13.1 User-defined data types.pptx

9618 Paper 3

1. 13- Data Representation 13.1 User-defined data types

2. 2 13.1 User-defined data types Candidates should be able to: Show understanding of why user-defined types are necessary Define and use non-composite data types Define and use composite data types Choose and design an appropriate user-defined data type for a given problem 13.1 User-defined data types

3. 3 13.1 User-defined data types A user-defined data type is a data type for which the programmer has included the definition in the program. Once the data type has been defined, variables can be created and associated with the user-defined data type. There are two categories of user defined data types.: 1. Non-composite data type a. Enumerated data type b. Pointer data type 2. Composite a. Record data type b. Set data type c. Objects and classes

4. 4 User-defined datatypes: Non-composite user-defined data type

5. 5 User-defined datatypes: Non-composite user-defined data type A non-composite data type is defined without referencing another data type. They don’t combine different built-in data types in one data type. Non-Composite data types are: Enumerated data type Pointers

6. 6 ENUMERATED DATATYPE User-defined datatypes: Non-composite user-defined data type

7. 7 ENUMERATED DATATYPE User-defined datatypes: Non-composite user-defined data type Enumerated Datatype An enumerated data type defines a list of possible values.

8. 8 ENUMERATED DATATYPE User-defined datatypes: Non-composite user-defined data type Pseudocode of data Type for Working Days can be declared as TWdays :

9. 9 ENUMERATED DATATYPE User-defined datatypes: Non-composite user-defined data type Variables can then be declared and assigned values, for example:

10. 10 ENUMERATED DATATYPE User-defined datatypes: Non-composite user-defined data type It is important to note that the values of the enumerated type look like string values but they are not. They must not be enclosed in quote marks. This makes the second example much more useful because the ordering can be put to many uses in a program. For example, a comparison statement can be used with the values and variables of the enumerated data type:

11. 11 POINTER DATATYPE User-defined datatypes: Non-composite user-defined data type

12. 12 POINTER DATATYPE User-defined datatypes: Non-composite user-defined data type A pointer data type is used to reference a memory location. This data type needs to have information about the type of data that will be stored in the memory location. In pseudocode the type definition has the following structure, in which ^ shows that the type being declared is a pointer and <TYPENAME> is the type of data to be found in the memory location: for example INTEGER or REAL : or any user-defined data type. TYPE <pointer> = ^<Typename>

13. 13 POINTER DATATYPE User-defined datatypes: Non-composite user-defined data type It could then be used as follows: monthPointer ← ^ thisMonth If the contents of the memory location are required rather than the address of the memory location, then the pointer can be dereferenced. For example, myMonth can be set to the value stored at the address monthPointer is pointing to: DECLARE myMonth : Tmonth myMonth ← monthPointer^

14. 14 An example of the definition of a pointer type which requires only the identification of a data type for which the pointer is to be used. TYPE TIntegerPointer ← ^Integer An example of the declaration of a variable of the pointer data type which does not require the use of the caret (^) symbol. DECLARE MyIntegerPointer : TIntegerPointer An example of the declaration of two ordinary variables of type integer and the assignment of a value for one of them. DECLARE Number1, Number2 : INTEGER Number1 ← 100 POINTER DATATYPE User-defined datatypes: Non-composite user-defined data type

15. 15 An example of an assignment to a pointer variable of a value which is the address of a different variable. MyIntegerPointer ← @Number1 An example of an assignment which uses the ‘dereferenced’ value which has been stored at the address defined by the pointer variable. This assigns the value 200 to Number2. Number2 ← MyIntegerPointer ^ * 2 POINTER DATATYPE User-defined datatypes: Non-composite user-defined data type

16. 16 User-defined datatypes: Composite user-defined data type

17. 17 RECORD DATATYPE User-defined datatypes: Composite user-defined data type

18. 18 RECORD DATATYPE User-defined datatypes: Composite user-defined data type A record data type is the most useful and therefore most widely used. It allows the programmer to collect together values with different data types when these form a coherent whole. As an example, a record could be used for a program using employee data. Pseudocode for defining the type could be:

19. 19 RECORD DATATYPE User-defined datatypes: Composite user-defined data type A variable can then be declared as follows: individual data item can then be accessed using a dot notation: A particular use of a record is for the implementation of a data structure where one or possibly two of the variables defined are pointer variables.

20. 20 Record Data Type example A Car Manufacturer and seller want to store details of cars. Details can be stored in Records RECORD DATATYPE User-defined datatypes: Composite user-defined data type

21. 21 SET DATATYPE User-defined datatypes: Composite user-defined data type

22. 22 A set is a given list of unordered elements that can use set theory operations such as intersection and union. A set data type includes the type of data in the set. In pseudocode, the type definition has this structure: SET DATATYPE User-defined datatypes: Composite user-defined data type TYPE <set-identifier>= SET OF <Base Type> The variable definition for a set includes the elements of the set. DEFINE <identifier> (value1, value2, value3, ... ) : <set-identifier>

23. 23 SET DATATYPE User-defined datatypes: Composite user-defined data type A set of vowels could be declared as follows: TYPE Sletter = SET OF CHAR DEFINE vowel ('a', 'e', ' i ', 'o', 'u') : Sletter Or we can declare sets in Pseudocodes this way Here is another example TYPE Sizes = SET OF STRING DEFINE SweaterSize (“XXL”,”XL”,”L”,”M”,”S”,”XS”): Sizes OR DEFINE Title : SET OF (“ Mr ”, “ Mrs ”,” Ms ”,”Miss”,” Dr ”)

24. 24 Set data type: A set data type allows a program to create sets and to apply the mathematical operations defined in set theory. The following is a representative list of the operations to be expected: Union Difference Intersection include an element in the set exclude an element from the set Check whether an element is in a set. SET DATATYPE User-defined datatypes: Composite user-defined data type

25. 25 CLASS DATATYPE User-defined datatypes: Composite user-defined data type

26. 26 CLASS DATATYPE User-defined datatypes: Composite user-defined data type A class is a composite data type that includes variables of given data types and methods (code routines that can be run by an object in that class). An object is defined from a given class; several objects can be defined from the same class. Classes and objects will be considered in more depth in Paper 4 (Chapter 20)