variables
strings
datetime
arrays
lists
sets
dictionaries
loops
enums
objects, classes

Variables

declared with type, name and optional value

type name = value;

different simple types are

int - all full numbers negative and positive
float - all floating point numbers up to 32 bit (7 digits)
double - all floating point numbers up to 64 bit (15-16 digits)
decimal - all floating point numbers up to 128 bit (28-29 significant digits)
char - single character
string - text, multiple characters, is also taken as char array
boolean or bool - truth value or binary value of single bit. can be true or false
array - list of elements with predefined length
object or enum - any object or enum is a type
list<type> - list of certain type, can be any length
set<type> or hashset etc - contains list of unique values. no repeats are inserted.
dictionary<type, type> - key, value list that can have a key value tied to value.

there is also special type var that will be automatically set to whatever you specify its value.

##Examples

int iNum = 3;
float fNum = 1.4;
double dblNumber = 1.4;
decimal decNumber = 1.4;
char letter = 'a'; // is important to note thet char type is defined between single quotation marks
string text = "Hello World";
bool isLie = false;
int[] arr = {1,2,3};
DateTime time = DateTime.Now;
List<int> numList = new List<int>();
HashSet<int> numSet = new Set<int>();
Dictionart<string, int> = new Dictionary<string, int>();
var vNum = 1;  // will be integer
var vStr = "Hello World"; // will be string

Operations

num = 1; assignment, sets value to variable
num += 1; addition, adds value to variable
num -= 1; subtraction, subtracts value from variable
num /= 2; division ...
num *= 2; multiplication ...
num++; increment by one
num--; decrement by one
a + b addition
a - b
a/b
a*b
a%b modulo, will display leftover from division

#Strings

Strings have many operations that can be performed on them. Most notable are.

Clone() Make clone of string.
CompareTo() Compare two strings and returns integer value as output. It returns 0 for true and 1 for false.
Contains() The C# Contains method checks whether specified character or string is exists or not in the string value.
EndsWith() This EndsWith Method checks whether specified character is the last character of string or not.
Equals() The Equals Method in C# compares two string and returns Boolean value as output.
GetHashCode() This method returns HashValue of specified string.
GetType() It returns the System.Type of current instance.
GetTypeCode() It returns the Stystem.TypeCode for class System.String.
IndexOf() Returns the index position of first occurrence of specified character.
ToLower() Converts String into lower case based on rules of the current culture.
ToUpper() Converts String into Upper case based on rules of the current culture.
Insert() Insert the string or character in the string at the specified position.
IsNormalized() This method checks whether this string is in Unicode normalization form C.
LastIndexOf() Returns the index position of last occurrence of specified character.
Length It is a string property that returns length of string.
Remove() This method deletes all the characters from beginning to specified index position.
Replace() This method replaces the character.
Split() This method splits the string based on specified value.
StartsWith() It checks whether the first character of string is same as specified character.
Substring() This method returns substring.
ToCharArray() Converts string into char array.
Trim() It removes extra whitespaces from beginning and ending of string.


    using System.Text;
    namespace string_function
    {
        class Program
        {
            static void Main(string[] args)
            {
                string firstname;
                string lastname;
               
               
                firstname = "Steven Clark";
                lastname = "Clark";
     
     
      Console.WriteLine(firstname.Clone());
    // Make String Clone
                Console.WriteLine(firstname.CompareTo(lastname));
    //Compare two string value and returns 0 for true and
    1 for false
     
     Console.WriteLine(firstname.Contains("ven")); //Check whether specified value exists or not in string
     
      Console.WriteLine(firstname.EndsWith("n")); //Check whether specified value is the last character of string
                Console.WriteLine(firstname.Equals(lastname));
    //Compare two string and returns true and false
     
     
      Console.WriteLine(firstname.GetHashCode());
    //Returns HashCode of String
     
      Console.WriteLine(firstname.GetType());
    //Returns type of string
     
      Console.WriteLine(firstname.GetTypeCode());
    //Returns type of string
     
      Console.WriteLine(firstname.IndexOf("e")); //Returns the first index position of specified value
    the first index position of specified value
     
      Console.WriteLine(firstname.ToLower());
    //Covert string into lower case
     
      Console.WriteLine(firstname.ToUpper());
    //Convert string into Upper case
     
      Console.WriteLine(firstname.Insert(0, "Hello")); //Insert substring into string
     
      Console.WriteLine(firstname.IsNormalized());
    //Check Whether string is in Unicode normalization
    from C
     
     
       Console.WriteLine(firstname.LastIndexOf("e")); //Returns the last index position of specified value
     
     Console.WriteLine(firstname.Length);
    //Returns the Length of String
     
     Console.WriteLine(firstname.Remove(5));
    //Deletes all the characters from begining to specified index.
     
