diff --git a/C# Full Course for free/12.arrays.md b/C# Full Course for free/12.arrays.md
index f9ae4e4..07773a6 100644
--- a/C# Full Course for free/12.arrays.md	
+++ b/C# Full Course for free/12.arrays.md	
@@ -16,3 +16,36 @@ Console.WriteLine(cars.Length)
 
 String[] cars = new string[3]
 ```
+
+## Multidimention arrays
+
+```C#
+String[] ford = {"Mustang", "F-150", "Explorer"};
+String[] chevy = {"Corvette", "Camaro", "Silverado"};
+String[] toyota = {"Corolla", "Camry", "Rav4"};
+
+String[,] parkingLot = {
+    {"Mustang", "F-150", "Explorer"}
+    {"Corvette", "Camaro", "Silverado"};
+    {"Corolla", "Camry", "Rav4"};
+};
+
+parkingLot[0,2] = "Fusion";
+//"Explorer" to "Fusion"
+
+parkingLot[2,0] = "Tacoma";
+//"Corolla" to "Tacoma"
+
+foreach(String car in parkingLot){
+    Console.WriteLine(car);
+}
+
+for(int i = 0; i < parkingLot.GetLength(0); i++)
+{
+    for(int j = 0; j < parkingLot.GetLength(1); i++)
+    {
+        Console.Write(parkingLot[i,j] + " ")
+    }
+    Console.WriteLine();
+}
+```
diff --git a/C# Full Course for free/13.methods.md b/C# Full Course for free/13.methods.md
index bf6a8fd..53652ea 100644
--- a/C# Full Course for free/13.methods.md	
+++ b/C# Full Course for free/13.methods.md	
@@ -23,3 +23,62 @@ Console.WriteLine("Happy birthday to you" + name)
 Console.WriteLine("you are " + age + "years old")
 }
 ```
+
+## return
+
+```C#
+double x = 5.3;
+double y = 3;
+
+double result = Multiply(x,y)
+
+static double Multiply(double x, double y){
+    double z = x * y;
+    return z;
+}
+```
+
+## method overloading
+
+```C#
+double x = 5.3;
+double y = 3;
+double z = 3;
+
+double result = Multiply(x,y)
+// Will return the first Multiply method
+double result = Multiply(x,y,z)
+// Will return the second Multiply method
+
+static double Multiply(double x, double y){
+    double z = x * y;
+    return z;
+}
+
+static double Multiply(double a, double b, double c){
+    double z = x * y;
+    return z;
+}
+```
+
+## params
+
+params keyword a method parameter that takes a variale number of arguments.
+the parameter type must be a single - dimensional array
+
+```C#
+
+double total = CheckOut(3.99, 5,75, 15);
+
+static double Checkout(params double[] prices){
+
+    double total =0;
+    foreach(double price in prices)
+    {
+        total += prices;
+    }
+
+return total;
+}
+```
+
diff --git a/C# Full Course for free/14.OOP.md b/C# Full Course for free/14.OOP.md
new file mode 100644
index 0000000..4ece27c
--- /dev/null
+++ b/C# Full Course for free/14.OOP.md	
@@ -0,0 +1,309 @@
+# Classes
+
+In another file
+```C#
+class Messages()
+{
+    public static void Hello()
+    {
+        Console.WriteLine("Hello! Welcome to the program");
+    }
+    public static void Waiting()
+    {
+        Console.WriteLine("I am waiting for somtething");
+    }
+    public static void Bye()
+    {
+        Console.WriteLine("Bye! Thanks for visiting");
+    }
+}
+```
+
+```C#
+    Messages.Hello();
+```
+
+## Object
+
+Object is an instance of a class
+can have fields & nethods
+
+```C#
+class Human
+{
+    String name;
+    int age;
+
+    public void Eat()
+    {
+        Console.WriteLine(name + " is eating");
+    }
+    public void Sleep()
+    {
+        Console.WriteLine(name + " is sleeping");
+    }
+}
+```
