Why is my class performing arithmetic when I haven't coded any?

I'm working on a homework project that is supposed to introduce us to classes. I've just started, but for some reason my member variables are displaying correctly until the end. It should just be passing those variables between functions then outputting them. It will take a numerator and denominator set by a parameterized constructor, set an object with them, then output what the numerator and denominator holds. It is taking the numerator and setting it to zero, even when it previously displayed the correct number in every function the class ran through. The denominator is even more weird because it turns into some huge number somehow. I just want to understand what is happening since I am new to this and the reason why isn't super apparent to me.

class RationalNum 

{

  public:

    RationalNum();
    RationalNum(int numer, int denom);
    int getNumerator();
    int getDenominator();
    void setNumerator(int);
    void setDenominator(int);
    void set(int& numer, int& denom);
    void output(ostream& outs);
    void add();
    void multiply();

  private:

    int reduce(int);
    int denom;
    int numer;

};

int main()

{

  RationalNum rn1, rn2(25, 10), rn3(24, -100);

  cout << "rn1 contains: ";
  rn1.output(cout);

  cout << endl;

  cout << "rn2 contains: ";
  rn2.output(cout);

  cout << endl;

  cout << "rn3 contains: ";
  rn3.output(cout);

  return 0;

}

RationalNum::RationalNum() : numer(1), denom(1)

{

}

RationalNum::RationalNum(int numer, int denom) //takes two integers for numer and denom, and reduces

{

  cout << "The numer and denom  in the param const are " << numer << denom << endl;
  set(numer, denom);

}

void RationalNum::set(int& numer, int& denom) //use other functions to take two params and set as numer and denom

{

  cout << "The numer and denom in set are " << numer << denom << endl;
  setNumerator(numer);
  setDenominator(denom);

}

void RationalNum::setNumerator(int numer) //takes an int, sets it as numer, and reduces it

{

cout << "in setNumer, the numer is: " << numer << endl;
  //reduce(newNumer); //Not using yet

}

void RationalNum::setDenominator(int denom) //takes an int, sets it as denom, and reduces it

{

cout << "in setDenom, the denom is: " << denom << endl;


  //reduce(newDenom); //Not using yet

}

void RationalNum::output(ostream& outs) //takes an ostream param

{

  cout << numer << "/" << denom << endl;

}

This is what the actual results are. It is correct until the last two lines, and that is where I'm lost. rn2 should display 25/10 and rn3 should display 24/-100

The numer and denom in the param const are 2510 The numer and denom in set are 2510 in setNumer, the numer is: 25 in setDenom, the denom is: 10

The numer and denom in the param const are 24-100 The numer and denom in set are 24-100 in setNumer, the numer is: 24 in setDenom, the denom is: -100 rn1 contains: 1/1

rn2 contains: 0/4196160

rn3 contains: 0/4197376