Converting between strings and numbers

Something that should be easy seems to be more difficult than expected. Below as some conversion code not fully understood at the time of writing - i.e. have to understand the difference between ostringstream and stringstream.

#include <iostream>
#include <sstream>
#include <string>

using namespace std;

int main()
{

    int x = 1234;
    int y;
    string result;

    // converts integer to string which is held in result
    ostringstream conv;
    conv << x * 2;
    conv << 000; //gives a funny result - adds on a 0 at the end of the stream because we are only adding on zero as an integer, but after conversion....
    conv << "00"; //this does padd the result with two zeros - i.e similar to multiplying by 100
    cout << conv.str() << " converts number to string" << endl;
    result = conv.str();
    cout << result << " converted integer assigned to string variable" << endl;


    //takes the string created above and converts back to number
    stringstream string_to_num; // I tried this with conv
    string_to_num << result;

    string_to_num >> y;
    cout << y / 2000 << " output y and do numerical operations on y gets you back to x" << endl;

    return 0;
}