Add value of playing cards - with pointers and structures - c

Question

I'm going through some c programming questions and I'm currently stuck on a pointer related question
Q: Write a function that takes the values of a two-card blackjack HAND as input, and returns the point total of the hand. The value
of the cards '2' through '9' is equal to their face value, the cards 'T', 'K', 'Q', 'J' are worth 10 points and the ace ('A') is worth 11 points
unless it comes with another ace, then that second ace is worth 1 point. The program should be able to catch incorrect input.
Examples:
Enter cards: A Q
The score is 21
Enter cards: A A
The score is 12
I've tackled this question before, but this time I'd have to use pointers which I'm still fairly new towards. Getting card values and calculating cards must be done in one function. Here's what i have so far:
#include <stdio.h>
#define HAND 2
struct player_hand
{
char card1;
char card2;
};
void getHandValue(struct player_hand * hnd_ptr, char size, char size2)
{
int first_card;
int second_card;
//get cards from user
scanf("%c %c",&hnd_ptr->card1, &hnd_ptr->card2);
printf("Enter Cards: %c %c", &hnd_ptr->card1, &hnd_ptr->card2);
//check value of first card in hand
if(hnd_ptr->card1<='9' && hnd_ptr->card1>='2')
{
first_card=(int)hnd_ptr->card1 -48;
}
//check for special cards: king, queen, jack, ten
else if(hnd_ptr->card1=='T'||hnd_ptr->card1=='K'||hnd_ptr->card1=='Q'||hnd_ptr->card1=='J')
{
first_card=10;
}
//if first card is Ace
else if(hnd_ptr->card1=='A')
{
first_card=11;
}
else
{
//card not valid
printf("Not a valid card: %c",hnd_ptr->card1);
return;
}
//check value of 2nd card
if(hnd_ptr->card2<='9' && hnd_ptr->card2>='2')
{
second_card=(int)hnd_ptr->card2 -48;
}
//if 2nd card is a special kind
else if(hnd_ptr->card2=='T'||hnd_ptr->card2=='K'||hnd_ptr->card2=='Q'||hnd_ptr->card2=='J')
{
second_card=10;
}
//if 2nd card is Ace
else if(hnd_ptr->card2=='A')
{
if(hnd_ptr->card1=='A')
second_card=1;
else
second_card=11;
}
else
{
//if 2nd card not valid
printf("Not a valid card: %c",hnd_ptr->card2);
return;
}
add cards
printf("\nThe total card value is: %d",first_card+second_card);
}
//call function, test if works
//calling it wrong?
int main(void)
{
struct player_hand hnd [HAND] = { {'A', 'A'}};
getHandValue (hnd, HAND);
return;
}

Answer 1

You have a few bugs.
Incorrect call in main.
The function doesn't need size arguments and if it did they should be int.
Bad return from main.
In the function, the printf is wrong.
Things are much more complicated than they need to be because the struct uses two scalars instead of an array.
I've created two versions of your program. One with bugs annotated. And another that cleans things up.
Here's the annotated version:
#include <stdio.h>
#define HAND 2
struct player_hand {
char card1;
char card2;
};
// NOTE/BUG: use 'int' for size and size2
void
getHandValue(struct player_hand *hnd_ptr, char size, char size2)
{
int first_card;
int second_card;
// get cards from user
scanf("%c %c", &hnd_ptr->card1, &hnd_ptr->card2);
// NOTE/BUG: this would print the _address_ of the values vs. the values
printf("Enter Cards: %c %c", &hnd_ptr->card1, &hnd_ptr->card2);
// NOTE/BUG [sort of]: the code below is cut-n-paste replication because you
// have separate card1 and card2 in the struct -- this "cries out" for an
// array and a loop. Consider the general case where you have 5 cards in the
// hand (e.g. five card charlie). The code would be easier even with an array
// of only two
// check value of first card in hand
if (hnd_ptr->card1 <= '9' && hnd_ptr->card1 >= '2') {
first_card = (int) hnd_ptr->card1 - 48;
}
// check for special cards: king, queen, jack, ten
else if (hnd_ptr->card1 == 'T' || hnd_ptr->card1 == 'K' || hnd_ptr->card1 == 'Q' || hnd_ptr->card1 == 'J') {
first_card = 10;
}
// if first card is Ace
else if (hnd_ptr->card1 == 'A') {
first_card = 11;
}
else {
// card not valid
printf("Not a valid card: %c", hnd_ptr->card1);
return;
}
// check value of 2nd card
if (hnd_ptr->card2 <= '9' && hnd_ptr->card2 >= '2') {
second_card = (int) hnd_ptr->card2 - 48;
}
// if 2nd card is a special kind
else if (hnd_ptr->card2 == 'T' || hnd_ptr->card2 == 'K' || hnd_ptr->card2 == 'Q' || hnd_ptr->card2 == 'J') {
second_card = 10;
}
// if 2nd card is Ace
else if (hnd_ptr->card2 == 'A') {
if (hnd_ptr->card1 == 'A')
second_card = 1;
else
second_card = 11;
}
else {
// if 2nd card not valid
printf("Not a valid card: %c", hnd_ptr->card2);
return;
}
printf("\nThe total card value is: %d", first_card + second_card);
}
//call function, test if works
//calling it wrong?
int
main(void)
{
// NOTE: based on usage, this is only an array because you're not using &hnd
// below
struct player_hand hnd[HAND] = {
{'A', 'A'}
};
// NOTE/BUG: too few arguments to function, but why pass count at all?
getHandValue(hnd, HAND);
// NOTE/BUG: need to return value (e.g. return 0)
return;
}
Here's the cleaned up version:
#include <stdio.h>
#define CARDS_PER_HAND 2
struct player_hand {
char card[CARDS_PER_HAND];
};
void
getHandValue(struct player_hand *hnd_ptr)
{
int idx;
int card;
int sum;
int count[CARDS_PER_HAND];
// get cards from user
printf("Enter Cards:");
fflush(stdout);
for (idx = 0; idx < CARDS_PER_HAND; ++idx)
scanf(" %c", &hnd_ptr->card[idx]);
// print cards
printf("Cards entered:");
for (idx = 0; idx < CARDS_PER_HAND; ++idx)
printf(" %c", hnd_ptr->card[idx]);
printf("\n");
for (idx = 0; idx < CARDS_PER_HAND; ++idx) {
card = hnd_ptr->card[idx];
// simple cards
if (card <= '9' && card >= '2') {
count[idx] = (card - '2') + 2;
continue;
}
switch (card) {
case 'A':
count[idx] = 11;
if ((idx == 1) && (count[0] == 11))
count[idx] = 1;
break;
case 'T':
case 'K':
case 'Q':
case 'J':
count[idx] = 10;
break;
default:
printf("Not a valid card: %c", card);
return;
break;
}
}
sum = 0;
for (idx = 0; idx < CARDS_PER_HAND; ++idx)
sum += count[idx];
printf("The total card value is: %d\n", sum);
}
int
main(void)
{
struct player_hand hnd;
getHandValue(&hnd);
return 0;
}

