selection sort for array of objects

Question

Iam trying to make selection sort for array of objects considering i have Data class

I want to sort them depending on the id attribute of the object

class Data
{
public:
    string name;
    int id;
};

    }
int main()
{
    Data m[3];
    m[0].id = 5;
    m[1].id = 4;
    m[2].id = 8;
    selsort(m, 3);
    cout << m[0].id;
};

I cannot understand what is wrong nothing happens to the array?

Answer 1

It seems there is a typo in the function declaration

void selsort(media mry[], int n)
             ^^^^^

I think you mean

void selsort( Data mry[], int n)
              ^^^^

This if statement

if ((mry[min].id < mry[j].id) < 0)

does not make sense.

You should write

if ( mry[min].id < mry[j].id )

Or if you want to sort in the ascending order then write the condition like

if ( mry[j].id < mry[min].id )

Answer 2

Change:

if ((mry[min].id < mry[j].id) < 0)

to:

if ((mry[min].id > mry[j].id) )

You are finding the minimum index, so you have to swap if you find an index with a value that is lesser than the current minimum.

A better way to accomplish this is to make your function take in another parameter called a comparator function which tells the function how to compare; that way you can reuse your function if you change to mind and what to sort it by another parameter.

void selsort(Data mry[], int n, std::function<int(Data, Data)> cmp) // mry[] is the object array, n is the 
                                     // number of objects in the array
    {
        int pass, j, min;
        Data temp;
        for (pass = 0; pass <= n - 2; pass++)  // passes
        {
            min = pass;
            for (j = pass + 1; j < n; j++)  // in each pass
                if (cmp(mry[min], mry[j]) > 0)
                    min = j;
            temp = mry[min];
            mry[min] = mry[pass];
            mry[pass] = temp;
        }

    }

And you can define a compare by id function:

int compare_by_id(Data d1, Data d2) 
{
    return d1.id - d2.id;
}

Call your function like this:

selsort(array, size, compare_by_id);

The best part is you can define your own function that can compare the elements as you want and that way your selsort() is versatile.