srand function is returning same values

问题

Hey guys take a look at this program.

/* The craps game, KN king page 218 */

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

int roll_dice(void);
bool play_game(void);

int roll_dice(void)
{
    int roll;

    getchar();
    srand((unsigned) time(NULL));

    roll = rand() % 13;

    if(roll == 0)
    roll = roll + 1;

    return roll;
}

bool play_game()
{
    int sum = 0, wins = 0, loss = 0, point;

    sum = roll_dice();

    printf("You rolled: %d", sum);

    if(sum == 7 || sum == 11)
    {
        printf("\nYou won!\n");
        return true;
    }

    if(sum == 2 || sum == 3 || sum == 12)
    {
        printf("\nYou lost!!");
        return false;
    }

    point = sum;

    printf("\n\nYour point is: %d", point);

    do
    {
        sum = roll_dice();
        printf("\nYou rolled: %d", sum);

    }while(sum != point);

    if(sum == point)
    {
        printf("\nYou won!!!");
        return true;
    }

}

int main()
{
    char c, wins = 0, losses = 0;
    bool check;

    do
    {
        check = play_game();

        if(check == true)
          wins++;

        else if(check == false)
          losses++;

        printf("\nPlay Again? ");
        scanf("%c", &c);

    }while(c == 'Y' || c == 'y');

    printf("\nWins: %d      Losses: %d", wins, losses);

    return 0;
}

The srand function keeps returning, same value 3 or 4 times, y is that?

I want different values each time when i roll the dice, copy the code and run it to see what i mean

回答1:

srand() is a function that sets the seed for the rand() function. What you are doing here is setting the seed to the current time before every rand() you call, which, if called fast enough, will get you the same value (since it will reset to the same seed, which if fast enough will be the same time value).

What you'll want to do is call srand() once, when the program starts (at the start of your main() function)

Then call rand() every time you want a random number, like you are doing currently, but without calling srand() every time.

来源：https://stackoverflow.com/questions/14494375/srand-function-is-returning-same-values

标签

coding-style

srand