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

void foo(string& s)
{
    cout << s << endl;
}
void goo(const string& s)
{
    cout << s << endl;
}
void delta(string& s)
{
    s = "I am changed";
}

int main()
{
    string s1 = "I am volatile";
    const string s2 = "I am const";

    foo(s1);
    //	foo(s2);	// Error: cannot convert from 'const std::string' to 'std::string &'
    foo(const_cast<string&>(s2));

    goo(s1);
    goo(s2);

    cout << "Before: s1 = " << s1 << endl;
    cout << "Before: s2 = " << s2 << endl;
    delta(s1);
    delta(const_cast<string&>(s2));
    cout << "After: s1 = " << s1 << endl;
    cout << "After: s2 = " << s2 << endl;
}