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VB.NET
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Program Structure
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C#
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Imports System
Namespace Hello
Class HelloWorld
Overloads Shared Sub Main(ByVal
args() As String)
Dim name As String =
"VB.NET"
'See if an argument was passed from the command line
If args.Length = 1
Then name = args(0)
Console.WriteLine("Hello, " & name & "!")
End Sub
End Class
End Namespace
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using System;
namespace Hello {
public class HelloWorld {
public static void Main(string[]
args) {
string name =
"C#";
//
See if an argument was passed from the command line
if (args.Length == 1)
name = args[0];
Console.WriteLine("Hello,
" + name + "!");
}
}
}
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' Single line
only
REM Single
line only
''' <summary>XML comments</summary>
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// Single line
/* Multiple
line */
/// <summary>XML comments on single line</summary>
/** <summary>XML comments on multiple lines</summary> */
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Value Types
Boolean
Byte, SByte
Char
Short, UShort, Integer, UInteger, Long, ULong
Single, Double
Decimal
Date (alias of System.DateTime)
structures
enumerations
Reference Types
Object
String
arrays
delegates
Initializing
Dim correct As Boolean = True
Dim b As Byte = &H2A 'hex or
&O52 for octal
Dim person As Object = Nothing
Dim name As String = "Dwight"
Dim grade As Char = "B"c
Dim today As Date = #12/31/2010 12:15:00 PM#
Dim amount As Decimal = 35.99@
Dim gpa As Single = 2.9!
Dim pi As Double = 3.14159265
Dim lTotal As Long = 123456L
Dim sTotal As Short = 123S
Dim usTotal As UShort = 123US
Dim uiTotal As UInteger = 123UI
Dim ulTotal As ULong = 123UL
Nullable Types
Dim x? As Integer = Nothing
Anonymous Types
Dim stu = New With {.Name = "Sue", .Gpa = 3.4}
Dim stu2 = New With {Key .Name = "Bob", .Gpa = 2.9}
Implicitly Typed Local Variables
Dim s = "Hello!"
Dim nums = New Integer() {1, 2, 3}
Dim hero = New SuperHero With {.Name = "Batman"}
Type Information
Dim x As Integer
Console.WriteLine(x.GetType()) ' Prints System.Int32
Console.WriteLine(GetType(Integer)) ' Prints System.Int32
Console.WriteLine(TypeName(x)) ' Prints Integer
Dim c as New Circle
isShape = TypeOf c Is Shape ' True if c is a Shape
isSame = o1 Is o2 //
True if o1 and o2 reference same object
Type Conversion / Casting
Dim d As Single = 3.5
Dim i As Integer = CType(d, Integer) ' set to 4 (Banker's rounding)
i = CInt(d) ' same result
as CType
i = Int(d) '
set to 3 (Int function truncates the decimal)
Dim s As New Shape
Dim c As Circle = TryCast(s, Circle) ' Returns Nothing if type cast fails
c = DirectCast(s, Circle) '
Throws InvalidCastException if type cast fails
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Value Types
bool
byte, sbyte
char
short, ushort, int, uint, long, ulong
float, double
decimal
DateTime (not a built-in
C# type)
structs
enumerations
Reference Types
object
string
arrays
delegates
Initializing
bool correct = true;
byte b = 0x2A; // hex
object person = null;
string name = "Dwight";
char grade = 'B';
DateTime today = DateTime.Parse("12/31/2010 12:15:00 PM");
decimal amount = 35.99m;
float gpa = 2.9f;
double pi = 3.14159265; // or
3.14159265D
long lTotal = 123456L;
short sTotal = 123;
ushort usTotal = 123;
uint uiTotal = 123; // or 123U
ulong ulTotal = 123; // or 123UL
Nullable Types
int? x = null;
Anonymous
