Thread: Increment a pointer variable

I am calling a function that contains an int pointer as an argument :

function (int *p)

How can I increase the pointer value by 1?

*p++ is not working;

Thank you.

It doesn't seem to work.
Here's the complete code list :

Code:

//Classifies a poker hand

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

#define NUM_RANKS 13
#define NUM_SUITS 4
#define NUM_CARDS 5

//external variables



//prototypes
void read_cards(int a[], int b[]);
void analyze_hand(int a[], int b[], bool *straight, bool *flush, bool *four, bool *three, int *pairs);
void print_result(bool *straight, bool *flush, bool *four, bool *three, int *pairs);


/***********************************************************
 * main: Calls read_cards, analyze_hand, and print_result  *
 *		 repeatedly.									   *
 ***********************************************************/
int main (int argc, const char * argv[]) {
    
	int num_in_rank[NUM_RANKS];
	int num_in_suit[NUM_SUITS];
	
	bool straight, flush, four, three;
	int pairs;	//can be 0, 1, or2
	
	
	for (;;)
	{
		read_cards(num_in_rank, num_in_suit);
		analyze_hand(num_in_rank, num_in_suit, &straight, &flush, &four, &three, &pairs);
		print_result(&straight, &flush, &four, &three, &pairs);
	}
}//end main


/***********************************************************
 * read_cards: Reads the cards into the external		   *
 *			   variables num_in_rank and num_in_suit;	   *
 *			   checks for bad cards and duplicate cards.   *
 ***********************************************************/
void read_cards(int num_in_rank[], int num_in_suit[])
{
	bool card_exists[NUM_RANKS][NUM_SUITS];
	char ch, rank_ch, suit_ch;
	int rank, suit;
	bool bad_card;
	int cards_read = 0;
	
	for (rank = 0; rank < NUM_RANKS; rank++) {
		num_in_rank[rank] = 0;
		for (suit = 0; suit < NUM_SUITS; suit++) {
			card_exists[rank][suit] = false;
		}//end inner for
	}//end outer for
	
	for (suit = 0; suit < NUM_SUITS; suit++)
		num_in_suit[suit] = 0;
	
	while (cards_read < NUM_CARDS) {
		bad_card = false;
		
		printf("Enter a card: ");
		
		rank_ch = getchar();
		switch (rank_ch) {
			case '0':	exit(EXIT_SUCCESS);
			case '2':	rank = 0;	break;
			case '3':	rank = 1;	break;
			case '4':	rank = 2;	break;
			case '5':	rank = 3;	break;
			case '6':	rank = 4;	break;
			case '7':	rank = 5;	break;
			case '8':	rank = 6;	break;
			case '9':	rank = 7;	break;
			case 't': case 'T':	rank = 8;	break;
			case 'j': case 'J':	rank = 9;	break;
			case 'q': case 'Q': rank = 10;	break;
			case 'k': case 'K': rank = 11;	break;
			case 'a': case 'A': rank = 12;	break;
			default:
				bad_card = true;
		}//end switch
		
		suit_ch = getchar();
		switch (suit_ch) {
			case 'c': case 'C':		suit = 0; break;
			case 'd': case 'D':		suit = 1; break;
			case 'h': case 'H':		suit = 2; break;
			case 's': case 'S':		suit = 3; break;
			default:
				bad_card = true;
		}//end switch
		
		while ( (ch = getchar()) != '\n')
			if (ch != ' ') bad_card = true;
		
		
		if (bad_card)
			printf("Bad card; ignored.\n");
		else if (card_exists[rank][suit])
			printf("Duplicate card; ignored.\n");
		else {
			num_in_rank[rank]++;
			num_in_suit[suit]++;
			card_exists[rank][suit] = true;
			cards_read++;
		}

	}//outer while that counts if we have reached 5 cards
	
}//end read_cards


/******************************************************************
 * analyze_hand: Determines whether the hand contains a straight, *
 *				 a flush, four-of-a-kind, and/or three-of-a-kind; *
 *				 determines the number of pairs; stores the       *
 *				 results into the external variables straight,    *
 *				 flush, four, three, and pairs.					  *
 ******************************************************************/
void analyze_hand(int num_in_rank[], int num_in_suit[], bool *straight, bool *flush, bool *four, bool *three, int *pairs)
{
	int num_consec = 0;
	int rank, suit;
	
	*straight = false;
	*flush = false;
	*four = false;
	*three = false;
	*pairs = 0;
	
	//check for flush
	for (suit = 0; suit < NUM_SUITS; suit++)
	{
		if (num_in_suit[suit] == NUM_CARDS)
			*flush = true;
	}
	
	//check for straight
	rank = 0;
	while (num_in_rank[rank] == 0) rank++;
	for (; rank < NUM_RANKS && num_in_rank[rank] > 0; rank++)
		num_consec++;
	if (num_consec == NUM_CARDS)
	{
		*straight = true;
		return;
	}
	
	//check for 4-of-a-kind, 3-of-a-kind, and pairs
	for (rank = 0; rank < NUM_RANKS; rank++) {
		if (num_in_rank[rank] == 4) *four = true;
		if (num_in_rank[rank] == 3) *three = true;
		if (num_in_rank[rank] == 2) *pairs++;
	}
}//end analyze_hand



/**********************************************************
 * print_result: Prints the classification of the hand,   *
 *				 based on the values of the external      *
 *				 variables straight, flush, four, three,  *
 *				 and pairs.								  *
 **********************************************************/
void print_result(bool *straight, bool *flush, bool *four, bool *three, int *pairs)
{
	if (*straight && *flush) printf("Straight flush");
	else if (*four)		   printf("Four of a kind");
	else if (*three && *pairs == 1)	printf("Full house");
	else if (*flush)		   printf("Flush");
	else if (*straight)	   printf("Straight");
	else if (*three)		   printf("Three of a kind");
	else if (*pairs == 2)   printf("Two pairs");
	else if (*pairs == 1)   printf("Pair");
	else
		printf("High card");
	
	printf("\n\n");
}//end print_result

If you run it and enter the following cards it should result a 'Pair' :
8c, as, 7c, ad, 3h

I assume the line in question is

Code:

        if (num_in_rank[rank] == 2) *pairs++;

In C, ++ has a higher precedence than the dereference (*) operation, so the ++ happens first. That statement basically says "increment the pointer, then dereference it". That means you make pairs point to some other place in memory (I think it's incremented by sizeof(int)), then you take the value at that new address and don't do anything with it. As a matter of fact, if you turn the warnings all the way up on your compiler you would get an error message like this:
main.c: In function ‘analyze_hand’:
main.c:159: warning: value computed is not used

That tells you that the statement doesn't really have an effect. It's like saying

Code:

if (x == 10) {
    array[3];
}

which is grammatically correct, and will compile, but does nothing.

As laserlight suggested, you want to increment the value that pairs points to, so use (*pairs)++.

Hope that wasn't too long winded.

(*pairs)++ worked!
Thanks a lot guys for your time and your clear explanations!