Objectives

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2. Objectives • Declare both a variable and a named constant • Write an assignment statement • Use the Convert class methods to convert data to an appropriate type • Write arithmetic expressions • Understand the scope of both a variable and a named constant Microsoft Visual Basic .NET: Reloaded

3. Objectives (continued) • Include internal documentation in the code • Use the Option Strict and Option Explicit statements • Use a TOE chart to code an application • Use pseudocode and a flowchart to plan an object’s code • Send focus to a control Microsoft Visual Basic .NET: Reloaded

4. Objectives (continued) • Explain the difference between syntax errors and logic errors • Format an application’s numeric output Microsoft Visual Basic .NET: Reloaded

5. Variables • Computer memory locations where users can temporarily store data • Must be assigned a data type by programmer • Data type determines type of data variable can store • Contents can change as application runs Microsoft Visual Basic .NET: Reloaded

6. Selecting a Data Type for a Variable Microsoft Visual Basic .NET: Reloaded

7. Selecting a Data Type for a Variable (continued) • Integers  whole numbers • Integer, Long, Short • Floating-point numbers  real numbers • Single, Double – use exponential notation • Example: 32000 = 3.2E4 • Decimal  uses fixed decimal point • Character Types • Char – one character • String – 0 to 2 billion characters Microsoft Visual Basic .NET: Reloaded

8. Selecting a Name for a Variable • Name should be descriptive • Use three-letter prefix • Use “m” for “module-scope” variables • Punctuate using Pascal-case • Type m and 3 letter prefix using lowercase, then capitalize the first letter of each word in the variable name Microsoft Visual Basic .NET: Reloaded

9. Selecting a Name for a Variable (continued) Microsoft Visual Basic .NET: Reloaded

10. Selecting a Name for a Variable (continued) Microsoft Visual Basic .NET: Reloaded

11. Declaring a Variable Microsoft Visual Basic .NET: Reloaded

12. Declaring a Variable (continued) • accessibility variablename as [datatype = initialvalue] • accessibility - sets scope of variable • Dim, Public, Private • variablename = programmer chosen name • datatype = data type of the variable • Anything in brackets is optional • initialvalue = default value at start of program • If no value specified numeric types = 0, character types = Nothing, boolean = false Microsoft Visual Basic .NET: Reloaded

13. Assigning Data to an Existing Variable • assignment statement • strName = “Mary” • intAge = 35 • “=“ sign is called assignment operator • Literal constant – value does not change • Number 35 is numeric literal constant • “Mary” is a string literal constant • String - a group of characters enclosed in quotes Microsoft Visual Basic .NET: Reloaded

14. Assigning Data to an Existing Variable (continued) Microsoft Visual Basic .NET: Reloaded

15. Assigning Data to an Existing Variable (continued) • Literal type characters force literal constants to assume new data type Microsoft Visual Basic .NET: Reloaded

16. Using the Convert Class • Convert class creates object that is either a number or a string by converting value to a specified data type and returning result strAge = Convert.ToString(intAge) Microsoft Visual Basic .NET: Reloaded

17. Writing Arithmetic Expressions • Precedence number indicates order in which VB performs operation in an expression Microsoft Visual Basic .NET: Reloaded

18. Writing Arithmetic Expressions (continued) • Integer division operator (\) • Returns integer portion of division discarding remainder • 8\3 results in answer of 2 • Modulus arithmetic operator (Mod) • Returns remainder portion of division discarding integer portion • 7 Mod 3 results in an answer of 1 • Often used to determine Leap years • Valid only with division of integer values Microsoft Visual Basic .NET: Reloaded

19. How To… Microsoft Visual Basic .NET: Reloaded

20. The Scope and Lifetime of a Variable • Scope • Indicates where in the application’s code the variable can be used • Lifetime • Indicates how long the variable remains in the computer’s internal memory Microsoft Visual Basic .NET: Reloaded

21. The Scope and Lifetime of a Variable (continued) • Procedure Scope • Procedure-level variable • Variable declared within a procedure • Variable can only be used in procedure in which declared • Module scope • Module-level variable • Variable declared in General Declarations section of the form • Variable can be used within all procedures in the form Microsoft Visual Basic .NET: Reloaded

22. Procedure-level variables example Microsoft Visual Basic .NET: Reloaded

23. Module-level variable example Microsoft Visual Basic .NET: Reloaded

24. The Scope and Lifetime of a Variable (continued) • Block scope • Block-level variable • Declared inside specific blocks of code • If…Then…Else or For….Next • Can be used only inside the block in which declared Microsoft Visual Basic .NET: Reloaded

25. Named Constants • A memory location inside a computer whose value cannot be changed while the application is running Microsoft Visual Basic .NET: Reloaded

