// Single line /* Multiple line */ /// XML comments on single line /** XML comments on multiple lines */
Data Types
Value TypesBoolean Byte Char (example: "A"c)Short, Integer, Long Single, Double Decimal Date
Reference TypesObject String
Dim x As Integer Console.WriteLine(x.GetType()) ' Prints System.Int32 Console.WriteLine(TypeName(x)) ' Prints Integer
' Type conversionDim numDecimal As Single = 3.5 Dim numInt As Integer numInt = CType(numDecimal, Integer) ' set to 4 (Banker's rounding)numInt = CInt(numDecimal) ' same result as CTypenumInt = Int(numDecimal) ' set to 3 (Int function truncates the decimal)
int x; Console.WriteLine(x.GetType()); // Prints System.Int32Console.WriteLine(typeof(int)); // Prints System.Int32
// Type conversion double numDecimal = 3.5; int numInt = (int) numDecimal; // set to 3 (truncates decimal)
Constants
Const MAX_STUDENTS As Integer = 25
const int MAX_STUDENTS = 25;
Enumerations
Enum Action Start [Stop] ' Stop is a reserved word Rewind Forward End Enum Enum Status Flunk = 50 Pass = 70 Excel = 90 End Enum Dim a As Action = Action.Stop If a <> Action.Start Then Console.WriteLine(a) ' Prints 1 Console.WriteLine(Status.Pass) ' Prints 70 Dim s As Type = GetType(Status) Console.WriteLine([Enum].GetName(s, Status.Pass)) ' Prints Pass
enum Action {Start, Stop, Rewind, Forward}; enum Status {Flunk = 50, Pass = 70, Excel = 90}; Action a = Action.Stop; if (a != Action.Start) Console.WriteLine(a + " is " + (int) a); // Prints "Stop is 1" Console.WriteLine(Status.Pass); // Prints Pass
Operators
Comparison= < > <= >= <>
Arithmetic+ - * / Mod \ (integer division)^ (raise to a power)
Assignment= += -= *= /= \= ^= <<= >>= &=
BitwiseAnd AndAlso Or OrElse Not << >>
LogicalAnd AndAlso Or OrElse Not
Note: AndAlso and OrElse are for short-circuiting logical evaluations
String Concatenation&
Comparison== < > <= >= !=
Arithmetic+ - * / % (mod)/ (integer division if both operands are ints)Math.Pow(x, y)
Assignment= += -= *= /= %= &= |= ^= <<= >>= ++ --
Bitwise& | ^ ~ << >>
Logical&& || !
Note: && and || perform short-circuit logical evaluations
String Concatenation+
Choices
greeting = IIf(age < 20, "What's up?", "Hello")
' One line doesn't require "End If", no "Else"If language = "VB.NET" Then langType = "verbose"
' Use : to put two commands on same lineIf x <> 100 Then x *= 5 : y *= 2
' or to break up any long single command use _If whenYouHaveAReally < longLine And itNeedsToBeBrokenInto2 > Lines Then _ UseTheUnderscore(charToBreakItUp)
'If x > 5 Then x *= y ElseIf x = 5 Then x += y ElseIf x < 10 Then x -= y Else x /= y End If
Select Case color ' Must be a primitive data typeCase "pink", "red" r += 1 Case "blue" b += 1 Case "green" g += 1 Case Else other += 1 End Select
greeting = age < 20 ? "What's up?" : "Hello";
if (x != 100) { // Multiple statements must be enclosed in {} x *= 5; y *= 2; }
No need for _ or : since ; is used to terminate each statement.
if (x > 5) x *= y; else if (x == 5) x += y; else if (x < 10) x -= y; else x /= y;
switch (color) { // Must be integer or stringcase "pink": case "red": r++; break;// break is mandatory; no fall-throughcase "blue": b++; break; case "green": g++; break; default: other++; break;// break necessary on default }
Loops
Pre-test Loops:
While c < 10 c += 1 End While
Do Until c = 10 c += 1 Loop
Do While c < 10 c += 1 Loop
For c = 2 To 10 Step 2 Console.WriteLine(c) Next
Post-test Loops:
Do c += 1 Loop While c < 10
Do c += 1 Loop Until c = 10
' Array or collection loopingDim names As String() = {"Fred", "Sue", "Barney"} For Each s As String In names Console.WriteLine(s) Next
Pre-test Loops:
// no "until" keywordwhile (i < 10) i++; for (i = 2; i < = 10; i += 2) Console.WriteLine(i);
Post-test Loop: do i++; while (i < 10);
// Array or collection looping string[] names = {"Fred", "Sue", "Barney"}; foreach (string s in names) Console.WriteLine(s);
Arrays
Dim nums() As Integer = {1, 2, 3} For i As Integer = 0 To nums.Length - 1 Console.WriteLine(nums(i)) Next ' 4 is the index of the last element, so it holds 5 elementsDim names(4) As String names(0) = "David" names(5) = "Bobby" ' Throws System.IndexOutOfRangeException ' Resize the array, keeping the existing values (Preserve is optional)ReDim Preserve names(6)
