Problem with C pointers "invalid parameter"?

Question

I have to make a game, playable with 2 or 3 players, for that I need a structure which I named Player. I wanted to ask the user for the number of "players", and do a for loop to generate players based on the number they enter, like this:

int playerNumbers = 0;
while (playerNumbers != 2 || playerNumbers != 3)
{
        printf("How many players are you ? 2 or 3 ? : \n");
        scanf_s("%d", playerNumbers); 

/* Error here: Unhandled exception to 0x7A72F2F6 (ucrtbased.dll) in Wheel.exe: 
An invalid parameter was passed to a function that considers invalid parameters
to be an unrecoverable cause of error. */

}
  // La boucle se répète 2 ou 3 fois
for (int i = 0; i < playerNumbers; i++)
{
        Player* player;
        if (i == 0)
        {
                player = &j1;
        }
        else if (i == 1)
        {
                player = &j2;
        }
        player = &j3;

        char tempo[50];
        printf("Enter your name : ");
        fgets(tempo, BUFFER_SIZE, stdin);
        i = 0;
        while (tempo[i] != '\n') {
                i++;
        }
        player->name = malloc(i * sizeof(char));
        strncpy_s(player->name, i, tempo, i);
        player->bank = 0;
        player->score = 0;
        player->ExtraTurn = 0;
        player->win = 0;
}

Problem: Error on my scanf_s line (see the comment), and finally I have a window that opens and basically tells me that in a file "input.h" at line 1567 Expression : result_pointer != nullptr

I never had to deal with these errors, and wondered if there was a need for a double pointer?

scanf_s("%d", playerNumbers); -> scanf_s("%d", &playerNumbers); — UnholySheep
– UnholySheep, Commented Apr 23, 2020 at 13:02
You have char tempo[50]; and fgets(tempo, BUFFER_SIZE, stdin);, so hopefully your BUFFER_SIZE is no more than 50. Also, tempo might not contain a newline, although it should contain a null terminator (assuming fgets returned something other than NULL). — Ian Abbott
– Ian Abbott, Commented Apr 23, 2020 at 13:13

abelenky · Accepted Answer · 2020-04-23 14:02:26Z

1

As UnholySheep pointed out, when trying to scanf an integer, you need to use the & (address-of) operator.

Your loop to test the input is wrong:

while (playerNumbers != 2 || playerNumbers != 3)

One of those two conditions is ALWAYS true, so the loop never terminates.
It should be:

while (playerNumbers != 2 && playerNumbers != 3)

Also, you really made that loop longer and more complicated than necessary. Here is a shorter, better version.

Player player[playerNumbers];
for (int i = 0; i < playerNumbers; i++)
{
    char tempo[50];
    printf("Enter your name : ");
    fgets(tempo, BUFFER_SIZE, stdin);
    player[i] = (Player){ .bank = 0, .score = 0, .ExtraTurn = 0, .win = 0, .name = _strdup(tempo) };
}

edited Apr 23, 2020 at 14:02

answered Apr 23, 2020 at 13:23

abelenky

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1 Comment

Maxence Quinet Over a year ago

Waw, I didn't know this way to initialize a structure! Thank you ! On the other hand, on Player player [playerNumbers], I am asked for a fixed variable, actually in my code it can be equal to 2 or 3. Should I replace it with 3 simply since it is the maximum number of player ?

Adrian Mole · Accepted Answer · 2020-04-23 13:27:18Z

0

As pointed out in the comments, the argument to the scanf_s function corresponding to a %d format field should be the address of an integer variable (in your case, playerNumbers), rather than the variable itself, so you should add a & before the variable's name in the argument list.

Also, your test condition for the 'input' loop, while (playerNumbers != 2 || playerNumbers != 3) is wrong, as the condition will always evaluate to 'true': playerNumbers cannot be both 2 and 3 at the same time, so at least one of the != tests will be true! To fix this, change the || (or) operator to && (and), so that the loop exits if either test is 'false':

while (playerNumbers != 2 && playerNumbers != 3) // Keep asking if it's not 2 AND not 3
{
    printf("How many players are you ? 2 or 3 ? : \n");
    scanf_s("%d", &playerNumbers); // Not the added "&" - to get the ADDRESS of playerNumbers
}

Further, again as pointed out in the comments, you almost certainly want to enclose the player = &j3; line in an else block:

    if (i == 0) {
        player = &j1;
    }
    else if (i == 1) {
        player = &j2;
    }
    else {
        player = &j3;
    }

otherwise, the previous assignments to player will always be overridden!

edited Apr 23, 2020 at 13:27

answered Apr 23, 2020 at 13:21

Adrian Mole

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1 Comment

Maxence Quinet Over a year ago

I changed that! Thank you very much, it is very logical now and it is mostly stupid errors ^^, unfortunately my program still does not work (see answers above)

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