ProgramGood.Net - c# language

TekPub C#4 Jon Skeet

Dave Mateer — Sat, 19 May 2012 20:20:34 GMT

Supposed to be the introduction episode

Dynamic

static void Main(string[]
args)

{

object x = new List<int>();

//will give an InvalidCastException at runtime

string y = (string)
x;

Console.WriteLine(y.Length);

}

object x
= "hello";

string y = (string)
x;

Console.WriteLine(y.Length);

gives answer of 5

object x
= null;

//we can cast a null reference

string y = (string)x;

//but we cant dereference it..get a nullReferenceException

Console.WriteLine(y.Length);

sdf

//don't
think of x at any type... sort out at execution time

dynamic x = "hello";

//5

Console.WriteLine(x.Length);

//an array

x = new int[]
{10, 20, 30 };

//3

Console.WriteLine(x.Length);

from

int x
= 123;

int y = 10;

Console.WriteLine(x-y);

using ildasm to disassemble the debug assembly. The nop statements are for debug.

This is op code (IL).. i4 is like int32

load 123 and put into stack position 0

load 10 and put into stack position 1

then put into dynamic types

Named Arguments

Whats an argument and whats a parameter?

static void Main(string[]
args)

{

//provide an argument

Foo("hello");

}

//x is a parameter

static void Foo(string x)

{

Console.WriteLine(x);

}

}

Got it the wrong way round.. hard to tell which is which in MessageBox.Show

static void Main(string[]
args)

{

//named argument C#4

Foo(x: "hello", y:"Rob");

//referenced System.Windows.Forms

MessageBox.Show(caption:"title",
text:"body");

}

//x is a parameter

static void Foo(string x, string y)

{

Console.WriteLine(x + "
" + y);

}

better!

Optional Parameters

static void Main(string[]
args)

{

//named arguments

Foo(y: "Rob");

Foo(y: "Dave");

Foo(y: "Mike");

Foo(y: "Bill");

Foo("Hi", "Anders");

Foo();

}

//optional parameters

//if first parameter is optional all have to be

static void Foo(string x
= "Hello", string y
= "Everone")

{ 

Console.WriteLine(x + "
" + y);

}

}

Covariance and Contravariance

Some code here.. poster child of the more used covariance is IEnumerable<T>.. look for out keword. And it is to do with hierarchies.

class Fruit {
}

class Banana : Fruit {
}

class Apple : Fruit {
}

//interface IEnumerable<out T>

//{

// IEnumerator<T> GetEnumerator();

//}

//interface IEnumerator<out T> : IDisposable

//{

// T Current { get; }

// bool MoveNext();

// void Reset();

//}

//covariance values coming out of an interface

//usually happens with IEnumerable of T

interface IFoo<out T>

{

T GiveMeAnInstanceOfT();

//void TakeanInstanceOfT(T instance);

}

//contravariance is in

class Program

{

static void Main(string[]
args)

{

//List<Banana> bunchOfBananas = new List<Banana>();

IFoo<Banana>
bunchOfBananas = null;

//cant convert from a list of banana to a list of fruit

//List<Fruit> fruitBowl = new List<Banana>();

//List<Fruit> fruitBowl = bunchOfBananas;

//fruitBowl.Add(new Apple());

//Banana banana = bunchOfBananas[0]; 

//IEnumerable - sequence..cant add.. can only observe

//IEnumerable<Fruit> fruitBowl = bunchOfBananas;

IFoo<Fruit>
fruitBowl = bunchOfBananas;

}

}

IEnumerable Yield Deferred / Lazy

Dave Mateer — Tue, 14 Feb 2012 22:11:30 GMT

http://stackoverflow.com/questions/2515796/deferred-execution-and-eager-evaluation

C# Names

Dave Mateer — Tue, 27 Dec 2011 04:07:14 GMT

variables or local variables – declared inside methods

fields – variable (public or private) that is a member of a class

property – has a getter or setter

Code Reviews, TDD, Kata

Dave Mateer — Thu, 26 May 2011 02:02:37 GMT

http://ayende.com/blog/4092/reviewing-nerddinner

http://osherove.com/tdd-kata-2/

Sudoku

Dave Mateer — Sun, 10 Apr 2011 07:40:37 GMT

About a week ago Keith and I went on a ‘tramp’.. thats trekking. We discussed Sudoku (apologies to Helen, Phil, Nora and others for starting the challenge without you..there was lots of time while walking to discuss strategy).

TDD

A single test project is VS2010. Everything in one file (!) and static methods to make starting easier.

Coding strategy was to firstly:

find a way to check the sudoku was solved
- Do all horizontal lines have only 1 to 9 used once
- Do all vertical columns have 1 to 9 used once
- Do all 3*3 squares have 1 to 9 used once

So I wanted a method to check if Array has only 1 instance of each number.

