Thread: Can't update value of variable outside of the function

I am passing the address of the variable 'jog' to the function 'aplica_cordenada', and I update its values inside that function's definition, but it is not being updated outside of it. I am aware of variable scope, but since I'm passing its address (&jog), shouldn't it be updated outside the function as well?

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#define TRUE 1
#define FALSE 0

/* === PROTÓTIPOS DAS FUNÇÕES. === {{{ */
int run_game(int);
void aplica_cordenada(char [], int *);
/* === Protótipos fim. }}} */

int main(void) { /* {{{ */

    /* === VARIABLES === {{{ */
    /* Jogador 1 ou 2. */
    int jog = 1;
    //int *ptr_jog;
    //ptr_jog = &jog;
    /* Mantém o jogo rodando. */
    int run = 1;
    int i = 0, j = 0; /* Iteradores. */
    char casas[10] = {'-', '-', '-', '-', '-', '-', '-', '-', '-'};
    int cord = 0; 
    /* End variables. }}} */

    do { /* {{{ */
        printf("jog %d\n", jog);
        if (jog % 2 != 0) { // {{{ 
            printf("Jogador um...\n\n");
        }
        else {
            printf("Jogador dois.\n\n");
        } // }}}

        for (i = 0; i < 10; i++) { // {{{
            printf(" %c ", casas[i]);
            if (i == 2 || i == 5) {
                printf("\n"); /* Formatar colunas. */
            }
        }
        printf("\n\n"); // }}}

        aplica_cordenada(casas, &jog);

    } while (run_game(run)); /* Fim de do while. }}} */

    return 0;
} /* main() fim. }}} */

/* === DEFINIÇÕES DAS FUNCÕES. {{{ */
int run_game(int T) { // {{{
    return TRUE;
} // }}}

void aplica_cordenada(char casas[], int *ptr_jog) { /* {{{ */
    char opt;
    do {
        printf("Digite uma posição: ");
        opt = getchar();
    } while (!isdigit(opt) || opt == '0');
    opt = atoi(&opt); /* Converter para número. */
    printf("casa %d -- \n", opt);
    if (casas[opt - 1] == '-') {
        casas[opt - 1] = 'x';
        *ptr_jog++;
    }
} /* Funções cordenada() fim. }}} */

int casa_disponivel(int n) { /* {{{ */

    return FALSE;
} /* }}} */

/* Definiçoes fim }}} */


/*
 * vim:foldmethod=marker foldmarker={{{,}}}
 */

Thanks in advance.

This line:

Code:

        *ptr_jog++;

Does not do what you (seem to) think it does. The ++ operator has higher precedence than the * operator (you generally go right as far as you can - i.e. from "ptr_jog" to "ptr_jog++" then left) so the above is equivalent to:

Code:

        *(ptr_jog++);

I.e. the pointer gets incremented, then dereferenced with nothing done with the value. You probably want:

Code:

        (*ptr_jog)++;

Originally Posted by JohnGraham

I.e. the pointer gets incremented, then dereferenced with nothing done with the value. You probably want:

Code:

        (*ptr_jog)++;

All right. It worked. Thanks a lot.