Code issue scanf() string line 28

Hi,

I'm developing a very small project, and while implementing it I got some issue. I already did this kind of exercises a few times, but I don't seem to understand what is wrong (the scanf to get string/char array input. A compiler error related to the type of variable and or number of arguments.)
I'm using code blocks and windows10 at this moment.

This is still a code in progress, and as a newbie I will also appreciate best practice's tips.

Code:

---

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


#define MAXINPUT 20 //use this value to max loop (apply later)


struct Book // Structure type definition
{
 char title [10];
 int pages;


}books[10];


int main()
{
    int i = 0;
    int option;


    while (i < 10)
    {
    printf("Do you want to enter details of BOOK 1 (yes) or 0 (No)? ");
    scanf("%d", &option);

        if (option == 1)
        {
            printf("\n Title name: ");
            scanf("%s", &books[i].title);


            printf("\n Number of pages: ");
            scanf("%d \n", &books[i].pages);


        }
        else if (option == 0)
        {
            printf("It was not yes \n");
            break;


        }
        else{


            printf("Valid input, go back to main menu \n");
            break;


        }
        i++;


    }

    // save records to file// to be written

    //display records created


    for (i = 0; i < 2; i++) {


      printf("Book title: ");
      puts(books[i].title);
      printf("Page number:  %d", books[i].pages);
      printf("\n");
    }


    //display all saved record//to be written






    return 0;
}

---

warning: format '%s' expects argument of type 'char *', but argument 2 has type 'char (*)[10]' [-Wformat=]

You mentioned string input, but it looks like you intended integer input.

Quote:

---

Originally Posted by laserlight

You mentioned string input, but it looks like you intended integer input.

---

When I past the code it seems it added extra lines. The issue seems to be here.

Code:

---

printf("\n Title name: ");
            scanf("%s", &books[i].title);

---

Also, the code doesn't perform anything else after getting the input.

EDITED:

Ok, so after a needed break from being hours looking at this I understood the difference between having & and not having it when getting a string input. I took it out from the example above. But the program now crashes.

I found a few errors.

Compare to this...

Code:

---

#include <stdio.h>
#include <stdlib.h>
 
#define MAXINPUT 20 //use this value to max loop (apply later)
 
struct Book {
    char title[10];
    int pages;
};
 
int main() {
    int i = 0, option = 0, bookCount = 0;
 
    struct Book books[10];

    while (i < 10) {
        printf("Do you want to enter details of BOOK 1 (yes) or 0 (No)? ");
        scanf("%d", &option);

        if (option == 1) {
            printf("\n Title name: ");
            scanf("%s", books[i].title);
            printf("\n Number of pages: ");
            scanf("%i", &books[i].pages);
            bookCount++;
        } else if (option == 0) {
            printf("It was not yes \n");
            break;
        } else {
            printf("Valid input, go back to main menu \n");
            break;
        };
        i++;
    };
 
    // save records to file// to be written
 
    //display records created
    for (i = 0; i < bookCount; i++) {
      printf("Book title: ");
      puts(books[i].title);
      printf("Page number:  %d", books[i].pages);
      printf("\n");
    };
 
    //display all saved record//to be written
    return 0;
};

---

tried to keep it close to the original.

@structure, the ; on the ends of statement block braces are unnecessary.

> scanf("%d \n", &books[i].pages);
@JazzDev, trailing characters on the ends of scanf format strings are seldom ever what you want to do.
What this will do is prevent scanf from returning until you type in something else.

Just a regular
scanf("%d", &books[i].pages);
will suffice.

Quote:

---

the ; on the ends of statement block braces are unnecessary.

---

It helps me keep a uniform design. For instance structures require it, it would be confusing because i'm easily confused lol. It is also a habit i have been doing it forever. Looking at code without the semicolon after the brackets looses me faster. I can look at the code and see what is going on easier. It's a preference really. I have a lot of preferences...

i.e: i would rather

Code:

---

int main() {
  return 0;
};

---

instead of...

