Displaying structs - c

Question

This program is meant to display a video game inventory based off of the user's input. The user needs to determine how long the loop runs with num_of_games. We have to use a switch loop to determine the genre. It compiles but it does not display correctly.
#include <stdio.h>
#include <string.h>
#define MAX 16
typedef enum genre_type{ action = 0, rpg = 1, simulation = 2,
strategy = 3, sports = 4} genre_t;
typedef struct{
char title[MAX];
int num_sold;
genre_t genre;
}game_s;
// suppose to use functions and enum list for determining the genre
void get_game_info(game_s *ptr);
void display_inventory(game_s game[], int num_of_games);
int
main(void){
int i=0, num_of_games;
int c_game=0;
game_s game[num_of_games];
printf("How many games are there in inventory? ");
scanf("%d", &num_of_games);
fflush(stdin);
printf("\n");
while(c_game < num_of_games){
printf("\n");
get_game_info(&game[c_game]);
c_game++;
}
printf("\n");
display_inventory(game, num_of_games);
return(0);
}
void get_game_info(game_s *ptr)
{
int i, str_len, genre, num_sold;
printf("Title of game <maximum of 15 characters>: ");
gets(ptr->title);
str_len = strlen(ptr->title);
if(str_len >= 15){
printf("Title will be truncated\n");
ptr->title[MAX]= '\0';
}
printf("Number sold: ");
scanf("%d", &ptr->num_sold);
fflush(stdin);
printf("Genre (0-action, 1-rpg, 2-simulation, 3-strategy, 4-sports): ");
scanf("%d", &ptr->genre);
fflush(stdin);
if(ptr->genre>4){
printf("Not a valid genre");
fflush(stdin);
}
}
void display_inventory(game_s game[], int num_of_games)
{
int i, genre;
printf("Title\t\t\t\t\t\tQuantity Sold\t\t\t\t\t\tGenre");
printf("\n=====\t\t\t\t\t\t=============\t\t\t\t\t\t=====\n");
for(i=0; i < num_of_games; i++){
switch(genre){
case action: printf("Action"); break;
case rpg: printf("RPG"); break;
case simulation: printf("Simulation"); break;
case strategy: printf("Strategy"); break;
case sports: printf("Sports"); break;
default: puts("Not a choice. Try again"); break;
I think this is the thing that is causing most of the problem. I don't know if I am calling the struct right with the game[I].title and others.
the problem is with the struct calls I think. If I use game_s[I].title I get "expected expression before" error and if I use game[I].title it doesn't print properly
printf("%s\t\t\t\t\t\t%d\t\t\t\t\t\t%s", game[i].title, game[i].num_sold, game[i].genre);
printf("\n");
}
}
}

Answer 1

I think the problem is game_s game[num_of_games]; because num_of_games isn't initiate.
It should be:
printf("How many games are there in inventory? ");
scanf("%d", &num_of_games);
game_s * game_s game = (game_s *) malloc(num_of_games * sizeof(game_s));