[TestClass]

public class UnitTest1

{

// Arrays are [row, col]


// 0,0 0,1 0,2


// 1,0 1,1 1,2




// SECTION 1 - tests are all about testing if the sudoku
is solved


// Single Array


[TestMethod]

public void SingleArrayCheckerFailsWhenArrayTooShort()

{

int[] numbers = { 1, 2, 3, 4, 5, 6, 7, 8 };

bool result = DoesArrayHaveOnlyOneInstanceOfEachNumber(numbers);

Assert.AreEqual(false, result);

}

and the Method:

public static bool DoesArrayHaveOnlyOneInstanceOfEachNumber(int[]
arrayOfNumbers)

{

if (arrayOfNumbers.Length != 9)

return false;



if (arrayOfNumbers.Contains(0))

throw new Exception("checking
of a line array contains a 0");



int[] howManyInstancesOfEachNumber = new int[9]
{ 0, 0, 0, 0, 0, 0, 0, 0, 0 };



for (int i
= 0; i < 9; i++)

{

int valueOfCurrentNumber = arrayOfNumbers[i];

howManyInstancesOfEachNumber[valueOfCurrentNumber - 1] += 1;

}



foreach (var result in howManyInstancesOfEachNumber)

{

if (result != 1)

return false;

}



return true;

}

An array is Enumerable.

then write the tests

[TestMethod]

public void AllHorizonalLinesPass()

{

int[,] sudokuArray = new int[9,
9]{ {1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9}

};



bool result = DoAllHorizontalRowsPass(sudokuArray);

Assert.AreEqual(true, result);

}



[TestMethod]

public void AllVerticalColsPass()

{

int[,] sudokuArray = new int[9,
9]{ {1,1,1,1,1,1,1,1,1},

{2,2,2,2,2,2,2,2,2},

{3,3,3,3,3,3,3,3,3},

{4,4,4,4,4,4,4,4,4},

{5,5,5,5,5,5,5,5,5},

{6,6,6,6,6,6,6,6,6},

{7,7,7,7,7,7,7,7,7},

{8,8,8,8,8,8,8,8,8},

{9,9,9,9,9,9,9,9,9}

};



bool result = DoAllVerticalColsPass(sudokuArray);

Assert.AreEqual(true, result);

}



[TestMethod]

public void AllSquaresPass()

{

int[,] sudokuArray = new int[9,
9]{ {1,2,3,1,2,3,1,2,3},

{4,5,6,4,5,6,4,5,6},

{7,8,9,7,8,9,7,8,9},

{7,8,9,7,8,9,7,8,9},

{4,5,6,4,5,6,4,5,6},

{1,2,3,1,2,3,1,2,3},

{4,5,6,4,5,6,4,5,6},

{1,2,3,1,2,3,1,2,3},

{7,8,9,7,8,9,7,8,9},

};



bool result = DoAllSquaresPass(sudokuArray);

Assert.AreEqual(true, result);

}

then make them pass:

public static bool DoAllHorizontalRowsPass(int[,]
sudoku)

{

for (int row
= 0; row < 9; row++) // go over each horizontal line


{

int[] horizonalLineArray = new int[9];

for (int col
= 0; col < 9; col++) // get each number in that line
and put into a new horizontalLineArray


horizonalLineArray[col] = sudoku[row, col];



if (!DoesArrayHaveOnlyOneInstanceOfEachNumber(horizonalLineArray))

return false;

}

return true;

}



public static bool DoAllVerticalColsPass(int[,]
sudoku)

{

for (int col
= 0; col < 9; col++) // go over each vertical line


{

int[] verticalLineArray = new int[9];



for (int row
= 0; row < 9; row++) // get each number in that vertical
line and put into a new verticalLineArray


verticalLineArray[row] = sudoku[row, col];



if (!DoesArrayHaveOnlyOneInstanceOfEachNumber(verticalLineArray))

return false;

}

return true;

}



public static bool DoAllSquaresPass(int[,]
sudoku)

{

int rowStart = 0;

int rowEnd = 2;

int colStart = 0;

int colEnd = 2;



int squareCounter = 1;

while (squareCounter < 9) //
take each 3*3 square and test it


{

int[] allNumbersInSquareArray = new int[9];

// go over first 3*3 square


int counter = 0;

for (int row
= rowStart; row <= rowEnd; row++)

{

for (int col
= colStart; col <= colEnd; col++)

{

allNumbersInSquareArray[counter] = sudoku[row, col];

counter++;

}

}



if (!DoesArrayHaveOnlyOneInstanceOfEachNumber(allNumbersInSquareArray))

return false;



// increment to the next 3*3 square going along horizontally
first


if (colEnd != 8)

{

colStart += 3;

colEnd += 3;

}

else // go down to
next 'row' of squares


{

colStart = 0;

colEnd = 2;

rowStart += 3;

rowEnd += 3;

}



squareCounter++;

}

return true;

}

Making a Solver

Strategy was to (For all the elements with 0 in them):

Get rid of numbers
- LookAtOtherNumbersInRowAndTakeOutOnesWeDontNeedToCheck
- LookAtOtherNumbersInColumnAndTakeOutOnesWeDontNeedToCheck
- LookAtOtherNumbersInSquareAndTakeOutOnesWeDontNeed
- Then select a random number from the ones left
- check if sudoku is solved

I used TDD on each Method eg

[TestMethod]

public void LookAtOtherNumbersInRowAndTakeThoseOffTheListOfNumbersToTry()

{

int row = 2;

