Type Conversion Functions 

• Coercion. In general, you can use the data type conversion functions to coerce the result of an operation to a particular data type rather than the default data type. For example, use CDec to force decimal arithmetic in cases where single-precision, double-precision, or integer arithmetic would normally take place.

• Failed Conversions. If the expression passed to the function is outside the range of the data type to which it is to be converted, an OverflowException occurs.

• Fractional Parts. When you convert a nonintegral value to an integral type, the integer conversion functions (CByte, CInt, CLng, CSByte, CShort, CUInt, CULng, and CUShort) remove the fractional part and round the value to the closest integer.

  If the fractional part is exactly 0.5, the integer conversion functions round it to the nearest even integer. For example, 0.5 rounds to 0, and 1.5 and 2.5 both round to 2. This is sometimes called banker's rounding, and its purpose is to compensate for a bias that could accumulate when adding many such numbers together.

  CInt and CLng differ from the Int, Fix Functions (Visual Basic), which truncate, rather than round, the fractional part of a number. Also, Fix and Int always return a value of the same data type as you pass in.

• Date/Time Conversions. Use the IsDate Function (Visual Basic) to determine if a value can be converted to a date and time. CDate recognizes date literals and time literals but not numeric values. To convert a Visual Basic 6.0 Date value to a Visual Basic 2005 Date value, you can use the System.DateTime.FromOADate(System.Double) method.

• Neutral Date/Time Values. The Date Data Type (Visual Basic) always contains both date and time information. For purposes of type conversion, Visual Basic considers 1/1/0001 (January 1 of the year 1) to be a neutral value for the date, and 00:00:00 (midnight) to be a neutral value for the time. If you convert a Date value to a string, CStr does not include neutral values in the resulting string. For example, if you convert #January 1, 0001 9:30:00# to a string, the result is "9:30:00 AM"; the date information is suppressed. However, the date information is still present in the original Date value and can be recovered with functions such as DatePart Function (Visual Basic).

• Culture Sensitivity. The type conversion functions involving strings perform conversions based on the current culture settings for the application. For example, CDate recognizes date formats according to the locale setting of your system. You must provide the day, month, and year in the correct order for your locale, or the date might not be interpreted correctly. A long date format is not recognized if it contains a day-of-the-week string, such as "Wednesday".

  If you need to convert to or from a string representation of a value in a format other than the one specified by your locale, you cannot use the Visual Basic type conversion functions. To do this, use the ToString(IFormatProvider) and Parse(String, IFormatProvider) methods of that value's type. For example, use System.Double.Parse(System.String,System.IFormatProvider) when converting a string to a Double, and use System.Double.ToString(System.IFormatProvider) when converting a value of type Double to a string.

The CType Function takes a second argument, typename, and coerces expression to typename, where typename can be any data type, structure, class, or interface to which there exists a valid conversion.

For a comparison of CType with the other type conversion keywords, see DirectCast and TryCast.

The following example uses the CBool function to convert expressions to Boolean values. If an expression evaluates to a nonzero value, CBool returns True; otherwise, it returns False.

Dim a, b, c As Integer
Dim check As Boolean
a = 5
b = 5
' The following line of code sets check to True.
check = CBool(a = b)
c = 0
' The following line of code sets check to False.
check = CBool(c)

The following example uses the CByte function to convert an expression to a Byte.

Dim aDouble As Double
Dim aByte As Byte
aDouble = 125.5678
' The following line of code sets aByte to 126.
aByte = CByte(aDouble)

The following example uses the CChar function to convert the first character of a String expression to a Char type.

Dim aString As String
Dim aChar As Char
' CChar converts only the first character of the string.
aString = "BCD"
' The following line of code sets aChar to "B".
aChar = CChar(aString)

The input argument to CChar must be of data type Char or String. You cannot use CChar to convert a number to a character, because CChar cannot accept a numeric data type. The following example obtains a number representing a code point (character code) and converts it to the corresponding character. It uses the InputBox Function (Visual Basic) to obtain the string of digits, CInt to convert the string to type Integer, and ChrW to convert the number to type Char.

Dim someDigits As String
Dim codePoint As Integer
Dim thisChar As Char
someDigits = InputBox("Enter code point of character:")
codePoint = CInt(someDigits)
' The following line of code sets thisChar to the Char value of codePoint.
thisChar = ChrW(codePoint)

The following example uses the CDate function to convert strings to Date values. In general, hard-coding dates and times as strings (as shown in this example) is not recommended. Use date literals and time literals, such as #Feb 12, 1969# and #4:45:23 PM#, instead.

