Run rand() in C language and loop with Shell Scirpts

Recently I had been stuck on a question. I have a C code file (call "test.c" and output is "test.out") like below and just a simple output of random number:

int main()
{
    srand(time(NULL)); 
    double r = (double)rand() / (double)RAND_MAX;
    printf("%f\n", r);
    return 0;
}

and now I use shell scripts to run "test.out" 5 times in Linux, the code below:

for i in 1 2 3 4 5
do
    test.out
done

but the result show like below

0.840188
0.840188
0.840188
0.840188
0.840188

It shows the same random number...
Can anyone have any suggestion?

Thanks a million!