Types
var stu = new {Name = "Sue", Gpa = 3.5};
var stu2 = new {Name = "Bob", Gpa = 2.9}; // no Key equivalent
Implicitly Typed Local Variables
var s = "Hello!";
var nums = new int[] { 1, 2, 3 };
var hero = new SuperHero() { Name = "Batman" };
Type Information
int x;
Console.WriteLine(x.GetType());
// Prints System.Int32
Console.WriteLine(typeof(int));
// Prints System.Int32
Console.WriteLine(x.GetType().Name); // prints Int32
Circle c = new Circle();
isShape = c is Shape; // true if c is a Shape
isSame = Object.ReferenceEquals(o1, o2) // true if o1 and o2 reference same object
Type Conversion / Casting
float d = 3.5f;
i = Convert.ToInt32(d); // Set to 4 (rounds)
int i = (int)d; //
set to 3 (truncates decimal)
Shape s = new Shape();
Circle c = s as Circle; // Returns null if type cast fails
c = (Circle)s; // Throws
InvalidCastException if type cast fails
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Const MAX_STUDENTS As Integer
= 25
' Can set to a const or var;
may be initialized in a constructor
ReadOnly MIN_DIAMETER As Single = 4.93
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const int MAX_STUDENTS =
25;
// Can set to a const or var; may be
initialized in a constructor
readonly float MIN_DIAMETER = 4.93f;
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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.ToString & " is " &
a) ' Prints "Stop
is 1"
Console.WriteLine(Status.Pass) ' Prints 70
Console.WriteLine(Status.Pass.ToString()) ' Prints Pass
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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((int) Status.Pass); // Prints 70
Console.WriteLine(Status.Pass); // Prints Pass
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Comparison
= < > <= >= <>
Arithmetic
+ - * /
Mod
\ (integer division)
^ (raise to a power)
Assignment
= += -= *= /= \= ^= <<=
>>= &=
Bitwise
And Or Xor Not << >>
Logical
AndAlso OrElse And Or Xor Not
Note: AndAlso and OrElse perform short-circuit
logical evaluations
String Concatenation
&
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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
+
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' Null-coalescing operator if called
with 2 arguments
x = If(y, 5) ' if y is
not Nothing then x = y, else x = 5
' Ternary/Conditional operator (IIf
evaluates 2nd and 3rd expressions)
greeting = If(age < 20, "What's up?",
"Hello")
' One line doesn't require "End
If"
If age < 20 Then greeting = "What's
up?"
If age < 20 Then greeting = "What's
up?" Else greeting = "Hello"
' Use : to put two commands on same
line
If x <> 100 AndAlso y < 5 Then x *=
5 : y *= 2
' Preferred
If x <> 100 AndAlso y < 5 Then
x *= 5
y *= 2
End If
' Use _ to break up long single line
or use implicit line break
If whenYouHaveAReally < longLine And
itNeedsToBeBrokenInto2 > Lines Then _
UseTheUnderscore(charToBreakItUp)
'If x > 5 Then
x *= y
ElseIf x = 5 OrElse y Mod 2 = 0 Then
x += y
ElseIf x < 10 Then
x -= y
Else
x /= y
End If
Select Case color ' Must be a primitive data type
Case "pink", "red"
r += 1
Case "blue"
b += 1
Case "green"
g += 1
Case Else
other += 1
End Select
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// Null-coalescing operator
x = y ?? 5; // if y
!= null then x = y, else x = 5
// Ternary/Conditional operator
greeting = age < 20 ? "What's up?" : "Hello";
if (age < 20)
greeting = "What's up?";
else
greeting = "Hello";
// Multiple statements must be
enclosed in {}
if (x != 100 && y < 5) {
x *= 5;
y *= 2;
}
No need for _ or : since ; is used
to terminate each statement.
