Running into a segfault in C

Question

Edit: working code at the bottom

Im relatively new to programming, and Im trying to understand why this isnt working. I decided to deal cards through a function instead of main() to keep it as modular as possible. Here's my code below; I know the error is something to do with the pointers, but I dont understand what Im doing wrong.

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

int dealCards (char* cards[52][30], int* x, int* y, int* a, int* b)
{
    time_t t;
    srand((unsigned) time(&t));

    printf("\n\nNow let's give you two random cards!\n\n");

    *x = rand() % 53;
    if (x != 0) {
        *x = x - 1;
    }

    *y = rand() % 53;
    if (y == x) {
        while (y == x) {
            y = rand() % 53;
        }
    }
    if (y != 0) {
        y = y - 1;
    }

    int i;
    printf("Card 1 >\n");
    for (i = 0; i < 30; i++) {
            printf("%c", cards[*x][i]);
        }
    printf("\nCard 2 >\n");
    for (i = 0; i < 30; i++) {
            printf("%c", cards[*y][i]);
        }

    printf("\n%d\n", x);
    printf("%d", y);

    printf("\n\nNow let's give your opponent two random cards!\n\n");

    *a = rand() % 53;
    if (a != 0) {
        a = a - 1;
    }
    if ((a == x) || (a == y)) {
        while ((a == x) || (a == y)) {
            *a = rand() % 53;
        }
    }

    *b = rand() % 53;
    if (b == a) {
        while ((b == a) || (b == x) || (b == y)) {
                *b = rand() % 53;
        }
    }
    if (b != 0) {
        *b = b - 1;
    }

    printf("Card 1 >\n");
    for (i = 0; i < 30; i++) {
            printf("%c", cards[*a][i]);
        }
    printf("\nCard 2 >\n");
    for (i = 0; i < 30; i++) {
            printf("%c", cards[*b][i]);
        }

    printf("\n%d\n", a);
    printf("%d", b);
}

int main()
{
    char deck[52][30] = { 
        {"_____\n|2♥ |\n|   |\n|_2♥|\n"},
        {"_____\n|3♥ |\n|   |\n|_3♥|\n"},
        {"_____\n|4♥ |\n|   |\n|_4♥|\n"},
        {"_____\n|5♥ |\n|   |\n|_5♥|\n"},
        {"_____\n|6♥ |\n|   |\n|_6♥|\n"},
        {"_____\n|7♥ |\n|   |\n|_7♥|\n"},
        {"_____\n|8♥ |\n|   |\n|_8♥|\n"},
        {"_____\n|9♥ |\n|   |\n|_9♥|\n"},
        {"_____\n|10♥|\n|   |\n|10♥|\n"},
        {"_____\n|J♥ |\n|   |\n|_J♥|\n"},
        {"_____\n|Q♥ |\n|   |\n|_Q♥|\n"},
        {"_____\n|K♥ |\n|   |\n|_K♥|\n"},
        {"_____\n|A♥ |\n|   |\n|_A♥|\n"},

        {"_____\n|2♦ |\n|   |\n|_2♦|\n"},
        {"_____\n|3♦ |\n|   |\n|_3♦|\n"},
        {"_____\n|4♦ |\n|   |\n|_4♦|\n"},
        {"_____\n|5♦ |\n|   |\n|_5♦|\n"},
        {"_____\n|6♦ |\n|   |\n|_6♦|\n"},
        {"_____\n|7♦ |\n|   |\n|_7♦|\n"},
        {"_____\n|8♦ |\n|   |\n|_8♦|\n"},
        {"_____\n|9♦ |\n|   |\n|_9♦|\n"},
        {"_____\n|10♦|\n|   |\n|10♦|\n"},
        {"_____\n|J♦ |\n|   |\n|_J♦|\n"},
        {"_____\n|Q♦ |\n|   |\n|_Q♦|\n"},
        {"_____\n|K♦ |\n|   |\n|_K♦|\n"},
        {"_____\n|A♦ |\n|   |\n|_A♦|\n"},

        {"_____\n|2♠ |\n|   |\n|_2♠|\n"},
        {"_____\n|3♠ |\n|   |\n|_3♠|\n"},
        {"_____\n|4♠ |\n|   |\n|_4♠|\n"},
        {"_____\n|5♠ |\n|   |\n|_5♠|\n"},
        {"_____\n|6♠ |\n|   |\n|_6♠|\n"},
        {"_____\n|7♠ |\n|   |\n|_7♠|\n"},
        {"_____\n|8♠ |\n|   |\n|_8♠|\n"},
        {"_____\n|9♠ |\n|   |\n|_9♠|\n"},
        {"_____\n|10♠|\n|   |\n|10♠|\n"},
        {"_____\n|J♠ |\n|   |\n|_J♠|\n"},
        {"_____\n|Q♠ |\n|   |\n|_Q♠|\n"},
        {"_____\n|K♠ |\n|   |\n|_K♠|\n"},
        {"_____\n|A♠ |\n|   |\n|_A♠|\n"},

