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# Project Task: Three — C++ shell sort

## Source Code: C++

```//
// C++ implementation of Shell Sort
//
// \$Id: shellsort.cc,v 0.2 2023/03/11 14:28:10 kc4zvw Exp kc4zvw \$
//

#include <iostream>

using namespace std;

/* function prototypes */

void printArray(int [], int);
int shellSort(int [], int);

int main()
{
int arr[] = {12, 34, 54, 2, 3, 45, 11, 10, 5, 67, 84}, i;
int n = sizeof(arr)/sizeof(arr[0]);

cout << "Sample program to sort a list of integers in an array\n" << endl;

cout << "Array before sorting: " << endl;
printArray(arr, n);

shellSort(arr, n);

cout << "\nArray after sorting: " << endl;
printArray(arr, n);

cout << endl;

return 0;
}

/* Function to sort arr using shellSort */

int shellSort(int arr[], int n)
{
// Start with a big gap, then reduce the gap
for (int gap = n/2; gap > 0; gap /= 2) {
// Do a gapped insertion sort for this gap size.
// The first gap elements a[0..gap-1] are already in gapped order
// keep adding one more element until the entire array is
// gap sorted
for (int i = gap; i < n; i += 1) {
// add a[i] to the elements that have been gap sorted
// save a[i] in temp and make a hole at position i
int temp = arr[i];

// shift earlier gap-sorted elements up until the correct
// location for a[i] is found
int j;
for (j = i; j >= gap && arr[j - gap] > temp; j -= gap)
arr[j] = arr[j - gap];

// put temp (the original a[i]) in its correct location
arr[j] = temp;
}
}
return 0;
}

void printArray(int arr[], int n)
{
for (int i = 0; i < n; i++)
cout << arr[i] << " ";
cout << endl;
}

/* End of File */

```

## Operation Notes

```
kc4zvw@www:~\$ ./shellsort3
Sample program to sort a list of integers in an array

Array before sorting:
12 34 54 2 3 45 11 10 5 67 84

Array after sorting:
2 3 5 10 11 12 34 45 54 67 84

kc4zvw@www:~\$

```