Code:

---

int main()
{
  return 0;
}

---

The second one just looks ridiculous.

Quote:

---

Originally Posted by Structure

For instance structures require it, it would be confusing because i'm easily confused lol.

---

That's because they wanted to allow declaring of variables of the struct type in a compact form... which ironically is generally seen as a poor practice these days because such variables would almost certainly be in file scope and hence be global variables. I cannot even think of another case offhand where a semi-colon is required after a closing brace (and of course it isn't even required here: you can still declare a variable of that type, even if it may be poor style). Hence, it looks like you took a special case and made it into a general rule for some notion of uniformity.

Quote:

---

Originally Posted by Structure

Looking at code without the semicolon after the brackets looses me faster. I can look at the code and see what is going on easier. It's a preference really. I have a lot of preferences...

---

In this case your preference goes against common C style, and may even be illegal syntax in other programming languages whose syntax was inspired by C (but tried to clean up C's syntax warts, which is a common pastime for such newer programming languages). I suggest that you change your preference when posting code on this forum. You're free to do what you want with your own code, but it isn't good form to use a quirky style in code meant to be read by others.

Quote:

---

Originally Posted by Structure

The second one just looks ridiculous.

---

Since it looks ridiculous to you, don't use it. But you should be aware that it is also extremely common style in C and a host of other programming languages, so you will have to live with it. The closest common style in C would be:

Code:

---

int main() {
  return 0;
}

---

That is, simply omitting the useless semi-colon. I'm not entirely sure what that semi-colon actually means in the context of file scope: I suspect it may still be a null statement, which is what you're certainly doing when you use it for if statements and loops: littering your code with null statements.

Quote:

---

Originally Posted by laserlight

That is, simply omitting the useless semi-colon. I'm not entirely sure what that semi-colon actually means in the context of file scope: I suspect it may still be a null statement, which is what you're certainly doing when you use it for if statements and loops: littering your code with null statements.

---

I'm not sure what it means either. But compiling with -pedantic both clang and gcc emit a warning. In the case of gcc: warning: ISO C does not allow extra ‘;’ outside of a function [-Wpedantic]

Quote:

---

Originally Posted by JazzDev

Ok, so after a needed break from being hours looking at this I understood the difference between having & and not having it when getting a string input.

---

Yes, a string will be converted to a pointer to its first char, so you shouldn't be taking its address with the address-of operator.

However, you should also be aware that using a %s without specifying the field with for scanf makes your code vulnerable to buffer overflow: the user can enter as long a string as they want, and the program will attempt to store it all into the destination array of char, even if there is not enough space to store it. In your case, title is an array of 10 char, so the scanf call should be: scanf("%9s", books[i].title) as one char is reserved for the terminating null character.

Quote:

---

Originally Posted by JazzDev

But the program now crashes.

---

What is your current code and test input?

Quote:

---

Originally Posted by Hodor

But compiling with -pedantic both clang and gcc emit a warning. In the case of gcc: warning: ISO C does not allow extra ‘;’ outside of a function [-Wpedantic]

---

That would be consistent with the semi-colon being a null statement: not being declarations, statements are not permitted at file scope outside a more local scope.

> It helps me keep a uniform design.
If you ever aspire to be a professional programmer or work in any kind of software team, it will be a source of friction for you.

People will not accept your ; riddled code into their larger code bases.

Quote:

---

If you ever aspire to be a professional programmer

---

I do not. It is a hobby, and i will keep my preferences.

Quote:

---

A semicolon terminates a statement.
If your statement doesn't do anything, that's your prerogative as a programmer.

---

Quote:

---

Originally Posted by Structure

I do not. It is a hobby, and i will keep my preferences.

---

Then don't try to "help" others if you don't care about proper style.

Quote:

---

proper style

---

not a thing.

Quote:

---

Originally Posted by Structure

not a thing.

---

It is a thing actually, without it things like linux would not have been born because the code would be chaos and noone could understand each others code, I may be a newb to coding styles but I at least get the point of a common style