Thread: check digit

@Jailan: Have you tried searching the forum?

http://cboard.cprogramming.com/search.php

Use "ISBN" as a key word. Sure several threads are about books. Several others offer previously asked version of your same question, and likely a solution lies therein as well.

Thread titles like "Processing a book ISBN" or "validate isbn" spring to mind.

Code:

            while(index < 20)
            {
               input[index] = '\0';
               index++;
            }

Why? Setting input[index] = '\0' may be fine, but there's no need to fill the entire rest of the string.

Code:

      weight = 10;
      noOfChars = 0;
      index = 0;
      sum = 0;
      flag = 0;

Stick these at the start of the code.

Code:

         if((input[index] >= 0x30 && input[index] <= 0x39) || 
            (input[index] == 'X' || input[index] == 'x'))

is easier to read (and write) as:

Code:

         if(isdigit(input[index]) || tolower(input[index]) == 'x')

Similarly, use:

Code:

            if(tolower(input[index]) == 'x')

I don't really see the point of your "flag" variable. Surely if there's no newline because the input is too long to fit in 20 chars, it will fail due to "not the right number of digits".

Code:

temp = temp * weight;
// why not
temp *= weight

--
Mats

These are the errors I am getting back:
==> Your program only contains the main function
Your program must be split into appropriate functions

==> At least one function in your code must use 'call by
You do not appear to have done this in your program.

Code:

      weight = 10;
      noOfChars = 0;
      index = 0;
      sum = 0;
      flag = 0;

Stick these at the start of the code.

I did this but I get

==> Global variables are not allowed in this subject.

Ehm, when I said start of the code, I meant the start of the for-loop. That is your current code (as posted earlier) sets these variables at the end of the loop, rather than at the start of the loop. It makes the code easier to read if you set the variables at the start of the loop.

You obviously have some requirement to use a function, and you should break out the function to check the number. I would write it something like this :

Code:

int main() 
{
     char str[20];
   
     do {
        printf("Enter a ISBN or empty line to exit:");
        fgets(str, sizeof(str), stdin);
        if (str[0] != '\n')  checkISBN(str);
    } while (str[0] != '\n');
    return 0;
}

I'll leave it to you to implement the "checkISBN" code - but essentially it is most of the code you've got in main that needs to move to the checkISBN function.

--
Mats

Removed

Whilst having inputFlush as a function is certainly a good idea, and checking digit in a function isn't bad either, I think the "correct" thing to do is to split the check of the ISBN part into a separate function that takes a string as input.

I personally have nothing against having main last - but that's probably heavily influenced by my previous Pascal experience, where code is built "bottom up", meaning that the most basic functions are declared first, the the functions calling the basic function etc. But there's no strict rule that you have to do it one way or the other in C.

The cause of errors in your second piece of code, however, are caused by the fact that a function has to be declared (as a prototype at least) before it is called.

There are some style points I'd like to point out too:
Your input flush is overcomplicated: Use something like this:

Code:

char ch;
while((ch = getchar()) != '\n' && ch != EOF) ;

Don't pass a flag to inputFlush, check the flag in the code before calling inputflush.

Code:

      if(flag != 1 || noOfChars != 10)

I'm sure that flag will only be zero if noOfChars is NOT ten, so checking both doesn't really lead to anything useful. [Because the only way that the string doesn't end on a '\n' is if there's more than 19 chars in the input, which is higher than 10].


I would also add that the only position in an ISBN that is allowed to be X is the last one, so it would be possible to enter an invalid ISBN and get an "OK" answer.

You also don't bail out if there's invalid input, e.g.
A12345B 6789AX would be accepted as 123456789X, ignoring the A's.

And you still don't use "tolower" to check if the 'X' is an x.

--
Mats

Did you make any other changes?

The error text you're showing doesn't quite match the code - you didn't by any chance do some of it and then forgot to save the final changes?

--
Mats

Removed

That isn't a good function prototype. You should have the arguments as well.

Like this:

Code:

int decodeDigit(char ch, int *temp);
void inputFlush(char flag);

--
Mats

I just realized that you have removed the arguments from your function calls in the code - you shouldn'tt do that.

--
Mats

Originally Posted by Jailan

ahhhh ok cheers!

Now I'm getting

"isb2.c", line 22: prototype mismatch: 0 args passed, 2 expected
"isb2.c", line 46: prototype mismatch: 0 args passed, 1 expected

I can't win!

You were writing as I was posting as well. I would have got there quicker if I hadn't had to remove your "doublespacing" - are you using WORD or something like that for your editing?

--