        {"_____\n|2♣ |\n|   |\n|_2♣|\n"},
        {"_____\n|3♣ |\n|   |\n|_3♣|\n"},
        {"_____\n|4♣ |\n|   |\n|_4♣|\n"},
        {"_____\n|5♣ |\n|   |\n|_5♣|\n"},
        {"_____\n|6♣ |\n|   |\n|_6♣|\n"},
        {"_____\n|7♣ |\n|   |\n|_7♣|\n"},
        {"_____\n|8♣ |\n|   |\n|_8♣|\n"},
        {"_____\n|9♣ |\n|   |\n|_9♣|\n"},
        {"_____\n|10♣|\n|   |\n|10♣|\n"},
        {"_____\n|J♣ |\n|   |\n|_J♣|\n"},
        {"_____\n|Q♣ |\n|   |\n|_Q♣|\n"},
        {"_____\n|K♣ |\n|   |\n|_K♣|\n"},
        {"_____\n|A♣ |\n|   |\n|_A♣|\n"},
    };

    int i, j;
    for (i = 0; i < 52; i++) {
        for (j = 0; j < 30; j++) {
            printf("%c", deck[i][j]);
        }
    }

    //dealing
    int heroFirst, heroSecond, villainFirst, villainSecond;

    dealCards(deck, &heroFirst, &heroSecond, &villainFirst, &villainSecond);


    //bets
}

Working code:

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

int dealCards (char cards[52][30], int *x, int *y, int *a, int *b)
{
    time_t t;
    srand((unsigned) time(&t));

    printf("\n\nYour cards:\n\n");

    *x = rand() % 53;
    if (*x != 0) {
        *x = *x - 1;
    }

    *y = rand() % 53;
    if (*y == *x) {
        while (*y == *x) {
            *y = rand() % 53;
        }
    }
    if (*y != 0) {
        *y = *y - 1;
    }

    int i;
    printf("Card 1 >\n");
    for (i = 0; i < 30; i++) {
            printf("%c", cards[*x][i]);
        }
    printf("\nCard 2 >\n");
    for (i = 0; i < 30; i++) {
            printf("%c", cards[*y][i]);
        }

    printf("\n\nVillain cards:\n\n");

    *a = rand() % 53;
    if (*a != 0) {
        *a = *a - 1;
    }
    if ((*a == *x) || (*a == *y)) {
        while ((*a == *x) || (*a == *y)) {
            *a = rand() % 53;
        }
    }

    *b = rand() % 53;
    if (*b == *a) {
        while ((*b == *a) || (*b == *x) || (*b == *y)) {
                *b = rand() % 53;
        }
    }
    if (*b != 0) {
        *b = *b - 1;
    }

    printf("Card 1 >\n");
    for (i = 0; i < 30; i++) {
            printf("%c", cards[*a][i]);
        }
    printf("\nCard 2 >\n");
    for (i = 0; i < 30; i++) {
            printf("%c", cards[*b][i]);
        }
}

int main()
{
    char deck[52][30] = { 
        {"_____\n|2♥ |\n|   |\n|_2♥|\n"},
        {"_____\n|3♥ |\n|   |\n|_3♥|\n"},
        {"_____\n|4♥ |\n|   |\n|_4♥|\n"},
        {"_____\n|5♥ |\n|   |\n|_5♥|\n"},
        {"_____\n|6♥ |\n|   |\n|_6♥|\n"},
        {"_____\n|7♥ |\n|   |\n|_7♥|\n"},
        {"_____\n|8♥ |\n|   |\n|_8♥|\n"},
        {"_____\n|9♥ |\n|   |\n|_9♥|\n"},
        {"_____\n|10♥|\n|   |\n|10♥|\n"},
        {"_____\n|J♥ |\n|   |\n|_J♥|\n"},
        {"_____\n|Q♥ |\n|   |\n|_Q♥|\n"},
        {"_____\n|K♥ |\n|   |\n|_K♥|\n"},
        {"_____\n|A♥ |\n|   |\n|_A♥|\n"},

        {"_____\n|2♦ |\n|   |\n|_2♦|\n"},
        {"_____\n|3♦ |\n|   |\n|_3♦|\n"},
        {"_____\n|4♦ |\n|   |\n|_4♦|\n"},
        {"_____\n|5♦ |\n|   |\n|_5♦|\n"},
        {"_____\n|6♦ |\n|   |\n|_6♦|\n"},
        {"_____\n|7♦ |\n|   |\n|_7♦|\n"},
        {"_____\n|8♦ |\n|   |\n|_8♦|\n"},
        {"_____\n|9♦ |\n|   |\n|_9♦|\n"},
        {"_____\n|10♦|\n|   |\n|10♦|\n"},
        {"_____\n|J♦ |\n|   |\n|_J♦|\n"},
        {"_____\n|Q♦ |\n|   |\n|_Q♦|\n"},
        {"_____\n|K♦ |\n|   |\n|_K♦|\n"},
        {"_____\n|A♦ |\n|   |\n|_A♦|\n"},

