a simple c++ data structure class

datastruct.cpp

///simple data structure program --> a simple exercise program from the book i've been study it might help to some people :D
//// for class Studentrecord --> methods
///  object.display(); - displays the values in the object :: expects no argument
///  object.setIdnum(int); - sets the id number :: expects a integer value argument
///  object.setCredits(double); - sets the credits value :: expects a double or integer  value argument
///  object.setGradeave(double); - sets the average grade :: expects a double or interger value argument
//// for class Studentinfo --> methods
///    object.display(); - displays the values in the object :: expects no argument
///    object.setStudentname(string); - sets the name of the student :: expects a string argument 
///    object.setDate(int, int, int); - sets a date :: expects a three integer argument
///    object.setCredits(double); - sets a credits value :: expects a double or integer argument
///    object.setGradeave(double); - sets the average grade :: expects a double or integer argument
//// for class Mail_list --> methods
///     object.display(); - displays the value in the object :: expects no argument;
///    object.setTitlefield(string); - sets the title of the mail :: expects a string argument
///    object.setLastname(string); - sets the last name :: expects a string argument
///    object.setFirstname(string); - sets the first name :: expects a string argument
///   object.setAddress1(string); - sets the first address :: expects a string argument
///    object.setAddress2(string); - sets the seconds address :: expects  a string argument
///    object.setCityfield(string); - sets the name of the city :: expects a string argument
///    object.setStatefield(string); - sets the state :: expects a string argument
//// for class Stockinfo --> methods
///   object.display(); - displays the values in the object :: expects no argument
///   object.setStockname(string); - set the name of stock :: expects a string argument
///   object.setPrice(double); - sets a price :: expects a double or integer argument
///   object.setDate(int, int, int); - sets a date :: expects three integer argument
//// for class Inventory --> methods
///    object.display(); - displays the values in the object :: expects no argument
///    object.setPartnum(int); - set the part no. :: expects a integer argument
///    object.setPartdescrip(string); - sets the some description :: expects a string argument
///    object.setNumparts(int); - sets the number of parts :: expects a integer argument
///    object.setReordernum(int); - sets the reorder no. :: expects a integer argument
//// you can use this code freely :D

#include <iostream>
#include <iomanip>
#include <string>

using namespace std;

class Studentrecord
{
private:
    int idnum;
    double credits;
    double gradeave;

public:
    Studentrecord(int i = 0, double c = 0, double g = 0)
    {idnum = i; credits = c; gradeave = g;}

    void display();
    void setIdnum(int);
    void setCredits(double);
    void setGradeave(double);
};

void Studentrecord::display()
{
    cout << "\nid number: " << idnum
         << "\nnumber of credits completed: " << credits
         << "\ngrade point average: " << gradeave << endl;

    return;
}

void Studentrecord::setIdnum(int i)
{
    idnum = i;
    return;
}

void Studentrecord::setCredits(double i)
{
    credits = i;
    return;
}

void Studentrecord::setGradeave(double i)
{
    gradeave = i;
    return;
}

class Studentinfo
{
private:
    string studentname;
    int month;
    int day;
    int year;
    double credits;
    double gradeave;
public:
    Studentinfo(string a = "NONE", int m = 2, int d = 22, int y = 2012)
    {studentname = a; month = m; day = d; year = y;}
    void display();
    void setStudentname(string);
    void setDate(int, int, int);
    void setCredits(double);
    void setGradeave(double);
};

void Studentinfo::display()
{
    cout << "\nstudent name: " << studentname
         << "\ndate of birth: " << setfill('0') << setw(2) << month << '/' << setw(2) << day << '/' << setw(2) << year
         << "\nnumber of credits completed: " << credits
         << "\ngrade point average: " << gradeave << endl;

    return;
}

void Studentinfo::setStudentname(string nameinput)
{
    studentname = nameinput;
    return;
}

void Studentinfo::setDate(int mm, int dd, int yyyy)
{
    month = mm;
    day = dd;
    year = yyyy;

    return;
}

void Studentinfo::setCredits(double creditinput)
{
    credits = creditinput;
    return;
}

void Studentinfo::setGradeave(double gradeinput)
{
    gradeave = gradeinput;
    return;
}

class Mail_list
{
private:
    string titlefield;
    string lastname;
    string firstname;
    string address1;
    string address2;
    string cityfield;
    string statefield;
    int zipcode;