if (x > 5)
x *= y;
else if (x == 5 || y % 2 == 0)
x += y;
else if (x < 10)
x -= y;
else
x /= y;
// Every case must end with break or goto case
switch (color) { // Must be integer or string
case "pink":
case "red":
r++; break;
case "blue":
b++; break;
case "green": g++; break;
default: other++; break; // break necessary on default
}
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Pre-test Loops:
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While c < 10
c += 1
End While
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Do Until c = 10
c += 1
Loop
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Do While c < 10
c += 1
Loop
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For c
= 2 To 10 Step 2
Console.WriteLine(c)
Next
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Post-test Loops:
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Do
c += 1
Loop While c < 10
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Do
c += 1
Loop Until c = 10
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' Array or collection looping
Dim names As String() = {"Fred", "Sue",
"Barney"}
For Each s As String In names
Console.WriteLine(s)
Next
' Breaking out of loops
Dim i As Integer = 0
While (True)
If (i = 5) Then Exit While
i += 1
End While
' Continue to next iteration
For i = 0 To 4
If i < 4 Then Continue For
Console.WriteLine(i) ' Only
prints 4
Next
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Pre-test
Loops:
// no "until" keyword
while (c < 10)
c++;
for (c = 2; c <= 10; c += 2)
Console.WriteLine(c);
Post-test Loop:
do
c++;
while (c < 10);
// Array or collection looping
string[] names = {"Fred", "Sue", "Barney"};
foreach (string s in names)
Console.WriteLine(s);
// Breaking out of loops
int i = 0;
while (true) {
if (i == 5)
break;
i++;
}
// Continue to next iteration
for (i = 0; i <= 4; i++) {
if (i < 4)
continue;
Console.WriteLine(i); // Only
prints 4
}
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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 elements
Dim 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
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int[] nums = {1, 2, 3};
for (int i = 0; i < nums.Length; i++)
Console.WriteLine(nums[i]);
// 5 is the size of the array
string[] names = new string[5];
names[0] = "David";
names[5] = "Bobby"; //
Throws System.IndexOutOfRangeException
// Add two elements, keeping the existing values
Array.Resize(ref names, 7);
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;
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' 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
arguments
Function 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("Mom")
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// 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
arguments
int 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# 4.0 supports optional
parameters. Previous versions required function overloading. */
void SayHello(string name, string prefix = "") {
Console.WriteLine("Greetings, " + prefix + " " +
name);
}
SayHello("Strangelove",
"Dr.");
SayHello("Mom");
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Special character constants (all
also accessible from ControlChars class)
vbCrLf, vbCr, vbLf, vbNewLine
vbNullString
vbTab
vbBack
vbFormFeed
vbVerticalTab
""
' String concatenation (use & or
+)
Dim school As String = "Harding" & vbTab
school = school & "University" ' school is "Harding (tab) University"
school &= "University" ' Same thing (+= does the same)
' Chars
Dim letter As Char = school.Chars(0) ' letter is H
letter = "Z"c
' letter is Z
letter =
Convert.ToChar(65)
' letter is A
letter = Chr(65) ' same thing
Dim word() As Char = school.ToCharArray() ' word holds Harding
' No string literal operator
Dim filename As String = "c:\temp\x.dat"
' String comparison
Dim mascot As String = "Bisons"
If (mascot = "Bisons") Then '
true
If (mascot.Equals("Bisons")) Then ' true
If (mascot.ToUpper().Equals("BISONS")) Then
' true
If (mascot.CompareTo("Bisons") = 0) Then ' true
' String matching with Like - Regex
is more powerful
If ("John 3:16" Like "Jo[Hh]? #:*") Then
'true
' Substring
s = mascot.Substring(2, 3)) ' s is
"son"
' Replacement
s = mascot.Replace("sons", "nomial")) ' s is "Binomial"
' Split
Dim names As String = "Michael,Dwight,Jim,Pam"
Dim parts() As String = names.Split(",".ToCharArray())
' One name in each slot
' Date to string
Dim dt As New DateTime(1973, 10, 12)
Dim s As String = "My birthday: " & dt.ToString("MMM dd,
yyyy") ' Oct 12, 1973
' Integer to String
Dim x As Integer = 2
Dim y As String = x.ToString() '
y is "2"
' String to Integer
Dim x As Integer = Convert.ToInt32("-5") ' x is -5
' Mutable string
Dim buffer As New
System.Text.StringBuilder("two ")
buffer.Append("three ")
buffer.Insert(0, "one ")
buffer.Replace("two", "TWO")
Console.WriteLine(buffer) ' Prints "one TWO three"
