a few questions

[UpcomingChris]

i am creating a game of Rock, paper, Scissors,

#include <iostream>
#include <string>

using namespace std;

string a;
int b;
int main()
{
    cout << "Welcome to Rock, Paper, Scissors\n";
    cout << "To play, Simply type R,P or S\n";
    cout << "\n";
    system("PAUSE");
    system("CLS");
 //Game Begins
 
   cout << "Your turn, R,P or S?\n";
   cin >> a;
   
   if (a == "R")
      {cout << "You chose Rock..\n";}
   else if (a == "P")
      {cout << "You chose Paper..\n";}
   else if (a == "S")
      {cout << "You chose Scissors\n";}
   else
      {cout << "Please enter R,P or C only\n";}
   system("PAUSE");
   
      
    
    
    
}

First off, How can i get the code to Start again after "Please enter R,P or C only" so it dosent have to restart?,


And, How can i make a random number generator, that randomly picks one number, from 3, so 1,2,or 3,?