Generate 8 unique random numbers from 0 to 7 - c++

Question

I'm making a simple script that generates 8 random values from 0 to 7 and stores them into an array named random_numbers.
This is my try:
int main(int argc, char** argv) {
int random_numbers[8];
srand((unsigned)time(NULL));
for (int i = 0; i < 8; i++) {
random_numbers[i] = 1+ rand() % 8;
cout << random_numbers[i] << endl;
}
return 0;
}
This gives me repeated values. I would like to have random_numbers filled of random values from 0 to 7, but without any repeated numbers.
How can I do that?

Answer 1

Generate the numbers 0 through 7, then shuffle them. Assuming this is actually C++, not C (because of the cout), use std::random_shuffle:
#include <algorithm>
#include <cstdlib>
#include <iostream>
int main()
{
int a[8] = {0, 1, 2, 3, 4, 5, 6, 7};
std::srand(unsigned(std::time(0)));
std::random_shuffle(a, a + 8);
for (int i=0; i<8; i++)
std::cout << a[i] << " ";
std::cout << std::endl;
}
Be warned: cppreference.com states that "The random number generator is implementation-defined, but the function std::rand is often used." I've seeded that with std::srand, but apparently that's not completely portable.

Answer 2

#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <ctime>
using namespace std;
class Random {
public:
Random(){
srand( static_cast<unsigned int>(time(NULL)));
}
unsigned int operator()(unsigned int max){
double tmp = static_cast<double>( rand() ) / static_cast<double>( RAND_MAX );
return static_cast<unsigned int>( tmp * max );
}
};
int main(int argc, char** argv) {
int random_numbers[8];
int size = sizeof(random_numbers)/sizeof(int);
for(int i=0;i<size;++i)
random_numbers[i]=i;
Random r;
random_shuffle(random_numbers, random_numbers + size, r);
for (int i = 0; i < 8; i++) {
cout << random_numbers[i] << endl;
}
return 0;
}

Answer 3

Since you are using c++ any way I modified you code a bit more. Use vector instead of array, this should make your life easier, and this generates 0-7 in a random order without duplicates:
compile with -std=c++0x
#include <iostream>
#include <algorithm>
#include <vector>
#include <numeric>
using namespace std;
int main(int argc, char** argv) {
srand(time(NULL));
vector<int> random_numbers(8);
iota(random_numbers.begin(), random_numbers.end(), 1);
random_shuffle(random_numbers.begin(), random_numbers.end());
for (unsigned i = 0; i < random_numbers.size(); i++) {
cout << random_numbers[i] << endl;
}
return 0;
}

Answer 4

try this code:
int random_numbers[8];
int main(int argc, char** argv) {
srand((unsigned)time(NULL));
for (int i = 0; i < 8; i++) {
random_numbers[i] =getRand(i);
cout << random_numbers[i] << endl;
}
return 0;
}
int getRand(int entries)
{
int flag = 0;
int randno ;
randno = rand() % 8;
for(int i=0;i<entries;i++)
{
if( random_numbers[i]==randno)
{
randno = rand() % 8;
continue;
}
}
return randno;
}