Explanation of ByVal and ByRef in Visual Basic

ByVal and ByRef are two different parameter passing mechanisms in Visual Basic:

ByVal: When using ByVal, a copy of the actual parameter is passed to the function or subroutine. Any changes made to the parameter within the function or subroutine do not affect the original value outside of it.

ByRef: When using ByRef, a reference to the actual parameter is passed, allowing the function or subroutine to modify the original value. Changes made to the parameter within the function or subroutine will be reflected outside of it.

Example of when to use ByVal:

```vb
Sub ExampleByVal(ByVal num As Integer)
num = num + 5
Console.WriteLine("Modified value inside the function: " & num)
End Sub

Dim value As Integer = 10
ExampleByVal(value)
Console.WriteLine("Original value outside the function: " & value)
```

Example of when to use ByRef:

```vb
Sub ExampleByRef(ByRef num As Integer)
num = num + 5
Console.WriteLine("Modified value inside the function: " & num)
End Sub

Dim value As Integer = 10
ExampleByRef(value)
Console.WriteLine("Original value outside the function: " & value)
```

Using ByVal and ByRef in Visual Basic allows for control over parameter modification and value propagation in functions and subroutines.