day5.am--拷贝构造与拷贝赋值

 Array& operator = Array(Array const& that){
         //避免自赋值
         if(&that != this){
             //释放旧资源
             if(m_array)
             {
                 delete[] m_array;
                 m_array = NULL;
             }
             //分配新资源
             m_array = new int[that.m_size];
             //拷贝新内容
             memcpy(m_array, that.m_array, that.m_size * sizeof(that.m_array[]));
             m_size = that.m_size;
         }
         //返回自引用
         return *this;
 }