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Escape sequences
\r // carriage-return
\n // line-feed
\t // tab
\\ // backslash
\" // quote
// String concatenation
string school = "Harding\t";
school = school + "University"; // school is "Harding (tab) University"
school += "University"; // Same thing
// Chars
char letter = school[0];
// letter is H
letter = 'Z';
//
letter is Z
letter = Convert.ToChar(65); //
letter is A
letter = (char)65; // same thing
char[] word = school.ToCharArray(); // word holds Harding
// String literal
string filename = @"c:\temp\x.dat"; // Same as "c:\\temp\\x.dat"
// String comparison
string mascot = "Bisons";
if (mascot == "Bisons") // true
if (mascot.Equals("Bisons")) // true
if (mascot.ToUpper().Equals("BISONS")) // true
if (mascot.CompareTo("Bisons") == 0) // true
// String matching - No Like
equivalent, use Regex
// Substring
s = mascot.Substring(2, 3)) // s is "son"
// Replacement
s = mascot.Replace("sons", "nomial"))
// s is "Binomial"
// Split
string names = "Michael,Dwight,Jim,Pam";
string[] parts = names.Split(",".ToCharArray());
// One name in each slot
// Date to string
DateTime dt = new DateTime(1973, 10, 12);
string s = dt.ToString("MMM dd, yyyy"); // Oct 12, 1973
// int to string
int x = 2;
string y = x.ToString(); // y
is "2"
// string to
int
int x = Convert.ToInt32("-5"); // x is -5
// Mutable string
System.Text.StringBuilder buffer = new System.Text.StringBuilder("two
");
buffer.Append("three ");
buffer.Insert(0, "one ");
buffer.Replace("two", "TWO");
Console.WriteLine(buffer); // Prints "one TWO three"
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VB.NET
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Regular Expressions
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C#
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Imports System.Text.RegularExpressions
' Match a string pattern
Dim r As New Regex("j[aeiou]h?. \d:*",
RegexOptions.IgnoreCase Or _
RegexOptions.Compiled)
If (r.Match("John 3:16").Success) Then 'true
Console.WriteLine("Match")
End If
' Find and remember all matching
patterns
Dim s As String = "My number is 305-1881, not 305-1818."
Dim r As New Regex("(\d+-\d+)")
Dim m As Match = r.Match(s) ' Matches 305-1881 and 305-1818
While m.Success
Console.WriteLine("Found number: " &
m.Groups(1).Value & " at position " _
& m.Groups(1).Index.ToString)
m = m.NextMatch()
End While
' Remeber multiple parts of matched
pattern
Dim r As New Regex("(\d\d):(\d\d) (am|pm)")
Dim m As Match = r.Match("We left at 03:15 pm.")
If m.Success Then
Console.WriteLine("Hour: " &
m.Groups(1).ToString) '
03
Console.WriteLine("Min: " & m.Groups(2).ToString)
' 15
Console.WriteLine("Ending: " &
m.Groups(3).ToString) ' pm
End If
' Replace all occurrances of a
pattern
Dim r As New Regex("h\w+?d", RegexOptions.IgnoreCase)
Dim s As String = r.Replace("I heard this was HARD!",
"easy") ' I easy this was
easy!
' Replace matched patterns
Dim s As String = Regex.Replace("123 < 456", "(\d+)
. (\d+)", "$2 > $1") ' 456 > 123
' Split a string based on a pattern
Dim names As String = "Michael, Dwight, Jim, Pam"
Dim r As New Regex(",\s*")
Dim parts() As String = r.Split(names) ' One name in each slot
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using System.Text.RegularExpressions;
// Match a string pattern
Regex r = new Regex(@"j[aeiou]h?. \d:*",
RegexOptions.IgnoreCase |
RegexOptions.Compiled);
if (r.Match("John 3:16").Success) // true
Console.WriteLine("Match");
// Find and remember all matching patterns
string s = "My number is 305-1881, not 305-1818.";
Regex r = new Regex("(\\d+-\\d+)");
// Matches 305-1881 and 305-1818
for (Match m = r.Match(s); m.Success; m = m.NextMatch())
Console.WriteLine("Found number: " + m.Groups[1] +
" at position " +
m.Groups[1].Index);
// Remeber multiple parts of matched pattern
Regex r = new Regex("@(\d\d):(\d\d) (am|pm)");
Match m = r.Match("We left at 03:15 pm.");
if (m.Success) {
Console.WriteLine("Hour: " + m.Groups[1]);
// 03
Console.WriteLine("Min: " + m.Groups[2]);
// 15
Console.WriteLine("Ending: " + m.Groups[3]);
// pm
}
// Replace all occurrances of a
pattern
Regex r = new Regex("h\\w+?d", RegexOptions.IgnoreCase);
string s = r.Replace("I heard this was HARD!",
"easy")); // I easy this
was easy!
// Replace matched patterns
string s = Regex.Replace("123 < 456", @"(\d+) .
(\d+)", "$2 > $1"); //
456 > 123
// Split a string based on a pattern
string names = "Michael, Dwight, Jim, Pam";
Regex r = new Regex(@",\s*");
string[] parts = r.Split(names); // One name in each slot
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VB.NET
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Exception Handling
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C#
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' Throw an exception
Dim ex As New Exception("Something is really wrong.")
