Search in 2D array

public bool IsElementPresent(int num)
        {
            if (array == null)
                return false;
 
            int nofRows = array.GetLength(0);
            int noColumns = array[0].Length;
            int rowIndex = 0, columnIndex = 0;
 
            while (rowIndex < nofRows - 1 && array[rowIndex][columnIndex] < num)
            {
                rowIndex++;
            }
            while (columnIndex < noColumns - 1 && array[rowIndex][columnIndex] < num)
            {
                columnIndex++;
            }
            while (rowIndex > 0 && array[rowIndex][columnIndex] > num)
            {
                rowIndex--;
            }
            while (columnIndex > 0 && array[rowIndex][columnIndex] > num)
            {
                columnIndex--;
            }
            if (array[rowIndex][columnIndex] == num)
                return true;
 
            return false;
        }