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An awesome C# (CSharp) cheatsheet.


1. Data Types

    Primitive   Size            Example

    String      2 bytes/char    s = "reference";
    bool                        b = true;
    char        2 bytes         ch = 'a';
    byte        1 byte          b = 0x78;
    short       2 bytes         val = 70;
    int         4 bytes         val = 700;
    long        8 bytes         val = 70;
    float       4 bytes         val = 70.0F;
    double      8 bytes         val = 70.0D;
    decimal     16 bytes        val = 70.0M;

2. Arrays

    2.1 Declaration

    //Initialized using a list defined with curly braces
    int[] nameArray = {100, 101, 102};

    //Define an empty array
    int[] nameArray = new int[3]; // 3 rows and 2 columns

    //To access a specific item in the array
    int[] nameArray = new int[10];
    int firstNumber = nameArray[0];
    nameArray[1] = 20;

    //Multidimensional arrays
    int [,] matrix = new int [2,2]
    matrix[0,0] = 1;
    matrix[0,1] = 2;
    matrix[1,0] = 3;
    matrix[1,1] = 4;

    int[,] predefinedMatrix = new int[2,2] { { 1, 2 }, { 3, 4 } };

    2.2 Array Operations

    //Sort ascending

    //Sort begins at element 6 and sorts 20 elements

    //Use 1 array as a key & sort 2 arrays
    string[] values = {"Juan", "Victor", "Elena"};
    string[] keys = {"Jimenez", "Martin", "Ortiz"};
    Array.Sort(keys, values);

    //Clear elements in array (array, first element, # elements)
    Array.Clear(nameArray, 0, nameArray.Length);

    //Copy elements from one array to another
    Array.Copy(scr, target, numOfElements);

3. String Operations

    //To concatenate between strings, use the plus operator:
    string firstName = "Erin";
    string lastName = "Roger";
    string fullName = firstName + " " + lastName;

    //To add one string to another, use the += operator:
    string secondLastName = "Green";
    string fullName += secondLastName;

    //ToString function
    //It converts an object to its string representation so that it is suitable for display

    //String formatting
    //Each additional argument to the function can be referred to in the string using the brackets operator with the index number.
    String.Format(String format, Object arg0);
     format - A composite format string that includes one or more format items
     arg0 - The first or only object to format

    //Returns a part of the string, beginning from the index specified as the argument. Substring also accepts a maximum length for the substring
    String.Substring(beginAt, maximum);

    string newStr = oldStr.Replace("old","new");

    //Finds the first occurrence of a string in a larger string
    //Returns -1 if the string is not found
    String.IndexOf(val, start, num)
    val - string to search for
    start - where to begin in string

    //Search from end of string

    //Split is used to break delimited string into substrings

    //Places selected characters in a string in a char array
    String str = "AaBbCcDd";
    //create array of 8 vowels
    var chars = str.ToCharArray();
    //create array of 'B' and 'C'
    var chars = str.ToCharArray(2,2);

4. System.Text.StringBuilder

    4.1 Constructor

    StringBuilder sb = new StringBuilder();
    StringBuilder sb = new StringBuilder(myString);
    StringBuilder sb = new StringBuilder(myString, capacity);

    myString - Initial value of StringBuilder object
    capacity - Initial size of buffer

5. DateTime

    5.1 DateTime Constructor

    DateTime(year, month, day)
    DateTime(year, month, day, hour, minute, second)

    DateTime newYear = DateTime.Parse("1/1/2018"):
    DateTime currentDate = DateTime.Now;
    DateTime nextYear = DateTime.AddYears(1);

6. TimeSpan

    6.1 TimeSpan Constructor

    TimpeSpan(hour, minute, sec)

    TimeSpan timeS = new TimeSpan(10, 14, 50);
    TimeSpan timeS_Hours = TimeSpan.FromDays(3640);

7. Formatting Values

    Format item syntax: {index[,alignment][:format string]}
    index - Specifies element in list of values to which format is applied
    alignment - Indicates minimum width (in characters) to display value
    format string - Contains the code which specifies the format of the displayed value

    7.1 Numeric

    Format   Name           Pattern             Value       Result
    C or c   Currency       {0:C2}, 1000.1      $ 1000.1    A currency value
    D or d   Decimal        {0:D5}, 30          00030       Integer digits with optional negative sign
    E or e   Exponential    {0,9:E2}, 120.2     1.20+E002   Exponential notation
    F or f   Fixed-point    {0,9:F2}, 120.2     120.2       Integral and decimal digits with optional negative sign
    G or g   General        {0,9:G2}, 120.2     120.2       The more compact of either fixed-point or scientific notation
    N or n   Number         {0,9:N1}, 1300.5    1,300,5     Integral and decimal digits, group separators, and a decimal separator with optional negative sign
    P or p   Percent        {0,9:P3}, .0903     9.03%       Number multiplied by 100 and displayed with a percent symbol
    R or r   Round-trip     {0,9:R}, 3.1416     3.1316      A string that can round-trip to an identical number
    X or x   Hexadecimal    {0,9:X4}, 31        001f        A hexadecimal string

