c++ - 如何在 C++ 中用数组和指针实现插入排序算法？

Question

我正在尝试学习 C++、数组和指针。我决定实现 insertion sort algorithm .所以，这是我的代码和错误的输出。我应该怎么做才能纠正它？你能告诉我我的错误是什么吗？如果是常见错误，我应该避免什么？

我的代码:

// InsertionSort.cpp

#include "stdafx.h"
#include <iostream>

int DeclareAnInteger();
int* DeclareAndShowTheArray(int n);
int* InsertionSort(int *A, int n);

int main()
{

   int n = DeclareAnInteger();
   int *A;
   A = DeclareAndShowTheArray(n);
   int *B;
   B = InsertionSort(A, n);

   system("PAUSE");
   return 0;
}

int DeclareAnInteger()
{
   int n;
   std::cout << "Please enter a positive integer n: ";
   std::cin >> n;
   return n;
}

int* DeclareAndShowTheArray(int n)
{
   int *A;
   A = (int *)alloca(sizeof(int) * n);
   for (int i = 0; i < n; i++)
   {
      std::cout << "Please enter the value of A[" << i + 1 << "]: ";
      std::cin >> A[i];
   }
   std::cout << "The unsorted array is: ";
   for (int i = 0; i < n; i++)
   {
      std::cout << A[i];
      std::cout << "\t";
   }
   std::cout << "\n";
   return A;
}

int* InsertionSort(int *A, int n)
{
   int k;
   //int *A = new int[n];
   for (k = 1; k < n; k++)
   {
      int key = A[k];
      int m   = k - 1;
      while (m >= 0 & A[m] > key)
      {
         A[m + 1] = A[m];
         m        = m - 1;
      }
      A[m + 1] = key;
   }
   std::cout << "The sorted array is: ";
   for (int i = 0; i < n; i++)
   {
      std::cout << A[i];
      std::cout << "\t";
   }
   std::cout << "\n" << std::endl;
   return A;
}

我的输出:

Answer 1

这是个大问题:

A = (int *)alloca(sizeof(int) * n);

alloca 函数在堆栈上分配，当函数返回时它会丢失，给你一个杂散指针和undefined behavior当您取消引用此指针时。

如果您正在编写 C++，则使用 new，如果您编写 C，则使用 malloc。