Answer 2

If, in addition to the other answers, your intent was to pass a 2-hand array, you would need to handle both hands within a loop in your scoring function. For example:
#include <stdio.h>
#define HAND 2
struct player_hand
{
char card1;
char card2;
};
void getHandValue (struct player_hand *hnd_ptr, int size)
{
int first_card;
int second_card;
/* get cards from user */
for (int i = 0; i < size; i++) {
printf ("\nenter cards for hand %d (card1 card2): ", i);
/* you must handle the '\n' that remains after last char */
if (scanf ("%c %c%*c", &hnd_ptr[i].card1, &hnd_ptr[i].card2) != 2) {
fprintf (stderr, "error: invalid entry.\n");
return;
}
printf ("you entered: %c %c\n", hnd_ptr[i].card1, hnd_ptr[i].card2);
}
for (int i = 0; i < size; i++)
{
/* check value of first card in hand */
if(hnd_ptr[i].card1 <= '9' && hnd_ptr[i].card1 >= '2')
{
first_card = (int)hnd_ptr[i].card1 - '0';
}
/* check for special cards: king, queen, jack, ten */
else if (hnd_ptr[i].card1 == 'T' || hnd_ptr[i].card1 == 'K' ||
hnd_ptr[i].card1 == 'Q' || hnd_ptr[i].card1 == 'J')
{
first_card = 10;
}
/* if first card is Ace */
else if (hnd_ptr[i].card1 == 'A')
{
first_card = 11;
}
else
{
/* card not valid */
printf("Not a valid card: %c",hnd_ptr[i].card1);
return;
}
/* check value of 2nd card */
if(hnd_ptr[i].card2 <= '9' && hnd_ptr[i].card2 >= '2')
{
second_card=(int)hnd_ptr[i].card2 - '0';
}
/* if 2nd card is a special kind */
else if (hnd_ptr[i].card2 == 'T' || hnd_ptr[i].card2 == 'K' ||
hnd_ptr[i].card2 == 'Q' || hnd_ptr[i].card2 == 'J')
{
second_card = 10;
}
/* if 2nd card is Ace */
else if (hnd_ptr[i].card2 == 'A')
{
if (hnd_ptr[i].card1 == 'A')
second_card = 1;
else
second_card = 11;
}
else
{
/* if 2nd card not valid */
printf ("Not a valid card: %c", hnd_ptr[i].card2);
return;
}
/* add cards */
printf ("\nThe total cards value (hand %d) is: %d\n",
i, first_card + second_card);
}
}
int main(void)
{
struct player_hand hnd[HAND] = { {'A', 'A'}, {'A', 'A'} };
getHandValue (hnd, HAND);
return 0;
}
Example Use/Output
$ ./bin/cards
enter cards for hand 0 (card1 card2): A A
you entered: A A
enter cards for hand 1 (card1 card2): 8 K
you entered: 8 K
The total cards value (hand 0) is: 12
The total cards value (hand 1) is: 18
If your intent was not to pass an array of struct, then obviously looping would not be necessary. Note: two loops were used. The first to get the cards for both hands, the second to compute the scores for both. (you could do it with one, but it looked as if you intended to have all cards entered before scoring) Look things over and let me know if you have further questions.

Answer 3

You're not passing the address of hnd to the function getHandValue(). To do this you have to pass the address using the & operator getHandValue(&hnd).
You're also not initializing struct player_hand hnd correctly. There's one set of {} too many.

Answer 4

Here's an edited version of your main() code that works, just some minor edits to how your pointer is set up.
// main
int main(void)
{
// minor edits to fix the code here
struct player_hand hnd = {'A', 'A'};
struct player_hand *hndPtr = &hnd;
getHandValue (hndPtr);
return 0;
}