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Chapter 4

Chapter 4. General Procedures. Outline & Objective. Creating Visual Basic Sub Procedures Creating programmer-defined Function Procedures Parameter Passing Modularizing in Programming Languages. What is Modularization. Breaking the program into smaller parts

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Chapter 4

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  1. Chapter 4 General Procedures Chapter 4 - Visual Basic Schneider

  2. Outline & Objective • Creating Visual Basic Sub Procedures • Creating programmer-defined Function Procedures • Parameter Passing • Modularizing in Programming Languages Chapter 4 - Visual Basic Schneider

  3. What is Modularization • Breaking the program into smaller parts • A Sub procedure or Function performs a well-defined task • Easier to test, debug and correct Chapter 4 - Visual Basic Schneider

  4. Modularizing Programs in Visual Basic • In Visual Basic, there are three types of procedures: • Event • Sub • Function • Note: To distinguish procedures from event procedures, Sub and Functions are referred to as general procedures. Chapter 4 - Visual Basic Schneider

  5. Passing Arguments to Subs: • When you define a Sub procedure; sometimes you need to transfer variables that are used in different Subs. This is called passing in programming languages. Chapter 4 - Visual Basic Schneider

  6. Sub Procedures Properties: • may be called • may be passed data called arguments • may return values to the calling program • may change the data stored in a received variable Chapter 4 - Visual Basic Schneider

  7. Components of Sub Procedure: • name: used to identify the Sub procedure • parameters: a Sub procedure accepts values from the caller through its parameters; it may also send values back to the caller through it’s parameters. Chapter 4 - Visual Basic Schneider

  8. Sub Procedure's Name • In this text, Sub procedure names begin with uppercase letters in order to distinguish them from variable names. Chapter 4 - Visual Basic Schneider

  9. Syntax of a Sub Procedure Private Sub ProcedureName ( ) statement(s) End Sub Chapter 4 - Visual Basic Schneider

  10. Creating Visual Basic Sub Procedure: • Activate a code window • Select Add Procedure from the Tools menu • Type in the name of the Sub procedure • Click on Private in Scope frame • Press the Enter key or click the OK button • Type the statements of the Sub procedure into this window Chapter 4 - Visual Basic Schneider

  11. Example of Call to a Sub Procedure: Private Sub cmdCompute_Click() Dim sngNum As Single sngNum = Val(InputBox("Enter a number:")) Call Triple(sngNum) End Sub Chapter 4 - Visual Basic Schneider

  12. Sub Procedure Triple: Private Sub Triple(num As Single) ' Multiply the value of the number by 3 picResult.Print "The number is"; 3 * num End Sub Chapter 4 - Visual Basic Schneider

  13. Passing Arguments to Sub Procedures • Arguments : Variables or expressions placed in parentheses in a Call statement. • Not only is the value of the argument passed to the parameter, but the value of the parameter is passed back to the argument. Chapter 4 - Visual Basic Schneider

  14. Parameters • Variables placed in parentheses after a Sub Procedure's name. • When the procedure is called, the values of the corresponding arguments are placed in the parameters. Chapter 4 - Visual Basic Schneider

  15. Example of Parameters • Private Sub Triple(num As Single) Chapter 4 - Visual Basic Schneider

  16. Passing arguments to parameters Call Triple(num ) Private Sub Triple (num As Single) Argument Parameter Chapter 4 - Visual Basic Schneider

  17. Passing Arguments to Parameters • Call Add (x, y ) • Private Sub Add ( num1 As Single, num2 As Single) Arguments Parameters Chapter 4 - Visual Basic Schneider

  18. Passing Arguments • The Sub Procedure receives the location of the arguments, the Sub Procedure may use and modify the value of the arguments. Chapter 4 - Visual Basic Schneider

  19. Important Rules for Passing Arguments to a Sub • The number of arguments and parameters must match. • The data type of each argument must match its corresponding parameter. Chapter 4 - Visual Basic Schneider

  20. Review • Visual Basic has three types of procedures: • Event • Sub • Function • Each Sub procedure performs a distinct task. • The Call statement causes a Sub procedure to be executed. Chapter 4 - Visual Basic Schneider

  21. Review • Values can be passed between the calling program and Sub by passing arguments. • The number and type of arguments in the calling program and Sub must match. Chapter 4 - Visual Basic Schneider

  22. Review • Variables that are used in a particular Sub are local variables. • Values that are assigned to them are not returned to the calling module. Chapter 4 - Visual Basic Schneider

  23. Common Errors • Passing incorrect data types. • Not returning the result of the computation back to the calling program. Chapter 4 - Visual Basic Schneider

  24. What is a function? • A function designed to perform a specific task also. • A function designed to return asingle value to the calling program. Chapter 4 - Visual Basic Schneider

  25. Types of Functions • Standard functions (built-in) • programmer-defined functions Chapter 4 - Visual Basic Schneider

  26. programmer-defined Function • A function designed to return a single value. • The value is returned in the function itself. • The arguments of a function should not be changed in the function body. Chapter 4 - Visual Basic Schneider

  27. The Function Syntax Private Function FunctionName (parameter-list) As datatype Statement(s)…… ….. FunctionName = …….. End Function Chapter 4 - Visual Basic Schneider

  28. Example of a Function(using a function to change from Fahrenheit to Celsius) Private Sub cmdConvert_Click() picTempC.Cls picTempC.Print FtoC(Val(txtTempF.Text)) End Sub Private Function FtoC(t As Single) As Single ‘ Convert Fahrenheit temperature to Celsius FtoC = (5 / 9) * (t - 32) End Function Chapter 4 - Visual Basic Schneider

  29. Rule for Defining and Calling a Function • programmer-defined function must include a statement that assigns the function name a value. • programmer-defined functions are called in the same way that built-in functions are called. • A programmer-defined function may be called in an expression. Chapter 4 - Visual Basic Schneider

  30. Common Errors • Passing incorrect data types • Not specifying the data type of the returned value • Forgetting the data type of a function's parameter Chapter 4 - Visual Basic Schneider

  31. Common Errors • Not assigning a value to the function name inside the function definition • Misspelling of the Function name • Wrong invoking of the function in an expression Chapter 4 - Visual Basic Schneider

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