C++ vector size()

#include <iostream>
#include <vector>
using namespace std;
int main()/*from   w  w w. j a  v  a2  s.  co m*/
{
   vector<int> v;                 // create a vector of ints
   v.push_back(10);               // put values at end of array
   v.push_back(11);
   v.push_back(12);
   v.push_back(13);
   v[0] = 20;                     // replace with new values
   v[3] = 23;
   for(int j=0; j<v.size(); j++)  // display vector contents
      cout << v[j] << ' ';        // 20 11 12 23
   cout << endl;
   return 0;
}