public:
    Mail_list(string t = "NONE", string l = "NONE", string f = "NONE", string a1 = "NONE", string a2 = "NONE", string c = "NONE", string s = "NONE")
     {titlefield = t; lastname = l; firstname = f; address1 = a1; address2 = a2; cityfield = c; statefield =s;}
    void display();
    void setTitlefield(string);
    void setLastname(string);
    void setFirstname(string);
    void setAddress1(string);
    void setAddress2(string);
    void setCityfield(string);
    void setStatefield(string);
};

void Mail_list::display()
{
    cout << "\ntitle: " << titlefield
         << "\nLast name: " << lastname
         << "\nFirst name: " << firstname
         << "\nAddress 1: " << address1
         << "\nAddress 2: " << address2
         << "\nCity: " << cityfield
         << "\nState: " << statefield << endl;

    return;
}

void Mail_list::setTitlefield(string title)
{
    titlefield = title;
    return;
}

void Mail_list::setLastname(string last)
{
    lastname = last;
    return;
}

void Mail_list::setFirstname(string first)
{
    firstname = first;
    return;
}

void Mail_list::setAddress1(string add1)
{
    address1 = add1;
    return;
}

void Mail_list::setAddress2(string add2)
{
    address2 = add2;
    return;
}

void Mail_list::setCityfield(string city)
{
    cityfield = city;
    return;
}

void Mail_list::setStatefield(string state)
{
    statefield = state;
    return;
}

class Stockinfo
{
private:
    string stockname;
    double price;
    int month;
    int day;
    int year;

public:
    Stockinfo(string s = "NONE", double p = 0, int mm = 2, int dd = 22, int yyyy = 2012)
     { stockname = s; price = p; month = mm; day = dd; year = yyyy;}
    void display();
    void setStockname(string);
    void setPrice(double);
    void setDate(int, int, int);
};

void Stockinfo::display()
{
    cout << "\nstock name: " << stockname
         << "\npurchase price: " << price
         << "\ndate purchase: " << setfill('0') << setw(2) << month << '/' << setw(2) << day << '/' << setw(2) << year
         << endl;

    return;
}

void Stockinfo::setStockname(string sname)
{
    stockname = sname;
    return;
}

void Stockinfo::setPrice(double assprice)
{
    price = assprice;
    return;
}

void Stockinfo::setDate(int mm, int dd, int yyyy)
{
    month = mm;
    day = dd;
    year = yyyy;

    return;
}


class Inventory
{
private:
    int partnum;
    string partdesprip;
    int numparts;
    int reordernum;

public:
    Inventory(int p = 0, string pd = "NONE", int n = 0, int r = 0)
     {partnum = p; partdesprip = pd; numparts = n; reordernum = r;}
    void display();
    void setPartnum(int);
    void setPartdescrip(string);
    void setNumparts(int);
    void setReordernum(int);
};

void Inventory::setPartnum(int pn)
{
    partnum = pn;
    return;
}

void Inventory::setPartdescrip(string pd)
{
    partdesprip = pd;
    return;
}

void Inventory::setNumparts(int np)
{
    numparts = np;
    return;
}

void Inventory::setReordernum(int rn)
{
    reordernum = rn;
    return;
}

void Inventory::display()
{
    cout << "\npart no: " << partnum
         << "\ndescription: " << partdesprip
         << "\nnumber in stock: " << numparts
         << "\nreorder number: " << reordernum << endl;

    return;
}

int main()
{
    Studentrecord student1;
    student1.setIdnum(1999);
    student1.setCredits(12.2);
    student1.setGradeave(99.9);
    student1.display();

    Studentinfo student2;
    student2.setStudentname("kryssel");
    student2.setDate(12, 22, 2012);
    student2.setCredits(22.2);
    student2.setGradeave(99.0);
    student2.display();

    Mail_list mail1;
    mail1.setTitlefield("hi");
    mail1.setLastname("de leon");
    mail1.setFirstname("kryssel");
    mail1.setAddress1("rivera compund saint joseph subd");
    mail1.setAddress2("i dont know what is my second address");
    mail1.setCityfield("las pinas city");
    mail1.setStatefield("city");
    mail1.display();

    Inventory inventory1;
    inventory1.setPartnum(1002);
    inventory1.setPartdescrip("what the fuck is this");
    inventory1.setNumparts(2);
    inventory1.setReordernum(4);
    inventory1.display();

    return 0;
}