Throw ex
' Catch an exception
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
' Deprecated unstructured error
handling
On Error GoTo MyErrorHandler
...
MyErrorHandler: Console.WriteLine(Err.Description)
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// Throw an exception
Exception up = new Exception("Something is really wrong.");
throw up; // ha ha
// Catch an exception
try {
y = 0;
x = 10 / y;
}
catch (Exception ex) { // Argument is optional, no "When" keyword
Console.WriteLine(ex.Message);
}
finally {
Microsoft.VisualBasic.Interaction.Beep();
}
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Namespace Harding.Compsci.Graphics
...
End Namespace
' or
Namespace Harding
Namespace Compsci
Namespace Graphics
...
End Namespace
End Namespace
End Namespace
Imports Harding.Compsci.Graphics
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namespace Harding.Compsci.Graphics {
...
}
// or
namespace Harding {
namespace Compsci {
namespace Graphics {
...
}
}
}
using Harding.Compsci.Graphics;
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VB.NET
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Classes &
Interfaces
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C#
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Access Modifiers
Public
Private
Friend
Protected
Protected Friend
Class Modifiers
MustInherit
NotInheritable
Method Modifiers
MustOverride
NotInheritable
Shared
Overridable
' All members are Shared
Module
' Partial classes
Partial Class Competition
...
End Class
' Inheritance
Class FootballGame
Inherits Competition
...
End Class
' Interface definition
Interface IAlarmClock
Sub Ring()
Property TriggerDateTime() As DateTime
End Interface
' Extending an interface
Interface IAlarmClock
Inherits IClock
...
End Interface
' Interface implementation
Class WristWatch
Implements IAlarmClock, ITimer
Public Sub Ring() Implements IAlarmClock.Ring
Console.WriteLine("Wake up!")
End Sub
Public Property TriggerDateTime As DateTime Implements IAlarmClock.TriggerDateTime
...
End Class
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Access Modifiers
public
private
internal
protected
protected internal
Class Modifiers
abstract
sealed
static
Method Modifiers
abstract
sealed
static
virtual
No Module equivalent - just use
static class
// Partial classes
partial class Competition {
...
}
// Inheritance
class FootballGame : Competition {
...
}
// Interface definition
interface IAlarmClock {
void Ring();
DateTime CurrentDateTime { get; set; }
}
// Extending an interface
interface IAlarmClock : IClock {
...
}
// Interface implementation
class WristWatch : IAlarmClock, ITimer {
public void Ring() {
Console.WriteLine("Wake up!");
}
public DateTime TriggerDateTime { get; set; }
...
}
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VB.NET
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Constructors &
Destructors
|
C#
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Class SuperHero
Inherits Person
Private powerLevel As Integer
Private name As String
' Default constructor
Public Sub New()
powerLevel = 0
name = "Super Bison"
End Sub
Public Sub New(ByVal powerLevel As Integer)
Me.New("Super Bison") ' Call other constructor
Me.powerLevel = powerLevel
End Sub
Public Sub New(ByVal name As String)
MyBase.New(name) ' Call base classes' constructor
Me.name = name
End Sub
Shared Sub New()
' Shared constructor invoked
before 1st instance is created
End Sub
Protected Overrides Sub Finalize()
' Destructor to free unmanaged
resources
MyBase.Finalize()
End Sub
End Class
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class SuperHero : Person {
private int powerLevel;
private string name;
// Default constructor
public SuperHero() {
powerLevel = 0;
name = "Super Bison";
}
public SuperHero(int powerLevel)
: this("Super Bison") { // Call other constructor
this.powerLevel = powerLevel;
}
public SuperHero(string name)
: base(name) { // Call base classes' constructor
this.name = name;
}
static SuperHero() {
// Static constructor invoked
before 1st instance is created
}
~SuperHero() {
// Destructor implicitly
creates a Finalize method
}
}
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Dim hero As SuperHero = New SuperHero
' or
Dim hero As New SuperHero
With hero
.Name = "SpamMan"
.PowerLevel = 3
End With
hero.Defend("Laura Jones")
hero.Rest() '
Calling Shared method
' or
SuperHero.Rest()
Dim hero2 As SuperHero = hero ' Both reference the same object
hero2.Name = "WormWoman"
Console.WriteLine(hero.Name) '
Prints WormWoman
hero = Nothing ' Free the object
If hero Is Nothing Then
_
hero = New SuperHero
Dim obj As Object = New SuperHero
If TypeOf obj Is SuperHero Then _
Console.WriteLine("Is a SuperHero object.")
