Section 6.1. The System Namespace

6.1 The System Namespace

The System namespace contains classes for such broad ranging things as:

• Data types

• Data type conversions

• Method-parameter manipulation

• Events and event handlers

• Mathematics

• Program invocation

• Application-environment management

6.1.1 Data Type Conversion

To illustrate data type conversion, the System namespace defines a class called Convert. If you check the documentation, you'll find that one of the methods of the Convert class is ToBoolean. The documentation lists the following for ToBoolean:

 Overloads Public Shared Function ToBoolean(String) As Boolean Overloads Public Shared Function ToBoolean(Double) As Boolean Overloads Public Shared Function ToBoolean(Single) As Boolean Overloads Public Shared Function ToBoolean(Char) As Boolean Overloads Public Shared Function ToBoolean(Byte) As Boolean Overloads Public Shared Function ToBoolean(Object) As Boolean Overloads Public Shared Function ToBoolean(Boolean) As Boolean Overloads Public Shared Function ToBoolean(Long) As Boolean Overloads Public Shared Function ToBoolean(Integer) As Boolean 

As you can see, there are many ToBoolean functions ” each one with a different argument signature ” to take care of converting various data types to Boolean.

Now, just for exercise, we can write:

 Dim s As String Dim b As Boolean s = "false" b = System.Convert.ToBoolean(s) msgbox(b) 

Because the System namespace is always available (or if we are programming outside of Visual Studio, we can import it using the Imports statement), we can omit the System qualifier and write:

 b = Convert.ToBoolean(s) 

Of course, we can also use the built-in VB.NET function CBool .

The Convert class contains methods for converting data to the standard Visual Basic data types, as well as to the data types supported by the .NET Framework but not wrapped by Visual Basic, such as the unsigned-integer data types. The most important of these methods are shown in Table 6-1.

Table 6-1. Members of the System.Convert class

Method	Description
ToBoolean	Converts a value to a Boolean
ToByte	Converts a value to a Byte
ToChar	Converts a value to a Char
ToDateTime	Converts a value to DateTime (Date in Visual Basic)
ToDecimal	Converts a value to Decimal
ToDouble	Converts a value to Double
ToInt16	Converts a value to Int16 (Short in Visual Basic)
ToInt32	Converts a value to Int32 (Integer in Visual Basic)
ToInt64	Converts a value to Int64 (Long in Visual Basic)
ToSByte	Converts a value to SByte, the unsigned-byte data type in the BCL
ToSingle	Converts a value to Single
ToString	Converts a value to String
ToUInt16	Converts a value to UInt16, an unsigned 16-bit integer
ToUInt32	Converts a value to UInt32, an unsigned 32-bit integer
ToUInt64	Converts a value to UInt64, an unsigned 64-bit integer

6.1.2 The Array Class

The Array class contains useful methods for dealing with arrays. For instance, the Array object has a Sort method (at last) that sorts the elements of an array. Here is an example:

 Sub sortArray(  ) Dim i As Integer Dim intArray(  ) As Integer = {9, 8, 12, 4, 5} For i = 0 To 4     console.WriteLine(CStr(intArray(i))) Next Array.Sort(intarray) Console.WriteLine("Sorted:") For i = 0 To 4     console.WriteLine(intArray(i)) Next End Sub 

The output is:

 9 8 12 4 5 Sorted: 4 5 8 9 12 

Some of the more important methods of the Array class are shown in Table 6-2.

Table 6-2. Some members of the System.Array class

Method	Description
BinarySearch	Searches a sorted one-dimensional array for a value
IndexOf	Returns the first occurrence of a particular value in a one-dimensional array
LastIndexOf	Returns the last occurrence of a particular value in a one-dimensional array
Reverse	Reverses the order of the elements in a one-dimensional array or a portion of a one-dimensional array
Sort	Sorts a one-dimensional array

6.1.3 The Math Class

The Math class has a number of mathematical-function methods (such as trigonometric functions), as well as some more useful methods, such as Max and Min. Therefore, we can just write:

 MsgBox(Math.Max(4,7)) 

Table 6-3 shows the members of the Math class.

