[Neophyte]

If you're using C++, you can do it like this:

#include <string>
#include <sstream>
#include <iostream>
using namespace std;

int main(void) {
  string str = "12345";
  int num;
  string conv;

  /* convert str to int */
  istringstream iss ( str );
  iss >> num;
  cout << "num: " << num << endl;

  /* convert num to string */
  ostringstream oss;
  oss << num;
  istringstream iss2 ( oss.str() );
  iss2 >> conv;
  cout << "conv: " << conv << endl;

}