Василий Банников

var input = "swer rrttyy uu iop!";
var result = Regex.Replace(input, "[a-z]", "+", RegexOptions.IgnoreCase);
Console.WriteLine(result); //++++ ++++++ ++ +++!

interface ISpeaking {
  public void Speak();
}

public class Dog: ISpeaking {
  public void Speak() => Console.WriteLine("Гав!");
}

public class Cat: ISpeaking {
  public void Speak() => Console.WriteLine("Мяу!");
}

public static void Main() {
 ISpeaking[] speakers = new ISpeaking[] {new Cat(), new Dog()};
 foreach(ISpeaking speaker in speakers)
   speaker.Speak();
}

static void PrintAll(string[] array) {
  foreach(var e in array)
    Console.WriteLine(e);
}

static void PrintAll(List<string> list) {
  foreach(var e in list) { // Дублирование!
    Console.WriteLine(e);
}

// Можно использовать и для string[], и для List<string>, и даже для того, о чём мы ещё не знаем!
static void PrintAll(IEnumerable<string> collection) {
  foreach(var e in collection) {
    Console.WriteLine(e);
  }
}

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": ".NET Core Launch (console)",
            "type": "coreclr",
            "request": "launch",
            "preLaunchTask": "build",
            "program": "${workspaceFolder}/bin/Debug/net5.0/Demo.dll",
            "args": [],
            "cwd": "${workspaceFolder}",
            "console": "internalConsole",
            "stopAtEntry": false
        }
    ]
}

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "build",
            "command": "dotnet",
            "type": "shell",
            "args": [
                "build",
                // Ask dotnet build to generate full paths for file names.
                "/property:GenerateFullPaths=true",
                // Do not generate summary otherwise it leads to duplicate errors in Problems panel
                "/consoleloggerparameters:NoSummary"
            ],
            "group": "build",
            "presentation": {
                "reveal": "silent"
            },
            "problemMatcher": "$msCompile"
        }
    ]
}