Use fill_n to Fill the three elements starting at offset position 3 with value -9 : fill_n « STL Algorithms Modifying sequence operations « C++ Tutorial

1. C++ Tutorial
2. STL Algorithms Modifying sequence operations
3. fill_n

#include <algorithm>
#include <vector>
#include <iostream>
using namespace std;
int main ()
{
    vector <int> v (3);

    v.resize (6);

    // Fill the three elements starting at offset position 3 with value -9
    fill_n (v.begin () + 3, 3, -9);

    cout << "Contents of the vector are: " << endl;
    for (size_t nIndex = 0; nIndex < v.size (); ++ nIndex){
        cout << "Element [" << nIndex << "] = ";
        cout << v [nIndex] << endl;
    }

    return 0;
}