C# and Cheat Sheet

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Download C# Cheat Sheet PDF for Your Quick Reference

C# Introduction

  • Object-oriented language, with syntax similar to C++ and Java.
  • Type safe
  • Component oriented, structured language
  • Automatic garbage collection
  • Rich set of libraries
  • Conditional compilation

Syntax

  • Case sensitive
  • Comments are typed within // (single-line) or /**/ (multi-line)
  • Code is typed inside code blocks {}
  • Line termination is done using semicolon ;
  • Supports comment task highlighters like TODO: , NOTE: , WARN: etc…

Variables

<datatype> <variablename> = <initialvalue>;

  • Variables should start with underscore and cannot contain white spaces.
  • It can contain numbers but should always start with a capital letter.
  • It cannot contain any symbols (other than underscore).

Naming Conventions

Class

StudentClass

Method

GetMarks

Local variable

firstName

Private variable

avgMarks

Constant

Percentile

Data types

Int

Integer values like 1234, 10000

Double

64-bit floating-point, 3.145644

Float

Floating point number, 3.1454

String

Set of characters, “Welcome.”

Byte

8bit unsigned integer

Char

16 bit Unicode character, ‘A.’

Long

64 bit signed integer, -9.0789

Decimal

High precision decimal numbers

Bool

True or false Boolean value

Enums

Value data type contains its value

Struct

value type that is used to represent a record

Initialisation of variables

int i = 7;
byte b = 255;
String s = “hackr.io”;
char c = ‘h’;

Constant values

const String lastDayOfWeek = “Friday”;

String Data type conversion

Method

Description

Example

AsInt(),
IsInt()

Convert string into integer

Check If the input is int

intVal = str.AsInt();

str.IsInt()

AsFloat(),

IsFloat()

Convert string into float

Check if the input is float

floatVal = str.AsFloat();

str.IsFloat()

AsDecimal()

IsDecimal()

Convert string into decimal

Check if input is decimal

decVal = str.AsDecimal();

str.IsDecimal()

AsDateTime()

IsDateTime()

Convert string into datetime type

Check if input is date-time

dateVal = str.AsDateTime();

 

str.isDateTime();

AsBool()
IsBool()

Convert string into Boolean

Check if input is Boolean

boolVal = str.AsBool();

str.IsBool();

ToString()

Convert another data type like int, array, list etc into String

myVal = 1111;

strVal = myVal.ToString();

Operators

Operator

Description

=

Assigns variable value. (i = 10)

+

Adds a value or variable. (i + j) or (i + 3)

-

Subtracts values or variables. (i – j)

*

Multiplies values or variables. (i*j)

/

Divides values or variables. (i/j)

+=

Increments a variable. ( i+=1)

-=

Decrements a variable. (i-=1)

==

Equality. Returns true if values are equal. (i==10)

!=

Inequality. Returns true if values are not equal. (I != 10)

<

Less Than (i < 5)

>

Greater Than (i > 5)

<=

Less Than or Equal to (i <= 5)

>=

Greater than equal to (i >= 5)

+

String concatenation (“Welcome to ” + websiteName)

.

Call methods, constant variables etc..

arrVal.ToString()

()

Calculations, passing parameters etc…

(i+10)*(i-10); multiply(i, j)

[]

Access values in arrays or collections. name[i]

!

Reversing Boolean value

if (!isMatching)

&&

Logical AND

if (isSingle && isMatching)

sizeof()

returns the size of a data type

typeof()

returns the type of object – string, integer etc…

String Operations

String Functions

Definitions

Example

Clone()

Make clone of string.

str2 = str1.Clone()

CompareTo()

Compare two strings and returns integer value as output. It returns 0 for true and 1 for false.

str2.CompareTo(str1)

Contains()

checks whether specified character or string is exists or not in the string value.

str2.Contains(“hack”);

EndsWith()

checks whether specified character is the last character of string or not.

str2.EndsWith(“io”);

Equals()

compares two string and returns Boolean value true as output if they are equal, false if not

str2.Equals(str1)

GetHashCode()

returns HashValue of specified string.

str1.GetHashCode()

GetType()

returns the System.Type of current instance.

str1.GetType()

GetTypeCode()

returns the Stystem.TypeCode for class System.String.

