Using rand() and srand(time(NULL)) right after doesn't generate a new random number

Question

for (x = 1; x < 10; x++)
{
    (armoPtr + x) ->def = rand() % b + a;
    if ((armoPtr + x) -> def > b)
        (armoPtr + x) -> def = b;

    srand(time(NULL));

    (armoPtr + x) -> hp = rand() % 5 + 1;
    srand(time(NULL));

    (armoPtr + x) -> valOItem = rand() % (lvlpnts + 1) + max(lvlpnts);
    if ((armoPtr + x) -> valOItem > (lvlpnts + 1))
        (armoPtr + x) -> valOItem = (lvlpnts + 1);
    (armoPtr + x) -> valOItem *= 10;
    srand(time(NULL));
}

Forgive me if it's a pretty mediocre mistake, but shouldn't this loop have new random numbers every time it loops? I'm still in my 2nd term of my first year in Com Sci. Sorry if I suck. Hahahaha

The value returned by `time(NULL)` doesn't change between loop iterations, so you're resetting your *pseudo*random number generator to the same starting value each time. — Andrew Henle, Mar 10 '16 at 14:58

4pie0 · Accepted Answer · 2016-03-10T15:08:01.380

Call srand once before you start to draw random numbers

srand(time(NULL));
for (x = 1; x < 10; x++)
{

and then just make calls top rand() inside the loop:

srand(time(NULL));
for (x = 1; x < 10; x++)
{
    (armoPtr + x) ->def = rand() % b + a;
    if ((armoPtr + x) -> def > b)
        (armoPtr + x) -> def = b;

    (armoPtr + x) -> hp = rand() % 5 + 1;

    (armoPtr + x) -> valOItem = rand() % (lvlpnts + 1) + max(lvlpnts);
    if ((armoPtr + x) -> valOItem > (lvlpnts + 1))
        (armoPtr + x) -> valOItem = (lvlpnts + 1);
    (armoPtr + x) -> valOItem *= 10;
}

Feeding srand with time(NULL) more than once in the same second will make you start to draw same numbers from the beginning because time(NULL) granularity is seconds.

Using rand() and srand(time(NULL)) right after doesn't generate a new random number

1 Answers1