+
+```C#
+// in the main class
+Human human1 = new Human()
+
+human1.name = "Rick";
+human1.age = 65;
+
+human1.Eat();
+human1.Sleep();
+
+Human human2 = new Human()
+
+human1.name = "Morty";
+human1.age = 16;
+
+human1.Eat();
+human1.Sleep();
+```
+
+## Construtor
+
+Constructor is a special method in a class
+
+```C#
+class Human
+{
+    String name;
+    int age;
+
+    public Human(String name, int age){
+        this.name = name;
+        this.age = age;
+    }
+
+    public void Eat()
+    {
+        Console.WriteLine(name + " is eating");
+    }
+    public void Sleep()
+    {
+        Console.WriteLine(name + " is sleeping");
+    }
+}
+
+```
+// in the main class
+
+Human human1 = new Human("Rick",65)
+Human human2 = new Human("Morty", 16)
+
+human1.Eat();
+human1.Sleep();
+human2.Eat();
+human2.Sleep();
+```
+
+## static
+
+static is a modifier to declare a static member, which belongs to the class itself
+rather than to any specific object
+
+```C#
+class Car
+{
+    String model;
+    public static int numberOfCars;
+
+    public Car(String model)
+    {
+        this.model = model;
+        numberOfCars++;
+    }
+    public static void StartRace()
+    {
+        Console.WriteLine("The race as begun !")
+    }
+}
+```
+
+```C#
+// in the main class
+
+Car car1 = new Car("Mustang");
+Car car2 = new Car("Corvette");
+ Console.WriteLine(Car.numberOfCars);
+
+Car.StartRace();
+```
+
+## overladed constructo
+
+Technique to create multiple constructors, with a different set of parameters but the same name.
+name + parameters = signature
+
+```C#
+class Pizza
+{
+    String bread;
+    String sauce;
+    String cheese;
+    String topping;
+
+    public Pizza(String bread,String sauce, String cheese, String topping)
+    {
+        this.bread = bread;
+        this.sauce = sauce;
+        this.cheese = cheese;
+        this.topping = topping;
+    }
+
+    public Pizza(String bread,String sauce, String cheese)
+    {
+        this.bread = bread;
+        this.sauce = sauce;
+        this.cheese = cheese;
+    }
+
+    public Pizza(String bread,String sauce)
+    {
+        this.bread = bread;
+        this.sauce = sauce;
+    }
+
+    public Pizza(String bread)
+    {
+        this.bread = bread;
+    }
+
+}
+```
+
+```C#
+// Main
+
+Pizza pizza = new Pizza("stuffed crust", "red sauce", "mozzarella");
+Pizza pizza1 = new Pizza("stuffed crust", "red sauce");
+```
+
+## inheritance
+
+1 or more child classes recieving fields, methods, etc. from a common parent
+
+```C#
+class Vehicle
+{
+    public int speed = 0
+    
+    public void go()
+    {
+        Console.WriteLine("this vehicle is moving !");
+    }
+}
+
+Class Car : Vehicle
+{
+    public int wheels = 4;
+}
+Class Bicycle : Vehicle
+{
+    public int wheels = 2;
+}
+Class Boat : Vehicle
+{
+    public int wheels = 0;
+}
+```
+
+```C#
+// Main
+
+Car car = new Car();
+Bicycle bicycle = new Bicycle();
+Boat boat = new Boat();
+
+Console.WriteLine(car.speed());
+Console.WriteLine(car.wheels());
+Console.WriteLine(car.go());
+
+Console.WriteLine(bicycle.speed());
+Console.WriteLine(bicycle.wheels());
+Console.WriteLine(bicycle.go());
+
+Console.WriteLine(boat.speed());
+Console.WriteLine(boat.wheels());
+Console.WriteLine(boat.go());
+```
+
+## abstract classes
