well, ending your while loop by breaking it with a letter is kind of goofy.
you could have user enter all the numbers on a single line and use getline, then push them into vector using a stringstream.
for example!
Code:
#include <iostream>
#include <sstream>
#include <vector>
using namespace std;
int main()
{
string str_num;
int current_number;
vector<int> numbers;
cout << "Please enter a list of numbers ";
getline(cin , str_num);
// takes a complete line (discarding newline character as well)
istringstream iss(str_num);
// inserts string into a stream (you should learn streams they are useful)
// now you can use this stream just as you would cin, which is a stream itself actually
while(iss >> current_number)
numbers.push_back(current_number);
cout << "How many elements do you wish to sum? ";
int sum;
cin >> sum;
system("pause");
}
GL!