Dim aDateString, aTimeString As String
Dim aDate, aTime As Date
aDateString = "February 12, 1969"
aTimeString = "4:35:47 PM"
' The following line of code sets aDate to a Date value.
aDate = CDate(aDateString)
' The following line of code sets aTime to Date value.
aTime = CDate(aTimeString)

The following example uses the CDec function to convert a numeric value to Decimal.

Dim aDouble As Double
Dim aDecimal As Decimal
aDouble = 10000000.0587
' The following line of code sets aDecimal to 10000000.0587.
aDecimal = CDec(aDouble)

The following example uses the CInt function to convert a value to Integer.

Dim aDbl As Double
Dim anInt As Integer
aDbl = 2345.5678
' The following line of code sets anInt to 2346.
anInt = CInt(aDbl)

The following example uses the CLng function to convert values to Long.

Dim aDbl1, aDbl2 As Double
Dim aLng1, aLng2 As Long
aDbl1 = 25427.45
aDbl2 = 25427.55
' The following line of code sets aLng1 to 25427.
aLng1 = CLng(aDbl1)
' The following line of code sets aLng2 to 25428.
aLng2 = CLng(aDbl2)

The following example uses the CObj function to convert a numeric value to Object. The Object variable itself contains only a four-byte pointer, which points to the Double value assigned to it.

Dim aDouble As Double
Dim anObject As Object
aDouble = 2.7182818284
' The following line of code sets anObject to a pointer to aDouble.
anObject = CObj(aDouble)

The following example uses the CSByte function to convert a numeric value to SByte.

Dim aDouble As Double
Dim anSByte As SByte
aDouble = 39.501
' The following line of code sets anSByte to 40.
anSByte = CSByte(aDouble)

The following example uses the CShort function to convert a numeric value to Short.

Dim aByte As Byte
Dim aShort As Short
aByte = 100
' The following line of code sets aShort to 100.
aShort = CShort(aByte)

The following example uses the CSng function to convert values to Single.

Dim aDouble1, aDouble2 As Double
Dim aSingle1, aSingle2 As Single
aDouble1 = 75.3421105
aDouble2 = 75.3421567
' The following line of code sets aSingle1 to 75.34211.
aSingle1 = CSng(aDouble1)
' The following line of code sets aSingle2 to 75.34216.
aSingle2 = CSng(aDouble2)

The following example uses the CStr function to convert a numeric value to String.

Dim aDouble As Double
Dim aString As String
aDouble = 437.324
' The following line of code sets aString to "437.324".
aString = CStr(aDouble)

The following example uses the CStr function to convert Date values to String values.

Dim aDate As Date
Dim aString As String
' The following line of code generates a COMPILER ERROR because of invalid format.
' aDate = #February 12, 1969 00:00:00#
' Date literals must be in the format #m/d/yyyy# or they are invalid.
' The following line of code sets the time component of aDate to midnight.
aDate = #2/12/1969#
' The following conversion suppresses the neutral time value of 00:00:00.
' The following line of code sets aString to "2/12/1969".
aString = CStr(aDate)
' The following line of code sets the time component of aDate to one second past midnight.
aDate = #2/12/1969 12:00:01 AM#
' The time component becomes part of the converted value.
' The following line of code sets aString to "2/12/1969 12:00:01 AM".
aString = CStr(aDate)

CStr always renders a Date value in the standard short format for the current locale, for example, "6/15/2003 4:35:47 PM". However, CStr suppresses the neutral values of 1/1/0001 for the date and 00:00:00 for the time.

For more detail on the values returned by CStr, see Return Values for the CStr Function.

The following example uses the CUInt function to convert a numeric value to UInteger.

Dim aDouble As Double
Dim aUInteger As UInteger
aDouble = 39.501
' The following line of code sets aUInteger to 40.
aUInteger = CUInt(aDouble)

The following example uses the CULng function to convert a numeric value to ULong.

Dim aDouble As Double
Dim aULong As ULong
aDouble = 39.501
' The following line of code sets aULong to 40.
aULong = CULng(aDouble)

The following example uses the CUShort function to convert a numeric value to UShort.

Dim aDouble As Double
Dim aUShort As UShort
aDouble = 39.501
' The following line of code sets aUShort to 40.
aUShort = CUShort(aDouble)