8. C# compiler at the Command Line

    csc File.cs -> Compiles Files.cs producing File.exe
    csc -target:library File.cs -> Compiles File.cs producing File.dll
    csc -out:My.exe File.cs -> Compiles File.cs and creates My.exe
    csc -define:DEBUG -optimize -out:File2.exe *.cs -> Compiles all the C# files in the current directory with optimizations enabled and defines the DEBUG symbol. The output is File2.exe
    csc -target:library -out:File2.dll -warn:0 -nologo -debug *.cs -> Compiles all the C# files in the current directory producing a debug version of File2.dll. No logo and no warnings are displayed
    csc -target:library *.cs -> Compiles all the C# files in the current directory to (a DLL)

    8.1 Compiler Options Listed

    Option                      Purpose
    @                           Reads a response file for more options.
    -?                          Displays a usage message to stdout.
    -additionalfile             Names additional files that don't directly affect code generation but may be used by analyzers for producing errors or warnings.
    -addmodule                  Links the specified modules into this assembly
    -analyzer                   Run the analyzers from this assembly (Short form: -a)
    -appconfig                  Specifies the location of app.config at assembly binding time.
    -baseaddress                Specifies the base address for the library to be built.
    -bugreport                  Creates a 'Bug Report' file. This file will be sent together with any crash information if it is used with -errorreport:prompt or -errorreport:send.
    -checked                    Causes the compiler to generate overflow checks.
    -checksumalgorithm:<alg>    Specifies the algorithm for calculating the source file checksum stored in PDB. Supported values are: SHA1 (default) or SHA256.
    -codepage                   Specifies the codepage to use when opening source files.
    -debug                      Emits debugging information.
    -define                     Defines conditional compilation symbols.
    -delaysign                  Delay-signs the assembly by using only the public part of the strong name key.
    -deterministic              Causes the compiler to output an assembly whose binary content is identical across compilations if inputs are identical.
    -doc                        Specifies an XML Documentation file to generate.
    -errorreport                Specifies how to handle internal compiler errors: prompt, send, or none. The default is none.
    -filealign                  Specifies the alignment used for output file sections.
    -fullpaths                  Causes the compiler to generate fully qualified paths.
    -help                       Displays a usage message to stdout.
    -highentropyva              Specifies that high entropy ASLR is supported.
    -incremental                Enables incremental compilation [obsolete].
    -keycontainer               Specifies a strong name key container.
    -keyfile                    Specifies a strong name key file.
    -langversion:<string>       Specify language version: Default, ISO-1, ISO-2, 3, 4, 5, 6, 7, 7.1, 7.2, 7.3, or Latest
    -lib                        Specifies additional directories in which to search for references.
    -link                       Makes COM type information in specified assemblies available to the project.
    -linkresource               Links the specified resource to this assembly.
    -main                       Specifies the type that contains the entry point (ignore all other possible entry points).
    -moduleassemblyname         Specifies an assembly whose non-public types a .netmodule can access.
    -modulename:<string>        Specify the name of the source module.
    -noconfig                   Instructs the compiler not to auto include CSC.RSP file.
    -nologo                     Suppresses compiler copyright message.
    -nostdlib                   Instructs the compiler not to reference standard library (mscorlib.dll).
    -nowarn                     Disables specific warning messages
    -nowin32manifest            Instructs the compiler not to embed an application manifest in the executable file.
    -optimize                   Enables/disables optimizations.
    -out                        Specifies the output file name (default: base name of file with main class or first file).
    -parallel[+|-]              Specifies whether to use concurrent build (+).
    -pathmap                    Specifies a mapping for source path names output by the compiler.
    -pdb                        Specifies the file name and location of the .pdb file.
    -platform                   Limits which platforms this code can run on: x86, Itanium, x64, anycpu, or anycpu32bitpreferred. The default is anycpu.
    -preferreduilang            Specifies the language to be used for compiler output.
    -publicsign                 Apply a public key without signing the assembly, but set the bit in the assembly indicating the assembly is signed.
    -recurse                    Includes all files in the current directory and subdirectories according to the wildcard specifications.
    -reference                  References metadata from the specified assembly files.
    -refout                     Generate a reference assembly in addition to the primary assembly.
    -refonly                    Generate a reference assembly instead of a primary assembly.
    -resource                   Embeds the specified resource.
    -ruleset:<file>             Specify a ruleset file that disables specific diagnostics.
    -subsystemversion           Specifies the minimum version of the subsystem that the executable file can use.
    -target                     Specifies the format of the output file by using one of four options: -target:appcontainerexe, -target:exe, -target:library, -target:module, -target:winexe, -target:winmdobj.
    -unsafe                     Allows unsafe code.
    -utf8output                 Outputs compiler messages in UTF-8 encoding.
    -warn                       Sets the warning level (0-4).
    -warnaserror                Reports specific warnings as errors.
    -win32icon                  Uses this icon for the output.
    -win32manifest              Specifies a custom win32 manifest file.
    -win32res                   Specifies the win32 resource file (.res).