' Mark object for quick disposal
Using reader As StreamReader = File.OpenText("test.txt")
Dim line As String = reader.ReadLine()
While Not line Is Nothing
Console.WriteLine(line)
line = reader.ReadLine()
End While
End Using
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SuperHero hero = new SuperHero();
// No "With" but can use
object initializers
SuperHero hero = new SuperHero() { Name = "SpamMan", PowerLevel = 3
};
hero.Defend("Laura Jones");
SuperHero.Rest(); // Calling
static method
SuperHero hero2 = hero; // Both
reference the 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.");
// Mark
object for quick disposal
using (StreamReader reader = File.OpenText("test.txt"))
{
string line;
while ((line = reader.ReadLine()) != null)
Console.WriteLine(line);
}
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Structure Student
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 Student = New
Student("Bob", 3.5)
Dim stu2 As Student = stu
stu2.name = "Sue"
Console.WriteLine(stu.name) '
Prints Bob
Console.WriteLine(stu2.name) ' Prints Sue
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struct Student {
public string name;
public float gpa;
public Student(string name, float gpa) {
this.name = name;
this.gpa = gpa;
}
}
Student stu = new Student("Bob",
3.5f);
Student stu2 = stu;
stu2.name = "Sue";
Console.WriteLine(stu.name); //
Prints Bob
Console.WriteLine(stu2.name); //
Prints Sue
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' Auto-implemented properties are
new to VB10
Public Property Name As String
Public Property Size As Integer = -1 ' Default value, Get and Set both Public
' Traditional property
implementation
Private mName As String
Public Property Name() As String
Get
Return mName
End Get
Set(ByVal value As String)
mName = value
End Set
End Property
' Read-only property
Private mPowerLevel As Integer
Public ReadOnly Property PowerLevel() As Integer
Get
Return mPowerLevel
End Get
End Property
' Write-only property
Private mHeight As Double
Public WriteOnly Property Height() As Double
Set(ByVal value As Double)
mHeight = If(value < 0, mHeight = 0, mHeight =
value)
End Set
End Property
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// Auto-implemented properties
public string Name { get; set; }
public int Size { get; protected set; }
// Set default value in
constructor
// Traditional property implementation
private string name;
public string Name {
get {
return name;
}
set {
name = value;
}
}
// Read-only property
private int powerLevel;
public int PowerLevel {
get {
return powerLevel;
}
}
// Write-only property
private double height;
public double Height {
set {
height = value < 0 ? 0 : value;
}
}
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' Enforce accepted data type at
compile-time
Dim numbers As New List(Of Integer)
numbers.Add(2)
numbers.Add(4)
DisplayList(Of Integer)(numbers)
' Subroutine can display any type of
List
Sub DisplayList(Of T)(ByVal list As List(Of T))
For Each item As T In list
Console.WriteLine(item)
Next
End Sub
' Class works on any data type
Class SillyList(Of T)
Private list(10) As T
Private rand As New Random
Public Sub Add(ByVal item As T)
list(rand.Next(10)) = item
End Sub
Public Function GetItem() As T
Return list(rand.Next(10))
End Function
End Class
' Limit T to only types that
implement IComparable
Function Maximum(Of T As IComparable)(ByVal ParamArray items As T())
As T
Dim max As T = items(0)
For Each item As T In items
If item.CompareTo(max) > 0 Then max = item
Next
Return max
End Function
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// Enforce accepted data type at
compile-time
List<int> numbers = new List<int>();
numbers.Add(2);
numbers.Add(4);
DisplayList<int>(numbers);
// Function can display any type of
List
void DisplayList<T>(List<T> list) {
foreach (T item in list)
Console.WriteLine(item);
}
// Class works on any data type
class SillyList<T> {
private T[] list = new T[10];
private Random rand = new Random();
public void Add(T item) {
list[rand.Next(10)] = item;
}
public T GetItem() {
return list[rand.Next(10)];
}
}
// Limit T to only types that
implement IComparable
T Maximum<T>(params T[] items) where
