you wanted portability?

#include <iostream>
#include <string>

using namespace std;

bool EnsureValid(char v){
    switch (v){
        case 'r':
        case 'p':
        case 's':
            return true;
        default:
            return false;
    }
}

string FriendlyName(char v){
    switch (v){
        case 'r':
            return "Rock";
        case 'p':
            return "Paper";
        case 's':
            return "Scissors";
    }
    return "Invalid";
}

bool Is1Win(char a, char b) {
        return a=='r'&&b=='s'||a=='p'&&b=='r'||a=='s'&&b=='p';
}

char Lowercase(char v){
    return v|0x20;
}

char silentGetChar();

char TakeInput(int player) {
    for (;;) {
        cout << "Player " << player << ": [R/P/S]" << endl;
        char v=silentGetChar();
        v=Lowercase(v);
        if(EnsureValid(v)){
            return v;
        }
        cout << "Player " << player << ": That is not Rock, Paper or Scissors!"<< endl;
    }
}

int main(int, char*[])
{
    char user[2] = {0,0};

    for (;;) {
        // Read inputs
        user[0]=TakeInput(1);
        user[1]=TakeInput(2);
        if(user[0]==user[1]) {// Tie check
                cout << "Both players chose " << FriendlyName(user[0]) << "!" << endl;
        }else if (Is1Win(user[0],user[1])){
                cout << "Player 1 wins with " << FriendlyName(user[0]) << "!" << endl;
        }else{// We have already checked the tie and p1 win, only other state is p2 win.
                cout << "Player 2 wins with " << FriendlyName(user[1]) << "!" << endl;
        }

        cout << "Play again [Y/N]" << endl;
        char v=silentGetChar();
        v=Lowercase(v);
        if(v!='y'){
                break;
        }
    }
    return 0;
}

#ifdef __unix__
    #include "termios.h"
    char silentGetChar() {
        struct termios current, ours;
        tcgetattr(0,&current);
        ours=current;
        ours.c_lflag&= ~ICANON & ~ECHO;
        tcsetattr(0,TCSANOW,&ours);
        char v;
        cin.get(v);
        tcsetattr(0,TCSANOW,&current);
        return v;
    }
#elif WIN32
    #include "conio.h"
    char silentGetChar(){
        char v =  _getch();
        if(v==3){//CTRL-C;
                exit(0);
        }
        return v;
    }
#else
    char silentGetChar(){
        char v;
        cin.get(v);
        return v;
    }
#endif