1)

using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      string firstName = "John ";
      string lastName = "Doe";
      string fullName = firstName + lastName;
      Console.WriteLine(fullName);
    }
  }
}

2)

using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int x = 5, y = 6, z = 50;
      Console.WriteLine(x + y + z);
    }
  

3)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int myNum = 5;               // integer (whole number)
      float myFloatNum = 5.99f;    // floating point number
      char myLetter = 'D';         // character
      bool myBool = true;          // boolean
      string myText = "Hello";     // string
      Console.WriteLine(myNum);
      Console.WriteLine(myFloatNum);
      Console.WriteLine(myLetter);
      Console.WriteLine(myBool);
      Console.WriteLine(myText);
    }
  }
}
4)
using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int myInt = 10;
      double myDouble = 5.25;
      bool myBool = true;

      Console.WriteLine(Convert.ToString(myInt));    // Convert int to string
      Console.WriteLine(Convert.ToDouble(myInt));    // Convert int to double
      Console.WriteLine(Convert.ToInt32(myDouble));  // Convert double to int
      Console.WriteLine(Convert.ToString(myBool));   // Convert bool to string
      }
  }
}

5)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      // Type your username and press enter
      Console.WriteLine("Enter username:");

      // Create a string variable and get user input from the keyboard and store it in the variable
      string userName = Console.ReadLine();

      // Print the value of the variable (userName), which will display the input value
      Console.WriteLine("Username is: " + userName);
    }
  }
}




6)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      Console.WriteLine("Enter your age:");
      int age = Convert.ToInt32(Console.ReadLine());
      Console.WriteLine("Your age is: " + age);
    }
  }
}

7)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      Console.WriteLine(Math.Max(5, 10));  
     }
  }
}

8)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      Console.WriteLine(Math.Sqrt(64));  
     }
  }
}

9)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      string txt = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
      Console.WriteLine("The length of the txt string is: " + txt.Length);
    }
  }
}

10)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      string firstName = "John ";
      string lastName = "Doe";
      string name = firstName + lastName;
      Console.WriteLine(name);
    }
  }
}

11)sing System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int x = 10;
      int y = 9;
      Console.WriteLine(x > y); // returns True, because 10 is higher than 9
    }
  }
}

12)sing System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int time = 20;
      if (time < 18) 
      {
        Console.WriteLine("Good day.");
      } 
      else 
      {
        Console.WriteLine("Good evening.");
      }
    }
  }
}

13)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int time = 22;
      if (time < 10) 
      {
        Console.WriteLine("Good morning.");
      } 
      else if (time < 20) 
      {
        Console.WriteLine("Good day.");
      } 
      else 
      {
        Console.WriteLine("Good evening.");
      }
    }
  }
}

14)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int day = 4;
      switch (day) 
      {
        case 1:
          Console.WriteLine("Monday");
          break;
        case 2:
          Console.WriteLine("Tuesday");
          break;
        case 3:
          Console.WriteLine("Wednesday");
          break;
        case 4:
          Console.WriteLine("Thursday");
          break;
        case 5:
          Console.WriteLine("Friday");
          break;
        case 6:
          Console.WriteLine("Saturday");
          break;
        case 7:
          Console.WriteLine("Sunday");
          break;
      }    
    }
  }
}

15)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int i = 0;
      while (i < 5) 
      {
        Console.WriteLine(i);
        i++;
      }
    }
  }
}

16)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      int i = 0;
      do 
      {
        Console.WriteLine(i);
        i++;
      }
      while (i < 5);
    }
  }
}

17)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      for (int i = 0; i < 5; i++) 
      {
        Console.WriteLine(i);
      }    
    }
  }
}

18)using System;

namespace MyApplication
{
  class Program
  {
    static void Main(string[] args)
    {
      string[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
      foreach (string i in cars) 
      {
        Console.WriteLine(i);
      }   
    }
  }
}

18)