Table 6-3. The members of the Math class

Topic	Description
Abs function	Absolute value
Acos function	Arccosine
Asin function	Arcsine
Atan function	Arctangent; returns the angle whose tangent is a specified number
Atan2 function	Arctangent; returns the angle whose tangent is the quotient of two specified numbers
Ceiling function	Returns the smallest integer greater than or equal to the argument number
Cos function	Cosine
Cosh function	Hyperbolic cosine
E field	The natural number e
Exp function	Exponential function
Floor function	Returns the largest integer less than or equal to the argument number
IEEERemainder function	Returns the remainder after dividing x by y
Log function	Natural (base e) logarithm
Log10 function	Common (base 10) logarithm
Max function	Maximum
Min function	Minimum
Mod operator	Returns the modulus , that is, the remainder when number1 is divided by number2
Pi field	Pi, the ratio of the circumference of a circle to its diameter
Pow function	Generalized exponential function
Randomize statement	Initializes the random number generator
Rnd function	Returns a random number
Round function	Rounds a given number to a specified number of decimal places
Sign function	Determines the sign of a number
Sin function	Sine
Sinh function	Hyperbolic sine
Sqrt function	Square root
Tan function	Tangent
Tanh function	Hyperbolic tangent

6.1.4 The String Class

The String class implements a collection of methods for string manipulation, including methods for locating substrings, concatenation, replacement, padding, trimming, and so on. One interesting method is Insert, which inserts a new string into an existing string.

The VB.NET String data type is equivalent to the System.String class, so we can apply the methods of System.String directly to VB strings, as in:

 Dim s As String = "To be to be" msgbox(s.Insert(6, "or not ")) 

This displays the message "To be or not to be." Table 6-4 shows the members of the String class.

Table 6-4. The members of the String class

Member	Description
Chars property	Returns the character at a specified character position in the string
Clone method	Returns a reference to an instance of the string
Compare method	A shared method that compares two string objects
CompareOrdinal method	A shared method that compares two string objects without considering localization
CompareTo method	Compares a string with a designated object
Concat method	Concatenates one or more instances of string
Copy method	A shared function that creates a new instance of a string with the same content as a designated string
CopyTo method	Copies a number of characters from a string to a specified position in an array of Unicode characters
Empty field	A read-only field that represents an empty string.
EndsWith method	Determines whether the end of a string matches a specified string
Equals method	Determines whether the string is equal to another string
Format method	Replaces a format specification with its textual equivalent
IndexOf method	Returns the position of the first occurrence of a substring within a string
IndexOfAny method	Returns the position of the first occurrence in a string of any of a set of characters
Insert method	Inserts a substring into a string
Join method	A shared method that concatenates a string separator and the elements of a string array
LastIndexOf method	Returns the position of the last occurrence of a substring within a string
LastIndexOfAny method	Returns the position of the last occurrence in a string of any of a set of characters
Length property	Returns the number of characters in the string
PadLeft method	Right aligns the characters in a string
PadRight method	Left aligns the characters in a string
Remove method	Deletes a specified number of characters from a string starting at a particular position
Replace method	Replaces all occurrences of a substring in a string with another substring
Split method	Splits a delimited string into a string array
StartsWith method	Determines whether the beginning of a string matches a particular substring
Substring method	Extracts a substring from a string
ToCharArray method	Copies the characters in a string to a character array
ToLower method	Converts a string to lowercase
ToUpper method	Converts a string to uppercase
Trim method	Removes all occurrences of a set of characters from the beginning and end of a string
TrimEnd method	Removes all occurrences of a set of characters from the end of a string
TrimStart method	Removes all occurrences of a set of characters from the beginning of a string