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Overview of Built-In Procedures |
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A procedure is referred to as "built-in" if
it shipped with its programming language. To make your job a little easier,
the Visual Basic language is equipped with many procedures that you can use right
away in your program. Based on this, before creating your own procedure,
first check whether the functionality you are looking for is already
implementing in one of the available procedures because those that ship
with the Visual Basic language are highly reliable and should be preferred.
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Before using a built-in procedure, you must of course
be familiar with it. This comes either by consulting the documentation or
by experience. This means that you must know its name, its argument(s),
its return value, and its role. The Visual Basic programming language provides one of the richest
libraries you will ever see. In fact, it is the richest of the .NET-based languages, giving
you access to functions that are not directly available to other languages
such as C# or C++/CLI. Because there so many of those functions, we will
review only the most usually used. Eventually, when necessary, in other
lessons, we may introduce new ones.
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 |
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| 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 |
These 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:
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- 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:
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- 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):
