Create csharp project to replace single file.

codes/csharp/.gitignore

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+.idea/
+.vs/
+obj/
+.Debug
+bin/

codes/csharp/hello-algo.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <RootNamespace>hello_algo</RootNamespace>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.4.0" />
+    <PackageReference Include="NUnit" Version="3.13.3" />
+	<PackageReference Include="NUnit3TestAdapter" Version="4.0.0" />
+	<PackageReference Include="coverlet.collector" Version="3.1.0" />
+  </ItemGroup>
+
+</Project>

codes/csharp/hello-algo.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.1.32421.90
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "hello-algo", "hello-algo.csproj", "{C88820BB-BD9C-4993-9FAE-D3C09FEF4E4B}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{C88820BB-BD9C-4993-9FAE-D3C09FEF4E4B}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{C88820BB-BD9C-4993-9FAE-D3C09FEF4E4B}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{C88820BB-BD9C-4993-9FAE-D3C09FEF4E4B}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{C88820BB-BD9C-4993-9FAE-D3C09FEF4E4B}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {93C0511D-8D01-43BB-BD42-8E053E46FD67}
+	EndGlobalSection
+EndGlobal