C++仅使用指针更改数组的元素

Question

我正在解决一个问题，我无法使用数组索引来更改元素，而且我真的很难处理指针。这段代码应该初始化一个数组，所有索引都初始化为 0，索引 0 和 1 除外。索引 0 和 1 初始化为 -1。我得到的数组里面有奇怪的数字，

int* arr(int size);
int main()
{
    int low, high;
    char again = 'y';
    high = low = 0;

    cout << "\tThe Sieve of Eratosthenes" << endl << endl;
    do
    {
        do
        {
            cout << "Enter the high boundary: ";
            cin >> high;
            cout << endl;
            if (high <= 0)
                cout << "ERROR: HIGH BOUNDARY MUST BE POSITIVE" << endl;
        } while (high < 0);

        int* thearr = arr(high);
        cout << "The prime numbers from to " << high << " are: " << endl;

        for (int ix = 0; ix <= high; ++ix)
        {
            cout << thearr[ix] << "  ";
        }

        cout << endl << endl;
        cout << endl << endl;
        cout << "Try again with new boundaries? (y/n):" << endl;
        cin >> again;

        delete[] thearr;

    } while (again == 'y');

    return 0;
}

int* arr(int size)
{
    int* thearray = new int[size];
    int last = size;
    cout << *thearray << " " << last;
    while (*thearray < last)
    {
        if (*thearray <= 1)
            thearray[*thearray] = 0;
        else
            thearray[*thearray] = -1;
        ++thearray;
        cout << *thearray;
    }
    return thearray;
}

Answer 1

有几种方法可以将数组初始化为全零:

• 使用值初始化

  int* thearray = new int[size]();
  

• 使用 std::fill_n

  int* thearray = new int[size];
  std::fill_n(thearray, size, 0);
  

• 使用 std::fill

  int* thearray = new int[size];
  int* end = thearray + size;
  std::fill(thearray, end, 0);
  

• 使用指针和显式循环

  int* thearray = new int[size];
  int* end = thearray + size;
  int* begin = thearray;
  
  while (begin < end)
  {
      *begin++ = 0;
  }
  
  // After loop thearray still points to the beginning of the array
  

• 使用 std::vector相反

  std::vector<int> thearray(size);
  

如果您必须使用原始指针(由于赋值或练习条件)，那么我建议使用前两种之一。