str1.GetTypeCode()

IndexOf()

Returns the index position of first occurrence of specified character.

str1.IndexOf(“:”)

ToLower()

Converts String into lower case based on rules of the current culture.

str1.ToLower();

ToUpper()

Converts String into Upper case based on rules of the current culture.

str1.ToUpper();

Insert()

Insert the string or character in the string at the specified position.

str1.Insert(0, “Welcome”);

str1.Insert(i, “Thank You”);

IsNormalized()

Check whether this string is in Unicode normalization form

str1.IsNormalized()

LastIndexOf()

Returns the index position of last occurrence of specified character.

str1.LastIndexOf(“T”);

Length

returns length of string.

str1.Length;

Remove()

deletes all the characters from beginning to specified index position.

str1.Remove(i);

Replace()

replaces the specified character with another

str1.Replace(‘a’, ‘e’);

Split()

This method splits the string based on specified value.

str1 = “Good morning and Welcome”;

String sep = {“and”};

strArray = str1.Split(sep, StringSplitOptions.None);

StartsWith()

Checks whether the first character of string is same as specified character.

str1.StartsWith(“H”)

Substring()

This method returns substring.

str1.Substring(1, 7);

ToCharArray()

Converts string into char array.

str1.ToCharArray()

Trim()

It removes extra whitespaces from beginning and ending of string.

str1.Trim();

Modifiers

public

field or function accessible by any other code in the same assembly or another assembly that references it

private

Only available by code in the same class or struct

protected

Only accessible by code in the same class or struct or a derived class

internal

Accessible by any code in the same assembly, but not from another assembly

protected internal

Accessible by any code in the same assembly, or by any derived class in another assembly

abstract

to indicate a class that is intended only to be a base class of other classes (has to be extended by other classes)

async

Indicates that the modified method, lambda expression, or anonymous method is asynchronous

const

Specifies that the value of the field or the local variable cannot be modified (constant)

event

Declares an event

extern

Indicates that the method is implemented externally

new

Explicitly hides a member inherited from a base class

override

Provides a new implementation of a virtual member inherited from a base class

partial

Defines partial classes, structs, and methods throughout the same assembly

read-only

Declares a field that can only be assigned values as part of the declaration or in a constructor in the same class

sealed

Specifies that a class cannot be inherited

static

Declares a member that belongs to the type itself instead of to a specific object, e.g., for static class or method, no object needs to be created

unsafe

Declares an unsafe context

virtual

Declares a method or an accessor whose implementation can be changed by an overriding member in a derived class

volatile

Indicates that a field can be modified in the program by something such as the operating system, the hardware, or a concurrently executing thread

Date/Time formatting

DateTime dt = new DateTime();

dt.ToString();

gives output as –

01-01-0001 00:00:00

dt = DateTime.Now;

gives current date and time

dt = new DateTime(yyyy, MM, dd);

gives the specified date in yyyy-MM-dd format. Time will be 00:00:00

dt = new DateTime(yyyy, MM, dd, hh, min, ss);

gives specified date and time in the 24-hour format

dt = new DateTime(yyyy, MM, dd, hh, mm, ss);

dt1 = dt.Date;

gives only the date, with the time part set to 00:00:00

DateTime.Now.ToShortDateString()

prints only the date part by completely omitting the time part

DateTime.Now.ToLongDateString()

prints the whole date and time based on region, month is printed in letters (JAN, FEB etc.. ) rather than number (01, 02)

DateTime format specifiers

Format specifier

Name

Description

d

Short date pattern

Represents a custom DateTime format string defined by the current ShortDatePattern property.

For example, the custom format string for the invariant culture is "MM/dd/yyyy."

D

Long date pattern

Represents a custom DateTime format string defined by the current LongDatePattern property.

For example, the custom format string for the invariant culture is "dddd, dd MMMM yyyy."

f

Full date/time pattern (short time)

Represents a combination of the long date (D) and short time (t) patterns, separated by a space.

F

Full date/time pattern (long time)

Represents a custom DateTime format string defined by the current FullDateTimePattern property.

For example, the custom format string for the invariant culture is "dddd, dd MMMM yyyy HH:mm: ss."

g

General date/time pattern (short time)

Represents a combination of the short date (d) and short time (t) patterns, separated by a space.

