Help.  This is my first semester programming in anything but dBase III+ (no
snickering, I know it's not really programming).I'm trying to write a
tic-tac-toe program and I'm confused by passing-by-reference.  I want the
user to input a char 1-9 that corresponds to a space on the ttt grid.  Do I
need to pass the string grid_input to the function?  Or should I pass a
pointer?  When passing by reference, does the function need a return type,
or does void function() work?  I have included some code below.  The error I
receive when compiling is "warning: improper pointer/integer combination:
arg #1.

Thanks
Cindy Katz

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

void print_grid(char *ptr);       /* prints tic-tac-toe board */
int game_won(char gi[]);          /* check to see if game is won */
void player_1(char *ptr);         /* player 1 move */
void player_2(char *ptr);         /* player 2 move */

void main(int argc, char *argv[])
{
   int num_games;                 /* number of games user wants to play */
   int won1=0, won2=0;            /* number of games each player has won */
   int i;                         /* loop counter */
   char grid_input[10];
   char *ptr;

more code here, then void player_1() is where the compile errors begin

  for (i=1; i<=num_games; i++)
   {
      grid_input[0] = '1';
      grid_input[1] = '2';
      grid_input[2] = '3';
      grid_input[3] = '4';
      grid_input[4] = '5';
      grid_input[5] = '6';
      grid_input[6] = '7';
      grid_input[7] = '8';
      grid_input[8] = '9';
      grid_input[9] = '\0';

      ptr = grid_input;

      if (i%2 == 1)
      {  player_1(*ptr, grid_input);

more code

void print_grid(char *ptr)
{
   printf(" %c | %c | %c \n",*ptr, *(ptr+1), *(ptr+2));
   printf("---+---+---\n");
   printf(" %c | %c | %c \n",*(ptr+3), *(ptr+4), *(ptr+5));
   printf("---+---+---\n");
   printf(" %c | %c | %c \n",*(ptr+6), *(ptr+7), *(ptr+8));

still more code

void player_1(char *ptr, char gi[])
{
   char go1;            /* player 1's move */

   print_grid(*ptr);
   printf("Player 1, enter your go: ");
   scanf("%c", go1);
   fflush(stdin);

   while ((ptr = strchr(gi,go1))== NULL)
  {   printf("Invalid move.  Please try again.\n");
      print_grid(*ptr);
      printf("Player 1, enter your go: ");
      scanf("%c", go1);
      fflush(stdin);
   }
   *ptr = 'X';

: Help.  This is my first semester programming in anything but dBase III+ (no
: snickering, I know it's not really programming).I'm trying to write a
: tic-tac-toe program and I'm confused by passing-by-reference.  I want the
: user to input a char 1-9 that corresponds to a space on the ttt grid.  Do I
: need to pass the string grid_input to the function?  Or should I pass a
: pointer?  When passing by reference, does the function need a return type,
: or does void function() work?  I have included some code below.  The error I
: receive when compiling is "warning: improper pointer/integer combination:
: arg #1.

: Thanks
: Cindy Katz

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

: void print_grid(char *ptr);       /* prints tic-tac-toe board */
: int game_won(char gi[]);          /* check to see if game is won */
: void player_1(char *ptr);         /* player 1 move */
/* ### this prototype doesn't match the actual function; it should
   be 'void player_1(char *, char *);'
*/
: void player_2(char *ptr);         /* player 2 move */

: void main(int argc, char *argv[])
: {
:    int num_games;                 /* number of games user wants to play */
:    int won1=0, won2=0;            /* number of games each player has won */
:    int i;                         /* loop counter */
:    char grid_input[10];
:    char *ptr;

: more code here, then void player_1() is where the compile errors begin

:   for (i=1; i<=num_games; i++)
:    {
:       grid_input[0] = '1';
:       grid_input[1] = '2';
:       grid_input[2] = '3';
:       grid_input[3] = '4';
:       grid_input[4] = '5';
:       grid_input[5] = '6';
:       grid_input[6] = '7';
:       grid_input[7] = '8';
:       grid_input[8] = '9';
:       grid_input[9] = '\0';
/* ### 'strcpy(grid_input, "123456789");' would be easier */
:       ptr = grid_input;

:       if (i%2 == 1)
:       {  player_1(*ptr, grid_input);
/* ### this call doesn't match the actual function or the prototype;
   it should be 'player_1(ptr, grid_input);'
*/

: more code

: void print_grid(char *ptr)
: {
:    printf(" %c | %c | %c \n",*ptr, *(ptr+1), *(ptr+2));
:    printf("---+---+---\n");
:    printf(" %c | %c | %c \n",*(ptr+3), *(ptr+4), *(ptr+5));
:    printf("---+---+---\n");
:    printf(" %c | %c | %c \n",*(ptr+6), *(ptr+7), *(ptr+8));
: }

: still more code

: void player_1(char *ptr, char gi[])
: {
:    char go1;            /* player 1's move */

:    print_grid(*ptr);
/* ### this call doesn't match the actual function parameters;
   use 'print_grid(ptr);'
*/
:    printf("Player 1, enter your go: ");
/* ### add 'fflush(stdout);' here */
:    scanf("%c", go1);
/* ### scanf takes pointers - use 'scanf(" %c", &go1);' */
:    fflush(stdin);
/* ### do not use fflush(stdin) */
:    while ((ptr = strchr(gi,go1))== NULL)
:   {   printf("Invalid move.  Please try again.\n");
:       print_grid(*ptr);
/* ### see above */
:       printf("Player 1, enter your go: ");
/* ### see above */
:       scanf("%c", go1);
/* ### see above */
:       fflush(stdin);
/* ### see above */
:    }
:    *ptr = 'X';
: }

Will