using System;

class Layout
{
    string[] _values = new string[100]; // Backing store

    public string this[int number]
    {
    get
	{
	    // This is invoked when accessing Layout instances with the [ ].
	    if (number >= 0 && number < _values.Length)
	    {
		// Bounds were in range, so return the stored value.
		return _values[number];
	    }
	    // Return an error string.
	    return "Error";
	}
	set
	{
	    // This is invoked when assigning to Layout instances with the [ ].
	    if (number >= 0 && number < _values.Length)
	    {
		// Assign to this element slot in the internal array.
		_values[number] = value;
	    }
	}
    }
}

class Program
{
    static void Main()
    {
	// Create new instance and assign elements
	// ... in the array through the indexer.
	Layout layout = new Layout();
	layout[1] = "Frank Gehry";
	layout[3] = "I. M. Pei";
	layout[10] = "Frank Lloyd Wright";
	layout[11] = "Apollodorus";
	layout[-1] = "Error";
	layout[1000] = "Error";

	// Read elements through the indexer.
	string value1 = layout[1];
	string value2 = layout[3];
	string value3 = layout[10];
	string value4 = layout[11];
	string value5 = layout[50];
	string value6 = layout[-1];

	// Write the results.
	Console.WriteLine(value1);
	Console.WriteLine(value2);
	Console.WriteLine(value3);
	Console.WriteLine(value4);
	Console.WriteLine(value5); // Is null
	Console.WriteLine(value6);
    }
}