statement 声明是Visual Basic程序中的完整指令。 它可以包含关键字,运算符,变量,字面值,常量和表达式。
2、Executable statements 可执行语句 - 这些是启动动作的语句。 这些语句可以调用方法或函数,通过代码块循环或分支,或者将值或表达式赋值给变量或常量。 在最后一种情况下,它被称为Assignment语句。
S.N | 声明和说明 | 示例 |
---|---|---|
1 | Dim Statement Dim语句 Declares and allocates storage space for one or more variables. 声明和分配一个或多个变量的存储空间。 | Dim number As Integer Dim quantity As Integer = 100 Dim message As String = "Hello!" |
2 | Const Statement Const语句 Declares and defines one or more constants. 声明和定义一个或多个常量。 | Const maximum As Long = 1000 Const naturalLogBase As Object = CDec(2.7182818284) |
3 | Enum Statement 枚举语句 Declares an enumeration and defines the values of its members. 声明一个枚举并定义其成员的值。 | Enum CoffeeMugSize Jumbo ExtraLarge Large Medium Small End Enum |
4 | Class Statement 类语句 Declares the name of a class and introduces the definition of the variables, properties, events, and procedures that the class comprises. 声明类的名称,并引入该类包含的变量,属性,事件和过程的定义。 | Class Box Public length As Double Public breadth As Double Public height As Double End Class |
5 | Structure Statement 结构声明 Declares the name of a structure and introduces the definition of the variables, properties, events, and procedures that the structure comprises. 声明结构的名称,并引入结构所包含的变量,属性,事件和过程的定义。 | Structure Box Public length As Double Public breadth As Double Public height As Double End Structure |
6 | Module Statement 模块语句 Declares the name of a module and introduces the definition of the variables, properties, events, and procedures that the module comprises. 声明模块的名称,并介绍模块包含的变量,属性,事件和过程的定义。 | Public Module myModule Sub Main() Dim user As String = InputBox("What is your name?") MsgBox("User name is" & user) End Sub End Module |
7 | Interface Statement 接口语句Declares the name of an interface and introduces the definitions of the members that the interface comprises. 声明接口的名称,并介绍接口包含的成员的定义。 | Public Interface MyInterface Sub doSomething() End Interface |
8 | Function Statement 函数语句 Declares the name, parameters, and code that define a Function procedure. 声明定义函数过程的名称,参数和代码。 | Function myFunction (ByVal n As Integer) As Double Return 5.87 * n End Function |
9 | Sub Statement 子语句 Declares the name, parameters, and code that define a Sub procedure. 声明定义Sub过程的名称,参数和代码。 | Sub mySub(ByVal s As String) Return End Sub |
10 | Declare Statement 声明语句 Declares a reference to a procedure implemented in an external file. 声明对在外部文件中实现的过程的引用。 | Declare Function getUserName Lib "advapi32.dll" Alias "GetUserNameA" ( ByVal lpBuffer As String, ByRef nSize As Integer) As Integer |
11 | Operator Statement 运算符声明 Declares the operator symbol, operands, and code that define an operator procedure on a class or structure. 声明的运算符符号、 操作数和在类或结构定义一个运算符过程的代码。 | Public Shared Operator + (ByVal x As obj, ByVal y As obj) As obj Dim r As New obj ' implemention code for r = x + y Return r End Operator |
12 | Property Statement 属性声明 Declares the name of a property, and the property procedures used to store and retrieve the value of the property. 声明属性的名称,以及用于存储和检索属性值的属性过程。 | ReadOnly Property quote() As String Get Return quoteString End Get End Property |
13 | Event Statement 事件声明 Declares a user-defined event. 声明用户定义的事件。 | Public Event Finished() |
14 | Delegate Statement 委托声明 Used to declare a delegate. 用于声明一个委托。 | Delegate Function MathOperator( ByVal x As Double, ByVal y As Double ) As Double |
以下示例演示了一个决策语句:
Module decisions Sub Main() 'local variable definition ' Dim a As Integer = 10 ' check the boolean condition using if statement ' If (a < 20) Then ' if condition is true then print the following ' Console.WriteLine("a is less than 20") End If Console.WriteLine("value of a is : {0}", a) Console.ReadLine() End Sub End Module
当上述代码被编译和执行时,它产生了以下结果:
a is less than 20; value of a is : 10