List<int> listOfNumbersToTry = new List<int>();

for (int i
= 1; i < 10; i++)

listOfNumbersToTry.Add(i);



int[,] trySudokuArray = new int[9,
9]{ {1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,0,4,5,6,0,8,0}, // this one


{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9},

{1,2,3,4,5,6,7,8,9}

};

LookAtOtherNumbersInRowAndTakeOutOnesWeDontNeedToCheck(trySudokuArray, row, listOfNumbersToTry);



Assert.AreEqual(3, listOfNumbersToTry.Count);

Assert.IsTrue(listOfNumbersToTry.Contains(3));

Assert.IsTrue(listOfNumbersToTry.Contains(7));

Assert.IsTrue(listOfNumbersToTry.Contains(9));

}

//level
1


public static int[,]
solve(int[,] inputSudokuArray) {



// fill in numbers which are correct


//int[,] sudokuArrayAfterB = new int[9, 9];


//sudokuArrayAfterB = solveB(inputSudokuArray);




// semi random code


Random random = new Random();

bool isSolved = false;

int numberOfIterations = 0;



while (!isSolved)

{

int[,] trySudokuArray = (int[,])sudokuArrayAfterB.Clone();

for (int row
= 0; row < 9; row++)

{

for (int col
= 0; col < 9; col++)

{

if (trySudokuArray[row,col] == 0) //
if it is blank


{

// setup numbers to try, then strategy is to take out
of this list


List<int> listOfNumbersToTry = new List<int>();

for (int i
= 1; i < 10; i++)

listOfNumbersToTry.Add(i);



LookAtOtherNumbersInRowAndTakeOutOnesWeDontNeedToCheck(trySudokuArray, row, listOfNumbersToTry);



LookAtOtherNumbersInColumnAndTakeOutOnesWeDontNeedToCheck(trySudokuArray, col, listOfNumbersToTry);



LookAtOtherNumbersInSquareAndTakeOutOnesWeDontNeed(trySudokuArray, row, col, listOfNumbersToTry);



// are there any possible numbers?


if (listOfNumbersToTry.Count > 0)

{

// pick a random number from listOfNumbersToTry


int indexOfListNumberToGet = random.Next(0, listOfNumbersToTry.Count());

trySudokuArray[row,col] = listOfNumbersToTry[indexOfListNumberToGet];

}

else


goto Foo;

}

}

}

isSolved = checkSudoku(trySudokuArray);



if (isSolved)

{

for (int row
= 0; row < 9; row++)

{

for (int col
= 0; col < 9; col++)

Debug.Write(trySudokuArray[row, col] + " ");

Debug.WriteLine("");

}

return trySudokuArray;

}

Foo:

if (numberOfIterations % 1000 == 0)

Debug.WriteLine("iterations: " + String.Format("{0:0,0}",numberOfIterations));

//Console.WriteLine("iterations: " + String.Format("{0:0,0}",
numberOfIterations));


numberOfIterations++;

}

return null;

}

StrategyB – Make numbers definite if we know they are

For each 0 square see if there is only 1 possible number
- ie look at LookAtOtherNumbersInRowAndTakeOutOnesWeDontNeedToCheck etc
- put that number in the square
- keep looping the whole board until nothing is changed

Asserting something is in a Collection

Dave Mateer — Mon, 07 Mar 2011 10:54:41 GMT

[TestMethod]

public void UnitTestThings()

{

Thing thing = new Thing();

IEnumerable<Thing> listOfThings = thing.giveMeAllThings(); 


Assert.AreEqual(3, listOfThings.Count()); // linq count


Assert.IsTrue(listOfThings.Any(t => t.name == "phone" &&
t.age == 3));

Assert.IsTrue(listOfThings.Any(t => t.name == "waterbottle" &&
t.age == 2));

Assert.IsTrue(listOfThings.Any(t => t.name == "pinecone" &&
t.age == 17));

}

Collection assertions http://msdn.microsoft.com/en-us/library/microsoft.visualstudio.testtools.unittesting.collectionassert.aspx

this is different from Contains:

[TestMethod]

public void when_asked_for_all_of_the_movies_it_should_receive_a_set_containing_each_movie_in_the_library()

{

Movie first_movie = new Movie();

Movie second_movie = new Movie();

movie_collection.Add(first_movie);

movie_collection.Add(second_movie);



MovieLibrary movieLibrary = new MovieLibrary(movie_collection);



IEnumerable<Movie> all_movies = movieLibrary.all_movies();



Assert.IsTrue(all_movies.Contains(first_movie));

Assert.IsTrue(all_movies.Contains(second_movie));

}

Asserting order of a Collection

Dave Mateer — Mon, 07 Mar 2011 10:50:09 GMT

[TestMethod]

public void when_sorting_movies_it_should_be_able_to_sort_all_movies_by_title_descending()

{

populateTestMovies(movie_collection);

MovieLibrary movieLibrary = new MovieLibrary(movie_collection);

IEnumerable<Movie> results = movieLibrary.sort_all_movies_by_title_descending();



IEnumerable<string> expected = new[] 


{ 


theres_something_about_mary.title,

the_ring.title,

shrek.title,

pirates_of_the_carribean.title,

indiana_jones_and_the_temple_of_doom.title,

cars.title,

a_bugs_life.title

};

