function - Writing a program in C++ and I need help -

so new this. trying write program function

double_product(vector< double > a, vector< double > b) computes scalar product of 2 vectors. scalar product

$a_{0}b_{0}+a_{1}b_{1}+...a_{n-1}b_{n-1}$.

here have. mess, trying!

#include<iostream>  #include<vector>  using namespace std;  class scalar_product {  public:      scalar_product(vector<double> a, vector<bouble> b);  };   double scalar_product(vector<double> a, vector<double> b)  {     double product = 0;     (int i=0; <=a.size()-1; i++)         (int i=0; <=b.size()-1; i++)             product = product + (a[i])*(b[i]);     return product;  }  int main() {      cout << product << endl;      return 0;  } 

you have pretty correct idea, @ fundamental level. couple of basic building blocks , you'll on way. scalar_product function close, not quite. you've created 2 loop iterators same name iterating on same values. should fine say

if (a.size() != b.size()) {} // error (int i=0; < a.size(); i++)    product = product + (a[i])*(b[i]); 

now have data, call it, , output result.

int main() {     std::vector<double> a;     std::vector<double> b;     // fill values     std::cout << scalar_product(a, b) << endl; } 

the whole class thing unnecessary here- classes need come in standard lib.