>> in VB.NET

Generation QR Code in VB.NET >>

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Description Type comparison. Compares the first operand to another object, a data type, or Nothing, and returns True if there is a match. I will document this operator in more detail later in the text, and in 8. Syntax: operand1 Is operand2 Example: someVariable Is Nothing Negated type comparison. This operator is a shortcut for using the Is and Not operators together. The following two expressions are equivalent:

first IsNot second Not (first Is second)

Instance comparison. Returns the data type of a value or variable. The type of every class or data type in .NET is implemented as an object, based on System.Type. The TypeOf operator can be used only with the Is operator: Syntax: TypeOf operand1 Is typeOperand Example: TypeOf someVariable Is Integer Delegate retrieval. Returns a delegate (described in 8) that represents a specific instance of a procedure or method. Syntax: AddressOf method1 Example: AddressOf one.SomeMethod Type retrieval. Returns the data type of a value or variable, just like the TypeOf operator. However, GetType works like a function, and does not need to be used with the Is operator. Syntax: GetType(operand1) Example: GetType(one)

Non-assignment operators use their operands to produce a result, but they do not cause the operands themselves to be altered in any way. The assignment operator does update the operand that appears on its left side. In addition to the standard assignment operator, Visual Basic includes several operators that combine the assignment operator with some of the binary operators. Table 6-8 lists these assignment operators.

+ (addition)

(subtraction)

* (multiplication) / (division) \ (integer division) ^ (exponentiation)

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& (concatenation) << (shift left) >> (shift right)

These assignment operators are just shortcuts for the full-bodied operators. For instance, to add 1 to a numeric variable, you can use either of these two statements:

' ----- Increment totalSoFar by 1. totalSoFar = totalSoFar + 1 ' ----- Another way to increment totalSoFar by 1. totalSoFar += 1

Normally, the lifetime of a local procedure-level variable ends when the procedure ends. But sometimes you might want a variable to retain its value between each call into the procedure. Sometimes you might also want a million dollars, but you can t always have it. But you can have variables that keep their values if you want. They re called static variables. To declare a static variable, use the Static keyword in place of the Dim keyword.

The assignment of 0 to keepingTrack is done only once, when creating the instance of the type that contains this statement. Thereafter, it keeps whatever value is assigned to it until the instance is destroyed. Static variables can only be created within procedures.

Software applications often work with sets of related data, not just isolated data values. Visual Basic includes two primary ways of working with such sets of data: collections (discussed in 16) and arrays. An array assigns a numeric position to each item included in the set, starting with 0 and ending with one less than the number of items included. An array of five items has elements numbering from 0 to 4. As an example, imagine that you were developing a zoo simulation application. You might include an array named animals that includes each animal name in your zoo: Animal #0: Aardvark Animal #1: Baboon Animal #2: Chimpanzee

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Animal #3: Donkey ...and so on... Visual Basic identifies array elements by a parenthesized number after the array name. For our animals, a simple assignment puts the String name of each animal in an array element.

animal(0) animal(1) animal(2) animal(3) = = = = "Aardvark" "Baboon" "Chimpanzee" "Donkey"