Add Lesson 4 Tasks 1 and 2

Lesson_4/Task_1/Customer.cs

@@ -0,0 +1,59 @@
+namespace SingleResponsibility
+{
+    public class Customer
+    {
+        public int Id { get; set; }
+        public string Name { get; set; }
+        public decimal Balance { get; set; }
+        
+        public Customer(int id, string name, decimal balance)
+        {
+            Id = id; 
+            Name = name; 
+            Balance = balance;
+        }
+
+        public void GetBalance()
+        {
+            Console.WriteLine($"Your balance is: {Balance}");
+        }
+    }
+
+    public class CustomerList
+    {
+        public List<Customer> Customers = new List<Customer>()
+        {
+            new Customer(1, "Fikus", 0),
+            new Customer(2, "VHarbar", 100000)
+        };
+
+        public decimal? GetBalanceById(int id)
+        {
+            var customer = Customers.FirstOrDefault(x => x.Id == id);
+            if (customer != null)
+                return customer.Balance;
+            else
+                return null;
+        }
+
+        public Customer? GetById(int id)
+        {
+            return Customers.FirstOrDefault(x => x.Id == id);
+        }
+
+        public void SaveToDatabase()
+        {
+            Console.WriteLine("Saved!");
+        }
+
+        public void UpdateBalance(int id, decimal newBalance)
+        {
+            var customer = GetById(id);
+            if (customer != null)
+            {
+                customer.Balance = newBalance;
+                SaveToDatabase();
+            }
+        }
+    }
+}

Lesson_4/Task_1/Program.cs

@@ -0,0 +1,2 @@
+// See https://aka.ms/new-console-template for more information
+Console.WriteLine("Hello, World!");

Lesson_4/Task_1/Task_1.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

Lesson_4/Task_2/MagicClass.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Open_Closed
+{
+    public class FireMagic : Magic
+    {
+        public override void CountYourMagic() 
+        {
+            Console.WriteLine("Wow, your magic is fire magic!");
+        }
+    }
+
+    public class WaterMagic : Magic
+    {
+        public override void CountYourMagic() 
+        {
+            Console.WriteLine("Incredible! You have 50 millions of power! It's water magic!");
+        }
+    }
+
+    public class Magic
+    {
+        public virtual void CountYourMagic() 
+        {
+            Console.WriteLine("I understand you...");
+        }
+    }
+}

Lesson_4/Task_2/Program.cs

@@ -0,0 +1,2 @@
+// See https://aka.ms/new-console-template for more information
+Console.WriteLine("Hello, World!");

Lesson_4/Task_2/Task_2.csproj

@@ -0,0 +1,10 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net7.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>

README.md

@@ -24,3 +24,8 @@ Checked means the task is Done.
 ### Lesson 3
 
 - [x] Task 1
+
+### Lesson 4
+
+- [ ] Task 1
+- [ ] Task 2