Rational Class help. Reduction funtion doesnt work. Linker error in Dev cpp.

[rjddude1]

I created a rational class, created member functions to add, subtract, multiply and divide. The reduction function however doesn't work. And the Dev cpp compiler gives a linker error. I have attached the header, implementation and the driver file in rational.zip
Could you help me fix this code?
What am I doing wrong?

[Banfa]

Please post your linker errors.

[rjddude1]

@Banfa
Linker errors are gone however my reduction function does not work.
How do I make it so that it stores the function in reduced form and reduces them before they are printed.

Thank you in advance.

Here's my function implementation file

 
#include "Rational.h"
 
Rational::Rational()
: is_valid_( false ), num ( 1 ), den ( 1 )
{
}
 
Rational::Rational( const int init_num, const int init_den )
: num( init_num ), den( init_den )
{
    if ( den == 0 || (den == 0 && num == 0))
        is_valid_ = false;
    else
        is_valid_ = true;
}
 
bool Rational::is_valid() const
{
    return is_valid_;
}
 
void Rational::check() const
{
    if ( ! ( is_valid() ) )
    {
        cout << "Indeterminate form of rational." << endl;
        system("pause");
        exit(1);
    }
}          
 
int Rational::get_num() const
{
   check();
   return num;
}
 
int Rational::get_den() const
{
   check();
   return den;
}
 
void Rational::set_num( const int val1 )
{
     num = val1;
}
 
void Rational::set_den( const int val2 )
{
     den = val2;
}
 
void Rational::reduce ()
{
     //Reduction function...
     //Help required
}
 
 
void Rational::printRational() const
{
        cout << num << '/' << den;
}
 
void Rational:: printRationalAsFloating() const
{
        cout << float(num)/den;
}
 
Rational Rational::addition ( const Rational &a )
{
         Rational add;
         add.num = (a.num * den) + (num * a.den);
         add.den = (den * a.den);
         reduce();
         return add;
}
 
Rational Rational::subtraction ( const Rational &a )
{
         Rational sub;
         sub.num = (num * a.den) - (den * a.num);
         sub.den = (den * a.den);
         reduce();
         return sub;
}
 
Rational Rational::multiplication ( const Rational &a )
{
         Rational multi;
         multi.num = (num * a.num);
         multi.den = (den * a.den);
         reduce();
         return multi;
}
 
Rational Rational::division ( const Rational &a )
{
         Rational div;
         div.num = (num * a.den);
         div.den = (den * a.num);
         reduce();
         return div;
}