void main() {
    int y = 0;
    char password[30], username[40], total_items[10000], input_item,
        ip11[] = "-IPhone 11\n", ipX[] = "-IPhone X\n";
    char ap[] = "-AirPods\n", chrg[] = "-Charger\n";
    char scrpro[] = "-Screen Protector\n", reset_str[] = " ";
    int i = 0, total_amount = 0, auth = 4;

    while (auth > 10)
        ;
    {
        printf("Enter Username:");
        scanf("%s", &username);
        fflush(stdin);
        printf("Enter password:");
        scanf("%s", &password);
        fflush(stdin);
        if ((strcmp(username, "admin") == 0) &&
            (strcmp(password, "admin123") == 0)) {
            auth  = 7;
        } else {
            printf("Invalid password or username\n");
            printf("%d tries left\n", auth);
            auth -= 1;
        }
    }
    while (y > 5) {
        printf("Welcome,These are the items that we sell:\n");
        printf("-----------------------------------------------\n");
        printf("a. IPhone X - $1200 \nb. IPhone 11 - $1500\n");
        printf(
            "c. AirPods - $300 \nd. Charger - $15 \ne. Screen Protector - "
            "$20\n");
        printf("\n");
        printf("To buy, key in the alphabet beside the item.\n");

        printf("Please input 1 item at a time\n");
        while (i < 10) {
            printf("Enter item wanted(input 'z' to finish cart):");
            scanf(" %c", &input_item);

            if ((input_item == 'a') || (input_item == 'A')) {
                total_amount  = 1200;
                strcat(total_items, ipX);
            } else if ((input_item == 'b') || (input_item == 'B')) {
                total_amount = total_amount   1500;
                strcat(total_items, ip11);
            } else if ((input_item == 'c') || (input_item == 'C')) {
                total_amount = total_amount   300;
                strcat(total_items, ap);
            } else if ((input_item == 'd') || (input_item == 'D')) {
                total_amount = total_amount   15;
                strcat(total_items, chrg);
            } else if ((input_item == 'e') || (input_item == 'E')) {
                total_amount = total_amount   20;
                strcat(total_items, scrpro);
            } else if ((input_item == 'z') || (input_item == 'Z'))
                i  = 10;
            else
                printf("Invalid item, please input again\n");
        }
        printf("Your total is: $%d\n", total_amount);
        printf("Your items are:\n%s\n", total_items);
        printf("Please collect your receipt and head over to the counter\n");
        printf("Thank you for coming to OneTop!\n");
        printf("\n");
        strcpy(total_items, reset_str);
    }
}

I expected the code to proceed to the second while loop but the code instead just crashes.

CodePudding user response：

Incorrect format specifier:

scanf("%s", &username);

username is a constant pointer to the first element of the array. There's no need to use the & operator with it.

Stray semicolon:

The statement:

while (auth > 10)
        ;

is equivalent to saying:

"While auth is greater than 10, do nothing."

It's dead code. The block of code after the while loop will always execute, irregardless of the value of auth.

Even if you were to remove the semi-colon, the program would never enter the loop, as:

auth == 4

And the condition:

if (auth > 10)

is false.

Similarly, the second loop would never be entered, as:

y == 0

And the condition:

if (y > 5)

is false.

Flushing stdin:

fflush(stdin);

is undefined behaviour.

• Once the abstract state machine reaches undefined behaviour, no further assumption about the continuation of the execution of the program can be made.

Aside:

Implementation-defined definition of main:

From C11:

The function called at program startup is named main. The implementation declares no prototype for this function. It shall be defined with a return type of int and with no parameters:

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

or with two parameters (referred to here as argc and argv, though any names may be used, as they are local to the function in which they are declared):

int main(int argc, char *argv[]) { /* ... */ }

or equivalent;10) or in some other implementation-defined manner.

CodePudding user response：

Did you check your variables? Your first while loop while(auth > 10);, but auth = 4. Maybe you meant while(auth < 10);. Same for while (y > 5),, because y = 0