Function looping when zero is entered - c

Question

I have a user_get_movement_index function that prompts user to enter a position 0 to 8 as part of a tic-tac-toe game.
This movement index is passed to is_position_empty where it determines if the movement index is invalid or the movement index is already taken, both shows an error message and returns false to trigger a recursion of user_get_movement_index.
Functions loop correctly when the same number is entered twice, and behave as expected when any other number is entered but 0.
The problem is when 0 is entered its causes a loop of the error message of invalid position.
I don't understand how it can be looping from within is_position_empty.
How is it not prompting user for input on each loop?
Why is 0 causing this loop?
Is it because we are comparing 0 < 0 in is_position_empty?
I'm new to C and stack overflow so please forgive my formatting, understanding and terrible code.
//--------------------------------------------------
// 05. FUNCTION my_getchar (IMPLEMENTED)
//--------------------------------------------------
char my_get_char() {
//1. We create the variable to be returned
char res = ' ';
//2. We create an extra variable to consume any other characters entered until a return is pressed
boolean line_consumed = False;
char dummy_char = ' ';
//3. We consume the first char entered, i.e., the one we are interested at
res = getchar();
//4. While still there are remaining characters
while (line_consumed == False) {
//4.1. We consume the next character
dummy_char = getchar();
//4.2. If the new character is the end of line one, we can ensure we have consumed the entire line.
if (dummy_char == '\n')
line_consumed = True;
}
//5. We return res
return res;
}
//------------------------------------
// 06. FUNCTION is_position_empty
//------------------------------------
boolean is_position_empty(game* g, int pos) {
//1. We create the variable to be returned
boolean res = False;
//2. We check if the index is a valid one and if the board is empty at that index.
//If it is valid and free, we return True.
//Otherwise, we return False and write a warning message.
int row= pos/3;
int column = pos%3;
if (pos<0 || pos>8){
printf("\t Invalid Position. Try again!\n\n");
return res;
}
else if (g->board[row][column]=='X' || g->board[row][column]=='O'){
printf("\t This postion is already busy. Try Again!\n\n");
return res;
}
else{
res=True;
return res;
}
}
//---------------------------------------
// 07. FUNCTION user_get_movement_index
//---------------------------------------
int user_get_movement_index(game* g) {
//2. We create a boolean variable to control that we have received a valid movement index.
boolean validMove=False;
//3. We create a char variable to control the index we are receiving by keyboard.
char indexChar;
int indexInt;
//We print a message asking for a new movement.
printf(" Enter a position 0 to 8: ");
//We call to my_get_char to get the index and we convert it to an integer.
indexChar=my_get_char();
indexInt=indexChar-'0';
//We call to is_position_empty to check that the index is a valid one.
validMove=is_position_empty(g, indexInt);
if (validMove==True)
return indexInt;
else
return user_get_movement_index(g);
}
Working Correctly
Working Correctly
Looping
I have boolean defined as the following:
enum Bool { False, True };
typedef enum Bool boolean;
When I initialise all elements of the matrix as 'a', the problem still persists.
When a valid movement is entered, process_movement function is called and it initialises the corresponding element of board to either an 'X' or 'O'.
char mark;
if (g->status==1)
mark='X';
else
mark='O';
int row = pos/3;
int column = pos%3;
g->board[row][column]=mark;
By adding an extra printf within is_position empty, I can tell that the whole function is looping, but it seems to not be exiting is_position_empty as the printf from the function it returns to user_get_movement is not being printed. How is this possible? There is only a loop in user_get_movement and none in is_position_empty, and only loops for 0?

Answer 1

the following proposed code:
is missing the main() function
is missing the function to determine if there was a winner and whom won
is missing the definition of game
does not have any unexpected looping
avoids the problem caused by having a 'recursive' function
and now the proposed code:
#include <stdio.h> // getchar()
#include <stdbool.h> // bool, true, false
#include <ctype.h> // isdigit()
// prototypes
int my_get_char( void );
bool is_position_empty(game* g, int pos);
int user_get_movement_index(game* g);
//--------------------------------------------------
// 05. FUNCTION my_getchar (IMPLEMENTED)
//--------------------------------------------------
int my_get_char()
{
//1. We create the variable to be returned
//3. We consume the first char entered, i.e., the one we are interested at
int res = getchar();
//4. While still there are remaining characters
while ( '\n' != getchar() );
//5. We return res
return res;
}
//------------------------------------
// 06. FUNCTION is_position_empty
//------------------------------------
bool is_position_empty(game* g, int pos)
{
//2. We check if the index is a valid one and if the board is empty at that index.
//If it is valid and free, we return True.
//Otherwise, we return False and write a warning message.
int row= pos/3; = 0
int column = pos%3; = 0
if (pos<0 || pos>8)
{
printf("\t Invalid Position. Try again!\n\n");
return false;
}
else if (g->board[row][column]=='X' || g->board[row][column]=='O')
{
printf("\t This postion is already busy. Try Again!\n\n");
return false;
}
return true;
}
//---------------------------------------
// 07. FUNCTION user_get_movement_index
//---------------------------------------
int user_get_movement_index(game* g)
{
//3. We create a char variable to control the index we are receiving by keyboard.
int indexInt;
do
{
//We print a message asking for a new movement.
printf(" Enter a position 0 to 8: ");
//We call to my_get_char to get the index and we convert it to an integer.
indexInt = my_get_char();
if( isdigit( indexInt ) )
{
indexInt -= '0';
}
else
{
printf( "entry was not in the inclusive range: 0...8\n" );
continue;
}
//We call to is_position_empty to check that the index is a valid one.
} while( !is_position_empty(g, indexInt) );
return indexInt;
}