Help with sorting program

[ezmesori]

Hello,
So I have to write a function called sortMe that sorts the elements of an array in numerical order from highest to lowest values (descending order) or vice versa (ascending order).

I was able to this but not how I'm supposed to.

The assignment asks to: NOT re-arrange elements in the array; instead, it uses a second array, an array of indexes for the elements in the original array and then sortMe sorts the second array based on the values in the original
array. A sorted version of the original array can then be produced with these sorted indexes.

Header of the function sortMe must be as shown below:
void sortMe(int array[],int sortedIndexes [], int size, char mode)

When mode is 'a', the function sorts the array in the ascending order, and when mode is 'd', the function sorts it in the descending order.

Declare and initialize the array array.
Declare the array sortedIndexes but do not initialize it. You are going to play with the array sortedIndexes in the
function sortMe.
EXAMPLE:
int array[5]={3, 5,-1,10,0};
int sortedIndexes[5];
sortMe(array,sortedIndexes, 5, 'a');

After the function call, the elements of the array sortedIndexes should
be: 2,4,0,1,3

Please notice that the function does not e-arrange the elements in the array.

#include <iostream>
using namespace std;
void sortMe(int[], int, char);
void main()
{
  int arr[6] = { 14, -5, 5, 0, 22, -99 };
  char input;
  cout << "Please select in what order you want the numbers sorted. \nFor     ascending order press a. For descending order press d: \n";
  cin >> input;
      if (input == 'a'){
          sortMe(arr, 6, 'a'); 
          for (int i = 0; i < 6; i++)
               cout << arr[i] << "\t"; //I want to print the sortedIndexes  array not array
      }
      else if (input == 'd'){
	    sortMe(arr, 6, 'd');
	    for (int j = 0; j < 6; j++)
	    cout << arr[j] << "\t";

      }
      else
	cout << "Please make a correct selection" << endl;

　
	system("pause");

}

void sortMe(int array[], int size, char mode)

{
	int temp;

	if (mode == 'd') //descending order
        {
	  for (int i = 0; i < size; i++)
          {
	    for (int j = i + 1; j < size; j++)
            {
	      if (array[j] > array[i])
              {
	         temp = array[i];
	         array[i] = array[j];
	         array[j] = temp;
               }
            }
          }
        }

	else if (mode == 'a') //ascending order
          for (int i = 0; i < size; i++)
          {
	    for (int j = i + 1; j < size; j++)
            {
	      if (array[j] < array[i])
              {
	         temp = array[i];
	         array[i] = array[j];
	         array[j] = temp;
               }
            }
          }
        }
}
	  

So I got it to ascend and descend by choosing a mode but I did this by rearranging, which is what it asks me not to do

[keskiverto]

What do the ints do? What does the standard library do?

See http://www.cplusplus.com/reference/algorithm/sort/
Did the usage example give enough hints?

Probably not. Lets copy it partially here.

struct Myclass {
  bool operator() ( int i, int j ) {
    return ( i < j );
  }
};

void sortMe( int array[], int size ) {
  Myclass functor;
  std::sort( array, array+size, functor );
}

That is just the ascending sort by rearranging the values.

We want indirection.

struct Indclass {
  const int * arr;
  Indclass( const int * values )
  : arr( values )
  {}

  bool operator() ( int i, int j ) {
    return ( arr[i] < arr[j] ); // all the magic is on this line
  }
};

void sortMe( int array[], int sortedIndexes[], int size ) {
  Indclass functor( array );
  std::sort( sortedIndexes, sortedIndexes+size, functor );
}

Two indices are swapped if the values in the array at those index positions do not seem to be in correct order.


PS. Standard requires that main() returns int (not void).

[ezmesori]

This is my first c++ course so that's why my program might look simple. The professor doesn't want us to use advanced coding.

So I quite don't understand your codes.

Is there anyway you can explain it in simpler terms.

I seriously apologize for the inconvenience.

Like I said I got it to ascend and descend, but I don't know where to include sortedIndexes. I don't know how to get sortedIndexes to print the ascending order of the indexes

[ezmesori]

I have this code that copies one array into another

#include <iostream>
using namespace std;
void sortMe(int[], int [], int);
void main()
{
	int arr[6] = { 14, -5, 5, 0, 22, -99 };
	int sortedIndex[6];
	sortMe(arr,sortedIndex,6);
		for (int i = 0; i < 6; i++)
			cout << sortedIndex[i] << "\t";     //I want to print the sortedIndexes array not array
	



	system("pause");
}
void sortMe(int array[], int sortedIndexes[], int size)
{
	int temp;
	for (int i = 0; i < size; i++)
		sortedIndexes[i] = array[i];
}

Im missing how to return the index of the array. But how do I include this in my code?

[keskiverto]

"Simpler":
You test array[j] < array[i] and swap elements of array

You should test array[sortedIndexes[j]] < array[sortedIndexes[i]] and swap elements of sortedIndexes


You don't want to copy values. You want indices.

int main()
{
  const int N = 6;
  int arr[N] = { 14, -5, 5, 0, 22, -99 };

  int sortedIndex[N];
  for ( int i = 0; i < N; ++i ) {
    sortedIndex[i] = i;
  }

  for ( int i = 0; i < N; ++i ) {
    cout << "Index " sortedIndex[i] << " has value " << arr[sortedIndex[i]] << '\n';
  }

  return 0;
}

[ezmesori]

Got it! Thank you so much!