scanf() usage

[slash.hack]

This program was basically a problem in an exam.

"A text file contains a list of real numbers separated by comma. Write to read the real numbers from the given text file and determine average of the numbers from the list of real numbers."

I used this code to generate the numbers as required.

#include<stdio.h>
#include<conio.h>
int main()
{
     FILE *fptr;
     fptr =  fopen ("numbers.txt","w");
     if(fptr == NULL)
     {
             printf("Error reading the file.");
     }
     fprintf(fptr,"1,2,3,4,5,6,7,8");
     fclose(fptr);
     getch();
}

This is what I coded to get the job done.

#include<stdio.h>
#include<conio.h>
int main()
{
     FILE *fptr;
     fptr =  fopen ("numbers.txt","r");
     if(fptr == NULL)
     {
             printf("Error reading the file.");
     }
     int count = 0, sum=0, num = 0, i,n;
     while((fscanf(fptr,"%d,",&n))!=EOF)
     {
                  count = count + 1;
                  sum = sum + n;
                  printf("check... \n"); //just to do a loop check
     }fclose(fptr);
     printf("The average of the given numbers are %d",sum/count);
     getch();
}

Well, the program did its task. But before I got to this, I used
while((fscanf(fptr,"%d",&n))!=EOF)
[without the comma inside the quotes, i.e. "%d"]

This cause the program to loop over and over which can easily be tracked by the "check..."

I wanted to know how this difference occured.

Plus, I'd love to get suggestions regarding my programming style and alternative solutions to this problem, if it isnt much to ask.
Thank you.

[Salem]

> while((fscanf(fptr,"%d,",&n))!=EOF)
Well checking for == 1 would be a more positive test than != EOF
Another answer you could have gotten from fscanf() was 0 (no conversion), and this is what happens when the format of the file breaks down.

As for style,
1. don't put code after closing braces.
2. avoid using conio.h and getch - neither of which are portable.

[MK27]

You could use the return value of fscanf() differently. Eg:

int n, check;
char skip[8];
check = fscanf(fptr, "%d%7[^0-9]", &n, skip");

The second item is anything non-numeric, but a maximum of 7 characters. Presuming there is not excessive garbage in the file, that will get you past commas, spaces, newlines, etc. You could use %*[^0-9] to discard this item, but by using the "skip" buffer instead, you should get a return value from fscanf of 2 as long as there is more data to read, <=0 when there is none, and 1 for the last number (if there is no additional commas, whitespace, newlines, et. al.).

That might be more reliable that using EOF.

[slash.hack]

Well, I wanted the loop to end if it read EOF, after reading your reply it seems, fscanf just returns either 1 or 0.
If you dont mind, can you modify the code so that this can be achieved using fread instead of fscanf?
Thank you very much for replying ^^

edit: @MK27 I read your post just after I posted this. Wow, this is a lot advanced form of code. (kinda difficult to understand, I'll check the usage, am a n00b ) So fscanf returns the number of variables that it was associated with?

[MK27]

No, the scanf() family of functions return the number of items successfully scanned or a negative number indicating EOF or error. That's why I said if you have two items, you will get either 2, 1, or <=0. It's better to test for success rather than EOF, because that is what counts.

Using a combination of fread() and sscanf() or strtok() is good if the file is small enough to slurp all at once, or has some kind of persistent chunked structure. But you'll have to try some code yourself, I won't write it for you.

[slash.hack]

MK27 is there any site or resource that I learn about functions such as scanf() in more detail, as you have used above?

[AndrewHunter]

MK27 is there any site or resource that I learn about functions such as scanf() in more detail, as you have used above?

There is:

• Your compiler's library documentation
• C library documentation and Cplusplus.com
• GNU C library
• C99 standard

Of course you could always look through the C book recommendations and select a good book, such as K&R.

[slash.hack]

Thank you so much for the links. I found something while looking up for advanced format modifiers, upon analyzing tutorial documentation I found that it was meant for language called Pike 7.0 but it seems pretty identical to sscanf usage as in C. This might help those who were looking up regarding format specifiers.

Hoping if this is valid for this thread
Analyzing Strings with sscanf

Found another, very useful this one :
http://beej.us/guide/bgc/output/html...age/scanf.html

[slash.hack]

This worked too!
I replaced while((fscanf(fptr,"%d,",&n))!=EOF) in the above code by : while((fscanf(fptr, "%d%*[^0-9]",&n)) == 1)
"%*" The * says throw away what is read, don't store it in an output variable, this was quoted from here.

Sorry about the double post. lol

[CommonTater]

MK27 is there any site or resource that I learn about functions such as scanf() in more detail, as you have used above?

The very best source of information on your C Library functions usually comes from your compiler's own documentation. The really good ones include the Libary Documentation in the download (or on the disk)... Second to that you can visit the compiler's home page and most often there will be help files, man pages, or pdf files with the documentation you can download. You should favor this because it is specific to your compiler, it's libraries and their various quicks and kinks...

Don't mistake this for an option. Any programming project bigger than "Hello World" is going to dog-ear the printouts in no time flat. Any function you are not familiar with should be looked up before use... and with literally hundreds of functions in the average library only a fool would try to memorize it. Of course this gets worse when you venture into an OS's Application Programming Interface (API) where tens of thousands of functions is very typical.

On a "best guess" basis, I'd say that an average programmer spends about 1/3 of his writing time "looking stuff up"...
So if you don't have this documentation you really do need to find it and get copies of it on your system.