In Visual Basic, a function is a block of code that performs a specific task and returns a value. It must be a unique name to identify the method. If we didn’t mention any access modifier, it is private by default. It is useful to define access levels, i.e., public or private, etc., to allow other classes to access the method.

When creating methods in Visual Basic, we have the option to use either the `Sub` or `Function` keyword based on our requirements. The main difference between the two is that a `Sub` procedure does not return a value, whereas a `Function` procedure always returns a value.

In addition to defining access levels and returning values, functions can also take parameters. Parameters are variables that are passed to the function when it is called, and they can be used within the function to perform calculations or other tasks.

Some common date and time functions in Visual Basic include:

* `DateDiff`: Returns the difference between two dates.

* `WeekdayName`: Returns the name of the day of the week for a given date.

* `Format`: Formats a date or time as a string.

* `DateAdd`: Adds a specified interval to a date and returns the result.

* `Now`: Returns the current date and time.

These functions can be used in a variety of ways, such as finding the beginning or end of a week, formatting dates and times, and performing calculations with dates and times.

For example, you could use the `WeekdayName` function to find out what day of the week today is:

```

TodaysWeekdayName = WeekdayName(Weekday(Now, vbUseSystem))

```

You could also use the `DateAdd` function to calculate a date 31 days in the future:

```

Later = DateAdd('d', 31, Now)

```

It is important to note that writing to system date or time changes can be problematic and should usually be avoided. Instead, you can treat dates and times as variables that can be read from and written to.

Some common uses of dates and times in Visual Basic include:

* Formatted = Format(Now, 'yyyy-MM-dd') ' e.g.

* Later = DateAdd('d', 31, Now) ' 31 days later

* TodaysWeekdayName = WeekdayName(Weekday(Now, vbUseSystem))

* If Weekday(Now) = vbSaturday Then MsgBox 'It is Saturday.'

Overall, functions in Visual Basic are a powerful tool for performing calculations and other tasks with dates and times. By understanding how to use these functions effectively, you can write more efficient and effective code.

Function in visual basic