希爾排序快速但不穩定，且根據增量的不同有多種不同的寫法。

// Selection sort
// 選擇排序
#include <iostream>
#include <cmath>
using namespace std;

void swap(int* a, int* b)
{
    int temp = *a;
    *a = *b;
    *b = temp;
}

void print(int a[], int size)
{
    for (int i = 0; i < size; i++)
    {
        cout << a[i] << " "
 
;
    }
    cout << endl;
}

void shell_sort(int a[], int size)
{
    int i, j, temp, gap = size/2;   // 設定希爾排序的增量
    while(gap >= 1)
    {
        for(i=gap; i<size; i++)    
        {    
            temp = a[i];
            j = i-gap;
            while(j>=0 && a[j]>temp)    
            {    
                a[j+gap] = a[j];    
                j = j-gap;    
            }    
            a[j+gap] = temp;
            print(a, size); // 列印每趟排序後的結果
 

        }
        gap = gap/2;// 縮小增量

    }    
    cout << "Sorting procedure ended!" << endl;
}

int main(int argc, char* argv[])
{
//#define DEBUG

#ifdef DEBUG
    int A[] = { 8,7,6,5,4,3,2,1 };  
    int size = sizeof(A)/sizeof(int);
#else // 假設個數未知
    int size = 0;
    cout << "Enter array size: "
 
;
    cin >> size;

    cout << "Enter array elements: ";
    int* A = new int[size];
    int i = 0;
    while ((cin >> A[i]) &&
            (i < size) )
    {
        i++;
    }

#endif

    shell_sort(A, size);

    print(A, size);

#ifndef DEBUG
    delete[] A;
#endif

    return 0;
}