Structure Sorting (By Multiple Rules) in C++

Prerequisite : Structures in C
Name and marks in different subjects (physics, chemistry and maths) are given for all students. The task is to compute total marks and ranks of all students. And finally display all students sorted by rank. 

Rank of student is computed using below rules. 

1. If total marks are different, then students with higher marks gets better rank.
2. If total marks are same, then students with higher marks in Maths gets better rank.
3. If total marks are same and marks in Maths are also same, then students with better marks in Physics gets better rank.
4. If total marks are same and marks in both Maths and Physics are also same, then students with better marks in Chemistry gets better rank.
5. If all marks (total, Maths, Physics and Chemistry) are same, then any student can be assigned better rank.

We use below structure to store details of students.

struct Student 
{
    string name; // Given
    int math;  // Marks in math (Given)
    int phy;   // Marks in Physics (Given)
    int che;   // Marks in Chemistry (Given)
    int total; // Total marks (To be filled)
    int rank;  // Rank of student (To be filled)
};  

We use std::sort() for Structure Sorting. In Structure sorting, all the respective properties possessed by the structure object are sorted on the basis of one (or more) property of the object.
In this example, marks of students in different subjects are provided by user. These marks in individual subjects are added to calculate the total marks of the student, which is then used to sort different students on the basis of their ranks (as explained above).

Implementation:

C++

// C++ program to demonstrate structure sorting in C++
#include <bits/stdc++.h>
using namespace std;

struct Student
{
    string name; // Given
    int math; // Marks in math (Given)
    int phy; // Marks in Physics (Given)
    int che; // Marks in Chemistry (Given)
    int total; // Total marks (To be filled)
    int rank; // Rank of student (To be filled)
};

// Function for comparing two students according
// to given rules
bool compareTwoStudents(Student a, Student b)
{
    // If total marks are not same then
    // returns true for higher total
    if (a.total != b.total)
        return a.total > b.total;

    // If marks in Maths are same then
    // returns true for higher marks
    if (a.math != b.math)
        return a.math > b.math;

    if (a.phy != b.phy)
        return a.phy > b.phy;

    return (a.che > b.che);
}

// Fills total marks and ranks of all Students
void computeRanks(Student a[], int n)
{
    // To calculate total marks for all Students
    for (int i = 0; i < n; i++)
        a[i].total = a[i].math + a[i].phy + a[i].che;

    // Sort structure array using user defined
    // function compareTwoStudents()
    sort(a, a + n, compareTwoStudents);

    // Assigning ranks after sorting
    for (int i = 0; i < n; i++)
        a[i].rank = i + 1;
}

// Driver code
int main()
{
    int n = 5;

    // array of structure objects
    Student a[n];

    // Details of Student 1
    a[0].name = "Bryan";
    a[0].math = 80;
    a[0].phy = 95;
    a[0].che = 85;

    // Details of Student 2
    a[1].name = "Kevin";
    a[1].math = 95;
    a[1].phy = 85;
    a[1].che = 99;

    // Details of Student 3
    a[2].name = "Nicky";
    a[2].math = 95;
    a[2].phy = 85;
    a[2].che = 80;

    // Details of Student 4
    a[3].name = "Steve";
    a[3].math = 80;
    a[3].phy = 70;
    a[3].che = 90;

    // Details of Student 5
    a[4].name = "Rohan";
    a[4].math = 80;
    a[4].phy = 80;
    a[4].che = 80;

    computeRanks(a, n);

    // Column names for displaying data
    cout << "Rank"
         << " "
         << "Name"
         << "     ";
    cout << "Maths"
         << " "
         << "Physics"
         << " "
         << "Chemistry";
    cout << " "
         << "Total\n";

    // Display details of Students
    for (int i = 0; i < n; i++) {
        cout << a[i].rank << "    ";
        cout << a[i].name << "      ";
        cout << a[i].math << "     " << a[i].phy << "     "
             << a[i].che << "       ";
        cout << a[i].total << " ";
        cout << "\n";
    }

    return 0;
}

Output

Rank Name     Maths Physics Chemistry Total
1    Kevin      95     85     99       279 
2    Nicky      95     85     80       260 
3    Bryan      80     95     85       260 
4    Rohan      80     80     80       240 
5    Steve      80     70     90       240 

Time complexity : O(nlogn)

Auxiliary Space :O(n) 

This article is contributed by Abhinav Tiwari . If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.