Sample Matrix Class

namespace MatrixClass
{
    using System;

    public class Matrix
    {
        private const string NoRowsExceptionMsg = "The Matrix must have at least one row.";
        private const string NoColsExceptionMsg = "The Matrix must have at least one column.";
        private const string OutOfRangeExceptionMsg = "Index is out of range.";

        private int rows;
        private int cols;
        private int[,] matrix;

        public Matrix(int rows, int cols)
        {
            this.Rows = rows;
            this.Cols = cols;
            this.matrix = new int[rows, cols];
        }

        public int Rows
        {
            get
            {
                return this.rows;
            }

            private set
            {
                if (value < 1)
                {
                    throw new ArgumentException(NoRowsExceptionMsg);
                }

                this.rows = value;
            }
        }

        public int Cols
        {
            get
            {
                return this.cols;
            }

            private set
            {
                if (value < 1)
                {
                    throw new ArgumentException(NoColsExceptionMsg);
                }

                this.cols = value;
            }
        }

        public int this[int rowIndex, int colIndex]
        {
            get
            {
                return this.matrix[rowIndex, colIndex];
            }

            set
            {
                if (rowIndex < 0 || rowIndex >= this.Rows || colIndex < 0 || colIndex >= this.Rows)
                {
                    throw new IndexOutOfRangeException(OutOfRangeExceptionMsg);
                }

                this.matrix[rowIndex, colIndex] = value;
            }
        }

        public override string ToString()
        {
            string rows = string.Empty;

            for (int row = 0; row < this.Rows; row++)
            {
                for (int col = 0; col < this.Cols; col++)
                {
                    rows += string.Format("{0,5}", this.matrix[row, col]);
                }

                rows += Environment.NewLine;
            }

            return rows;
        }
    }

    public class MatrixClass
    {
        public static void Main()
        {
            Matrix matrix = new Matrix(3, 3);
        int matrixRowsCount = matrix.Rows;
        int matrixColsCount = matrix.Cols;
        int index = matrix[1, 1];
        }
    }
}