     Console.WriteLine(firstname.Replace('e','i')); // Replace the character
     
      string[] split = firstname.Split(new char[] { 'e' }); //Split the string based on specified value
     
     
                Console.WriteLine(split[0]);
                Console.WriteLine(split[1]);
                Console.WriteLine(split[2]);
     
      Console.WriteLine(firstname.StartsWith("S")); //Check wheter first character of string is same as specified value
     
      Console.WriteLine(firstname.Substring(2,5));
    //Returns substring
     
      Console.WriteLine(firstname.ToCharArray());
    //Converts an string into char array.
     
      Console.WriteLine(firstname.Trim());
    //It removes starting and ending white spaces from
    string.
               
            }
        }
    }

Datetime

https://docs.microsoft.com/en-us/dotnet/api/system.datetime?view=netcore-2.2#methods

Arrays

Arrays are way to keep values in a list which lenght is known from start.

int[] arr = {1,2,3};
int[] arr1 = new int[5];
arr1[0] = 2;
Console.WriteLine(arr[0]);
Console.WriteLine(arr1[0]);

#List

Lists are to keep values in a list which length is variable and you do not know it at the start of the code

List<int> numList = new List<int>();
numList.Add(1);
Console.WriteLine(numList[0]);

Sets

Sets are to keep values that are unique if you insert value that allready exists it will not be added again.

HashSet<int> numSet = new HashSet<int>();
numSet.Add(1);
Console.WriteLine(numSet.Contains(1));
Console.WriteLine(numSet.Count);
numSet.Add(2);
Console.WriteLine(numSet.Count);
numSet.Add(1);
Console.WriteLine(numSet.Count);

Dictionaries

Are list of key,value elements where key must be unique

Dictionary<string, int> numDict = new Dictionary<string, int>();
numDict.Add("hi", 1);
Console.WriteLine(numDict["hi"]);

Loops

Loops are used to iterate over same code multiple times.

for loop

for loop is used when number of times we want to iterate is known for loop consists of 3 parts.

initial value, usually we create new variable here
condition when we end the loop
action we take after each loop

for(int i=0; i<=10; i++){
    Console.WriteLine(i);
}

while loop

while loop is when we do not know the iteration count, but only know when to end it only parameter here is statement when to end.

int i = 0;
while(i<=10){
    Console.WriteLine(i);
    i++;
}

do while loop

Same as while loop but instead of checking if the statement is true in the beginning we do it at the end. so if while statement is false from start it will skip code entirely. do while loop will run atleast once.

int i = 0;
do{
    Console.WriteLine(i);
    i++;
} while(i<=10);

foreach

foreach loop is used to easily iterate over array, list, dictonary ... values

List<int> numlist = new List<int>();
foreach (var num in numlist)
{
    Console.WriteLine(num);
}

Enums

Is custom type that specifies values that can belong in it.

class Program
    {
        enum WeekDays
        {
            Monday = 0,
            Tuesday = 1,
            Wednesday = 2,
            Thursday = 3,
            Friday = 4,
            Saturday = 5,
            Sunday = 6
        }
        static void Main(string[] args)
        {
            Console.WriteLine(WeekDays.Thursday);
        }
    }

Objects,Classes

Object is its own type and can hold values and methods that can be called outside or inside of the object. Class is blueprint for an object in code form. Object is when new is called on the class.

class Car
{
    
}

constructor

Class has a special constructor function that is called when new is called on it. Constructor is special method because it does not have return type. Input arguments work as intended these are arguments that are passed down to new Object like this new Car("Maali");

class Car
{
    public Car(string CarName){
        
    }
}

visibility

Class methods (functions) and properties (variables) will need a visibility

public - anything can edit and read
protected - class and its child classes can edit and read
private - only class itself can read and edit

object properties

Object or Class can have properties that can be accessed on the object. Property must also have visibility that defines what parts of code can access it.

class Car
{

    private int prodYear = 1992;
    public string model = "astra";
    protected float gas = 5.2;
    public Car(){
        
    }
}

object methods

methods must have visibility and return type defined and can also have input parameters

class Car
{

    private int prodYear = 1992;
    public string model = "astra";
    protected float gas = 5.2;
    public Car(){
        
    }
    public void drive(int km){
        Console.WriteLine("wroom wroom " + km);
    }
}

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