T : IComparable<T> {
T max = items[0];
foreach (T item in items)
if (item.CompareTo(max) > 0)
max = item;
return max;
}
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VB.NET
|
Delegates & Lambda Expressions
|
C#
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Delegate Sub HelloDelegate(ByVal s As String)
Sub SayHello(ByVal s As String)
Console.WriteLine("Hello, " & s)
End Sub
' Create
delegate that calls SayHello
Dim hello As HelloDelegate = AddressOf SayHello
hello("World") ' Or
hello.Invoke("World")
' Use lambda expression (anonymous
method) instead of a delegate
Dim hello2 = Sub(x) Console.WriteLine("Hello, " & x)
hello2("World")
' Use Func(Of T, TResult) delegate
to call Uppercase
Dim convert As Func(Of String, String) = AddressOf Uppercase
Console.WriteLine(convert("test"))
Function Uppercase(s As String) As String
Return s.ToUpper()
End Function
' Declare and invoke lambda
expression
Console.WriteLine((Function(num As Integer) num + 1)(2))
' Pass lambda expression as an
argument
TestValues(Function(x, y) x Mod y = 0)
Sub TestValues(ByVal f As Func(Of
Integer, Integer, Boolean))
If f(8, 4) Then
Console.WriteLine("true")
Else
Console.WriteLine("false")
End If
End Sub
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delegate void HelloDelegate(string s);
void SayHello(string s) {
Console.WriteLine("Hello, " + s);
}
// C# 1.0 delegate syntax with named
method
HelloDelegate hello = new HelloDelegate(SayHello);
hello("World"); // Or
hello.Invoke("World");
// C# 2.0 delegate syntax with
anonymous method
HelloDelegate hello2 = delegate(string s) {
Console.WriteLine("Hello, " + s);
};
hello2("World");
// C# 3.0 delegate syntax with
lambda expression
HelloDelegate hello3 = s => {
Console.WriteLine("Hello, " + s); };
hello3("World");
// Use Func<in T, out TResult>
delegate to call Uppercase
Func<string, string> convert = Uppercase;
Console.WriteLine(convert("test"));
string Uppercase(string s) {
return s.ToUpper();
}
// Declare and invoke Func using a
lambda expression
Console.WriteLine(new Func<int, int>(num => num
+ 1)(2));
// Pass lamba expression as an
argument
TestValues((x, y) => x % y == 0);
void TestValues(Func<int, int,
bool> f) {
if (f(8, 4))
Console.WriteLine("true");
else
Console.WriteLine("false");
}
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Delegate Sub MsgArrivedEventHandler(ByVal message
As String)
Event MsgArrivedEvent As MsgArrivedEventHandler
' or to define an event which
declares a delegate implicitly
Event 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 variable
MyButton = New Button
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
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delegate void MsgArrivedEventHandler(string
message);
event MsgArrivedEventHandler MsgArrivedEvent;
// Delegates must be used with
events in C#
MsgArrivedEvent += new
MsgArrivedEventHandler(My_MsgArrivedEventCallback);
MsgArrivedEvent("Test message"); // Throws exception if obj is null
MsgArrivedEvent -= new
MsgArrivedEventHandler(My_MsgArrivedEventCallback);
using System.Windows.Forms;
Button MyButton = new Button();
MyButton.Click += new System.EventHandler(MyButton_Click);
void MyButton_Click(object sender,
System.EventArgs e) {
MessageBox.Show(this, "Button was clicked",
"Info",
MessageBoxButtons.OK, MessageBoxIcon.Information);
}
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Dim nums() As Integer = {5, 8, 2, 1, 6}
' Get all numbers in the array above 4
Dim results = From n In nums
Where n
> 4
Select n
' Same thing using lamba expression
results = nums.Where(Function(n) n > 4)
' Displays 5 8 6
For Each n As Integer In results
Console.Write(n & " ")
Next
Console.WriteLine(results.Count()) ' 3
Console.WriteLine(results.First()) ' 5
Console.WriteLine(results.Last()) ' 6
Console.WriteLine(results.Average()) ' 6.33333
results = results.Intersect({5, 6, 7}) ' 5 6
results = results.Concat({5, 1, 5}) ' 5 6 5 1 5
results = results.Distinct() ' 5 6 1
Dim Students() As Student = {
New Student With {.Name = "Bob", .Gpa = 3.5},
New Student With {.Name = "Sue", .Gpa = 4.0},
New Student With {.Name = "Joe", .Gpa = 1.9}
}