G

General date/time pattern (long time)

Represents a combination of the short date (d) and long time (T) patterns, separated by a space.

M or m

Month day pattern

Represents a custom DateTime format string defined by the current MonthDayPattern property.

For example, the custom format string for the invariant culture is "MMMM dd."

o

Round-trip date/time pattern

Represents a custom DateTime format string using a pattern that preserves time zone information. The pattern is designed to round-trip DateTime formats, including the Kind property, in text. Then the formatted string can be parsed back using Parse or ParseExact with the correct Kind property value.

The custom format string is "yyyy'-'MM'-'dd'T'HH':' mm': 'ss.fffffffK."

The pattern for this specifier is a defined standard. Therefore, it is always the same, regardless of the culture used or the format provider supplied.

R or r

RFC1123 pattern

Represents a custom DateTime format string defined by the current RFC1123Pattern property. The pattern is a defined standard, and the property is read-only. Therefore, it is always the same regardless of the culture used, or the format provider supplied.

The custom format string is "DDD, dd MMM yyyy HH':' mm': 'ss 'GMT'".

Formatting does not modify the value of the DateTime object that is being formatted. Therefore, the application must convert the value to Coordinated Universal Time (UTC) before using this format specifier.

s

Sortable date/time pattern; conforms to ISO 8601

Represents a custom DateTime format string defined by the current SortableDateTimePattern property. This pattern is a defined standard, and the property is read-only. Therefore, it is always the same regardless of the culture used, or the format provider supplied.

The custom format string is "yyyy'-'MM'-'dd'T'HH':'mm': 'ss."

t

Short time pattern

Represents a custom DateTime format string defined by the current ShortTimePattern property.

For example, the custom format string for the invariant culture is "HH:mm."

T

Long time pattern

Represents a custom DateTime format string defined by the current LongTimePattern property.

For example, the custom format string for the invariant culture is "HH:mm: ss".

u

Universal sortable date/time pattern

Represents a custom DateTime format string defined by the current UniversalSortableDateTimePattern property. This pattern is a defined standard and the property is read-only. Therefore, it is always the same regardless of the culture used or the format provider supplied.

The custom format string is "yyyy'-'MM'-'dd HH':'mm':'ss'Z'".

No time zone conversion is done when the date and time is formatted. Therefore, the application must convert a local date and time to Coordinated Universal Time (UTC) before using this format specifier.

U

Universal sortable date/time pattern

Represents a custom DateTime format string defined by the current FullDateTimePattern property.

This pattern is the same as the full date/long time (F) pattern. However, formatting operates on the Coordinated Universal Time (UTC) that is equivalent to the DateTime object being formatted.

Y or y

Year month pattern

Represents a custom DateTime format string defined by the current YearMonthPattern property.

For example, the custom format string for the invariant culture is "yyyy MMMM".

Custom format

Custom patterns –

"MM'/'dd yyyy"

"dd.MM.yyyy"

"MM.dd.yyyy HH:mm"

"dddd, MMMM (yyyy): HH:mm:ss"

03/17 2019

17.03.2019

03.17.2019 06:23

Tuesday, march (2019) : 06:23:00

Any other single character

(Unknown specifier)

An unknown specifier throws a runtime format exception.

Arrays

For creating, modifying, sorting and searching arrays.

PROPERTY

DESCRIPTION

EXAMPLE

IsFixedSize

checks whether the Array has a fixed size.

string[] arrVal = new string[] {“stud1”, “stud2”, “stud3”};

 

arrVal.IsFixedSize;

IsReadOnly

Checks whether the Array is read-only.

arrVal.IsReadOnly;

IsSynchronized

Checks whether access to the Array is synchronized (thread safe).

arrVal.IsSynchronized;

Length

Gets the total number of elements in all the dimensions of the Array.

arrVal.Length;

LongLength

Length in 64-bit integer

arrVal.LongLength;

Rank

Gets the rank (number of dimensions) of the Array. For example, a one-dimensional array returns 1, a two-dimensional array returns 2, and so on.

arrVal.Rank;

SyncRoot

Gets an object used to synchronize Array access

arrVal.SyncRoot;

AsReadOnly()

Returns a read-only wrapper for the specified array.