Answer 2

Your effort is commendable. You provide code and a good-faith attempt to understand why things don't work, but unfortunately, your code was riddled with errors. Not the least of which was your almost immediate invocation of Undefined Behavior by attempting to declare a VLA with an uninitialized num_of_games. No matter what you did in your code from that point forward, it was nothing but a dice-roll whether you actually processed something or SegFaulted.
Your lack of output in display_inventory (regardless what was actually in memory) is due the placement of your printf statements within the body of the switch statement. When you break from a switch you don't just jump below the default case, you jump out of the switch completely. So even if the rest of your code was correct, you would never produce output.
fflush(stdin) is wrong and invokes undefined behavior on all but windoze. It is only defined for seekable streams for the rest of the world -- don't use it. Instead, you can define a simple function to empty stdin and call it as required instead.
When you compile, always compile with compiler warnings enabled, and do not accept code until it compiles cleanly without warning. To enable warnings add -Wall -Wextra to your gcc compile string. (add -pedantic for several additional warnings). For VS (cl.exe on windoze), add /Wall. For clang, add -Weverything. Read and understand each warning. They will identify any problems, and the exact line on which they occur. You can learn as much about coding by simply listening to what your compiler is telling you as you can from most tutorials.
The number of errors in your code are too voluminous to itemize and speak to every point, so I have included comments inline below addressing the errors.
#include <stdio.h>
#include <stdlib.h> /* for EXIT_FAILURE */
#include <string.h>
#define MAX 16
typedef enum genre_type {
action = 0,
rpg = 1,
simulation = 2,
strategy = 3,
sports = 4
} genre_t;
typedef struct {
char title[MAX];
int num_sold;
genre_t genre;
} game_s;
// suppose to use functions and enum list for determining the genre
void get_game_info (game_s *ptr);
void display_inventory (game_s *game, int num_of_games);
void fflush_stdin();
int main (void) {
int num_of_games,
c_game = 0,
scnfrtn; /* scanf return - must always check EOF */
printf ("How many games are there in inventory? ");
for (;;) { /* loop until valid input or EOF (user cancels) */
if ((scnfrtn = scanf ("%d", &num_of_games)) == 1) {
fflush_stdin(); /* manually empty stdin */
break;
}
else if (scnfrtn == EOF) { /* user cancels? */
fprintf (stderr, "user canceled input.\n");
exit (EXIT_FAILURE);
}
/* handle error */
fprintf (stderr, "error: invalid input.\n");
fflush_stdin();
}
putchar ('\n'); /* don't printf a single-char */
/* declare VLA only AFTER num_of_games has a value */
game_s game[num_of_games];
memset (game, 0, sizeof game); /* optional, zero VLA */
while (c_game < num_of_games) {
putchar ('\n');
get_game_info (&game[c_game]);
c_game++;
}
putchar ('\n');
display_inventory (game, num_of_games);
return 0;
}
void get_game_info (game_s *ptr)
{
int scnfrtn; /* scanf return - must always check EOF */
size_t len = 0; /* strlen return is size_t */
printf ("Title of game <maximum of 15 characters>: ");
fgets (ptr->title, MAX, stdin); /* NEVER, NEVER, NEVER use gets */
len = strlen (ptr->title);
if (len && ptr->title[len-1] == '\n') /* check for trailing \n */
ptr->title[--len] = '\0'; /* overwrite with nul-character */
else /* warn of truncation */
fprintf (stderr, "error: title too long, truncated.\n");
for (;;) { /* loop until valid input or EOF (user cancels) */
printf ("Number sold: ");
if ((scnfrtn = scanf ("%d", &ptr->num_sold)) == 1) {
fflush_stdin();
break;
}
else if (scnfrtn == EOF) {
fprintf (stderr, "user canceled input.\n");
exit (EXIT_FAILURE);
}
fprintf (stderr, "error: invalid input.\n");
fflush_stdin();
}
for (;;) { /* loop until valid input or EOF (user cancels) */
printf ("Genre (0-action, 1-rpg, 2-simulation, "
"3-strategy, 4-sports): ");
if ((scnfrtn = scanf ("%d", (int*)&ptr->genre)) == 1) {
fflush_stdin();
break;
}
else if (scnfrtn == EOF) {
fprintf (stderr, "user canceled input.\n");
exit (EXIT_FAILURE);
}
else if (ptr->genre > 4) /* additional check for genre */
fprintf (stderr, "error: invalid genre.\n");
else
fprintf (stderr, "error: invalid input.\n");
fflush_stdin();
}
}
void display_inventory (game_s *game, int num_of_games)
{
int i;
printf ("%11s%-24s %-24s %s\n========================="
"==============================================\n",
" ", "Title","Quantity Sold", "Genre");
for (i = 0; i < num_of_games; i++) {
switch (game[i].genre) {
case action:
printf ("%-11s", "Action");
break;
case rpg:
printf ("%-11s", "RPG");
break;
case simulation:
printf ("%-11s", "Simulation");
break;
case strategy:
printf ("%-11s", "Strategy");
break;
case sports:
printf ("%-11s", "Sports");
break;
default:
puts ("Not a choice. Try again");
break;
}
printf ("%-24s %-24u %d\n", game[i].title,
game[i].num_sold, game[i].genre);
}
}
void fflush_stdin()
{
for (int c = getchar(); c != '\n' && c != EOF; c = getchar()) {}
}
(note: use printf minimum field with modifier to control spacing instead of a bunch of tabs smushed together)
Example Use/Output
$ ./bin/gamegenre
How many games are there in inventory? 3
Title of game <maximum of 15 characters>: first title
Number sold: 12
Genre (0-action, 1-rpg, 2-simulation, 3-strategy, 4-sports): 2
Title of game <maximum of 15 characters>: second title
Number sold: 13
Genre (0-action, 1-rpg, 2-simulation, 3-strategy, 4-sports): 1
Title of game <maximum of 15 characters>: third title
Number sold: 14
Genre (0-action, 1-rpg, 2-simulation, 3-strategy, 4-sports): 3
Title Quantity Sold Genre
=======================================================================
Simulation first title 12 2
RPG second title 13 1
Strategy third title 14 3
(note: I didn't know where you intended your genre descriptions to go, so they are simply output at the beginning of each line above)
Look things over and let me know if you have further questions.