pin.cpp

#include <iostream>
#include <string>
#include <conio.h>

using namespace std;

template<typename T>
class password {
    public:
        template<typename T>
        friend ostream& operator<<(ostream &os, password<T> &in);
        friend istream& operator>>(istream &is, password<T> &out);
    protected:
        T value;
};

template<typename T>
ostream& operator<<(ostream &os, password<T> &in) {
    return os << in.value;
}

istream& operator>>(istream &is, password<int> &out) {
    string str;
    while(true) {
        int c = getch();
        if(c >= '0' && c <= '9') {
            str.push_back(c);
            cout << '*';
        } else if(c == '\b') {
            if(str.length() > 0) {
                str.pop_back();
                cout << "\b \b";
            }
        } else if(c == '\r') {
            cout << endl;
            break;
        }
    }
    out.value = atoi(str.c_str());
    return is;
}

istream& operator>>(istream &is, password<string> &out) {
    out.value.clear();
    while(true) {
        int c = getch();
        if(c >= ' ' && c <= '~') {
            out.value.push_back(c);
            cout << '*';
        } else if(c == '\b') {
            if(out.value.length() > 0) {
                out.value.pop_back();
                cout << "\b \b";
            }
        } else if(c == '\r') {
            cout << endl;
            break;
        }
    }
    return is;
}

int main() {
    password<int> pw_int;
    password<string> pw_str;

    cout << "Enter integer password: ";
    cin >> pw_int;

    cout << "Enter string password: ";
    cin >> pw_str;

    cout << "pw_int = " << pw_int << endl
         << "pw_str = " << pw_str << endl;

    getch();
    return 0;
}