Writing a program in C++ and I need help

Question

So I am a new to this. I am trying to write a program with a function

double_product(vector< double > a, vector< double > b) that computes the scalar product of two vectors. The scalar product is

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

Here is what I have. It is a mess, but I am 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;

   for (int i=0; i <=a.size()-1; i++)

       for (int i=0; i <=b.size()-1; i++)

           product = product + (a[i])*(b[i]);

   return product;

}

int main()
{

    cout << product << endl;

    return 0;

}

Answer 1

You have a pretty correct idea, at the fundamental level. A couple of basic building blocks extra and you'll be well on your way. Your scalar_product function is close, but not quite. You've created two loop iterators with the same name iterating over the same values. It should be fine to simply say

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

Now all you have to do is get some data, call it, and then output the result.

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

The whole class thing is completely unnecessary here- the only classes you need come in the Standard lib.

Answer 2

since I cannot comment I am forced to reply.

apparently there is exactly the same question, word by word , here:

Computing the scalar product of two vectors in C++