Array.AsReadOnly(arrVal);

BinarySearch()

Searches a value in a one-dimensional sorted array using a binary search algorithm.

Array.BinarySearch(arrVal, obj); where obj is the object to be searched.

Clear()

Sets a range of elements in an array to the default value of each element type.

Array.Clear(arrVal, 0, 2);

If arrVal is an array of integers, the elements at position 0 to 2 will be set to zero after doing Clear().

Clone()

Create a shallow copy of the Array.

Array.Clone(arrVal);

ConstrainedCopy()

Copies a range of elements from an Array starting at the specified source index and pastes them to another Array starting at the specified destination index. Guarantees that all changes are undone if the copy does not succeed completely.

Array.ConstrainedCopy(srcArr, 0, destArr, 3, 5);

where srcArr is the source array,

0 is the start index from where copy should begin,

destArr is the destination array,

3 is the place where copy should start in the destination array,

5 is the number of elements to copy

ConvertAll()

Converts an array of one data type to an array of another data type.

conArr = Array.ConvertAll(arrVal, new Converter<dtype1, dtype2> (method));

Copy()

Copies a range of elements in one Array to another Array and performs type casting and boxing as required.

Array.Copy(srcArr, destArr, 2);

copies first two elements from srcArr to destArr

CopyTo()

Copies all the elements of the current one-dimensional array to the specified one-dimensional array.

Array.CopyTo(destArr, 4);

copy starts from index 4

CreateInstance()

Initializes a new instance of the Array class.

Array.CreateInstance(typeof(String), length);

Empty()

Returns an empty array.

arrVal.Empty()

Equals()

Determines whether the specified object is equal to the current object.

arrVal.Equals(arrVal2);

Exists()

Determines whether the specified array contains elements that match the conditions defined by the specified predicate.

Array.Exists(srcArr, “<elementname>”);

Find()

Searches for an element that matches the conditions defined by the specified predicate, and returns the first occurrence within the entire Array.

Array.Find(arrVal, <matching pattern>);

FindAll()

Retrieves all the elements that match the conditions defined by the specified predicate.

Array.FindAll(arrVal, <matching pattern>);

FindIndex()

Searches for an element that matches the conditions defined by a specified predicate, and returns the zero-based index of the first occurrence within an Array or a portion of it.

Array.FindIndex(arrVal, <matching pattern>);

FindLast()

Searches for an element that matches the conditions defined by the specified predicate, and returns the last occurrence within the entire Array.

Array.FindLast(arrVal, <matching pattern>);

FindLastIndex()

Searches for an element that matches the conditions defined by a specified predicate, and returns the zero-based index of the last occurrence within an Array or a portion of it.

Array.FindLastIndex(arrVal, <matching pattern>);

ForEach()

Loops through each element of the array and performs the specified action

Array.ForEach(arrVal, Action)

GetEnumerator()

Returns an IEnumerator for the Array.

arrVal.GetEnumerator()

GetHashCode()

default hash function.

arrVal.GetHashCode()

GetLength()

Gets a 32-bit integer that represents the number of elements in the specified dimension of the Array.

arrVal.GetLength(i) where i is an integer

GetLongLength()

Gets a 64-bit integer that represents the number of elements in the specified dimension of the Array.

arrVal.GetLongLength(i) where i is an integer

GetLowerBound()

Gets the index of the first element of the specified dimension in the array.

arrVal.GetLowerBound(i) where i is an integer

GetType()

Gets the Type of the current instance.

arrVal.GetType()

GetUpperBound()

Gets the index of the last element of the specified dimension in the array.

arrVal.GetUpperBound(i) where i is an integer

GetValue()

Gets the value of the specified element in the current Array.

 

IndexOf()

Searches for the specified object and returns the index of its first occurrence in a one-dimensional array or in a range of elements in the array.

arrVal.IndexOf(object)

Initialize()

Initializes every element of the value-type Array by calling the default constructor of the value type.

 

LastIndexOf()

Returns the index of the last occurrence of a value in a one-dimensional Array or in a portion of the Array.

arrVal.LastIndexOf(i)

MemberwiseClone()

Creates a shallow copy of the current Object.

 

Resize()

Changes the number of elements of a one-dimensional array to the specified new size.

