Do two elements in a sorted array sum up to a value?

#include <vector>
#include <iostream>

using namespace std;

pair* find2Elems(vector& a, size_t len, int findme)
{
    int iFront = 0, iBack = len-1, sum;
    while (iFront < iBack)
    {
        sum = a[iFront] + a[iBack];
        // sum is too large
        if (sum > findme)
        {
            iBack--;
        }
        // sum is too small
        else if (sum < findme)
        {
           iFront++;
        }
        else // if (sum == findme)
        {
            return new pair(iFront,iBack);
        }
    }
    return NULL;
}

int main() {
    const size_t size = 20;
    vector a(size);
    srand(time(NULL));
    // make a vector with random elements
    for (int i=0; i < size; i++)
    {
        a[i] = rand()%50;
    }
    sort(a.begin(), a.end());
    for (int i=0; i < size; i++)
        cout << a[i] << " ";
    cout << endl;
    pair *p = find2Elems(a, size, 20);
    if (p)
    {
        cout << a[p->first] << ", " << a[p->second] << endl;
    }
    else
        cout << "not found" << endl;
    return 0;
}