[Dev-C++] PLEASE HELP: a prgm not working

[chromatonus 7. <chr...@ho...>]

hi, this program is supposed to add, subtract, multiply and divide two 
fractions and simplify the answers, using class objects. But the prgm 
displays 0/0 for the sums, differences, etc. How can I fix this program? 
THank you for your time :)


#include <iostream.h>
#include <conio.h>
#include <stdlib.h>


//=============================== CLASS HEADER 
===============================

class rational
  {
    public:
    	//	constructors
            rational();
            rational( int n, int d );
    	//	accessors
      	    int get_numerator();
            int get_denominator();
     	//	modifiers
      	    void change_numerator(int n);
            void change_denominator(int d);
        //  enter from keyboard
            void enter();
        //      precondition:   two numbers are sent in for each rational 
number
        //      postcondition:  they are stored as two rational numbers
        //  display
      	    void display();

            void reduce(int pn, int pd, int sn, int sd, int tn, int td, int 
fn, int fd);
        //		precondition:	send in rational @n/@d (@ meaning an operation)
        //		postcondition:  calculate  d = gcd(@n,@d)
        //						reset @n = @n/d   and  @d = @d/d

    private:
        int  my_numerator,my_denominator;
  };

//============================FREE FUNCTIONS 
==================================

  //  assignment operator
      void assign( rational a , rational &b );
      	//	precondition:	rational number  a  is sent in
        //	postcondition:	b = a
        //					bn = an   and   bd = ad

  //  comparison operator
   	  bool are_equal( rational a, rational b);
      	//	precondition:	rational numbers a and b are sent in
      	//	postcondition:  returns true if a = b else returns false
        //					a = b iff  an*bd = ad*bn

  //  add rational numbers
   	  rational add( rational a, rational b );
      	//	precondition:	send in rational numbers a,b where
        //					b != 0
        //	postcondition:	calculate c = a + b by:
        //					a = an/ad     b = bn/bd
      	//					cn = an*bd + ad*bn
        //					cd = ad*bd
        //					reduce to lowest terms
  //  subtract
   	  rational subt(rational, rational b);

  //  multiply rationals
   	  rational mult( rational a, rational b);
      	//	precondition:	b != 0
        //	postcondition:	calculate  c = a*b by:
       	//               	cn = an * bn
       	//					cd = ad * bd
        //					reduce to lowest terms

  //  divide rationals
      rational div(rational a, rational b);
        //  precondition:   b !=0
        //  postcondition:  calculate c = a/b by:
        //                  cn = an * bd
        //                  cd = ad * bn
        //                  reduce to lowest terms



//===============================IMPLEMENTATION================================
    rational::rational()
               {
                  my_numerator = 0;
                  my_denominator = 0;
               }
    void rational::enter()
               {
                  cout<< "A rational (numerator first)= " << "\n" << "\n";
                  cin>> my_numerator;
                  cin>> my_denominator;
                  cout<< "\n";
               }
    void rational::change_numerator(int n)
               {
                  my_numerator = n;
               }
    void rational::change_denominator(int d)
               {
                  my_denominator = d;
               }
    int rational::get_numerator()
               {
                  return (my_numerator);
               }
    int rational::get_denominator()
               {
                  return (my_denominator);
               }

    rational::rational(int n, int d)
               {
                  my_numerator = n;
                  my_denominator = d;
               }

//===============================CLIENT 
PROGRAM================================

int main()
  {
     rational a,
              b,
              p,
              s,
              t,
              f;
     a.enter();
     b.enter();
     cout<< "\n";
     a.display();
     b.display();
     cout<< "\n" << "\n";
     cout<< "Sum= " << "\n";
     p.display();
     cout<< "Difference= " << "\n";
     s.display();
     cout<< "Product= " << "\n";
     t.display();
     cout<< "Quotient= " << "\n";
     f.display();
  }

bool are_equal(rational a, rational b)
  {
     int an = a.get_numerator(),
         ad = a.get_denominator(),
         bn = b.get_numerator(),
         bd = b.get_denominator();
     if (an * bd == ad * bn)
       return( true );
     else
       return( false );
  }

rational add(rational a, rational b)
  {
     int an = a.get_numerator(),
         ad = a.get_denominator(),
         bn = b.get_numerator(),
         bd = b.get_denominator(),
         pn = an * bd + bn * ad,
         pd = ad * bd;
     rational p(pn, pd);
     return p;
  }

rational subt(rational a, rational b)
  {
     int an = a.get_numerator(),
         ad = a.get_denominator(),
         bn = b.get_numerator(),
         bd = b.get_denominator(),
         sn = an * bd - bn * ad,
         sd = ad * bd;
     rational s(sn, sd);
     return s;
  }

rational mult(rational a, rational b)
  {
     int an = a.get_numerator(),
         ad = a.get_denominator(),
         bn = b.get_numerator(),
         bd = b.get_denominator(),
         tn = an * bn,
         td = ad * bd;
     rational t(tn, td);
     return t;
  }

rational div(rational a, rational b)
  {
     int an = a.get_numerator(),
         ad = a.get_denominator(),
         bn = b.get_denominator(),
         bd = b.get_numerator(),
         fn = an * bn,
         fd = ad * bd;
     rational f(fn, fd);
     return f;
  }

void rational::reduce(int pn, int pd, int sn, int sd, int tn, int td, int 
fn, int fd)
  {
                  int j, d;
                  if( pd >= pn)
                    j = pn;
                  else
                    j = pd;
                  for( d = j; d>0; d--)
                    {
                       if( pn%d ==0 && pd%d ==0)
                         {
                            pn = pn/d;
                            pd = pd/d;
                         }
                    }
                  if( sd >= sn)
                    j = sn;
                  else
                    j = sd;
                  for( d = j; d>0; d--)
                    {
                       if( sn%d ==0 && sd%d ==0)
                         {
                            sn = sn/d;
                            sd = sd/d;
                         }
                    }
                  if( td >= tn)
                    j = tn;
                  else
                    j = td;
                  for( d = j; d>0; d--)
                    {
                       if( tn%d ==0 && td%d ==0)
                         {
                            tn = tn/d;
                            td = td/d;
                         }
                    }
                  if( fd >= fn)
                    j = fn;
                  else
                    j = fd;
                  for( d = j; d>0; d--)
                    {
                       if( fn%d ==0 && fd%d ==0)
                         {
                            fn = fn/d;
                            fd = fd/d;
                         }
                    }
  }

void rational::display()
  {
     cout<< my_numerator << "/" << my_denominator << "\n";
     system("PAUSE");
  }

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