Sorting Objects

[Tomau000]

Hey everyone, this is my first post on this site. I have been playing around with C++ a little and I require a bit of help.

I have made this simple program that creates a Student class and asks the user to input a Student I.D, Last Name and First Name. You can store multiple students and the file is output as a .txt file.

The question I have is this...I wish to make it so that the students are stored in order in relation to their I.D number (smallest to largest),

For example,

ID: 011111
Last name: Holland
First Name: Tom

ID: 022222
Last Name: Abode
First Name: Andrew

I have tried using vectors, but it just turned out to be a mess. Any help would be greatly appreciated.

Here is my program...

#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

class Student
{
	private:
		string id;
		string fName;
		string lName;
	public:
		Student();
		~Student();
		void makeFile();
		string getId();
		string getFirstName();
		string getLastName();
};

Student::Student()
{
	id = "N/A";
	fName = "N/A";
	lName = "N/A";
}

Student::~Student()
{
	
}

void makeFile()
{
	fstream newFile("The Program File.txt");
}

string Student::getId()
{
	cout << "Enter the Student ID of the student: ";
	cin >> id;
	return id;
}

string Student::getFirstName()
{
	cout << "Enter the Students first name: ";
	cin >> fName;
	return fName;
}

string Student::getLastName()
{
	cout << "Enter the students last name: ";
	cin >> lName;
	return lName;
}

void setFile(Student student)
{
	ofstream file;
	file.open("The Program File.txt",ios::app);
	if(!file)
	{
		cout << "File couldn't be created :(";
		exit(1);
	}
	else
	{
		file << "I.D Number: " << student.getId() << "\n";
		file << "Last Name: " << student.getLastName() << "\n";
		file << "First Name: " << student.getFirstName() << "\n\n";
		file.close();
	}
}

char next()
{
		char c;
		cout << endl << "Do you wish to input another Student? y/n: ";
		cin>>c;
		cout << endl;
		if (c=='y' || c=='Y' || c=='n' || c=='N')
		{
			return c;
		}
		else
		{
			cout << "You did not enter a valid option!";
			next();
		}
}

void runProg()
{
	char y;
	do
	{
	Student T;
	setFile(T);
	y = next();
	}
	while(y =='y' || y == 'Y');
	cout << endl << "Thank you, have a good day.";
	exit(1);
}

int main()
{
	makeFile();
	runProg();
	return 0;
}

[pyschoder]

makeFile() is a member of your class.

[Tomau000]

Yeah woops, shouldn't be there, it didn't affect anything though.

[Silvermaul]

There are two ways to do this in my opinion. One is manipulating the data in ram and then storing it. The other would be storing it then rearranging it. I would prefer the first one. So instead of directly writing to the file you could save your key : in this case ID in an array. Since it is a number you could use the standard qsort algorithm. If you need something more advanced you could use the STL set container and overload the < operator for your student class. Then inserting elements to the Set will mean that those elements are sorted automatically and also printing out to a file is a game :)

Hope that helped :)

[Tomau000]

Thanks Silvermaul. Yeah so I get it to store the I.D numbers in an array, from there I can sort them numerically however once this is done I have no idea how to assign them back with their original first and last names?

[Silvermaul]

Don't store the I.D's in the arrays. Store the objects themselves or pointers of the objects and sort them by using the I.D as comparison. This way your objects as a whole will be sorted :)

[Tomau000]

Oh yup, thats what I originally thought of doing before I came onto the forum. I just didn't know how to do it! I will give it another try though, It sounds straight forward!
Thanks man.

[PanGalactic]

Create an operator<() for Student that just returns the comparison for student::id, then store them in a std::set(). They will be in sorted order.

[kingkurt0089]

Hi Tomau, I was wondering if you figured out how to do the sorting, because I was facing a similar problem. I had set up a multidimensional array, instead of a class, to store names and numbers in different columns, and wanted to sort the rows of names based on the numbers, highest to lowest. I made my own topic, and someone suggested using classes instead, so I just wanted to know if you were able to figure out the sorting with the classes before I went to rewrite my own code. If possible, can you tell me what sorting code or algorithm you used?

[Zhuge]

Likely he did as the previous posters suggested; overloading the < operator and inserting into an std::set.

[Tomau000]

@Kingkurt, Ill let you know if I manage.

@PanGalactic, I am not very familiar with operator overloading and have just been googling but still can't get it to work??

[Silvermaul]

Think of the operator as a plain function :

class CMyClass
{
public : 
   bool operator < (const CMyClass&arg)
   {
      return this.int32MyValue<arg.int32MyValue;
   }

private : 
   int int32MyValue;

};

[PanGalactic]

In your case, it would look something like this:

bool Student::operator<(const Student& other) const
{
    return (id < other.id);
}

Then you would create:

typedef std::set<Student> Students;

However, there are some real problems with your class. You have no way to access the elements without also setting them.

The user I/O should not occur in your getters. The user I/O should be done in a free function or separate class, as should the file I/O.

[Tomau000]

Hey thanks for the reply's guys! I still couldn't get it to work though, so I think I'll ask a professor once I get back to university in a couple of weeks.

[jmcomsci]

#include <cstdlib>
#include <iostream>
#include <iomanip>
#include <string>
#include <vector>
using namespace std;


struct studentStruct { 
        int scores[5];
        string studName[5];
} studInfo; 

int main(){

	int i,y,t;
        cout << "Please enter the last name of the student and the score of the student, separated by a space" << endl;
        cout << " For example: Doe 88" << endl; 
        vector<studentStruct*> vec; 
        studentStruct * studInfo = new studentStruct; 
        
		for(i=0;i<5;i++)
        cin >> studInfo->studName[i] >> studInfo->scores[i]; 
        vec.push_back(studInfo);


		
		for (i=0;i<5;i++)
	{
		for(int y=0;y<4;y++)
		{
			if(studInfo->scores[y]<studInfo->scores[y+1])
			{
				t=studInfo->scores[y];
				studInfo->scores[y]=studInfo->scores[y+1];
				studInfo->scores[y+1]=t;
			}
		}
	}

for(i=0;i<5;i++)
        cout << vec.at(0)->scores[i] << " " << vec.at(0)->studName[i] << endl; 


        delete studInfo;

	 

system("pause");
	return 0;
}

i have a problem ...a cant sort the names by their scores..
the scores are descending but the names are not..