Trying to generate random array of integers, getting the same list each run. C++

Question

Why does this result in the same array every time i run it?

int arr[100];
for (int i = 0; i < 100; i++) {
    arr[i] = rand() % 11 + (-5); 
}

score 2 · Answer 1 · answered Sep 05 '16 at 21:45

2

You need to seed the random number generator, for example with the current time.

#include <time.h>
#include <stdlib.h>
srand(time(NULL));

answered Sep 05 '16 at 21:45

Aganju

Using `srand` for random numbers has not been the best standard-based solution for several years. – Lightness Races in Orbit Sep 05 '16 at 21:56

score 1 · Accepted Answer · answered Sep 05 '16 at 21:46

1

Use std::srand(std::time(0)); to set the random seed. For reproducible results, use the same seed, see http://en.cppreference.com/w/cpp/numeric/random/srand.

answered Sep 05 '16 at 21:46

David Stutz

Using `srand` for random numbers has not been the best standard-based solution for several years. – Lightness Races in Orbit Sep 05 '16 at 21:56
Ok, that's news for me - what is a better solution? – David Stutz Sep 05 '16 at 22:07
@DavidStutz See here: http://en.cppreference.com/w/cpp/numeric/random – πάντα ῥεῖ Sep 05 '16 at 22:20
Ah ok, for C++11 - thanks for the heads up ;) – David Stutz Sep 05 '16 at 23:43

2 Answers2