# How to: Pass Procedures to Another Procedure in Visual Basic

This example shows how to use delegates to pass a procedure to another procedure.

A delegate is a type that you can use like any other type in Visual Basic. The AddressOf operator returns a delegate object when applied to a procedure name.

This example has a procedure with a delegate parameter that can take a reference to another procedure, obtained with the AddressOf operator.

### Create the delegate and matching procedures

1. Create a delegate named MathOperator.

Delegate Function MathOperator(
ByVal x As Double,
ByVal y As Double
) As Double

2. Create a procedure named AddNumbers with parameters and return value that match those of MathOperator, so that the signatures match.

Function AddNumbers(
ByVal x As Double,
ByVal y As Double
) As Double
Return x + y
End Function

3. Create a procedure named SubtractNumbers with a signature that matches MathOperator.

Function SubtractNumbers(
ByVal x As Double,
ByVal y As Double
) As Double
Return x - y
End Function

4. Create a procedure named DelegateTest that takes a delegate as a parameter.

This procedure can accept a reference to AddNumbers or SubtractNumbers, because their signatures match the MathOperator signature.

Sub DelegateTest(
ByVal x As Double,
ByVal op As MathOperator,
ByVal y As Double
)
Dim ret As Double
ret = op.Invoke(x, y) ' Call the method.
MsgBox(ret)
End Sub

5. Create a procedure named Test that calls DelegateTest once with the delegate for AddNumbers as a parameter, and again with the delegate for SubtractNumbers as a parameter.

Protected Sub Test()

When Test is called, it first displays the result of AddNumbers acting on 5 and 3, which is 8. Then the result of SubtractNumbers acting on 9 and 3 is displayed, which is 6.