数组超出范围？该怎么处理

                int[] Iday =null;
                for (int a = 0; a <= ehour; a++)
                {
                    Iday[a] = shour;
                    shour++;
                }

                int[] Iday = new int[ehour+1];
                for (int a = 0; a <= ehour; a++)
                {
                    Iday[a] = shour;
                    shour++;
                }

------解决方案--------------------

C# code

        int[] Iday = null;
        for (int a = 0; a < Iday.Length; a++)
        {
            Iday[a] = shour;
            shour++;
        }