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

int main(int argc,char *argv[])
{
    srand((unsigned)time(NULL));
    int a,b,c;
    a=rand()%4;
    while((b=rand()%4)!=a)
        break;
    while((c=rand()%4)!=a && c!=b)
        break;
    printf("%d,%d,%d\n",a,b,c);
    return 0;
}

可以产生啊，每次都不同。
#include <iostream>
#include <ctime>
#include <cstdlib>
#include <cstdio>
using namespace std;

int main(int argc,char *argv[])
{
    srand((unsigned)time(NULL));
    int a,b,c;
    a=rand()%4;

    while((b = rand() %4 ) == a) ;

    while((c = rand() %4 ) == a || c == b);

    printf("%d,%d,%d\n",a,b,c);

    return 0;
}