how do i generate random #'s that do not repeat? below is some small code for generating 20 random #s btw 1 and 20...but i don't know how to make sure the sequence of picking the #s does not repeat...

Code:
// rgen.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <ctime>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <fstream>
#include <iostream>
#include <iomanip>
using namespace std;

int main()
{
	srand((unsigned)time(0)); 
	int random_integer; 
	for(int index=0; index<20; index++)
	{
		random_integer = (rand()%20)+1; 

		cout << random_integer << endl; 
	}
}