Sorting a Class [closed] - c++

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So, I am learning about classes in C++, I created two classes, one for a University that contains a list of class Students, i managed to create students, and introduce some values to the classes, but now i want to sort the class students by student number, i tryed using the sort function, but im not succeeding. I will leave my code bellow, please give some good tips and advises, so I can improve my code. thanks
main.css
#include <iostream>
#include "university.h"
#include "students.h"
using namespace std;
int main() {
university univ = university();
return 0;
}
university.h
#pragma once
#include <iostream>
#include <string>
#include <list>
#include <algorithm>
#include "students.h"
using namespace std;
class university
{
private:
list<students> lstudents;
list<students>::iterator itstudents;
public:
university();
void setStudents(list<students> lstudents);
void registerStudent();
void list();
void average();
//void sortstudents();
};
university.cpp
#include "university.h"
using namespace std;
university::university() { //constructor
string resp = "s";
int op;
bool out = true;
cout << "Enter Students:" << endl;
while (resp != "n")
{
this->registerStudent();
cout << "Continue inserting? (s/n)" << endl;
cin >> out;
cin.ignore();
}
while (out)
{
cout << "What you Want to do? (1- List Students 2- Sudent Average 3- Sort Students by Number 4- Leave)" << endl;
cin >> op;
switch (op)
{
case 1:
this->list();
break;
case 2:
this->average();
break;
/*case 3:
this->sortStudents();
break;*/
case 4:
out = false;
break;
};
}
}
void university::setStudents(list<students> lstudents) {
this->lstudents = lstudents;
}
void university::registerStudent()
{
lstudents.push_back(students());
}
void university::list()
{
int sum = 0;
cout << "------------------------- LIST STUDENTS -------------------------------\n\n";
cout << left << setw(11) << "Number"
<< left << setw(30) << "Name"
<< left << setw(30) << "Course"
<< left << setw(10) << "Average";
cout << "\n";
for (itstudents = lstudents.begin(); itstudents != lstudents.end(); itstudents++)
{
(*itstudents).list();
++sum;
}
//cout << "Total de pacientes:" << somatorio << endl;
//somatorio = 0;
}
void university::average()
{
int sum = 0;
double average = 0;
for (itstudents = lstudents.begin(); itstudents != lstudents.end(); itstudents++)
{
average += (*itstudents).getaverage();
++sum;
}
cout << "Average:" << average / sum << endl;
}
//void university::sortstudents() {
// sort(lstudents.begin(), lstudents.end(), &students::compare);
//}
students.h
as you can see the commented code is my attempts on sorting the class student my number
#pragma once
#include <iomanip>
#include <algorithm>
#include <list>
#include "university.h"
using namespace std;
class students {
private:
std::string name;
std::string course;
int number;
double average;
public:
//friend bool operator<(estudantes& left,estudantes& right) { return left.matricula < right.matricula; };
students();
void list();
double getaverage();
int getnumber();
//bool compare(estudantes a, estudantes b);
};
students.cpp
#include "students.h"
students::students() {
cout << "Name: ";
getline(cin, name);
cout << "Course: ";
getline(cin, course);
cout << "Number: ";
cin >> this->number;
cout << "Average: ";
cin >> this->average;
}
void students::list() {
cout << left << setw(11) << number;
cout << left << setw(30) << name;
cout << left << setw(30) << course;
cout << left << setw(10) << average << endl;
}
double students::getaverage() {
return average;
}
int students::getnumber() {
return number;
}
//bool estudantes::compare(student a, student b) {
//
// if (a.number < b.number)
// return 1;
// else
// return 0;
//}

Answer 1

Made it selfcontained and fixed. I'll post and then aexplain as surely people will have closed the question too soon:
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <list>
#include <string>
class students {
private:
std::string name;
std::string course;
int number;
double average;
public:
// friend bool operator<(students& left,students& right) { return
// left.matricula < right.matricula; };
students();
void list();
double getaverage();
int getnumber();
static bool compare(students const& a, students const& b);
};
students::students()
{
std::cout << "Name: "; getline(std::cin, name);
std::cout << "Course: "; getline(std::cin, course);
std::cout << "Number: "; std::cin >> this->number;
std::cout << "Average: "; std::cin >> this->average;
}
void students::list() {
std::cout << std::left << std::setw(11) << number;
std::cout << std::left << std::setw(30) << name;
std::cout << std::left << std::setw(30) << course;
std::cout << std::left << std::setw(10) << average << std::endl;
}
double students::getaverage() {
return average;
}
int students::getnumber() {
return number;
}
bool students::compare(students const& a, students const& b) {
return a.number > b.number;
}
class university {
private:
std::list<students> lstudents;
std::list<students>::iterator itstudents;
public:
university();
void setStudents(std::list<students> lstudents);
void registerStudent();
void list();
void average();
void sortStudents();
};
university::university() // constructor
{
std::string resp = "s";
int op;
bool out = true;
std::cout << "Enter Students:" << std::endl;
while (resp != "n") {
this->registerStudent();
std::cout << "Continue inserting? (s/n)" << std::endl;
std::cin >> out;
std::cin.ignore();
}
while (out) {
std::cout << "What you Want to do? (1- List Students 2- Sudent Average "
"3- Sort Students by Number 4- Leave)"
<< std::endl;
std::cin >> op;
switch (op) {
case 1: this->list(); break;
case 2:
this->average();
break;
case 3: this->sortStudents(); break;
case 4: out = false; break;
};
}
}
void university::setStudents(std::list<students> lstudents) {
this->lstudents = lstudents;
}
void university::registerStudent()
{
lstudents.push_back(students());
}
void university::list()
{
int sum = 0;
std::cout << "------------------------- LIST STUDENTS -------------------------------\n\n";
std::cout << std::left << std::setw(11) << "Number"
<< std::left << std::setw(30) << "Name"
<< std::left << std::setw(30) << "Course"
<< std::left << std::setw(10) << "Average";
std::cout << "\n";
for (itstudents = lstudents.begin(); itstudents != lstudents.end(); itstudents++)
{
(*itstudents).list();
++sum;
}
//std::cout << "Total de pacientes:" << somatorio << std::endl;
//somatorio = 0;
}
void university::average()
{
int sum = 0;
double average = 0;
for (itstudents = lstudents.begin(); itstudents != lstudents.end(); itstudents++)
{
average += (*itstudents).getaverage();
++sum;
}
std::cout << "Average:" << average / sum << std::endl;
}
void university::sortStudents() {
lstudents.sort(&students::compare);
}
int main() {
university univ = university();
return 0;
}
Explanation
There were a number of issues.
students::compare was a non-static member function, meaning it can only be called on an instance of student. To have a 2-argument sort predicate as required, simply making it static can work
The implementation could be much more idiomatic:
bool students::compare(students const& a, students const& b) {
return a.number > b.number;
}
That avoids the C-ism of using 1 as if it were true, and the useless if/else
You used std::sort but it requires random access iterators. std::list doesn't provide that. For that reason std::list::sort exists:
void university::sortStudents() {
lstudents.sort(&students::compare);
}
Among many other style issues:
don't using namespace std;
don't do side-effects in constructors?
error-check IO
avoid division by zero (e.g. in average()