//1. Using vector<string>::iterator:
vector<string> vs = GetVector();

for(vector<string>::iterator it = vs.begin(); it != vs.end(); ++it)
{
   *it = "Am I faster?";
}

//2. Using size_t index:
for(size_t i = 0; i < vs.size(); ++i)
{
   //One option:
   vs.at(i) = "Am I faster?";
   //Another option:
   vs[i] = "Am I faster?";
}

#include <vector>
#include <iostream>
#include <ctime>
using namespace std;;

int main() {
    const int BIG = 20000000;
    vector <int> v;
    for ( int i = 0; i < BIG; i++ ) {
    	v.push_back( i );
    }

    int now = time(0);
    cout << "start" << endl;
    int n = 0;
    for(vector<int>::iterator it = v.begin(); it != v.end(); ++it) {
    	n += *it;
    }

    cout << time(0) - now << endl;
    now = time(0);
    for(size_t i = 0; i < v.size(); ++i) {
    	n += v[i];
    }
    cout << time(0) - now << endl;

    return n != 0;
}

//1. Using vector<string>::iterator:

vector<string> vs = GetVector();
for(vector<string>::iterator it = vs.begin(), end = vs.end(); it != end; ++it)
{
   //...
}

//2. Using size_t index:

vector<string> vs = GetVector();
for(size_t i = 0, size = vs.size(); i != size; ++i)
{
   //...
}

#include <vector>
#include <iostream>
#include <ctime>
using namespace std;;


struct AAA{
    int n;
    string str;
};
int main() {
    const int BIG = 5000000;
    vector <AAA> v;
    for ( int i = 0; i < BIG; i++ ) {
        AAA a = {i, "aaa"};
        v.push_back( a );
    }

    clock_t now;
    cout << "start" << endl;
    int n = 0;
    now = clock();
    for(vector<AAA>::iterator it = v.begin(); it != v.end(); ++it) {
        n += it->n;
    }
   cout << clock() - now << endl;

    n = 0;
    now = clock();
    for(size_t i = 0; i < v.size(); ++i) {
        n += v[i].n;
    }
    cout << clock() - now << endl;

    getchar();
    return n != 0;
}