Assert.IsTrue(results.Select(m => m.title).SequenceEqual(expected));

}

thanks to http://stackoverflow.com/questions/5218505/assert-that-a-collection-is-in-the-right-order

IEquatable

Dave Mateer — Mon, 07 Mar 2011 10:48:47 GMT

[TestMethod]

public void when_adding_two_different_copies_of_the_same_movie_it_should_store_only_1_copy_in_the_collection()

{

MovieLibrary movieLibrary = new MovieLibrary(movie_collection);

Movie speed_racer = new Movie { title = "Speed
Racer" };

Movie another_copy_of_speed_racer = new Movie
{ title = "Speed Racer" };



movieLibrary.add(speed_racer);

movieLibrary.add(another_copy_of_speed_racer);



Assert.AreEqual(1, movie_collection.Count);

}

Here is MovieLibrary:

public void add(Movie
movie)

{

// .Contains is from List


// Actually uses .Equals method to see if any movies
in collection is .Equal to the new one


if (!_list_of_movies_passed_to_us.Contains(movie))

_list_of_movies_passed_to_us.Add(movie);

}

And here is Movie, with the shorter way commented out with a longer way working

public class Movie
: IEquatable<Movie>

{

// Properties


public string title
{ get; set; }

public ProductionStudio production_studio { get;
set; }

public Genre genre { get; set; }

public int rating
{ get; set; }

public DateTime date_published { get; set; }



// Method


public bool Equals(Movie
other)

{

//return other == null ? false : other.title == this.title;


if (other == null)

return false;

else if (other.title
== this.title)

return true;

else


return false;

}

}

Returning an Interface IEnumerable, ICollection, IList

Dave Mateer — Mon, 07 Mar 2011 10:13:41 GMT

http://stackoverflow.com/questions/3686739/what-does-return-type-of-icollectionperson-mean

It is often better to return an interface instead of ‘concrete’ class (or implementation).

The reason for this is the freedom it provides – the implementation may change at a later date without affecting the calling code.

eg giveMeAllThings can change internally as long as I implement the methods that ICollection requires. And as a List implements these (and more), then this works.

Inside giveMeAllThings, I could have anything I like (doesn’t have to be a List).

public class Thing

{

public string name
{ get; set; }

public int age
{ get; set; }



public ICollection<Thing> giveMeAllThings() 


{

IList<Thing> listOfThings = new List<Thing>();

Thing thing1 = new Thing { name = "phone",
age = 3 };

Thing thing2 = new Thing { name = "waterbottle",
age = 2 };

Thing thing3 = new Thing { name = "pinecone",
age = 17 };

listOfThings.Add(thing1);

listOfThings.Add(thing2);

listOfThings.Add(thing3);

//foreach (Thing t in listOfThings)


// yield return t;




return listOfThings;

}

}



[TestClass]

public class UnitTest1

{

[TestMethod]

public void UnitTestThings()

{

Thing thing = new Thing();

IEnumerable<Thing> listOfThings = thing.giveMeAllThings(); 


Assert.AreEqual(3, listOfThings.Count()); // linq count


Assert.IsTrue(listOfThings.Any(t => t.name == "phone" &&
t.age == 3));

Assert.IsTrue(listOfThings.Any(t => t.name == "waterbottle" &&
t.age == 2));

Assert.IsTrue(listOfThings.Any(t => t.name == "pinecone" &&
t.age == 17));

}



[TestMethod]

public void UnitTestThingsWhereNeedAnICollection()

{

Thing thing = new Thing();

ICollection<Thing> listOfThings = thing.giveMeAllThings();

Assert.AreEqual(3, listOfThings.Count); // ICollection
count


}



// Won't compile as return type of giveMeAllThings is
an ICollection


//[TestMethod]


//public void UnitTestThingsWhereINeedAnActualList()


//{


// Thing thing = new Thing();


// IList<Thing> listOfThings = thing.giveMeAllThings();


// Assert.AreEqual(3, listOfThings.Count); // List count


//}

http://elegantcode.com/2008/04/07/replace-your-collections-with-ienumerablet/

Good article here.. basically saying that he is using IEnumerable<T> mostly, and Linq for things like Count, ElementAt etc..

Implementing an Interface

Dave Mateer — Fri, 04 Mar 2011 18:44:42 GMT

From http://msdn.microsoft.com/en-us/library/ms173156.aspx

public class Car
: IEquatable<Car>

{

public string Make
{get; set;}

public string Model
{ get; set; }

public string Year
{ get; set; }



// Implementation of IEquatable<T> interface


public bool Equals(Car
car)

{

if (this.Make
== car.Make &&

this.Model == car.Model &&

this.Year == car.Year)

{

return true;

}

else


return false;

}

}

When a class implements an interface, the class provides an implementation for all the members (properties and methods) defined by the interface

The IEquatable<T> interface announces to the user of the object that the object can determine whether it is equal to other objects of the same type, and the user of the interface does not have to know how this is implemented.

http://www.devarticles.com/c/a/C-Sharp/Interface-IEnumerable-and-IEnumerator-in-C-sharp/1/

What is an interface?
"An interface is a collection of method definitions (without implementations) and constant values".

