C# programming language

--- Arrays section (C#) ---

Create new array

Create new array to store values.

int[] cat = new int[5];

// cat = 0, 0, 0, 0, 0

string[] s = new string[10];

// s = null, null, ...

Initialize array

Create new int or string array with certain values.

int[] cat = {1, 4, 6};

string[] a = {"dog", "cat", "plant"};

Assign array

Set element in array to value.

cat[0] = 3;

cat[1] = 4;

cat[4] = 7;

Check array size

Use array's length property, then access elements.

if (cat.Length == 3)

{

    // 3 elements

}

Sort array

Sort an array alphabetically (A - Z).

string[] a = new string[]

{

    "z", "a", "b"

};

Array.Sort(a);

// "a", "b", "z"

Use 2D array

Use a two-dimensional array to store a grid of values.

int[,] i = new int[2, 2];

i[0, 0] = 0;

i[0, 1] = 1;

i[1, 0] = 2;

i[1, 1] = 3;

// 0, 1

// 2, 3

Convert List to array

Use instance method ToArray() to convert List to equivalent array.

List e = new List();

e.Add(1);

e.Add(2);

int[] a = e.ToArray();

// a = 1, 2

Loop through List

Iterate through each item in an array or list.

List e = new List();

e.Add(1);

e.Add(2);

foreach (int i in e)

{

    // 1, 2

}

Reverse array

Reorder elements in array backwards.

int[] a = {5, 6, 1};

Array.Reverse(a);

// 1, 6, 5

--- Methods section (C#) ---

Ref parameter

Allow another method to directly change value.

class C

{

    void Method()

    {

        int a = 4;

        Method2(ref a);

        // a = 5

    }

    void Method2(ref int p)

    {

        p = 5;

    }

}

Out parameter

Allow another method to directly change value.

With compile-time checking.

class C

{

    void Method()

    {

        int a;

        Method2(out a);

        // a = 5

    }

    void Method2(out int p)

    {

        p = 5;

    }

}

--- Strings section (C#) ---

Split string

Divide string into separate parts.

string c = "one,two";

string[] s = c.Split(',');

// s[0] = "one"

// s[1] = "two"

String new lines

Declare a string with newlines in it. Use "" for a quote.

string s = @"line 1

line 2

line 3";

Combine strings

Add strings together (also called concatenation).

Use overloaded + operator.

string s1 = "cat";

string s2 = "dog";

string c = s1 + " and " + s2;

// c = "cat and dog"

Compare strings

See if two strings have equal characters and lengths.

string s1 = "cat";

string s2 = "dog";

string s3 = "cat";

if (s1 == s2)

{

    // not true

}

if (s1 == s3)

{

    // success

}

Empty string check

See if string is empty or null (has no value).

string s1 = "";

string s2 = null;

string s3 = "cat";

if (string.IsNullOrEmpty(s1))

{

    // true

}

if (string.IsNullOrEmpty(s2))

{

    // true

}

if (string.IsNullOrEmpty(s3))

{

    // not true

}

Get string length

Find number of characters in string.

string c = "cat";

if (c.Length == 3)

{

    // true

}

Append strings quickly

Use StringBuilder and convert back to string.

StringBuilder b = new StringBuilder();

b.Append("Text");

b.Append(" more");

string r = b.ToString();

// r = "Text more"

Uppercase entire string

Uppercase each letter in string.

string s = "cat";

s = s.ToUpper();

// s = "CAT"

Uppercase first letter

Uppercase the first letter in string.

string s = "cat";

char[] a = s.ToCharArray();

a[0] = char.ToUpper(a[0]);

string u = new string(a);

// u = "Cat"

Convert string to int

Take string containing digits and convert it to int value.

string s = "105";

int i = int.Parse(s);

// i = 105

string s2 = "105.5";

double d = double.Parse(s2);

// d = 105.5

Substring of string

Get part of string based on indexes.

string s = "developer";

string b = s.Substring(0, 7);

// b = "develop"

Remove whitespace

Trim whitespace at beginning and ending of string.

string s = " cat  ";

string t = s.Trim();

// t = "cat"

Change string characters

Modify the letters in string in-place.

string s = "cat";

char[] a = s.ToCharArray();

    // a = 'c', 'a', 't'

a[0] = 'h';

    // a = 'h', 'a', 't'

string s2 = new string(a);

    // s2 = "hat"

--- Classes section (C#) ---

Declare constructor

Create new constructor for class.

class C

{

    public C(int a)

    {

        // initialize

    }

}

Cast safely

Use as operator or is operator.