Array.Resize(ref arrVal, len-2);

where len is the original length of the array

Reverse()

Reverses the order of the elements in a one-dimensional Array or in a portion of the Array.

arrVal.Reverse()

SetValue()

Sets the specified element in the current Array to the specified value.

Array.SetValue(arrVal[i])

Sort()

Sorts the elements in a one-dimensional array.

Array.Sort(arrVal)

ToString()

Returns a string that represents the current object.
(Inherited from Object)

arrVal.ToString()

TrueForAll()

Determines whether every element in the array matches the conditions defined by the specified predicate.

Array.TrueForAll(arrVal, <matching pattern>)

Control Statements

if-else

if (true) {...}
else if (true) {...}
else {...}

switch

switch (var)

{
case 1: break;

case 2: break;
default: break;

}

for

for (int i =0; i <=len; i++) {...}

foreach-in

foreach (int item in array) {...}

while

while (true) {...}

do... while

do {...}
while (true);

try-catch-finally

try {...}
catch (Exception e) {...}
catch {...}
finally {...}

Regular Expressions

+

match one or more occurrence

*

match any occurrence (zero or more)

?

match 0 or 1 occurrence

\d \D

match decimal digit or non-character

\w \W

match any word character

\s \S

match white space or no white space

[]

match any character inside the square brackets

[^]

match any character not present in the square brackets

a | b

either a or b

\n

new line

\r

carriage return

\t

tab

Collections

Arraylist

Capacity

Gets or sets the number of elements that the ArrayList can contain.

Count

Gets the number of elements actually contained in the ArrayList.

IsFixedSize

Gets a value indicating whether the ArrayList has a fixed size.

IsReadOnly

Returns whether the ArrayList is read-only

Item

Gets or sets the element at the specified index.

Add(object value)

Adds an object to the end of the ArrayList

AddRange(ICollection c);

Adds the elements of an ICollection to the end of the ArrayList.

Clear();

Removes all elements of an ArrayList.

Contains(object item);

Checks whether an element is in the ArrayList.

GetRange(int index, int count);

Returns an ArrayList which represents a subset of the elements in the source ArrayList.

IndexOf(object);

Returns the zero-based index of the first occurrence of a value in the ArrayList or in a portion of it.

Insert(int index, object value);

Inserts an element into the ArrayList at the specified index.

InsertRange(int index, ICollection c);

Inserts the elements of a collection into the ArrayList at the specified index.

Remove(object obj);

Removes the first occurrence of a specific object from the ArrayList.

RemoveAt(int index);

Removes the element at the specified index of the ArrayList.

RemoveRange(int index, int count);

Removes a range of elements from the ArrayList

Reverse();

Reverses the order of the elements in the ArrayList.

SetRange(int index, ICollection c);

Copies the elements of a collection over a range of elements in the ArrayList.

Sort();

Sorts the elements in the ArrayList.

TrimToSize();

Sets the capacity to the actual number of elements in the ArrayList.

Hashtable

Count

Gets the number of key-and-value pairs contained in the Hashtable.

IsFixedSize

Gets a value indicating whether the Hashtable has a fixed size

IsReadOnly

Gets a value indicating whether the Hashtable is read-only.

Item

Gets or sets the value associated with the specified key.

Keys

Gets an ICollection containing the keys in the Hashtable.

Values

Gets an ICollection containing the values in the Hashtable

Add(object key, object value);

Adds an element with the specified key and value into the Hashtable

Clear();

Removes all elements from the Hashtable.

ContainsKey(object key);

Determines whether the Hashtable contains a specific key.

ContainsValue(object value);

Determines whether the Hashtable contains a specific value.

Remove(object key);

Removes the element with the specified key from the Hashtable.

SortedList

Capacity

Gets or sets the capacity of the SortedList.

Count

Gets the number of elements in the SortedList.

IsFixedSize

Checks if the SortedList is of fixed size.

IsReadOnly

Checks if the SortedList is read-only.

Item

Gets and sets the value associated with a specific key in the SortedList.

Keys

Gets the keys in the SortedList.

Values

Gets the values in the SortedList.

Add(object key, object value)

Adds an element with the specified key and value into the SortedList.

Clear()

Removes all elements from the SortedList.

ContainsKey(object key);

Checks if the SortedList contains a specific key.

