Question

I am practicing with functions on the vector class. i have written a function ‘sumVector’ to add up all elements of vector ‘ages’, but it is not returning the total
i am copying my code block; i know the STL provides a sum function but this is for my own practice. i would appreciate if someone would point out what i am doing wrong

    #include <vector>
    #include <fstream>
    #include <sstream>
    #include <iostream>
    #include <iterator>
    #include <algorithm>
    using namespace std;
    template<typename T>
    int sumVector(const vector<T> &integers2)
    {
         typename vector<T>::const_iterator constIterator;
         //display vector elements using constIterator
         for 

         (constIterator=integers2.begin();                                             
         constIterator!=integers2.end();++constIterator);
         int sum=0;
         sum+=*constIterator;
         return sum;
         cout<<sum;
    }




    int main ()
    {
    vector<int> ages;
    vector<float>var;
    ifstream inFile;
    inFile.open("data.txt");
    if(!inFile)
    {
        cout<<"didn't work";
        cin.get();
        exit (1);
    }

    string line;
    getline(inFile, line);
    istringstream in(line);
    copy(std::istream_iterator<int>(in),
      std::istream_iterator<int>(),
      std::back_inserter(ages));
    cout<<ages.at(2)<<endl;
    getline(inFile, line);
    istringstream gin(line);
    copy(istream_iterator<float>(gin),
                                     istream_iterator<float>(),
                                     back_inserter(var));
    cout<<var.at(0)<<endl;
    cout<<"whats the sum";
    sumVector (ages);

    cin.get();

    inFile.close();
    cin.get();

    }

Answer 1

The for loop is incorrect and the cout << sum occurs after the return from sumVector(). The return type (and type of sum) should also be T otherwise sumVector() is restricted to vectors of elements of int (or types convertible to ints).

Something like the following I think is what your looking for:

template<typename T>
T sumVector(const vector<T> &integers2)
{
    typename vector<T>::const_iterator constIterator;
    T sum=0;
    //display vector elements using constIterator
    for (constIterator=integers2.begin();
         constIterator!=integers2.end();
         ++constIterator)
    {
        sum+=*constIterator;
    }

    cout<<sum;
    return sum;
}

Consider not printing the value of sum within sumVector() as (IMO) this is clearer:

cout << "whats the sum: " << sumVector(ages);

It may also be required to store the result of sumVector() in a variable and not write anything to standard output at the point the sum is calculated.