How can I generate different random numbers for each player?

Question

Both players get the same random number! ّI want each player to get a different number since they are throwing dice. here is the code:

#include <stdlib.h>
#include <stdio.h>
#include <time.h>

int roll_a_dice(void);

int main(int argc, const char *argv[])
{   
    int flag;
    int answer1 = roll_a_dice();
    int answer2 = roll_a_dice();

    printf("Die 1 (rolled by player 1): %d\n", answer1);
    printf("Die 2 (rolled by player 2): %d\n", answer2);

    if (answer1>answer2) {
        printf("Player 1 is starting!\n");
        flag = 1;
    } else {
        printf("Player 2 is starting!\n");
        flag = 2;
    }

    printf("Goodbye!\n");

    return 0;        
}

int roll_a_dice(void)
{
    int r;

    srand(time(NULL));
    r = 1 + rand() % 6;

    return r;
}

The players are throwing dice. So number has to be 1-6. How can I fix this?

Put the different options 1..6 in an array. Select a random array index. Remove that item from the array (by swapping it with the last in the array and shortening its length). — Weather Vane, Apr 11 '16 at 20:34
Ah so I misread the question. OP does not want different random numbers, he wants random numbers that are not the same. — Weather Vane, Apr 11 '16 at 20:45
Looking for a better dupe .... re-opened, but certainly a dupe — chux - Reinstate Monica, Apr 11 '16 at 21:44

score 5 · Answer 1 · answered Apr 11 '16 at 20:34

5

srand ( time(NULL) ); is used to seed the pseudo-random number generator. time() having a granularity of 1 second, if you seed the PNRG every time you call the roll_a_dice() function, for all the calls made within the granularity period, rand() will end up returning the same random number.

Move the srand ( time(NULL) ); out of the roll_a_dice() function, call that only once in main().

answered Apr 11 '16 at 20:34

Sourav Ghosh

133,132
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Thank you so much!! Sorry if this was a noobie question I'm very new into coding and I'm trying my hardest. – RedDoumham Apr 11 '16 at 20:39
1

Why didn't you flag this as one of the thousand duplicates: http://stackoverflow.com/search?q=[c]+srand+ ? – 2501 Apr 11 '16 at 20:44
He can still get the same dice roll for each player. – Weather Vane Apr 11 '16 at 20:46
@WeatherVane Well yes, but only by chance, instead of every time. – user253751 Apr 11 '16 at 20:51

score 0 · Answer 2 · answered Apr 11 '16 at 20:36

0

You only need to seed once. Move srand to the top of main and it will work.

answered Apr 11 '16 at 20:36

Kake_Fisk

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score 0 · Answer 3 · answered Apr 11 '16 at 22:20

srand( int ); is used to initialize a seed. From there each time you call rand() you'll get a new random value. By calling srand() in roll_a_dice() you keep reseting the seed every time. Just move srand() at the start of your main().

How can I generate different random numbers for each player?

3 Answers3

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