ContainsValue(object value);

Checks if the SortedList contains a specific value.

GetByIndex(int index);

Gets the value at the specified index of the SortedList.

GetKey(int index);

Gets the key at the specified index of the SortedList.

GetKeyList();

Returns list of keys in the SortedList

GetValueList();

Returns list of values in the SortedList

IndexOfKey(object key);

Returns the zero-based index of the specified key in the SortedList.

IndexOfValue(object value);

Returns the zero-based index of the first occurrence of the specified value in the SortedList.

Remove(object key);

Removes the element with the specified key from the SortedList.

RemoveAt(int index);

Removes the element at the specified index of SortedList.

TrimToSize();

Sets the capacity to the actual number of elements in the SortedList.

Stack

Count

Number of elements in the Stack.

Clear();

Removes all elements from the Stack.

Contains(object obj);

Checks if an element is in the Stack.

Peek();

Returns the object at the top of the Stack without removing it.

Pop();

Removes and returns the object at the top of the Stack.

Push(object obj);

Inserts an object at the top of the Stack.

ToArray();

Copies the Stack to a new array.

Queue

Count

number of elements in the Queue.

Clear();

Removes all elements from the Queue.

Contains(object obj);

Checks if the specified object is present in the Queue.

Dequeue();

Removes and returns the object at the beginning of the Queue.

Enqueue(object obj);

Adds an object to the end of the Queue.

ToArray();

Copies the Queue to a new array.

TrimToSize();

Sets the capacity to the actual number of elements in the Queue.

Dictionary

Count

Gets the total number of elements exists in the Dictionary<TKey,TValue>.

IsReadOnly

Returns a boolean after checking if the Dictionary<TKey,TValue> is read-only.

Item

Gets or sets the element with the specified key in the Dictionary<TKey,TValue>.

Keys

Returns collection of keys of Dictionary<TKey,TValue>.

Values

Returns collection of values in Dictionary<TKey,TValue>.

Add

Add key-value pairs in Dictionary<TKey, TValue> collection.

Remove

Removes the first occurrence of specified item from the Dictionary<TKey, TValue>.

ContainsKey

Checks if the specified key exists in Dictionary<TKey, TValue>.

ContainsValue

Checks if the specified value exists in Dictionary<TKey, TValue>.

Clear

Removes all the elements from Dictionary<TKey, TValue>.

TryGetValue

Returns true and assigns the value with specified key, if key does not exists then return false.

Exception Handling

try{
} catch (Exception e){
throw;
}

Methods

No return type

public void MyMethod(){}

static method, no object needed to call method

public static void MyMethod(){}

with return type

public returnType MyMethod(){

return val;

}

passing parameters

public void MyMethod(String s, int i) {

}

Classes

Class MyClass
{
/*Class definition*/
}
Object creation –
MyClass ClassObj = new MyClass();

Partial Class

Classes within the same namespace can be split into smaller classes with same name.

// PartialClass1.cs
using System;
namespace PartialClasses
{
public partial class PartialClass
{
public void HelloWorld()
{
Console.WriteLine("Hello, world!");
}
}
}
// PartialClass2.cs
using System;
namespace PartialClasses
{
public partial class PartialClass
{
public void HelloUser()
{
Console.WriteLine("Hello, user!");
}
}
}

A single instance is enough to call the methods of these partial classes.

PartialClass pc = new PartialClass();
pc.HelloWorld();
pc.HelloUser();

File Handling

File.Exists

Check the existence of the file in the specified path

File.Exists(path)

File.ReadAllLines

Read all the lines from the file specified by the path

File.ReadAllLines(path)

Console.WriteLines(File.ReadAllLines(path)

// Write to console

File.ReadAllText

Read all the text from the file and store it as a single string

File.ReadAllText(path)

File.Copy

Copy content from one file to another

File.Copy(srcfilepath, destfilepath);

File.Delete

Delete an existing file from the specified path

File.Delete(path)

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Ramya Shankar

Ramya Shankar

A cheerful, full of life and vibrant person, I hold a lot of dreams that I want to fulfill on my own. My passion for writing started with small diary entries and travel blogs, after which I have moved on to writing well-researched technical content. I find it fascinating to blend thoughts and research and shape them into something beautiful through my writing. View all posts by the Author

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