Dim twoD(rows-1, cols-1) As Single twoD(2, 0) = 4.5 Dim jagged()() As Integer = { _ New Integer(4) {}, New Integer(1) {}, New Integer(2) {} } jagged(0)(4) = 5
int[] nums = {1, 2, 3}; for (int i = 0; i < nums.Length; i++) Console.WriteLine(nums[i]); // 5 is the size of the arraystring[] names = new string[5]; names[0] = "David"; names[5] = "Bobby"; // Throws System.IndexOutOfRangeException // C# doesn't can't dynamically resize an array. Just copy into new array.string[] names2 = new string[7]; Array.Copy(names, names2, names.Length); // or names.CopyTo(names2, 0);
float[,] twoD = new float[rows, cols]; twoD[2,0] = 4.5f;
int[][] jagged = new int[3][] { new int[5], new int[2], new int[3] }; jagged[0][4] = 5;
Functions
' Pass by value (in, default), reference (in/out), and reference (out)Sub TestFunc(ByVal x As Integer, ByRef y As Integer, ByRef z As Integer) x += 1 y += 1 z = 5 End Sub
Dim a = 1, b = 1, c As Integer ' c set to zero by default TestFunc(a, b, c) Console.WriteLine("{0} {1} {2}", a, b, c) ' 1 2 5
' Accept variable number of argumentsFunction Sum(ByVal ParamArray nums As Integer()) As Integer Sum = 0 For Each i As Integer In nums Sum += i Next End Function' Or use Return statement like C# Dim total As Integer = Sum(4, 3, 2, 1) ' returns 10
' Optional parameters must be listed last and must have a default value Sub SayHello(ByVal name As String, Optional ByVal prefix As String = "") Console.WriteLine("Greetings, " & prefix & " " & name) End Sub SayHello("Strangelove", "Dr.") SayHello("Madonna")
// Pass by value (in, default), reference (in/out), and reference (out)void TestFunc(int x, ref int y, out int z) { x++; y++; z = 5; }
int a = 1, b = 1, c; // c doesn't need initializing TestFunc(a, ref b, out c); Console.WriteLine("{0} {1} {2}", a, b, c); // 1 2 5
// Accept variable number of argumentsint Sum(params int[] nums) { int sum = 0; foreach (int i in nums) sum += i; return sum; }
int total = Sum(4, 3, 2, 1); // returns 10
/* C# doesn't support optional arguments/parameters. Just create two different versions of the same function. */ void SayHello(string name, string prefix) { Console.WriteLine("Greetings, " + prefix + " " + name); } void SayHello(string name) { SayHello(name, ""); }
Exception Handling
' Deprecated unstructured error handlingOn Error GoTo MyErrorHandler ... MyErrorHandler: Console.WriteLine(Err.Description) Dim ex As New Exception("Something is really wrong.") Throw ex
Try y = 0 x = 10 / y Catch ex As Exception When y = 0 ' Argument and When is optional Console.WriteLine(ex.Message) Finally Beep() End Try
Exception up = new Exception("Something is really wrong."); throw up; // ha ha
try { y = 0; x = 10 / y; } catch (Exception ex) { // Argument is optional, no "When" keyword Console.WriteLine(ex.Message); } finally { // Must use unmanaged MessageBeep API function to beep }
Namespaces
Namespace Harding.Compsci.Graphics ... End Namespace
' or
Namespace Harding Namespace Compsci Namespace Graphics ... End NamespaceEnd Namespace End Namespace
Class SuperHero Private _powerLevel As Integer Public Sub New () _powerLevel = 0 End Sub Public Sub New (ByVal powerLevel As Integer) Me._powerLevel = powerLevel End Sub Protected Overrides Sub Finalize () ' Desctructor code to free unmanaged resources MyBase.Finalize() End Sub End Class
class SuperHero { private int _powerLevel; public SuperHero() { _powerLevel = 0; } public SuperHero(int powerLevel) { this._powerLevel= powerLevel; } ~SuperHero() { // Destructor code to free unmanaged resources. // Implicitly creates a Finalize method } }
Objects
Dim hero As SuperHero = New SuperHero With hero .Name = "SpamMan" .PowerLevel = 3 End With hero.Defend("Laura Jones") hero.Rest() ' Calling Shared method' orSuperHero.Rest()
Dim hero2 As SuperHero = hero ' Both refer to same object hero2.Name = "WormWoman" Console.WriteLine(hero.Name) ' Prints WormWoman
hero = Nothing' Free the object
If hero IsNothing Then _ hero = New SuperHero
Dim obj As Object = New SuperHero If TypeOf obj Is SuperHero Then _ Console.WriteLine("Is a SuperHero object.")
