error: overloaded ‘operator<<' must be a binary operator (has 3 parameters)

The problem is that you declared operator>> and operator<< as non-member functions, but defined as a member function.

This should fix that problem (but open another set of problems). So instead of

  ostream& Fraction::operator<<(ostream &os, Fraction& n)
  {
     ...


  istream& Fraction::operator>>(istream &os, Fraction& n)
  {
     ...

implement as :

  ostream& operator<<(ostream &os, Fraction& n)
{
...

  istream& operator>>(istream &os, Fraction& n)
{
...

Also, take a note that you declared functions as :

friend ostream& operator<<(ostream &os, const  Fraction& n);
friend istream& operator>>(istream &is, const Fraction& n);

but defined as (therefore you changed the signature) :

  ostream& Fraction::operator<<(ostream &os, Fraction& n)
  istream& Fraction::operator>>(istream &os, Fraction& n)

Proper way is to declare and define as :

  ostream& Fraction::operator<<(ostream &os, const Fraction& n)
  istream& Fraction::operator>>(istream &os, Fraction& n)

I am adding just changes. The rest is the same as in the question:

class Fraction{
    friend ostream& operator<<(ostream &os, const  Fraction& n);
    friend istream& operator>>(istream &is, Fraction& n);
  // the rest is the same
};

ostream& operator<<(ostream &os, const Fraction& n)
{
    if (n.numera == 0)
    {
        cout << 0 << endl;
        return os;
    }
    else if (n.numera == n.denom)
    {
        cout << 1 << endl;
        return os;
    }
    else
    {
        cout << n.numera << '/' << n.denom << endl;
        return os;
    }
}

  istream&  operator>>(istream &os, Fraction& n)
{
    char slash = 0;
    return os >> n.numera >> slash >> n.denom;

}

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