Visual Basic Built-In Functions: Conversions

	Visual Basic Built-In Functions: Conversions

Introduction

You may recall that when studying data types, we saw that each had a corresponding function used to convert a string value or an expression to that type. As a reminder, the general syntax of the conversion functions is:

ReturnType = FunctionName(Expression)

The Expression could be of any kind. For example, it could be a string or expression that would produce a value such as the result of a calculation. The conversion function would take such a value, string, or expression and attempt to convert it. If the conversion is successful, the function would return a new value that is of the type specified by the ReturnType in our syntax.

The conversion functions are as follows:

Function
Name	Return Type	Description
CBool	Boolean	Converts an expression into a Boolean value
CByte	Byte	Converts an expression into Byte number
CDbl	Double	Converts an expression into a floating-point number with double precision
CDec	Decimal	Converts an expression into a decimal number
CInt	Integer	Converts an expression into an integer (natural) number
CLng	Long	Converts an expression into a long integer (a large natural) number
CObj	Object	Converts an expression into an Object type
CSByte	SByte	Converts an expression into a signed byte
CShort	Short	Converts an expression into a short integer
CSng	Single	Converts an expression into a floating-point number with single precision
CUInt	UInt	Converts an expression into an unsigned integer
CULng	ULong	Converts an expression into an unsigned long integer
CUShort	UShort	Converts an expression into an unsigned short integer

Type Conversion

Conversion functions allow you to convert a known value to a another type. Besides these functions, the Visual Basic language provides a function named CType. Its syntax is:

CType(expression, typename)

As you can see, the CType() function takes two arguments. The first argument is the expression or the value that you want to convert. An example could be name of a variable or a calculation:

CType(250.48 * 14.05, ...)

The second argument is the type of value you want to convert the first argument to. From what have learned so far, this second argument can be one of the data types we reviewed in Lesson 3. Here is an example:

CType(250.48 * 14.05, Single)

If you choose one of the Visual Basic language's data types, the expression produced by the first argument must be able to produce a value that is conform to the type of the second argument:

The conversion from the first argument to the type of the second argument must be possible: the value produced by the first must be convertible to the second arguments. For example, if the first argument is a calculation, the second argument must be a number-based data type. In the same way, you cannot convert a date to a number-based type

If the first argument is a number or the result of a calculation, its resulting value must be lower than or up to the range of values of the second argument. Here is an example:

Public Module Exercise

    Public Function Main() As Integer

        MsgBox(CType(250.48 * 14.05, Single))

        Return 0
    End Function

End Module

This would produce:

Conversion

If the first argument is a number or the result of a calculation that produces an integer or a floating-point number, its resulting value must be convertible to an integer or a floating point number up to the range of values of the second argument. Here is an example:

Public Module Exercise

    Public Function Main() As Integer

        MsgBox(CType(7942.225 * 202.46, UInteger))

        Return 0
    End Function

End Module

This would produce:

Conversion

If the first argument is a number or the result of a calculation that produces an integer or a floating-point number, the second argument is a number-based data type but whose range cannot hold the resulting value of the first argument, the conversion would not be allowed (the conversion will fail):

After the CType() function has performed its conversion, it returns a value that is the same category as the second argument. For example, you can call a CType() function that converts an expression to a long integer. Here is an example:

Public Module Exercise

    Public Function Main() As Integer
        Dim Number As Long

        Number = CType(7942.225 * 202.46, Long)

        Return 0
    End Function

End Module

The function can also return a different type, as long as its type can hold the value produced by the expression. Here are two examples:

Public Module Exercise

    Public Function Main() As Integer
        Dim Number As UInteger

        Number = CType(7942.225 * 202.46, Long)

        Return 0
    End Function

End Module

Public Module Exercise

    Public Function Main() As Integer
        Dim Number As Single

        Number = CType(7942.225 * 202.46, Long)

        Return 0
    End Function

End Module

If you try storing the returned value into a variable that cannot hold it, you would receive an error:

Conversion