26. Named Constants (continued) Microsoft Visual Basic .NET: Reloaded

27. Internally Documenting the Program Code • Internal documentation: • Term used by programmers for comments placed in code • Place an apostrophe (‘) before text you want treated as internal documentation (comment) • VB ignores everything after apostrophe on line • Place comments at beginning of each procedure Microsoft Visual Basic .NET: Reloaded

28. Internally Documenting the Program Code (continued) • Include comments: • as necessary to explain various sections of code • at beginning of application explaining application’s: • Name • Purpose • Author • Date of creation or modification Microsoft Visual Basic .NET: Reloaded

29. Internally Documenting the Program Code (continued) Microsoft Visual Basic .NET: Reloaded

30. Option Explicit and Option Strict • Option Explicit On • Tells computer to warn you if your code contains name of an undeclared variable • Prevents unintentional declaration of variables which automatically are of type Object • Option Strict On • Tells computer not to perform any implicit type conversions which may lead to loss of data • Implicit type conversions are automatic conversions from one data type to another performed by the computer to fit data into an assigned memory location Microsoft Visual Basic .NET: Reloaded

31. Option Explicit and Option Strict (continued) Microsoft Visual Basic .NET: Reloaded

32. Coding the SKATE-AWAY SALES Application • Application calculates and displays total number of skateboards ordered and total price of skateboards including 5% sales tax • Planning steps: • Identify tasks the application needs to perform • Identify objects to which you will assign those tasks • Identify events required to trigger an object into performing its assigned tasks • Design the user interface Microsoft Visual Basic .NET: Reloaded

33. Coding the SKATE-AWAY SALES Application (continued) Microsoft Visual Basic .NET: Reloaded

34. Using Pseudocode to Plan a Procedure • Pseudocode: short phrases to describe steps a procedure needs to take to accomplish its goal Microsoft Visual Basic .NET: Reloaded

35. Using a Flowchart to Plan a Procedure • Flowchart – uses standardized symbols to show steps procedure must follow to reach its goal • Standard symbols utilized: • Flowlines - connection lines between symbols • Start/stop – ovals indicating starting and ending points of procedure • Process – rectangles designating tasks such as calculations • Input/Output – parallelogram designating input and output tasks such as getting information from user Microsoft Visual Basic .NET: Reloaded

36. Using a Flowchart to Plan a Procedure (continued) Microsoft Visual Basic .NET: Reloaded

37. Using a Flowchart to Plan a Procedure (continued) • Coding the one task of bntExit_Click event using either pseudocode or flowchart tools Microsoft Visual Basic .NET: Reloaded

38. Coding the btnClear control’s Click Event Procedure Microsoft Visual Basic .NET: Reloaded

39. Assigning a Value to the Property of a Control • Zero-length string - “” • Also called empty string • Set of quotation marks with nothing between them • Assigned to the text property of a control at run-time removes contents of control • Me.txtname.Text • Me refers to the current form • txtName refers to a textbox control on the form • Text refers to a property of the txtName control Microsoft Visual Basic .NET: Reloaded

40. HOW TO… Microsoft Visual Basic .NET: Reloaded

41. Using the Focus Method • Focus indicates the control that can accept input and/or is awaiting an action from user Microsoft Visual Basic .NET: Reloaded

42. btnClear_Click Event Procedure code Microsoft Visual Basic .NET: Reloaded

43. Coding the btnCalc Control’s Click Event Procedure Microsoft Visual Basic .NET: Reloaded

44. Coding the btnCalc Control’s Click Event Procedure (continued) Microsoft Visual Basic .NET: Reloaded

45. Completed Code for Application Microsoft Visual Basic .NET: Reloaded

46. Completed Code for Application (continued) Microsoft Visual Basic .NET: Reloaded

47. Testing and Debugging the Application • Invalid data - data the application is not expecting • Debugging: • Process of locating syntax and logic errors in the program • Syntax errors • Typographical errors that violate rules governing valid syntax of the language • Me.Colse() instead of Me.Close() • Logic errors • Instruction that does not give expected results • decAverage = decNum1 + decNum2 / 2 Microsoft Visual Basic .NET: Reloaded

48. Testing and Debugging the Application (continued) • First test with valid data Microsoft Visual Basic .NET: Reloaded

49. Testing and Debugging the Application (continued) • Then test with invalid data Microsoft Visual Basic .NET: Reloaded

50. Formatting Numeric Output • Formatting: • Specifying number of decimal places and special characters to display in a number • Format string: • String used to specify format • Example: “Axx” must beenclosed in quotes • Format specifier - A • Alphabetic character that specifies format you wish to use • Precision specifier – xx • xx is the sequence of digits desired Microsoft Visual Basic .NET: Reloaded