C#

class Hello {
  // main method
  static void Main(string[] args)
  {
    // Output: Hello, world!
    Console.WriteLine("Hello, world!");
  }
}

$ dotnet new console

$ dotnet new list

$ dotnet run
Hello, world!

int intNum = 9;
long longNum = 9999999;
float floatNum = 9.99F;
double doubleNum = 99.999;
decimal decimalNum = 99.9999M;
char letter = 'D';
bool @bool = true;
string site = "cheatsheets.zip";

var num = 999;
var str = "999";
var bo = false;

// Single-line comment

/* Multi-line
   comment */

// TODO: Adds comment to a task list in Visual Studio

/// Single-line comment used for documentation

/** Multi-line comment
    used for documentation **/

string first = "John";
string last = "Doe";

// string concatenation
string name = first + " " + last;
Console.WriteLine(name); // => John Doe

Console.WriteLine("Enter number:");
if(int.TryParse(Console.ReadLine(),out int input))
{
  // Input validated
  Console.WriteLine($"You entered {input}");
}

int j = 10;

if (j == 10) {
  Console.WriteLine("I get printed");
} else if (j > 10) {
  Console.WriteLine("I don't");
} else {
  Console.WriteLine("I also don't");
}

char[] chars = new char[10];
chars[0] = 'a';
chars[1] = 'b';

string[] letters = {"A", "B", "C"};
int[] mylist = {100, 200};
bool[] answers = {true, false};

int[] numbers = {1, 2, 3, 4, 5};

for(int i = 0; i < numbers.Length; i++) {
  Console.WriteLine(numbers[i]);
}

foreach(int num in numbers) {
  Console.WriteLine(num);
}

string first = "John";
string last = "Doe";

string name = first + " " + last;
Console.WriteLine(name); // => John Doe

string first = "John";
string last = "Doe";

string name = $"{first} {last}";
Console.WriteLine(name); // => John Doe

string longString = @"I can type any characters in here !#@$%^&*()__+ '' \n \t except double quotes and I will be taken literally. I even work with multiple lines.";

// Using property of System.String
string lengthOfString = "How long?";
lengthOfString.Length           // => 9

// Using methods of System.String
lengthOfString.Contains("How"); // => true