Convert from one type to another.

void Method(object a)

{

    if (a is MyClass)

    {

        // correct type

    }

}

void Method2(object a)

{

    MyClass m = a as MyClass;

    if (m != null)

    {

        // correct type

    }

}

Null reference

Causes exception in programs. Null variable used.

string s = null;

if (s.Length == 0)

{

    // exception raised

}

New object

Create a new object of a kind.

class C

{

    // impl.

}

class Program

{

    void Main()

    {

        C name = new C();

    }

}

Singleton

Make a single object. One instance per AppDomain.

class S

{

    private static readonly _inst = new S();

    public static S Instance

    {

        get { return _inst; }

    }

    S()

    {

        // init

    }

}

Properties, Accessors, Getters, setters

Create properties to access fields of classes publicly.

class C

{

    public int P { get; set; }

}

void Method(C name)

{

    name.P = 4;

    int i = name.P;

    // i = 4

}

--- File/IO section (C#) ---

Read file lines

Read in each line of file into array.

string[] lines = File.ReadAllLines("file.txt");

// lines[0] = "..."

// lines[1] = "..."

Read text file

Read in entire file containing text.

string f = File.ReadAllText("file.txt");

// f = "..."

Read lines separately

Read file line-by-line with StreamReader.

Fastest and lowest memory.

using (StreamReader s = new StreamReader("file.txt"))

{

    string t;

    while ((t = s.ReadLine()) != null)

    {

        // t = "..."

    }

}

Append to file

Add text to end of file on disk.

File.AppendAllText("file.txt", "..." + Environment.NewLine);

Write file

Write text to file on disk, replacing any existing files.

File.WriteAllText("file.txt", "...");

Directory exists

See if folder exists on file system. Add using System.IO;

if (Directory.Exists("C:\\f"))

{

    // ...

}

File exists

See if file exists on disk at path.

if (File.Exists("file.txt"))

{

    // ...

}

--- Hashtables section (C#) ---

Use Dictionary

Use the generic Dictionary object with string keys.

Dictionary d = new Dictionary();

d.Add("cat", 2);

d.Add("dog", 4);

if (d.ContainsKey("cat"))

{

    // true

}

if (d.ContainsKey("hat"))

{

    // not true

}

Lookup Dictionary value

Get value from hashtable/Dictionary based on key.

Dictionary d = new Dictionary();

d.Add("cat", 2);

if (d.ContainsKey("cat"))

{

    int v = d["cat"];

    // v = 2

}

Scan Dictionary values

Use KeyValuePair on Dictionary to list each key/value combo.

Use this style to convert to string.

foreach (KeyValuePair p in d)

{

    // p.Key, p.Value

}

Use Hashtable

Implements older version of Dictionary, slower but required sometimes.

Hashtable h = new Hashtable();

h.Add(400, "Blazer");

string s = h[400] as string; // Cast

if (s != null) // True

{

    Console.WriteLine(s);

}

--- Language section (C#) ---

Namespaces

Put at top of file. 

using System;

using System.IO;

using System.Linq;

using System.Text;

Current time

Get current time using DateTime.

DateTime d = DateTime.Now;

string s = d.ToString();

// s = "8/20/2008 4:18:52 PM"

Debug message

Write diagnostics message to console.

using System.Diagnostics;

class C

{

    void Method()

    {

        Debug.WriteLine("...");

    }

}

Enums

Use enum type to assign names to numbers.

enum E

{

    None,

    Cat,

    Dog

};

void Method()

{

    E name = E.Cat;

    if (name == E.Dog)

    {

        // not true

    }

}

Loop through numbers

Use the for loop to loop through range of values.

for (int i = 0; i <>

{

    // 0, 1, 2, 3, ... 99

}

Catch exceptions

Detect errors and try to recover from them.

try

{

    int i = 1 / int.Parse("0");

}

catch (Exception)

{

    // log error

}

Switch statement

Compare value against constant values. Faster than if.

switch(v)

{

    case "cat":

    case "tiger":

        {

            // feline

            break;

        }

    case "dog":

    default:

        {

            // other

            break;

        }

}

--- Interfaces section (C#) ---

Interfaces, code contracts

Define required methods for classes so they can be swapped.

public interface IName

{

    void Method();

}

class C : IName

{

    public void Method()

    {

        // ...

    }

}

class D : IName

{

    public void Method()

    {

        // ...

    }

}

Use interfaces

Use classes by their common interfaces. Improves code reuse.

void Method()

{

    C name = new C();

    Method2((IName)name);

    D name2 = new D();

    Method2((IName)name2);

}

void Method2(IName i)

{

    // ...

}