+
+modifier that indicates missing components or incomplete implemetation
+
+```C#
+abstract class Vehicle
+{
+    public int speed = 0
+    
+    public void go()
+    {
+        Console.WriteLine("this vehicle is moving !");
+    }
+}
+
+Class Car : Vehicle
+{
+    public int wheels = 4;
+    int maxSpeed = 500; 
+}
+Class Bicycle : Vehicle
+{
+    public int wheels = 2;
+    int maxSpeed = 50; 
+}
+Class Boat : Vehicle
+{
+    public int wheels = 0;
+    int maxSpeed = 100; 
+}
+```
+
+```C#
+// Main
+Car car = new Car();
+Bicycle bicycle = new Bicycle();
+Boat boat = new Boat();
+Vehicle vehicle new Vehicle();
+// error can't instanciate
+```
+
+## array of object
+
+```C#
+Class Car 
+{
+    public String model;
+    public Car(String model)
+    {
+        this.model = model;
+    }
+}
+```
+
+```C#
+Car[] garage = new Car[3]
+
+Car car1 = new Car("Mustang");
+Car car2 = new Car("Corvette");
+Car car3 = new Car("Lambo");
+
+garage[0] = car1
+garage[1] = car2
+garage[2] = car3
+
+// or with anonymous object
+
+Car[] garage = {new Car("Mustang"), new Car("Corvette"), new Car("Lambo")}
+
+forach(Car car in garage)
+{
+    Console.WriteLine(car.model());
+}
+```
+
diff --git a/C# Full Course for free/7.Strings methods.md b/C# Full Course for free/7.Strings methods.md
index 8ba8860..34260d3 100644
--- a/C# Full Course for free/7.Strings methods.md	
+++ b/C# Full Course for free/7.Strings methods.md	
@@ -47,3 +47,16 @@ String fullName = "mrsh online";
 String firstName = fullName.Substring(0,4); 
 String lastName = fullName.Substring(5,6); 
 ```
+
+## String interpolation
+
+```C#
+String firstName = "mrsh";
+String lastName = "Online";
+int age = 21;
+
+Console.WriteLine($"Hello {firstName} {lastName}.");
+
+// include 10 spaces
+Console.WriteLine($"You are {age, 10} years old.");
+```
diff --git a/C# Full Course for free/8.Conditions.md b/C# Full Course for free/8.Control Flow.md
similarity index 63%
rename from C# Full Course for free/8.Conditions.md
rename to C# Full Course for free/8.Control Flow.md
index ee06ac1..d18ba6e 100644
--- a/C# Full Course for free/8.Conditions.md	
+++ b/C# Full Course for free/8.Control Flow.md	
@@ -85,3 +85,55 @@ if(temp >= 10 && temp <= 25){
 }
 ```
 
+## try / catch / exception
+
+errors that occur during execution
+
+try = try some code that is considered "dangerous"
+catch = catches and handles execptions when they occur
+finally = always executes regardless if exception is caught or not
+
+```C#
+double x;
+double y;
+double result;
+
+try 
+{ 
+    Console.Write("Enter number 1: ");
+    x = Convet.ToDouble(Console.ReadLine());
+
+    Console.Write("Enter number 2: ");
+    y = Convet.ToDouble(Console.ReadLine());
+
+    result = x / y;
+
+    Console.WriteLine("result: " + result);
+
+}
+catch(FormatExecption e)
+{
+    Console.WriteLine("Enter ONLY numbers Please!");
+}
+catch(DivideByZeroExecption e)
+{
+    Console.WriteLine("you can't divide by zero");
+}
+catch ( Exeption e)
+{
+    Console.WriteLine("something went wrong !");
+}
+finally
+{
+    Console.WriteLine("Tanks for visiting");
+}
+```
+
+## Conditional Operator
+
+// (condition) ? y : x
+
+```C#
+double temperature = 20;
+Console.WriteLine((tempure >= 15) ? "It's warm outside!" : "It's cold outside!"; )
+```