语句是Visual Basic程序中的完整说明.它可能包含关键字,运算符,变量,文字值,常量和表达式.
语句可以归类为 :
声明声明 : 这些是您为变量,常量或过程命名的语句,也可以指定数据类型.
可执行语句 &减去;这些是发起行动的陈述.这些语句可以调用方法或函数,循环或分支代码块或将值或表达式赋值给变量或常量.在最后一种情况下,它被称为赋值语句.
声明语句用于命名和定义过程,变量,属性,数组和常量.当您声明编程元素时,您还可以定义其数据类型,访问级别和范围.
您可以声明的编程元素包括变量,常量,枚举,类,结构,模块,接口,过程,过程参数,函数返回,外部过程引用,运算符,属性,事件和委托.
以下是VB.Net中的声明语句 :
Sr.No | 语句和描述 | 示例 |
---|---|---|
1 | Dim Statement 为一个或多个变量声明并分配存储空间. | Dim number As Integer Dim quantity As Integer = 100 Dim message As String = "Hello!" |
2 | Const Statement 声明并定义一个或多个常量. | Const maximum As Long = 1000 Const naturalLogBase As Object = CDec(2.7182818284) |
3 | Enum Statement 声明枚举并定义其成员的值. | Enum CoffeeMugSize Jumbo ExtraLarge Large Medium Small End Enum |
4 | Class Statement 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 声明结构的名称并引入变量,属性,事件和过程的定义结构包括. | Structure Box Public length As Double Public breadth As Double Public height As Double End Structure |
6 | Module Statement 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 声明接口的名称,并介绍接口所包含的成员的定义. | Public Interface MyInterface Sub doSomething() End Interface |
8 | Function Statement 声明定义Function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 声明定义Sub程序的名称,参数和代码e. | Sub mySub(ByVal s As String) Return End Sub |
10 | Declare Statement 声明对实现的程序的引用外部文件. | Declare Function getUserName Lib "advapi32.dll" Alias "GetUserNameA" ( ByVal lpBuffer As String, ByRef nSize As Integer) As Integer |
11 | Operator Statement 声明在类或结构上定义运算符过程的运算符符号,操作数和代码. | 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 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 宣布用户定义的事件. | Public Event Finished() |
14 | Delegate Statement 用于声明委托. | Delegate Function MathOperator( ByVal x As Double, ByVal y As Double ) As Double |
可执行语句执行操作.调用过程,分支到代码中的另一个位置,循环遍历多个语句或计算表达式的语句是可执行语句.赋值语句是可执行语句的特例.
示例
以下示例演示了决策制定语句 :
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
编译并执行上述代码时,会生成以下代码结果 :
a is less than 20; value of a is : 10