9. Control flow statements

    9.1 Switch

    switch (expression) {
    //expression may be integer, string or enum
    case expression:
        break/ goto / return()

    case ..
        break/ goto / return()

    9.2 If

    if (condition) {
    } else {

10. Loop

    10.1 While

    while (condition) {body}

    10.2 Do while

    do {body} while condition;

    10.3 For

    for (initializer; termination condition; iteration;) {

    10.4 For each

    foreach (type identifier in collection)  {

11. Class Definition

    11.1 Class

    public | protected | internal | private
    abstract | sealed | static

    class className [:class/interfaces inherited from]

    11.2 Constructor

    [access modifier] className (parameters) [:initializer]

    initializer -base calls constructor in base class.
                 this calls constructor within class.

    public class nameClass : Initializer {
        public className(dataType param1 , dataType param2, ...) : base(param1, param2)
        { constructor body }

    11.3 Method

    [access modifier]
    static | virtual | override | new | sealed | abstract
    methodName (parameter list) { body }

    virtual  --- method can be overridden in subclass
    override --- overrides virtual method in base class
    new      --- hides non-virtual method in base class
    sealed   --- prevents derived class from inheriting
    abstract --- must be implemented by subclass

    Passing parameters:

        1. By default, parameters are passed by value
        2. Passing by reference: ref, in and out modifiers

    To pass a parameter by reference with the intent of changing the value, use
    the ref, or out keyword. To pass by reference with the intent of avoiding
    copying but not changing the value, use the in modifier

    11.4 Property

    [modifier] <dataType> property name{
        public string BrandName
            get { return brandName; }
            set { brandName = value; }

12. Struct

    12.1 Defining a structure

    [attribute][modifier] struct name [:interfaces] { struct-body }

    12.2 Class vs Structure

       -> Classes are reference types and structs are value types
       -> Structures do not support inheritance
       -> Structures cannot have default constructor

13. Enum

    13.1 Declaring enum variable

    menu <enumName> {
        enumeration list

    enumName - Specifies the enumeration type name
    enumeration list is a comma-separated list of identifiers

    //Each of the symbols in the enumeration list stands for an integer value, one greater than the symbol that precedes it.

14. Delegates

    //A delegate is a reference type variable that holds the reference to a method. The reference can be changed at runtime.

    14.1 Declaring delegates

    //Delegate declaration determines the methods that can be referenced by the delegate.

    delegate <return type> <delegate-name> <parameter list>

    14.2 Instantiating delegates

    //When creating a delegate, the argument passed to the new expression is written similar to a method call, but without the arguments to the method

    public delegate void printString(string s);
    printString ps1 = new printString(WriteToScreen);
    printString ps2 = new printString(WriteToFile);

15. Events

    15.1 Declaring events

    //To declare an event inside a class, first a delegate type for the event must be declared.

    public delegate string MyDelegate(string str);

    //The event itself is declared by using the event keyword

    event MyDelegate MyEvent;

    15.2 Commonly used Control Events

    Event                                           Delegate

    Click, MouseEnter, DoubleClick, MouseLeave      EventHandler( object sender, EventArgs e)
    MouseDown, Mouseup, MouseMove                   MouseEventHandler(object sender, MouseEventArgs e)
                                                        e.X, e.Y --- x and y coordinates
                                                        e.Button --- MouseButton.Left, Middle, Right
    KeyUp, KeyDown                                  KeyEventHandler(object sndr, KeyEventArgs e)
                                                        e.Handled --- Indicates whether event is handled.
                                                        e.KeyCode --- Keys enumeration, e.g., Keys.V
                                                        e.Modifiers --- Indicates if Alt, Ctrl, or Shift key.
    KeyPress                                        KeyPressEventHandler(object sender, KeyPressEventArgs e)