c++ - Polynomial Class: Polynomial Multiplication -

i have polynomial class has get_vect member function stores integers in vector representation of coefficients of polynomial. now, trying multiply 2 polynomials using multiply non-member function, stuck when comes actual multiplication of vectors. far, have shown below:

polynomial multiply(const polynomial & poly1, const polynomial & poly2) {     vector<int> poly1 = poly1.get_vect();     vector<int> poly2 = poly2.get_vect();     vector<int> poly3;      if( poly1.size() < poly2.size() )     {         for(size_t = 0 ; poly2.size()-poly1.size() ; ++i )         {             poly2.push_back(0);         }     }     else if( poly1.size() > poly2.size() )     {         for(size_t = 0 ; poly1.size()-poly2.size() ; ++i )         {             poly1.push_back(0);         }     }      return poly3; } 

i see how has follow below pattern:

ok, if understand problem correctly, want poly3 vector<int> holds coefficients result polynomial multiplication between polynomials represented poly1 , poly2.

tacit in request 3 polynomials polynomials in single variable, each coefficient representing coefficient in front of increasing power of variable. ie. { 4, 5, 6, 7 } corresponds 4 + 5x + 6x² + 7x³.

if so, actual multiplication shouldn't difficult @ all, long polynomials aren't terribly huge. need code looks approximately this:

    poly3.resize(poly1.size() + poly2.size() - 1, 0);  // make output big enough; init 0      (size_t = 0; != poly1.size(); i++)         (size_t j = 0; j != poly2.size(); j++)             poly3[i+j] += poly1[i] * poly2[j]; 

now result in poly3 should product of poly1 , poly2.

it's entirely possible forgot edge condition; i'll watch comments here point out did. in meantime, though, did few tests , appears gives correct output.

if have rather large polynomials, might want math libraries handle multiplication. under 20 - 30 terms? unless code leans hard on polynomial evaluation, suspect won't bottleneck.