' Get a list of students ordered by Gpa with Gpa
>= 3.0
Dim goodStudents = From s In Students
Where s.Gpa >=
3.0
Order By s.Gpa Descending
Select s
Console.WriteLine(goodStudents.First.Name) ' Sue
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int[] nums = { 5, 8, 2,
1, 6 };
// Get all numbers in the array above 4
var results = from n in nums
where n
> 4
select n;
// Same thing using lamba expression
results = nums.Where(n => n > 4);
// Displays 5 8 6
foreach (int n in results)
Console.Write(n + " ");
Console.WriteLine(results.Count()); // 3
Console.WriteLine(results.First()); // 5
Console.WriteLine(results.Last()); // 6
Console.WriteLine(results.Average()); // 6.33333
results = results.Intersect(new[] {5, 6, 7}); // 5 6
results = results.Concat(new[] {5, 1, 5}); // 5 6 5 1 5
results = results.Distinct(); // 5 6 1
Student[] Students = {
new Student{ Name = "Bob", Gpa = 3.5 },
new Student{ Name = "Sue", Gpa = 4.0 },
new Student{ Name = "Joe", Gpa = 1.9 }
};
// Get a list of students ordered by Gpa with
Gpa >= 3.0
var goodStudents = from s in Students
where s.Gpa >=
3.0
orderby s.Gpa descending
select s;
Console.WriteLine(goodStudents.First().Name); // Sue
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' Attribute can be applied to
anything
Public Class IsTestedAttribute
Inherits Attribute
End Class
' Attribute can only be applied to classes or structs
<AttributeUsage(AttributeTargets.Class Or
AttributeTargets.Struct)>
Public Class AuthorAttribute
Inherits Attribute
Public Property Name As String
Public Property Version As Integer = 0
Public Sub New(ByVal name As String)
Me.Name = name
End Sub
End Class
<Author("Sue", Version:=3)>
Class Shape
<IsTested()>
Sub Move()
' Do
something...
End Sub
End Class
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// Attribute
can be applied to anything
public class IsTestedAttribute : Attribute
{
}
// Attribute can only be applied to classes or
structs
[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct)]
public class AuthorAttribute : Attribute {
public string Name { get; set; }
public int Version { get; set; }
public AuthorAttribute(string name) {
Name = name;
Version = 0;
}
}
[Author("Sue", Version = 3)]
class Shape {
[IsTested]
void Move() {
// Do
something...
}
}
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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"
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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);
// or
Console.WriteLine(name + " is " + age + " years old.");
int c = Console.Read(); // Read
single char
Console.WriteLine(c); //
Prints 65 if user enters "A"
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Imports System.IO
' Write out to text file
Dim writer As StreamWriter =
File.CreateText("c:\myfile.txt")
writer.WriteLine("Out to file.")
writer.Close()
' Read all lines from text file
Dim reader As StreamReader =
File.OpenText("c:\myfile.txt")
Dim line As String = reader.ReadLine()
While Not line Is Nothing
Console.WriteLine(line)
line = reader.ReadLine()
End While
reader.Close()
' Write out to binary file
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()
' Read from binary file
Dim binReader As New BinaryReader(File.OpenRead("c:\myfile.dat"))
str = binReader.ReadString()
num = binReader.ReadInt32()
binReader.Close()
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using System.IO;
// Write out to text file
StreamWriter writer =
File.CreateText("c:\\myfile.txt");
writer.WriteLine("Out to file.");
writer.Close();
// Read all lines from text file
StreamReader reader =
File.OpenText("c:\\myfile.txt");
string line = reader.ReadLine();
while (line != null) {
Console.WriteLine(line);
line = reader.ReadLine();
}
reader.Close();
// Write out to binary file
string str = "Text data";
int num = 123;
BinaryWriter binWriter = new BinaryWriter(File.OpenWrite("c:\\myfile.dat"));
binWriter.Write(str);
binWriter.Write(num);
binWriter.Close();
// Read from binary file
BinaryReader binReader = new
BinaryReader(File.OpenRead("c:\\myfile.dat"));
str = binReader.ReadString();
num = binReader.ReadInt32();
binReader.Close();
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