SuperHero hero = new SuperHero(); // No "With" constructhero.Name = "SpamMan"; hero.PowerLevel = 3;
SuperHero hero2 = hero; // Both refer to same object hero2.Name = "WormWoman"; Console.WriteLine(hero.Name); // Prints WormWoman
hero = null ; // Free the object
if (hero == null) hero = new SuperHero();
Object obj = new SuperHero(); if (obj is SuperHero) Console.WriteLine("Is a SuperHero object.");
Structs
Structure StudentRecord Public name As String Public gpa As Single Public Sub New(ByVal name As String, ByVal gpa As Single) Me.name = name Me.gpa = gpa End Sub End Structure
Dim stu As StudentRecord = New StudentRecord("Bob", 3.5) Dim stu2 As StudentRecord = stu stu2.name = "Sue" Console.WriteLine(stu.name) ' Prints Bob Console.WriteLine(stu2.name) ' Prints Sue
struct StudentRecord { public string name; public float gpa; public StudentRecord(string name, float gpa) { this.name = name; this.gpa = gpa; } }
StudentRecord stu = new StudentRecord("Bob", 3.5f); StudentRecord stu2 = stu; stu2.name = "Sue"; Console.WriteLine(stu.name); // Prints BobConsole.WriteLine(stu2.name); // Prints Sue
Properties
Private _size As Integer Public Property Size() As Integer Get Return _size End GetSet (ByVal Value As Integer) If Value < 0 Then _size = 0 Else _size = Value End If End SetEnd Property
foo.Size += 1
private int _size; public int Size { get { return _size; } set { if (value < 0) _size = 0; else _size = value; } }
foo.Size++;
Delegates / Events
Delegate Sub MsgArrivedEventHandler(ByVal message As String)
Event MsgArrivedEvent As MsgArrivedEventHandler
' or to define an event which declares a delegate implicitlyEvent MsgArrivedEvent(ByVal message As String)
AddHandler MsgArrivedEvent, AddressOf My_MsgArrivedCallback ' Won't throw an exception if obj is Nothing RaiseEvent MsgArrivedEvent("Test message") RemoveHandler MsgArrivedEvent, AddressOf My_MsgArrivedCallback
Imports System.Windows.Forms
Dim WithEvents MyButton As Button ' WithEvents can't be used on local variableMyButton = New Button
Private Sub MyButton_Click(ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyButton.Click MessageBox.Show(Me, "Button was clicked", "Info", _ MessageBoxButtons.OK, MessageBoxIcon.Information) End Sub
// Delegates must be used with events in C# MsgArrivedEvent += new MsgArrivedEventHandler(My_MsgArrivedEventCallback); MsgArrivedEvent("Test message"); // Throws exception if obj is nullMsgArrivedEvent -= new MsgArrivedEventHandler(My_MsgArrivedEventCallback);
using System.Windows.Forms;
Button MyButton = new Button(); MyButton.Click += new System.EventHandler(MyButton_Click);
Special character constantsvbCrLf, vbCr, vbLf, vbNewLine vbNullString vbTab vbBack vbFormFeed vbVerticalTab "" Chr(65) ' Returns 'A'
Console.Write("What's your name? ") Dim name As String = Console.ReadLine() Console.Write("How old are you? ") Dim age As Integer = Val(Console.ReadLine()) Console.WriteLine("{0} is {1} years old.", name, age) ' or Console.WriteLine(name & " is " & age & " years old.") Dim c As Integer c = Console.Read() ' Read single char Console.WriteLine(c) ' Prints 65 if user enters "A"
Escape sequences\n, \r \t \\ \"
Convert.ToChar(65) // Returns 'A' - equivalent to Chr(num) in VB // or(char) 65
Console.Write("What's your name? "); string name = Console.ReadLine(); Console.Write("How old are you? "); int age = Convert.ToInt32(Console.ReadLine()); Console.WriteLine("{0} is {1} years old.", name, age); // orConsole.WriteLine(name + " is " + age + " years old.");
int c = Console.Read(); // Read single charConsole.WriteLine(c); // Prints 65 if user enters "A"
File I/O
Imports System.IO
Dim writer As StreamWriter = File.CreateText("c:\myfile.txt") writer.WriteLine("Out to file.") writer.Close()
Dim reader As StreamReader = File.OpenText("c:\myfile.txt") Dim line As String = reader.ReadLine() While Not line Is Nothing Console.WriteLine("line=" & line) line = reader.ReadLine() End While reader.Close()
Dim str As String = "Text data" Dim num As Integer = 123 Dim binWriter As New BinaryWriter (File.OpenWrite("c:\myfile.dat")) binWriter.Write(str) binWriter.Write(num) binWriter.Close()
Dim binReader As New BinaryReader (File.OpenRead("c:\myfile.dat")) str = binReader.ReadString() num = binReader.ReadInt32() binReader.Close()
using System.IO;
StreamWriter writer = File.CreateText("c:\\myfile.txt"); writer.WriteLine("Out to file."); writer.Close();
StreamReader reader = File.OpenText("c:\\myfile.txt"); string line = reader.ReadLine(); while (line != null) { Console.WriteLine(line); line = reader.ReadLine(); } reader.Close();
string str = "Text data"; int num = 123; BinaryWriter binWriter = new BinaryWriter(File.OpenWrite("c:\\myfile.dat")); binWriter.Write(str); binWriter.Write(num); binWriter.Close();
BinaryReader binReader = new BinaryReader(File.OpenRead("c:\\myfile.dat")); str = binReader.ReadString(); num = binReader.ReadInt32(); binReader.Close();
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