Its purpose is to captures similarities between unrelated classes without forcing a class relationship,

IEnumerable and IEnumerator are the best interface examples there are for you to understand the role of interface. Classes implementing these two interfaces are classified as an enumerable collection. This means that class behaves like any other collection object written by Microsoft, such as an ArrayList.

There are many features that define an enumerable collection, and by implementing these two interfaces, the framework guarantees that this object has these features. For example, an enumerable collection must have a method called MoveNext, which moves the cursor within the collection one step forward. By implementing the IEnumerator interface, the class is promising (and is required) to implement this method.

As mentioned above, when a class implements these interfaces and is defined as an enumerable collection, it behaves like one as well. This means that it is capable of being iterated using a foreach statement, just like we can do with an ArrayList object.

Programming to an Interface

http://stackoverflow.com/questions/383947/what-does-it-mean-to-program-to-an-interface

common traits or behaviors that were exhibited by potentially many non-related classes of objects

Enums and Public Static Readonly

Dave Mateer — Thu, 03 Mar 2011 21:13:20 GMT

“..enums a great way to declare a variable of a type that can be one of a fixed set of values.”

http://geekswithblogs.net/BlackRabbitCoder/archive/2010/07/08/c-fundamentals-the-joys-and-pitfalls-of-enums.aspx

public enum ProductionStudio
{ MGM, Paramount, Universal, Pixar, Disney, Dreamworks};





public class ProductionStudio

{

public static readonly ProductionStudio
MGM = new ProductionStudio();

public static readonly ProductionStudio
Paramount = new ProductionStudio();

public static readonly ProductionStudio
Universal = new ProductionStudio();

public static readonly ProductionStudio
Pixar = new ProductionStudio();

public static readonly ProductionStudio
Disney = new ProductionStudio();

public static readonly ProductionStudio
Dreamworks = new ProductionStudio();

}

In some situations you may want to use public static readonly… a constant really. Gives intellisense.

Fields and Properties and AutoProperties

Dave Mateer — Thu, 03 Mar 2011 20:44:31 GMT

http://stackoverflow.com/questions/295104/what-is-the-difference-between-a-field-and-a-property-in-c

public class Movie

{

// this is a field. It is private to your class and stores
the actual data.


private string _title;



// this is a public field. Almost never used, as its
exposing the internals of the class to the outside world


public string _title;



// this is a property. When you access it uses the underlying
field, but only exposes


// the contract that will not be affected by the underlying
field


public string Title

{

get

{

return _title;

}

set

{

_title = value;

}

}



// Auto implemented property in C#3


public string Title1
{ get; set; } 


}

Changing a Time in C#

Dave Mateer — Thu, 17 Feb 2011 22:45:00 GMT

http://stackoverflow.com/questions/1859248/how-to-change-time-in-datetime

Coverting DateTimes to different TimeZones in .NET

Dave Mateer — Thu, 17 Feb 2011 22:26:22 GMT

http://www.xiirus.net/articles/article-_net-convert-datetime-from-one-timezone-to-another-7e44y.aspx

Dynamic Operators – Guernsey challenge

Dave Mateer — Thu, 13 Jan 2011 10:27:55 GMT

From the Guernsey adult literacy project, page 51.

What arithmetical symbols do you have to insert in between the numbers to get the correct result?

1 3 5 7 9 = 3

1 3 5 7 9 = 47

1 3 5 7 9 = 18

Note that only the symbols +, –, * and / are used.

An interesting challenge – do they mean that operator precedence is invoked too? ie MIDAS – Multiply before divide before add before subtract?

http://msdn.microsoft.com/en-us/library/aa691323(v=vs.71).aspx - order of all operators

a very useful sanity check in google..

Answers I found are:

-1-3+5-7+9 = (-1) - 3 + 5 - 7 + 9 = 3

1+3*5-7+9 = 1 + (3 * 5) - 7 + 9 = 18
-1*3+5+7+9 = 181 + (3 * 5) - 7 + 9 = 18

1*3+5*7+9 = (1 * 3) + (5 * 7) + 9 = 47
-1-3*5+7*9 =(-1) - (3 * 5) + (7 * 9) = 47

Code I used is:

string opZ
= "";

string opA = "";

string opB = "";

string opC = "";

string opD = "";

for (int h
= 1; h <= 2; h++) // making the first number positive
or negative


{

if (h == 1) opZ = "";

if (h == 2) opZ = "-";



for (int i
= 1; i <= 4; i++)

{

if (i == 1) opA = "*";

if (i == 2) opA = "/";

if (i == 3) opA = "+";

if (i == 4) opA = "-";

for (int j
= 1; j <= 4; j++)

{

if (j == 1) opB = "*";

if (j == 2) opB = "/";

if (j == 3) opB = "+";

if (j == 4) opB = "-";

for (int k
= 1; k <= 4; k++)

{

if (k == 1) opC = "*";

if (k == 2) opC = "/";

if (k == 3) opC = "+";

if (k == 4) opC = "-";

for (int l
= 1; l <= 4; l++)

{

if (l == 1) opD = "*";

if (l == 2) opD = "/";

if (l == 3) opD = "+";

if (l == 4) opD = "-";

string expression = opZ + 1 + opA + 3 + opB +
5 + opC + 7 + opD + 9;

DataTable dummy = new DataTable();

double result = Convert.ToDouble(dummy.Compute(expression, string.Empty));

if (result == 3)

Debug.WriteLine(expression + " = 3");



if (result == 47)

Debug.WriteLine(expression + " = 47");



if (result == 18)

Debug.WriteLine(expression + " = 18");



}

}

}

}

}

thanks to http://stackoverflow.com/questions/174664/operators-as-strings for the DataTable help.

