Need turotial/help class array/vector

**ajpeters** · 09-06-2005

It has become apparent to me that I do not understand the rleation ship of a class array and a vector.

Assume I have the following and I want to change it to vector format

Code:

#include <cstdlib>
#include <iostream>

using namespace std;

class School
{ 
public:
    School ();
    School (string,double);
    string name;
    float tuition;
};
School::School()
{
    name="";
    tuition=0.;
}
School::School(string n,double t)
{
     name=n;
     tuition= t;
}

int main ()
{
     School mySchool [5] = {School ("John", 10.),
                                          School ("Jim", 11.),
                                          School ("Greg", 12.),
                                           School ("Spencer", 13.),
                                          School ("Joan", 14.)};
int i=0;
while (i < 5)
{
   cout << mySchool[i].name << "  " << mySchool[i].tuition << endl;
   ++i;
}



    system("PAUSE");
    return EXIT_SUCCESS;
}

Give me some options. Assume I am a coplete idiot.

**ZuK** · 09-06-2005

Code:

#include <iostream>
#include <vector>

using namespace std;

class School
{ 
public:
    School ();
    School (string,double);
    string name;
    float tuition;
};
School::School()
{
    name="";
    tuition=0.;
}
School::School(string n,double t)
{
     name=n;
     tuition= t;
}

int main ()
{
     vector<School> mySchool;
     mySchool.push_back(School ("John", 10.));
     mySchool.push_back(School ("Jim", 11.)),
     mySchool.push_back(School ("Greg", 12.));
     mySchool.push_back(School ("Spencer", 13.));
     mySchool.push_back(School ("Joan", 14.));
   
     int i=0;
     while (i < mySchool.size()) {
        cout << mySchool[i].name << "  " << mySchool[i].tuition << endl;
        ++i;
     }
    system("PAUSE");
    return EXIT_SUCCESS;
}

Kurt

**ajpeters** · 09-06-2005

Thanks, I will work on and try to get a tougher question.

**ajpeters** · 09-06-2005

I am using bloodshed C

I got the reverse to work in the following sample, but the sort blows all to h* in the compile. Where did I go wrong

Code:

#include <cstdlib>
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

class School
{ 
public:
    School ();
    School (string,double);
    string name;
    float tuition;
};
School::School()
{
    name="";
    tuition=0.;
}
School::School(string n,double t)
{
     name=n;
     tuition= t;
}

int main ()
{
       vector<School> mySchool;
     mySchool.push_back(School ("John", 10.));
     mySchool.push_back(School ("Jim", 11.)),
     mySchool.push_back(School ("Greg", 12.));
     mySchool.push_back(School ("Spencer", 13.));
     mySchool.push_back(School ("Joan", 14.));
  
    int i=0;
     while (i < mySchool.size()) {
        cout << mySchool[i].name << "  " << mySchool[i].tuition << endl;
        ++i;
     }
      cout << endl;
   reverse(mySchool.begin(),mySchool.end());
     i=0;
     while (i < mySchool.size()) {
        cout << mySchool[i].name << "  " << mySchool[i].tuition << endl;
        ++i;
     }
     cout <<endl;
    sort(mySchool.begin(),mySchool.end());
     i=0;
     while (i < mySchool.size()) {
        cout << mySchool[i].name << "  " << mySchool[i].tuition << endl;
        ++i;
     }
    system("PAUSE");
    return EXIT_SUCCESS;
}

**prog-bman** · 09-06-2005

That is because sort has no idea how to sort a School only basic types. Here is a better School class and I also implemented a sorting function for you it is commented so you should be able to figure out what is going on.

