polynom

[dana18]

i don't know what's wrong with my code.
it is supposed to calculate a polynome but the result it's always 0

  #include <iostream>
#include <vector>

using namespace std;

double power(double a, unsigned int n) {
   double res = 0.;
   for (unsigned int i = 0; i<n; i++)
     res = res*a;
   return res;
}

double evalpoly(vector<double> pol, double x) {
   double res = 0.;
   for (unsigned int i = 1; i <= pol.size(); i++)
     res = res + pol[i]*power(x, i);
   return res;
}

int main() {
   vector<double> pol = {1.5, 2.5, 2.5, 4.0};
   vector<double> vals = {0, 1, 1.5, 2};
   for (unsigned int i = 0; i < vals.size(); i++)
     cout << "P(" << vals[i] << ") = " << evalpoly(pol, vals[i]) << endl;
   return 0;
}

[Chervil]

the result it's always 0

look at lines 7 and 9. What happens when multiplying by zero?

At line 15
for (unsigned int i = 1; i <= pol.size(); i++)
the loop skips the first element of pol, and then tries to access an out of range element one position past the end of the vector.