From http://stackoverflow.com/questions/4679056/code-smell-in-dynamic-expression

TDD

To help in the refactoring I used tests to make sure I hadn’t broken anything:

using System;

using System.Text;

using System.Collections.Generic;

using System.Linq;

using Microsoft.VisualStudio.TestTools.UnitTesting;

using System.Data;

using System.Diagnostics;



namespace Guernsey1

{

/// <summary>


/// What arithmetical symbols do you have to insert in
between the numbers to get the correct result?


/// 1 3 5 7 9 = 3


/// 1 3 5 7 9 = 47


/// 1 3 5 7 9 = 18


/// There may be more than one answer for each one.


/// </summary>


[TestClass]

public class UnitTest1

{

[TestMethod]

public void GetAnswersForResultIs3()

{

List<string> listOfExpressions = findArithmeticSymbolsInNumericOrder13579ThatGivesThisResult(3);

foreach (string expression in listOfExpressions)

Assert.AreEqual("-1-3+5-7+9", expression);

}



[TestMethod]

public void GetAnswersForResultIs47()

{

List<string> listOfExpressions = findArithmeticSymbolsInNumericOrder13579ThatGivesThisResult(47);

Assert.AreEqual(true, listOfExpressions.Contains("1*3+5*7+9"));

Assert.AreEqual(true, listOfExpressions.Contains("-1-3*5+7*9"));

}



[TestMethod]

public void GetAnswersForResultIs18()

{

List<string> listOfExpressions = findArithmeticSymbolsInNumericOrder13579ThatGivesThisResult(18);

Assert.AreEqual(true, listOfExpressions.Contains("-1*3+5+7+9"));

Assert.AreEqual(true, listOfExpressions.Contains("1+3*5-7+9"));

}







public List<string>
findArithmeticSymbolsInNumericOrder13579ThatGivesThisResult(int resultExpected) //
Jons


{

List<string> listOfExpressions = new List<string>();

string[] prefixes = { "", "-" };

string[] operators = { "*", "/", "+", "-" };

IEnumerable<string> expressions = from prefix in prefixes

from opA in operators

from opB in operators

from opC in operators

from opD in operators

select prefix + 1 + opA + 3 + opB + 5 + opC + 7 + opD + 9;



foreach (string expression in expressions)

{

DataTable dummy = new DataTable();

double result = Convert.ToDouble(dummy.Compute(expression, string.Empty));

if (result == resultExpected)

listOfExpressions.Add(expression);

}

return listOfExpressions;

}



public List<string>
findArithmeticSymbolsInNumericOrder13579ThatGivesThisResult(int resultExpected) //
Cines


{

string[] prefixes = { "", "-" };

string[] operators = { "*", "/", "+", "-" };

List<string> listOfExpressions = new List<string>();

foreach (string opA in operators)

foreach (string opB in operators)

foreach (string opC in operators)

foreach (string opD in operators)

foreach (string prefix in prefixes)

{

string expression = prefix + 1 + opA + 3 + opB
+ 5 + opC + 7 + opD + 9;

DataTable dummy = new DataTable();

double result = Convert.ToDouble(dummy.Compute(expression, string.Empty));

if (result == resultExpected)

listOfExpressions.Add(expression);

}

return listOfExpressions;

}





public List<string>
findArithmeticSymbolsInNumericOrder13579ThatGivesThisResult(int resultExpected) //
Anton1


{

List<string> listOfExpressions = new List<string>();

var calculator = new DataTable();

var operators = "*/+-";

for (int i
= 0; i < 0x200; ++i)

{

string expression = String.Format("{0}1{1}3{2}5{3}7{4}9",

(i & 0x100) != 0 ? "-" : "",

operators[(i >> 0) & 3],

operators[(i >> 2) & 3],

operators[(i >> 4) & 3],

operators[(i >> 6) & 3]);



var result = calculator.Compute(expression, String.Empty);

if (Convert.ToDouble(result) == resultExpected)

listOfExpressions.Add(expression);

}

return listOfExpressions;

}



public List<string>
findArithmeticSymbolsInNumericOrder13579ThatGivesThisResult(int resultExpected) //
Anton2 - not working yet.. how to get the listOfExpressions?


{

List<string> listOfExpressions = new List<string>();

var operators = new Func<int, int, int>[]
{

(a, b) => a + b,

(a, b) => a - b,

(a, b) => a * b,

(a, b) => a / b 


};



for (int i
= 0; i < 0x200; ++i)

{

var stack = 0; // max stack depth is 2 because only 2
priorities


var last = 0; // imitate + for lowest precedence


var value = (i & 0x100) != 0 ? -1 : 1;



for (int j
= 0; j < 5; ++j) // extra item to force last reduction


{

var oper = (i >> j * 2) & 3; // "input"
operator


if (oper / 2 <= last / 2) //
reduce?


