Create multiple structs then sort by elements

Question

So I have to allow the user to create a certain amount of structs with 5 different types of information, and then sort based on one of those types. For example, they would input all the data and then sort by grade or name. How would I go about creating an array of just the different names or grades across the different structs?

#include <iostream>
#include <string>

struct student
{
    std::string studentName;
    std::string studentIDNumber;
    int currentExamGrade;
    int priorExamGrade;
    double GPA;
};

void createStudent()
{
    int numStudents;
    std::cout << "Enter number of students\n";
    std::cin >> numStudents;

    while (numStudents > 0)
    {
        student name;

        std::cout << "Enter the student's name\n";
        std::cin >> name.studentName;

        std::cout << "Enter the student's ID number\n";
        std::cin >> name.studentIDNumber;

        std::cout << "Enter the student's current exam grade\n";
        std::cin >> name.currentExamGrade;

        std::cout << "Enter the student's prior exam grade\n";
        std::cin >> name.priorExamGrade;

        std::cout << "Enter the student's GPA\n";
        std::cin >> name.GPA;

        numStudents -= 1;
    }
}

int main()
{
    createStudent();

    int choice;
    std::cout << "How do you want to sort the list?\n (Enter 1 for name, 2     for ID number, 3 for current exam grade, 4 for prior exam grade, 5 for GPA\n";
    std::cin >> choice; 

    return 0;

}

So, Captn, where's your array to be sorted? You read student alright, but after reading one, you discard the data and read another. — Adrian Colomitchi, Sep 26 '16 at 04:45
Ok. Time for you to read about [std::vector](http://www.cplusplus.com/reference/vector/vector/) - look over examples too. — Adrian Colomitchi, Sep 26 '16 at 04:50
One step at a time. First get the input working, then worry about sorting. Garbage in, garbage out. Garbage in, you sort garbage. Why debug sorting garbage? — user4581301, Sep 26 '16 at 05:05

score 0 · Answer 1 · edited May 23 '17 at 11:48

Ok. I assume you don't know the in-built sort functions in C++. Take a look at std::sort()

Take Input :

input values into struct array + printing out

Now to make an array of structs :

How do you make an array of structs in C?

Creating an array of structs in C++

Now to sort these arrays :

Sorting a vector of custom objects

How to approach this problem :

std::sort() allows you to give custom functions based on which non-tivial objects are comparable. Example of one such function is :

bool gpa_comparision_function (student s1,student s2)
{
    return s1.GPA < s2.GPA;
}

It takes argument as 2 students that need to be compared by the sorting function and returns the ordering of students s1 and s2 based on GPA.

This is why the statement s1.GPA < s2.GPA is important.

So if the student s1 has GPA = 5.0 and s2 has GPA = 4.0 we want the order to be s2,s1 (ascending) so this function returns false, stating that s2 should come before s1.

So in the call of the sorting function :

sort (arr_of_students,arr_of_students+N,gpa_comparision_function);

notice the 3rd argument, gpa_comparision_function, this is telling the in-built function to use our comparison function.

Talk is cheap show me the code :

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
struct student
{
    std::string studentName;
    std::string studentIDNumber;
    int currentExamGrade;
    int priorExamGrade;
    double GPA;
};
bool gpa_comparision_function (student s1,student s2)
{
    return s1.GPA < s2.GPA;
}
bool currentExamGrade_comparision_function (student s1,student s2)
{
    return s1.currentExamGrade < s2.currentExamGrade;
}
int main ()
{
    // Create an array of structs
    student arr_of_students[100]; // A better way will be vector<student>

    // Take input
    // ...

    // Now lets sort, assuming number of students is N
    // Based on GPA
    sort (arr_of_students,arr_of_students+N,gpa_comparision_function);

    // Based on currentExamGrade
    sort (arr_of_students,arr_of_students+N,currentExamGrade_comparision_function);

    return 0;
}

If you stepped on the providing the code path, at least go all the way - show him how to read into those structures and **explain to him what is happening**. Otherwise this is an exercise of vanity at best or reputation wh..ing at worst - it has nothing to do with helping him learn. — Adrian Colomitchi, Sep 26 '16 at 05:46
@AdrianColomitchi I have added the explanation for the use of custom comparision function. I am not going to explain how the input is to be taken. I will find a link a provide it with the answer — Rohith R, Sep 26 '16 at 05:57

Create multiple structs then sort by elements

1 Answers1