Sorting an array of structures

Question

I'm studying c++ and I was given the task. I need to created structure Student

#include "stdafx.h"
using namespace std;

const int num = 5;

struct Student  {
    string name;
    int groupNumber;
    int progress[num];
};

and work with it.
it's my programm

#include "stdafx.h"
#include "Student.h"
using namespace std;

int _tmain(int argc, _TCHAR* argv[])
{
srand((unsigned)time(NULL));

int n;
cout << "Input n = ";
cin >> n;
cin.ignore();

Student * Group = new Student[n];

for (int i = 0; i < n; ++i)
{
    cout << "Input name: ";
    getline (cin, Group[i].name);
    Group[i].groupNumber = rand()%5 + 1;
    for (int j = 0; j < num; ++j)
    {
        Group[i].progress[j] = rand()%5 + 2;
    }
}

int * groupNumberArray = new int[n];
for (int i = 0; i < n; ++i)
{
    groupNumberArray[i] = Group[i].groupNumber;
}

for (int i; i < n - 1; ++i)
{
    int min = i;
    for (int j = i + 1; j < n; ++j)
    {
        if (groupNumberArray[min] <= groupNumberArray[j]) continue;
        min = j;
    }
    if (min != i)
    {
        int temp = groupNumberArray[i];
        groupNumberArray[i] = groupNumberArray[min];
        groupNumberArray[min] = temp;

        Student * tempStudent = &Group[i];
        &Group[min] = &Group[i];
        &Group[i] = tempStudent;
    }
}

cout << "\n\n";

delete [] Group;
delete [] groupNumberArray;

system("PAUSE");
return 0;
}

I need to sort students in accordance with the growth of groupNumber.
I tried to use pointers but it works wrong. How to make the sorting works the right way?

Please state your requirements, otherwise we'll just say "use std::sort with a suitable predicate, the end". — juanchopanza
– juanchopanza, Commented Oct 11, 2013 at 12:45
The C++ way would be: Provide a comparator for the Student struct and just use the sort algorithm. — dornhege
– dornhege, Commented Oct 11, 2013 at 12:45
Declare group as std::vector<Student> group; then use std::sort .... — Basile Starynkevitch
– Basile Starynkevitch, Commented Oct 11, 2013 at 12:45
I'm just starting to learn С++, I dont know about std::sort and about std::vector. I need to use simple ways. — Heidel
– Heidel, Commented Oct 11, 2013 at 12:49

Thomas Matthews · Accepted Answer · 2013-10-11 13:19:42Z

3

A possibility is to use std::sort with a comparator method on your array.

Example:

bool Compare_By_Group(const Student& a, const Student& b)
{
  return a.groupNumber /* insert comparison operator here */ b.groupNumber;
}

// The sort function call
    std::sort(&Group[0],
              &Group[/* last index + 1*/],
              Compare_By_Group);

answered Oct 11, 2013 at 13:19

Thomas Matthews

58.1k18 gold badges105 silver badges165 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Konrad Rudolph Over a year ago

&Group[/* last index + 1*/] is illegal C++ (UB). Use Group + N instead (there’s really no reason to use &Group[0] instead of pointer decay of Group, except for reasons of overload resolution).

Neil Kirk · Accepted Answer · 2013-10-11 13:21:50Z

1

    vector<Student> students(n);
    .. populate students
    sort(students.begin(), students.end(), [](const Student& left, const Student& right){ return left.groupNumber < right.groupNumber; });

answered Oct 11, 2013 at 13:21

Neil Kirk

22k9 gold badges57 silver badges96 bronze badges

Collectives™ on Stack Overflow

Sorting an array of structures

2 Answers 2

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related