        {"_____\n|2♠ |\n|   |\n|_2♠|\n"},
        {"_____\n|3♠ |\n|   |\n|_3♠|\n"},
        {"_____\n|4♠ |\n|   |\n|_4♠|\n"},
        {"_____\n|5♠ |\n|   |\n|_5♠|\n"},
        {"_____\n|6♠ |\n|   |\n|_6♠|\n"},
        {"_____\n|7♠ |\n|   |\n|_7♠|\n"},
        {"_____\n|8♠ |\n|   |\n|_8♠|\n"},
        {"_____\n|9♠ |\n|   |\n|_9♠|\n"},
        {"_____\n|10♠|\n|   |\n|10♠|\n"},
        {"_____\n|J♠ |\n|   |\n|_J♠|\n"},
        {"_____\n|Q♠ |\n|   |\n|_Q♠|\n"},
        {"_____\n|K♠ |\n|   |\n|_K♠|\n"},
        {"_____\n|A♠ |\n|   |\n|_A♠|\n"},

        {"_____\n|2♣ |\n|   |\n|_2♣|\n"},
        {"_____\n|3♣ |\n|   |\n|_3♣|\n"},
        {"_____\n|4♣ |\n|   |\n|_4♣|\n"},
        {"_____\n|5♣ |\n|   |\n|_5♣|\n"},
        {"_____\n|6♣ |\n|   |\n|_6♣|\n"},
        {"_____\n|7♣ |\n|   |\n|_7♣|\n"},
        {"_____\n|8♣ |\n|   |\n|_8♣|\n"},
        {"_____\n|9♣ |\n|   |\n|_9♣|\n"},
        {"_____\n|10♣|\n|   |\n|10♣|\n"},
        {"_____\n|J♣ |\n|   |\n|_J♣|\n"},
        {"_____\n|Q♣ |\n|   |\n|_Q♣|\n"},
        {"_____\n|K♣ |\n|   |\n|_K♣|\n"},
        {"_____\n|A♣ |\n|   |\n|_A♣|\n"},
    };

    int i, j;
    for (i = 0; i < 52; i++) {
        for (j = 0; j < 30; j++) {
            printf("%c", deck[i][j]);
        }
    }

    double heroStack, villainStack;
    printf("\n-----------------------------");
    printf("\nWelcome to Heads Up Hold 'Em!");
    printf("\n-----------------------------");

    printf("\nHow many chips are your going to start off with?\n> ");
    scanf("%lf", &heroStack);
    villainStack = heroStack;

    printf("\nYour chipstack: %.lf\n", heroStack);
    printf("Villain's chipstack: %.lf\n", villainStack);

    //dealing
    int heroFirst, heroSecond, villainFirst, villainSecond;

    dealCards(deck, &heroFirst, &heroSecond, &villainFirst, &villainSecond);
    printf("\n%d\n", heroFirst);
    printf("%d\n", heroSecond);
    printf("%d\n", villainFirst);
    printf("%d\n", villainSecond);

    //bets
    //double heroBet, villainBet;
    //printf("\nYour move");
}

Answer 1

The problem is you are mixing confusingly between getting value and calculating value This if (and similar), do you know what are you doing?

*x = rand() % 53; if (x != 0) { *x = x - 1; }

Well, x in your function is a pointer, which means, if you want to get or to assign a value, you must use operator * like *x = rand() % 53 But when you compare x != 0, the compiler will think that you are checking whether x is NULL or not (by default, NULL is 0). So, it is not the value of the above statement, which will lead you to logic error.

If you look closer in your main, you should see that x, y, and similar argument you pass is never NULL, since they are created locally in main function and still existing until you leave it. Therefore, your statement *x = x - 1 will work unexpectedly, which may cause your segfault

I think that you are using the deal function to get randomly values of these variables

int heroFirst, heroSecond, villainFirst, villainSecond;

Thus, you can pass those value by reference by declare the function like this: int dealCards (char cards[52][30], int& x, int& y, int& a, int& b) then call your function like this dealCards (deck, heroFirst, heroSecond, villainFirst, villainSecond)

In your dealCards definition, just remove the * like *x or something like that, your function will work normally (if you know what you are going to do, with those x y) Moreover, you can safely print the whole string without using for loop like this, it seem crappy, isn't it?

for (i = 0; i < 30; i++) { printf("%c", cards[*y][i]); }

Just print it normally by printf("%s", cards[*y]);

Eddited:

• Grammar

• You should re-declare your cardDecks as above comments to make it works