to declare an enumeration • Enumerations are value types

12. Enumerations (Example 1) • The StartPosition property is really an enumeration

13. Enumerations (Example 2) • Message box constants are really enumerations

14. Enumerations (Declaring) • Declare an enum named Season with 4 possible values enum Season {Spring, Summer, Fall, Winter) • Note that the underlying values are 0-based integers • Spring = 0 • Summer = 1 • …

15. Enumerations (Using) • Declare a variable named CurrentSeason having a data type of Seasons public Seasons CurrentSeason; • Use the variable in an assignment statement CurrentSeason = Seasons.Spring;

16. Enumerations (Converting) • The following prints the enumeration name txtDemo.Text = CurrentSeason.ToString(); • The following prints the enumeration value int x = (int) CurrentSeason; txtDemo.Text = x.ToString();

17. Structures • Structures allow us to logically group data • a name (first, middle, last) • A coordinate (x, y, z) • Structures are value types • Declare with the struct statement

18. Structures (Declaring) • Declare a struct named NameInfo with two string members public structNameInfo { public string FirstName; public string LastName; }

19. Structures (Declaring Variables) • Declare a variable having the structure as its data type NameInfo n; n.FirstName = "Joe"; n.LastName = "Beets";

20. Structures (Assigning) • As long as the left and right hand side of an expression have the same data type, assignment is legal. • See btnStructureDemo2 in form1.cs