Добавьте файлы проекта.

var3.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.2.32526.322
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "var3", "\main\RDP\31П\МалевАВ\Desktop\Malev.PM02\var3\var3\var3.csproj", "{50DFD7D3-FE79-4A6B-AF55-4513EEBDB9C6}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{50DFD7D3-FE79-4A6B-AF55-4513EEBDB9C6}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{50DFD7D3-FE79-4A6B-AF55-4513EEBDB9C6}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{50DFD7D3-FE79-4A6B-AF55-4513EEBDB9C6}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{50DFD7D3-FE79-4A6B-AF55-4513EEBDB9C6}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {8D316261-0A81-4E78-A67E-AB82FB400140}
+	EndGlobalSection
+EndGlobal

var3/Class1.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Diagnostics;
+using System.IO;
+
+namespace var3
+{
+    internal class Class1
+    {
+        public static void read()
+        {
+            string data = "data.txt";
+            string[] da = new string[400];
+            da = File.ReadAllLines(data);
+            for (int i = 0; i < da.Length; i++)
+            {
+                Console.WriteLine(da[i]);
+            }
+        }
+    }
+}

var3/Debugcs.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Diagnostics;
+using System.IO;
+
+namespace var3
+{
+    internal class Debugcs
+    {
+    }
+}

var3/Program.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Diagnostics;
+using System.IO;
+
+

var3/var3.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>