private void button1_Click(object sender, EventArgs e)
    {
        string msg = "";
        int i = 1;

        while (i < 6)
        {
            int col = 0;
            while (col < i)
            {
                msg += i;
                col++;
            }
            msg += "n";
            i++;
        }

        MessageBox.Show(msg);
    }

private void button1_Click(object sender, EventArgs e)
{
 string msg = "";
   for (var i = 1; i < 6; i++)
   {
     for (var col = 0; col < i; col++)
     {
       msg += "*";
     }
     msg += "n";
   }
   for (var i = 5; i >= 1; i--)
     {
        for (var col = 0; col< i; col++)
        {
          msg += "*";
        }
        msg += "n";
     }
   MessageBox.Show(msg.Trim());
}

string output = string.Empty;
const string symbol = "*";

//Loop up to the half to print the upcomming way
for (int i = 1; i <= 5; i++)
{
    //Based on index i we need to print asterix
    for (int up = 0; up < i; up++)
    {
      output += symbol;
    }

    //After all asterix are written to string we need a NewLine.
    output += Environment.NewLine;
 }

 //Here we start the same part as above but reverse it
 //So counting from upper end down
 for (int i = 5; i >= 1; i--)
 {
    for (int down = 0; down < i; down++)
    {
      output += symbol;
    }

    output += Environment.NewLine;
  }

  //The Trim(); will cut any free spaces before and after the string
  //So we can easily cut the last NewLine which is inserted but not needed
  MessageBox.Show(output.Trim());

private void button1_Click(object sender, EventArgs e)
{
    string msg = "";
    for (var i = 1; i < 6; i++)
    {
        for (var col = 0; col < i; col++)
        {
            msg += i;
        }
        msg += "n";
    }
    MessageBox.Show(msg);
}