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Sub Procedure Parameters: ByVal vs ByRef

Learn about passing variables in sub procedures by value (ByVal) or by reference (ByRef), and understand the differences between local and class-level variables. Also, explore debugging techniques.

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Sub Procedure Parameters: ByVal vs ByRef

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  1. Sub Procedures, Part II • Passing by Value • Passing by Reference • Local Variables • Class-Level Variables • Debugging Chapter 4

  2. ByVal and ByRef • Parameters in Sub procedure headers are proceeded by ByVal or ByRef • ByVal stands for By Value • ByRef stands for By Reference Chapter 4

  3. Passing by Value • When a variable argument is passed to a ByVal parameter, just the value of the argument is passed. • After the Sub procedure terminates, the variable has its original value. Chapter 4

  4. Example Dim n As Double = 4 Triple(n) txtBox.Text = CStr(n) End Sub Sub Triple(ByVal num As Double) num = 3 * num End Sub Output: 4 Chapter 4

  5. Same Example: n num Dim num As Double = 4 Triple(num) txtBox.Text = CStr(num) End Sub Sub Triple(ByVal num As Double) num = 3 * num End Sub Output: 4 Chapter 4

  6. Passing by Reference • When a variable argument is passed to a ByRef parameter, the parameter is given the same memory location as the argument. • After the Sub procedure terminates, the variable has the value of the parameter. Chapter 4

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