C++ program using vectors -

i'm having difficulties finding problem here , program must read number n , read 2 vectors n lenght, multiply each number of first vector relevant number of second 1 , substract each of previous multiplies (example a[0]*b[0] - a[1]*b[1] .... a[n-1]*b[n-1] ) replies appreciated. input values : 3/ 1 2 -3 /4 -5 -6 output : -4 here's code:

#include <iostream> #include <string> #include <sstream> #include <vector> #include <cstdlib>  using namespace std;  /* splits string using whitespace delimeter */ void split_input(vector<double> &vector_values, const string &input) {     char delim = ' ';      stringstream mysstream(input);      string temp;      while(getline(mysstream, temp, delim))     {         vector_values.push_back(atof(temp.c_str()));     } }  double multiply(vector<double> &first_vector, vector<double> &second_vector) {        double result = 0;      for(int = 0; < first_vector.size(); i++)     {         if (i == 0)         {             result = first_vector[i]*second_vector[i];         }         else          {             result -= first_vector[i]*second_vector[i];         }         cout << result << endl;     }      return result; }   int main() {     vector<double> first_vector;     vector<double> second_vector;     int num;     string input_values;      cout << "please enter number: " << endl;     cin >> num ;      /* ignores endline char previous cin */     cin.ignore();       /* read first string, split , store values in vector */     getline(cin, input_values);     split_input(first_vector, input_values);      cin.ignore();       /* read second string, split , store values in vector */     getline(cin, input_values);     split_input(second_vector, input_values);       /* multiply vectors */     cout << multiply(first_vector, second_vector) << endl;      return 0; } 

remove cin.ignore() after split_input(first_vector, input_values);. cin.ignore() first element of second vector alway 0. main() should this:

int main() {     vector<double> first_vector;     vector<double> second_vector;     int num;     string input_values;      cout << "please enter number: " << endl;     cin >> num ;      /* ignores endline char previous cin */     cin.ignore();       /* read first string, split , store values in vector */     getline(cin, input_values);     split_input(first_vector, input_values);      // following line causes first element of second vector become 0     // cin.ignore();       /* read second string, split , store values in vector */     getline(cin, input_values);     split_input(second_vector, input_values);       /* multiply vectors */     cout << multiply(first_vector, second_vector) << endl;      return 0; }