Built-in Functions

The table below lists some of the common mathematical functions.

String Functions

Visual Basic string functions return a string, and usually accept one or more strings as arguments. The table below lists some of the common string functions.

Time and Date Functions

Visual Basic includes the date and time functions described in the table below. Note that the functions Date(), Now(), and Time() do not accept arguments, so parentheses are not actually required.

You can assign values returned from Date(), Time(), and Now() to variables declared as datatype Date. You can use the Format() function to put the date into the required format. DateSerial() enables you to convert a three-part date into a date that matches the internal Date datatype so that you can work with variables that hold dates. If the year falls within the 20th century, you can omit the 19 before the year. TimeSerial() also returns an internal Date datatype for three time parts, as shown below.

dteClockedIn = TimeSerial(16, 29, 25) 'Stores 4:29:25 P.M.

Time and date functions work on a 24-hour clock, so 16 represents 4:00 p.m. The DateAdd(), DateDiff(), and DatePart() functions require a special string interval value (see table below). The interval tells these date functions how to process the date argument.

The DateDiff() function uses the interval string value to return the number of intervals between two dates. For example, the following expression returns the number of weeks between two date values:

dateDiff("ww", dteUser1, dteUser2)

You can use the interval value and the DatePart() function to obtain the integer number that represents the specified value. You can determine the day of the week (assuming that the week starts with Sunday as day 1) on which you were born using the following expression:

DatePart("d", dteUserBDay)

Visual Basic includes three additional functions that strip off the day, month, and year values from a Date datatype variable: Day(), Month(), and Year(). If you want to work with the current year, you can strip off the year from the current date like this:

intYear = Year(Date) ' Get this year

The Timer() function is useful for determining the amount of time that has elapsed between two events. It requires no arguments or parentheses, and the values returned can be stored in separate variables to enable the amount of time that has elapsed between the two events to be calculated.

Data-Testing Functions

The Is...() functions are called data inspection functions, since they inspect a data item and return information about its datatype. When you store a value in a variable declared as a Variant datatype, the data inspection functions can be used to determine the datatype of the stored value. They are especially useful for working with user-supplied data. The table below describes the data inspection functions.

Note that Visual Basic does not have an IsString() function. If you want to test for a String value, use the VarType() function. This function returns a value that indicates the datatype of the supplied argument. If you want a user to enter an integer value, for example, you can use VarType() to test whether the input actually supplied byn the user is a valid integer. The table below shows the values returned by VarType() for the various datatypes.

Data Conversion Functions

Once you have determined what kind of value a Variant type variable or a control holds, you can convert the value to the required datatype using one of the conversion functions described in the following table.

Normally, the following assignment would store 0.1428571 in a label named myValue:

myValue.Caption = (1 / 7)

The following statement, however, increases the precision used for the calculation, assigning the value 0.142857142857143 to the label:

myValue.Caption = CDbl(1 / 7)

The conversion functions are useful when you need to specify the exact datatype for a calculation or for a control.

The format function

Format() returns a Variant datatype (easily coverted to a String datatype) in the specified format. The syntax of the Format() function is shown below.

Format(Expression, strFormat)

The result of Format() can be assigned to a variable or a control. Expression can be a variable, an expression, or a constant, while strFormat must be one of the values given in the table below.

You will probably not need to use format codes often. If none of the predefined formats match the requirements of your program, you can define your own edit mask using custom formatting codes. These are usually a combination of the hash and zero characters to represent a digit (#) or a leading or trailing zero (0). The following assignment displays the value of Weight to three decimal places:

GrossWeight.Caption = Format(Weight, "######.000")

The value can also be formatted to appear without the decimal point as a rounded value. The following assignment displays the value of Weight in this way:

GrossWeight.Caption = Format(Weight, "######")

An edit mask is a format string, such as "#,###.##", that specifies how you want numeric and string data to appear.