Code:

#include <iostream>
#include <string>
#include <vector>

class School
{
    public:
        School();
        School(const std::string &toName, const double &setTuition);
        const std::string &Get_Name() const;
        const double &Get_Tuition() const;
        void Set_Name(const std::string &toName);
        void Set_Tuition(const double &setTuition);
    private:
        std::string schoolName;
        double tuition;
};

//Default construtor just sets everything to "nothing"
School::School()
{
    schoolName = "";
    tuition = 0.0;
}
//Copy Constructor that takes the name and double passed to it and
//sets them as the School's name and tuition.
School::School(const std::string &toName, const double &setTuition)
{
    schoolName = toName;
    tuition = setTuition;
}

//Returns the current name of our school
const std::string &School::Get_Name() const
{
    return schoolName;
}

//Returns the current tuition
const double &School::Get_Tuition() const
{
    return tuition;
}

//Sets the name of our school
void School::Set_Name(const std::string &toName)
{
    schoolName = toName;
}

//Takes the double passed to it and sets the tuition to
//it
void School::Set_Tuition(const double &setTuition)
{
    tuition = setTuition;
}

//Sort the class based on who has the least tuition
bool TuitionSort(const School &s1, const School &s2)
{
    return (s1.Get_Tuition() < s2.Get_Tuition());
}

int main()
{
    std::vector<School> mainSchool;
    
    //Fill the vector
    mainSchool.push_back(School("Billy",600.25));
    mainSchool.push_back(School("Joe",800.70));
    mainSchool.push_back(School("Jon",200.50));
    mainSchool.push_back(School("Bob",300.25));
    mainSchool.push_back(School("Dave",1000.75));
    
    std::cout<<"Not Sorted"<<std::endl;
    
    for(int i = 0; i < mainSchool.size(); i++)
    {
        //Print out the unsorted elements
        std::cout<<mainSchool[i].Get_Name()<<std::endl;
        std::cout<<mainSchool[i].Get_Tuition()<<std::endl;
    }
    
    std::cout<<std::endl;
    //Do the sort thing by calling our sort function to do the
    //sorting
    std::sort(mainSchool.begin(),mainSchool.end(),TuitionSort);
    std::cout<<"Sorted"<<std::endl;
    
    for(int i = 0; i < mainSchool.size(); i++)
    {
        //Print out the sorted entries
        std::cout<<mainSchool[i].Get_Name()<<std::endl;
        std::cout<<mainSchool[i].Get_Tuition()<<std::endl;
    }
    
    std::cin.get();
    return 0;
}

**ajpeters** · 09-06-2005

I assume "Tuit ionSort" is tuitionSort?

and to sort by namde I change Get_Tuition to Get_Name? I will try of course, but just verifiying?

Best to have a function for each type of sort, or can I generalize the sort field?

**Daved** · 09-06-2005

Yes it should be TuitionSort (it's a bug in the forum).

It will work if you change Get_Tuition to Get_Name in that code because Get_Name returns a string and strings already have a less than operator that will compare them.

It is best to have a function for each type of sort (remember that was my advice in your last thread) and just call sort with the appropriate function based on which you want to use.

**ajpeters** · 09-06-2005

thanks, I think I am starting to understand. I have created sort by name and sort by tuition and it works.

sorry about missing the comment on generalizing the sort. .

Where is there documentation on using std:sort with 3 arguements? everything I have found only has 2 arguements

**Daved** · 09-06-2005

Don't worry about missing any comments... there are a lot to go through.

What documentation are you using? The third argument is optional, and defaults to using less which defaults to using the operator< for whatever object is held in the container. There are several ways to create the predicate to be used for the third argument. The simplest is the standalone function that you are using now. To get more details on these things a book is really the best idea. The C++ Standard Library by Josuttis for reference and Effective STL by Meyers for tips are two good options. Otherwise you use the tools you got and learn from practice.

**ajpeters** · 09-08-2005

I have been using the book by Deitel plus doing google searches. Most tutorials only talk about the 2 arguements. devshed, about etc. Also look at Linux documentation. I will check into the other 2 books you mentions, Thanks

**hk_mp5kpdw** · 09-08-2005

You can either overload the less-than operator for your class and use the 2-argument version of the sort function, or if that operator is not provided, you can provide a predicate as part of the 3-argument version of the function.

The Josuttis book is excellent... carry it with me wherever I go. Don't personally know about the Meyers book though.

Originally Posted by prog-bman

Code:

//Copy Constructor  that takes the name and double passed to it and
//sets them as the School's name and tuition.
School::School(const std::string &toName, const double &setTuition)
{
    schoolName = toName;
    tuition = setTuition;
}

Copy constructor?

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Need turotial/help class array/vector

thanks.

getting sort to work

quick query

thanks, it is starting to make sense

vector sort info

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