{

stack = operators[last](stack, value);

}

else // stack is
empty; prepare to shift


stack = value;



if (j == 4) break;



last = oper; // shift operator


value = 3 + j * 2; //
"input" number


}

}

// result in stack




return listOfExpressions;

}

}

}

Lambda Expressions

Dave Mateer — Sat, 11 Dec 2010 07:43:38 GMT

Lambda expressions are a simpler syntax for anonymous delegates

//
anonymous delegate


var evens = Enumerable

.Range(1, 100)

.Where(delegate(int x)
{ return (x % 2) == 0; })

.ToList();



// lambda expression


var evens = Enumerable

.Range(1, 100)

.Where(x => (x % 2) == 0)

.ToList();

I think this is clearer:

//
anonymous delegate


IEnumerable<int> evens = Enumerable

.Range(1, 100)

.Where(delegate(int x)
{ return (x % 2) == 0; })

.ToList(); // forcers immediate query evaluation

Many thanks to http://stackoverflow.com/questions/167343/c-lambda-expression-why-should-i-use-this

Projecteuler.net – Problem #1 (Linq Method and Query Syntax)

Dave Mateer — Wed, 08 Dec 2010 04:42:36 GMT

This is a fun site:

http://projecteuler.net

The first problem is:

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

static void Main(string[]
args)

{

int overallSum = 0;

for (int i
= 1; i < 1000; i++)

{

if ((i % 3 == 0) || (i % 5 == 0))

overallSum += i;

}

Console.WriteLine("overall sum is: " +
overallSum.ToString());

Console.ReadLine();

}

// should be 233168

or Phils way:

//Find
the sum of all the multiples of 3 or 5 below 1000.


//There is a summation formula which states


//The sum of all numbers from i = 1 to i = n is n(n+1)/2


static void Main(string[]
args)

{

int total = (3 * Convert.ToInt32(999 / 3) * (Convert.ToInt32((999
/ 3)) + 1)) / 2

+ (5 * Convert.ToInt32(999 / 5) * (Convert.ToInt32((999 / 5)) + 1)) / 2

- (15 * Convert.ToInt32(999 / 15) * (Convert.ToInt32((999 / 15)) + 1)) / 2;



Console.WriteLine("overall sum is: " +
total.ToString());

Console.ReadLine();



}

from http://answers.yahoo.com/question/index?qid=20100422031504AAfmpJ5)

or Simons way using method syntax (or fluent)

int result
= Enumerable.Range(0, 1000) // generates a sequence of
numbers in a range


.Where(i => i % 3 == 0 || i % 5 == 0) // filter using
lambda expression 


.Sum(); // sum of int32 using extension methods

and for fun, using method and query syntax

//
get the ones divisible by 3 in the list - Method syntax


IEnumerable<int> listOfDivisibleBy3Method
= listOfInts

.Where(i => i % 3 == 0);



// get the ones divisible by 3 in the list - Query syntax


IEnumerable<int> listOfDivisibleBy3Query
= from number in listOfInts

where (number % 3 == 0)

select number;

http://stackoverflow.com/questions/214500/which-linq-syntax-do-you-prefer-fluent-or-query-expression

Iterating over an Array

Dave Mateer — Thu, 18 Nov 2010 00:56:35 GMT

something like:

Array arraything = "abc, def";

           foreach (var item in arrayThing)
           {
               Console.WriteLine("item is: " + item);
           }

This works becuase an array in enumerable

Out Parameter

Dave Mateer — Wed, 17 Nov 2010 21:36:01 GMT

DateTime EffectiveDate;

if (!DateTime.TryParse(cert.GetEffectiveDateString(), out EffectiveDate))

{

return false;

}

For Loops

Dave Mateer — Sat, 25 Sep 2010 02:21:54 GMT

I saw some interesting code:

for (;
contours != null; contours = contours.HNext)

{

Contour<Point> approxContour = contours.ApproxPoly(contours.Perimeter * 0.02,
contours.Storage);

img.Draw(approxContour, new Bgr(1, 1, 251), 2);

}

I’d never seen the initial part of the for statement missing so I played:

class Program

{

static void Main(string[]
args)

{

for (int i
= 1; i <= 5; i++) // normal usage


{

Console.WriteLine("i count is {0}",
i);

}



int k = 1;

for (; k<=5; k++) //
missing first bit


{

Console.WriteLine("k count is {0}",
k);

}



int m = 1;

for (; m <= 5;) //
missing last bit too


{

Console.WriteLine("m count is {0}",
m);

m++;

}



for (; ; ) // infinite
loop, never breaks out


{



}







Contour contA = new Contour { x = 10, y = 20 };

Contour contB = new Contour { x = 50, y = 60 };

Contour contC = new Contour { x = 90, y = 100
};



List<Contour> listOfContours = new List<Contour>();

listOfContours.Add(contA); // better way to add to a
collection?


listOfContours.Add(contB);

listOfContours.Add(contC);



foreach (Contour contour in listOfContours)

{

Console.WriteLine("x is {0}", contour.x.ToString());

