Sub procedures perform an operation or series of operations but don't return a value. You can create your own Sub procedures or use the event procedure templates that Microsoft Access creates for you.

Each form and report in your database has a built-in form module (form module: A module that includes code for all event procedures triggered by events occurring on a specific form or its controls.) or report module (report module: A module that includes code for all event procedures triggered by events occurring on a specific report or its controls.) that contains event procedure templates. You can add code that runs in response to events that occur on the form, the report, or the controls (control: A graphical user interface object, such as a text box, check box, scroll bar, or command button, that lets users control the program. You use controls to display data or choices, perform an action, or make the user interface easier to read.) on the form or report. When Microsoft Access recognizes that an event has occurred on a form, report, or control, it automatically runs the event procedure named for the object and event. For example, you can write an event procedure that sets the focus to a Spouse Name text box when the user selects a Married check box.

Many wizards (for example, the Command Button Wizard) that create objects also create event procedures for the object. You can look at these event procedures to see examples of how procedures work.

Function procedures (often just called functions) return a value, such as the result of a calculation. Microsoft Visual Basic includes many built-in functions; for example, the Now function returns the current date and time. In addition to these built-in functions, you can create your own custom functions.

Because functions return values, you can use them in expressions (expression: Any combination of mathematical or logical operators, constants, functions, and names of fields, controls, and properties that evaluates to a single value. Expressions can perform calculations, manipulate characters, or test data.). You can use functions in expressions in many places in Microsoft Access, including in a Visual Basic statement or method, in many property settings, or in a criteria expression in a filter or query.

The following example of a Function procedure, FirstOfNextMonth, returns the date of the first day of the month following the current date:

Function FirstOfNextMonth()
 FirstOfNextMonth = _
 DateSerial(Year(Now), Month(Now) + 1, 1)
End Function
						

This custom function consists of a single assignment statement that assigns the results of an expression (on the right side of the equal sign) to the name of the function, FirstOfNextMonth (on the left side of the equal sign). The function calculates a result by using the built-in Visual Basic DateSerial, Year, Now, and Month functions.

After you create this function, you can use it in an expression almost anywhere in Microsoft Access. For example, you could specify that a text box display the first day of the month following the current date as its default value by setting the text box control's DefaultValue property to the following expression in the property sheet:

=FirstOfNextMonth()
						

Note  To use a function as a property setting, the function must be in the form (form module: A module that includes code for all event procedures triggered by events occurring on a specific form or its controls.) or report module (report module: A module that includes code for all event procedures triggered by events occurring on a specific report or its controls.), or in a standard module (standard module: A module in which you can place Sub and Function procedures that you want to be available to other procedures throughout your database.). You can't use a function in a class module (class module: A module that can contain the definition for a new object. When you create a new instance of a class, you create the new object. Procedures defined in the module become the properties and methods of the object.) that isn't associated with a form or report as a form or report property setting.