Passing value from one function to another

// http://stackoverflow.com/questions/13670796/passing-value-from-one-function-to-another
#include <iostream>
#include <string>

using namespace std;

void fnMainMenu();

void fnLogin()
{
  std::string s = "hello";
  fnMainMenu(s); // call Main Menu and I want to pass "hello"

}

void fnMainMenu(const std::string& msg)
{
  std::cout << msg << "\n";
}

int main()
{

    fnLogin();
    return 0;
}