Console.WriteLine("y is {0}", contour.y.ToString());

Console.WriteLine();

}



int j = 0;

while (j < 5)

{

Console.WriteLine("While loop counter is {0}",
j.ToString());

j++;

}

}

}



class Contour

{

public int x;

public int y;

//public int x { get; set; }


//public int y { get; set; }


}

Default Values in Eval

Dave Mateer — Thu, 05 Aug 2010 02:25:49 GMT

I’m getting data using LINQ to SQL, then showing on the front end. If I want a null coming from the database to default to something:

<telerik:GridTemplateColumn HeaderText="Image" UniqueName="Image"> 


<ItemTemplate> 


<asp:Label ID="asdf" runat="server" Text='<%#
String.IsNullOrEmpty(Convert.ToString(Eval("Image1"))) ? "noImage.jpg"
: Eval("Image1")%>'></asp:Label>

<a href="<%=VirtualPathUtility.ToAbsolute("~/")%>showFrontEndMaterialDetail.aspx?materialId=<%#
Eval("Id")%>">

<img src="<%=VirtualPathUtility.ToAbsolute("~/")%>Images/Uploaded/Thumbs/<%#
Eval("Image1") ?? "noPhoto.jpg"
%>"></img></a>



</ItemTemplate> 


</telerik:GridTemplateColumn>

Thanks to these people:

http://stackoverflow.com/questions/3411155/c-eval-aspx-fun

http://stackoverflow.com/questions/3410942/linq-to-sql-default-value-nullable

Difference Between a Property and a Field using Repeaters

Dave Mateer — Wed, 04 Aug 2010 23:04:00 GMT

When displaying a repeater on an aspx page:

<asp:Repeater ID="Repeater1" runat="server">

<ItemTemplate>

<%#DataBinder.Eval(Container.DataItem, "FileName")%>

</ItemTemplate>

</asp:Repeater>

or shorter:

<asp:Repeater ID="Repeater1" runat="server">

<ItemTemplate>

<%#Eval("FileName")%>

</ItemTemplate>

</asp:Repeater>

It is important to remember to make FileName a property and not just a public field ie this works

public class ImageThing

{

public string FileName
{get; set; }

}



private void DisplayThumbnailImages()

{

ImageThing imageThing1 = new ImageThing();

ImageThing imageThing2 = new ImageThing();

imageThing1.FileName = "asdf.jpg";

imageThing2.FileName = "aaa.jpg";



List<ImageThing> imagesToRender = new List<ImageThing>();

imagesToRender.Add(imageThing1);

imagesToRender.Add(imageThing2);



Repeater1.DataSource = imagesToRender;

Repeater1.DataBind();

}

this doesn’t

public class ImageThing

{

public string FileName;

}

A property encapsulates a field.

Anonymous Types

Dave Mateer — Wed, 23 Jun 2010 03:35:49 GMT

While trying to figure out what is meant by the 3rd new section in a view in MVC

<%: Html.ActionLink("Edit", "Edit", new { id=item.DinnerID }) %>

So it is really creating an object with a single property id, which is an int, equal to that of the item, which is a Dinner.

“Anonymous types provide a convenient way to encapsulate a set of read-only properties into a single object without having to first explicitly define a type”

class Program

{

static void Main(string[]
args)

{

// Anonymous types provide a convenient way to encapsulate
a set of read-only properties


// into a single object without having to first explicitly
define a type


var person = new { Name = "Terry",
Age = 21 };

Console.WriteLine("name is " + person.Name);

Console.WriteLine("age is " + person.Age.ToString());



// Anonymous types just get rid of Person1 really.


Person1 person1 = new Person1 { Name = "Bill",
Age = 55 };

Console.WriteLine("name is " + person1.Name);

Console.WriteLine("age is " + person1.Age.ToString());

}

}



class Person1

{

public string Name
{ get; set; }

public int Age
{ get; set; }

}

Many thanks to the question here for clarifying:

http://stackoverflow.com/questions/3098643/anonymous-type-syntax-in-asp-net-mvc

Static Classes / Extension Methods

Dave Mateer — Thu, 11 Feb 2010 00:54:17 GMT

Static classes are usually used as ‘utility’ classes

You don’t need an instance

class Program

{

static void Main()

{

double result = thing.daveSubtract(10);

Console.WriteLine(result);

}

}



static class thing

{

static public double daveSubtract(double number)

{

return (number - 2);

}

}

Extension Methods

From: http://msdn.microsoft.com/en-us/library/bb383977.aspx

Extension methods enable you to "add" methods to existing types without creating a new derived type,

Extension methods are a special kind of static method, but they are called as if they were instance methods on the extended type.

For client code, there is no apparent difference between calling an extension method and the methods that are actually defined in a type.

using System;



namespace ConsoleApplication1

{

class Program

{

static void Main(string[]
args)

{

string s = "hello
extension methods are good";

Console.WriteLine(s);

int i = s.WordCount();

Console.WriteLine("number of words is {0}",
i.ToString());

}

}



public static class MyExtensions

{

public static int WordCount(this String
str)

{

return str.Split(new char[]
{ ' ', '.', '?' },
StringSplitOptions.RemoveEmptyEntries).Length;

}

}

}