C: Simple program compiles fine but crashes at a certain point

Question

All the values seem to be where they should be when I use or display them, but for some reason every time I get to a certain point (flagged in code), the program crashes.

The program is supposed to be adding a struct to an array. This struct contains another struct along with an int denoting quantity. These are also being stored in an array.

Included are the main.c and functions surrounding the crash.

int main()
{
    int choice;
    int item_num;
    int item_amount;

    printf("*****MEAL PLANNER*****");

    while(choice != 0)
    {
        prepopulate();

        printf("\n\nTo view items, enter 1. \nTo view current menu, enter 2. \nTo add an item to the menu, enter 3. \nEnter 0 to exit.\n\n");
        scanf("%d", &choice);

        if(choice > 0 && choice < 5)
        {
            switch(choice)
            {
            case 1 : printf("\nView Items\n\n");

                displayAllFoodStuff();

                break;

            case 2 :printf("\nView Current Menu\n\n");
                display_meal();
                break;

            case 3 :printf("\nAdd Item to Menu\n\n");
                printf("Enter item number.\n");
                scanf("%d", &item_num);
                printf("Enter item amount.\n");
                scanf("%d", &item_amount);
                if(item_num <= fs_count)
                {
                    printf("Enter 1 to confirm.\n");
                    scanf("%d", choice);
                    fflush(stdin);
                    ////////CRASHING HERE!!!////////

                    if(choice == 1)
                    {
                        choose_food_item(food_list[item_num], item_amount);
                    }
                    break;

                }
                else
                {
                    printf("\nThat is not a valid entry.\n");
                }
                break;



            default: choice = 0;
                break;
            }
        }

    }

    return 0;
}

FUNCTIONS

//Define 'add_food_plan_item' function.
void add_food_plan_item(food_plan_item  fs)
{
    meal[item_count] = fs;
    item_count++;
}

//Define 'choose_food_item' function.
void choose_food_item(food_stuff fs, int qty)
{
    food_plan_item fpi;
    fpi.fs = fs;
    fpi.qty = qty;
    add_food_plan_item(fpi);
}

Thanks in advance for any and all help.

Could you recommend a good free one? (That's allowed in the comments, right?) — Aezur, Dec 13 '13 at 07:28

score 3 · Answer 1 · answered Dec 13 '13 at 07:18

3

scanf() takes pointers to the variables it reads the input into.

You do this by taking the address of choice, using an &:

scanf("%d", &choice);

answered Dec 13 '13 at 07:18

Phillip Kinkade

1,382
12
18

score 3 · Accepted Answer · answered Dec 13 '13 at 07:19

3

You pass choice to scanf but you meant to pass &choice. Your code should read:

scanf("%d", &choice);

What happens is scanf needs an address for it to write the value to. You pass a value rather than the value's address and so scanf treats that value as an address. So, suppose that choice is a variable with the value 0. Passing the value of choice rather than its address leads to scanf attempting to write to the address 0. And that typically leads to segmentation fault.

answered Dec 13 '13 at 07:19

David Heffernan

601,492
42
1,072
1,490

I knew it was going to be embarrassingly simple. Thank you. I'll accept the answer when it lets me. – Aezur Dec 13 '13 at 07:23
Answer with reason of failure ... I m lovin it :) – Dayal rai Dec 13 '13 at 07:24
Wow! Thank you for explaining that. I love this place! – Aezur Dec 13 '13 at 07:29

score 0 · Answer 3 · 2013-12-13T07:25:25.860

0

fflush(stdin); is undefined behavior, that might be the cause for crash!!!

Also as others pointed out, you have missed & (address of operator) in scanf

Also, don't use fflush(stdin), instead if you want to clear the stdin you can do something like below...

int c;
while ((c = getchar()) != '\n' && c != EOF);

edited Dec 13 '13 at 07:25

answered Dec 13 '13 at 07:18

1

It's undefined in the C specification, but defined in e.g. Linux using glibc as well as Windows. – Some programmer dude Dec 13 '13 at 07:19
@JoachimPileborg: That's a new learning I got. Was not knowing this... As per this post, http://stackoverflow.com/a/11604639/1814023 Thanks – Dec 13 '13 at 07:24

C: Simple program compiles fine but crashes at a certain point

3 Answers3