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 | |