Adding int to long - c++

Question

I am creating a recursive formula to add up all the elements in a vector. The problem them I'm having is that my result is not adding to the vector results so it always returns 0. I have tried static_cast to turn it into an int but I'm still not able to figure it out. Here's my code:
long vectorSum(const std::vector<int>& data, unsigned int position) {
int ret = 0;
if(position == data.size()-1) {
return ret;
} else {
ret += data[position];
return vectorSum(data, position+1);
}
}
I am calling the function like this:
std::vector<int> test1;
for(int i = 0; i < 10; i++) {
test1.push_back(i);
}
cout << vectorSum(test1, 0) << "\n";

Answer 1

This is not correct:
ret += data[position];
return vectorSum(data, position+1);
The new value of ret (+= data[position]) isn't being used anywhere or passed back to the caller.
Remeber: ret is strictly local to each invocation of vectorSum(). It doesn't exist outside of your vectorSum(); it's being set to "0" every time you invoke vectorSum().

Answer 2

long vectorSum(const std::vector<int>& data, unsigned int position) {
if(position == data.size())
return 0;
else
return data[position]+vectorSum(data, position+1);
}
Then call it as
int sum=vectorSum(data,0);

Answer 3

Normally, one adds to the value of a recursive call. You are not doing that. In your code, it will keep calling with a modified position until it hits the terminating condition, then that return 0; goes all the way back up to the caller.
long vectorSum(const std::vector<int>& data, unsigned int position) {
int ret = 0;
if(position == data.size()-1) {
return ret;
} else {
ret += data[position]; //this line has no affect on the result!
return vectorSum(data, position+1); //you don't accumulate anything
//this will always return 0
}
}
Instead, you want to add the current value plus the value from the recursive call:
long vectorSum(const std::vector<int>& data, unsigned int position) {
if(position == data.size()-1) {
//terminating condition, return 0
return 0;
} else {
//add current value plus value from processing the rest of the list
return data[position] + vectorSum(data, position+1);
}
}
As a side note: recursion is a great tool, but it can easily be misused by applying it to problems that already have better and more elegant solutions. For this, something like std::accumulate would probably be the most "natural" solution for C++.