1. 1 Pertemuan 03 Representing Data Matakuliah: D0524 / Algoritma dan Pemrograman Komputer Tahun: 2005 Versi:

2. 2 Learning Outcomes Pada akhir pertemuan ini, diharapkan mahasiswa akan mampu : Menunjukkan representasi data, konstanta dan variabel

3. 3 Outline Materi Data Categorization Constants Variables

4. 4 Data Categorization Two broad categories of data are numeric and string. –Numeric data must contain only numbers. –String data can contain any symbol. –Numeric data is used in arithmetic calculations. –String data cannot be used in calculations.

5. 5 Constants Data item whose value is assigned at design time and remains the same at run time. A literal constant is just a value. A symbolic constant is a descriptive name substituted for a literal constant. Four different kinds of constants: –Numeric literal. –String literal. –Numeric symbolic. –String symbolic.

6. 6 Literal Constans Writing Numeric Literal Constants –Ex. 3.45 +231.1 9.4E+7 Writing String Literal Constants –Ex. “Hello Jean” Symbolic Constants –INTERESTRATE represents 0.045. Creating/Choosing Symbolic Constant Names –Names are chosen by the developer. –Naming rules must be adhered to. The Constant Definition Statement –Ex. Const INTERESTRATE = 0.045

7. 7 Literal Constans Run Time: How the Computer Uses Symbolic Constants –Stored in a reference table for later use. Advantages of Using Symbolic Constants –Make program easier to understand. –Reduce the chance of program inconsistencies. Literal versus Symbolic Constants –The null string (“”) and numeric data used in formulas should be the only literal constants. Typical Uses of Symbolic Constants –Prime interest rate. –Overtime rate. –Number of print lines for a printed page. Predefined Symbolic Constants –Visual Basic contains a large set. –Contained in classes, such as the Math and Color classes.

8. 8 Data Types Data typeDescriptionRange Byte 1-byte binary data0 to 255 Integer 2-byte integer– 32,768 to 32,767 Long 4-byte integer– 2,147,483,648 to 2,147,483,647 Single4-byte floating-point number – 3.402823E38 to – 1.401298E – 45 (negative values) 1.401298E – 45 to 3.402823E38 (positive values) Double8-byte floating-point number – 1.79769313486231E308 to – 4.94065645841247E – 324 (negative values) 4.94065645841247E – 324 to 1.79769313486231E308 (positive values) Currency 8-byte number with fixed decimal point– 922,337,203,685,477.5808 to 922,337,203,685,477.5807 String String of charactersZero to approximately two billion characters Variant Date/time, floating-point number, integer, string, or object. 16 bytes, plus 1 byte for each character if a string value. Date values: January 1, 100 to December 31, 9999 Numeric values: same range as Double String values: same range as String Can also contain Error or Null values Boolean 2 bytesTrue or False Date 8-byte date/time valueJanuary 1, 100 to December 31, 9999 Object 4 bytesAny Object reference

9. 9 Declaring Variables A variable declaration statement. –Examples: Dim StreetAddress As String Dim GrossWeight As Integer Dim HomePhone As String Dim NetIncome As Decimal Dim CurrentStudent As Boolean Syntax of the Assignment Statement –variablename = expression Ex. CourseCode = “CISB119” Run Time: The Effect of the Assignment Statement –Evaluates expression on right side of equal sign. –Stores value of expression in variable on left side of equal sign. Changing Variable Values during Execution –Storing a value in a variable will overwrite any existing value. Control Properties in Assignment Statements –Ex. lblHomePrice.Text = 210000 Why Use Variables –Ideal to store results of intermediate calculations. –Values stored in variables may be retrieved and formatted.

10. 10 Variable Scope The domain within which a variable can be accessed. Set of all the code that can refer to a variable. Determined by where and how the variable is declared. There are four levels: block, procedure (local), module, and global.

11. 11 Variable Scope Block and Procedure Level Scope: –Any variable declared inside a procedure has procedure-level scope. –Variable can only be accessed by statements in that procedure. –Scope can be narrowed to a single block of code within the procedure. Module Level Variables: –Any variable declared inside a procedure has procedure-level scope. –Variable can only be accessed by statements in that procedure. –Scope can be narrowed to a single block of code within the procedure.

12. 12 Variable Scope Global Variable: –Variables that can be shared across all forms have global scope. –The Public Statement Used to create a global variable. –Modules Repository for data that need to be shared by forms. Repository for global variables. –Hiding Global Variables A procedure-level variable in a procedure “hides” a global variable with the same name. A module-level variable will “hides” a global variable with the same name. –Procedure-Level, Module-Level, and Global Scope A procedure-level variable is declared in a procedure using a Dim statement. A module-level variable is declared in the declarations section of a form using a Dim statement. A global variable is declared in the declarations section of a module using the Public statement.

13. 13 Project Structure Project –Forms General Declarations Section Controls –Properties –Event Procedures –Methods –Code Modules General Declarations Section

14. 14 Variable Naming Convention Must begin with a letter Cannot have a period (remember that we use the period to set a property; in other words the period is an operator) Can have up to 255 characters. Please, just because it is allowed, don't use 255 characters. Must be unique inside of the procedure or the module it is used in Must not be a VB keyword.