Example of struct in book causing a headache

Can someone point out what is wrong with this small program it is similar to an example in book I am reading but I am getting a segment core dump? Thanks.

Code:

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      struct football {
          int yards;
          int points;
          char team[30];
          } nfl;
   
      void print_it(struct football new);
   
      int main()
    {
   
          printf("Who is your favorite team?\n");
          scanf("%s", nfl.team);
   
          printf("How many points did they score?\n");
          scanf("%d", nfl.points);
   
          printf("How many yards did they gain?\n");
          scanf("%d", nfl.yards);
   
          print_it(nfl);

          return 0;
      }

        void print_it(struct football new)
        {
        printf("Your fav team is:%s They scored %d points Gained %d yards\n", new.team, new.points, new.yards);
        }

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Try raising the warning level, as it should be able to complain about scanf() needing a pointer as the argument receiving the result.

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Mats

Quote:

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Originally Posted by matsp

Try raising the warning level, as it should be able to complain about scanf() needing a pointer as the argument receiving the result.

--
Mats

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not all compilers do it...

but yes - should be

Code:

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scanf("%d", &nfl.points);

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Why do you use global vars? there is no need here

I made the changes below but I am confused if I need user input for the struct members. How would I do this properly?

Code:

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struct football {
          int yards;
          int points;
          char team[30];
          } nfl;
   
      void print_it(struct football new);
   
      int main()
    {
                 
          strcpy(nfl.team,"Pittsburgh Steelers");
   
          nfl.points = 42;
          nfl.yards = 250;
   
          print_it(nfl);

          return 0;
      }

        void print_it(struct football new)
        {
        printf("Your fav team is:%s They scored %d points Gained %d yards\n", new.team, new.points, new.yards);
        }

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I am trying to use global variables in my studies because that is how the programs here at work are done. I figure I might as well get used to this now rather then later. Thanks for the feedback. I really appreciate everyones help.

Quote:

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How would I do this properly?

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Code:

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if(scanf("%d", &nfl.points) == 1)
{
  /* number read */
}

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Quote:

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how the programs here at work are done

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horrible... better start learning good practices... Worst will hunt you by theirself...

When this happens:

Code:

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if(scanf("%d", &nfl.points) == 1)
{
  /* number read */
}

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I am unsure what to place in between if statement. I see you said number read but nfl.points would now already hold the value based on user input right? Still confused a little but what you posted is making some sense. I just want to get it right now to avoid mistakes in the future.

Thanks.

scanf will return the "number of items successfully read", so if the format string contains "%d", then you should expect to get 1 back. Anything else means something went wrong - if it's zero, someone probably typed in an illegal number (such as "a" instead of "123"), if you get -1 (EOF), then the first character read in scanf() was EOF - so no data is available.

It would in some ways, make more sense to do:

Code:

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if(scanf("%d", &nfl.points) != 1)
{
  /* read error */
}

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The red bits indicate my changes.

--
Mats

Thank you very much for the detailed explanation. I can now see where and how I can use this. Thanks everyone!!

If I use

Code:

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    85    if(scanf("%d", &nfl.points) != 1)
    86    {
    87      printf("Please enter a number!/n");
    88    }

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How could I force the user to enter a correct value before proceeding?

I'd do it like:

Code:

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while (scanf("%d", &nfl.points) != 1)
{
    printf("Please enter a number!\n");
}

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If you want to you could of course also add the original line asking for the number after printing "Please enter a number". This way it will loop until scanf... is equal to 1.

Quote:

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I'd do it like:

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what is missing here - cleaning of the stdin from the garbage left there...
also note that if the stdin was redirected to be read from file - it could be nothing left to read from there...

When I changed the code to

Code:

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      while(scanf("%d", &nfl.points) != 1)
        {
          printf("Please enter a number!/n");/* read error */
        }

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and enter a character the program is stuck in printf statement. Am I missing something?

Sorry about that. I usually don't use scanf, but he's right, you should clean the stdin before looping again.

The reason I'm not worried about reaching the end of the file however is because in this case he asks a specific question to the user, so I assume the stdin won't be redirected to read from file in this case.

This could help Flush the input buffer

Code:

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    84    if (scanf("%d", &nfl.points) != 1)
    85            printf("Please try again\n");
    86
    87    while ((ch = getchar()) != '\n' && ch != EOF);
    88      {
    89    if (scanf("%d", &nfl.yards) != 1)
    90            printf("Please try again\n");
    91      }

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-reading what getchar does I am puzzled how this while loop solved my problems. I declared int ch; in program also. This loop seems to clear out string from previous if statement. Can someone explain why this works now? I am using link you posted above but still confused.

Well I am guessing it just verifies there is data in stdin and overwrites those contents??

-Also how could I add code to make user enter a correct number instead of using printf and exiting with no valid input?

And more importantly utilize the quotee below:

Quote:

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fgets( buff, BUFSIZ, stdin );
Then validate buff in whatever way you choose, and copy the data to it's final destination.

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Do I just assign buff = nfl.points and then see ifisdigit?

if user pesses something like
qw<ENTER>
scanf("&#37;d"...
will not be able to read anything from the stream leaving 3 chars there
'q' , 'w' , '\n'

while loop added just reads all chars till it encounters \n - leaving stdin empty

so probably your alltogether loop should be

Code:

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while(scanf("%d",&nfl.points) != 1)
{
  /* clean the stdin */
  int ch;
  while ((ch = getchar()) != '\n' && ch != EOF);

  /* and try again */

  printf("Please try again\n");
}

/* succesfully read nfl.points number - could continue*/

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Quote:

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Do I just assign buff = nfl.points and then see ifisdigit?

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no, if you want to use fgets approch - it will be like

Code:

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char buffer[BUFSIZ];
char* res;
while((res = fgets(buffer,sizeof buffer, stdin)) != NULL)
{
  if(sscanf(buffer, "%d" , &nfl.points) != 1) /* we can use strtol to make more carefull testing of the user input */
  {
      /* successfully read number */
      break;
  }
  /* line format was incorrect */
  printf("Please try again\n");
}

if(res == NULL)
{
  /* fgets failed - probably EOF riched - need to abort */
  return -1;
}

/* successfully read number - we can continue */

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I will add to my program both methods you explained. Thanks for the help!

Works very well. Thanks again!

Quote:

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Originally Posted by cjohnman

I will add to my program both methods you explained. Thanks for the help!

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do not mix fgets and scanf in the same program - stick to one method - or read everything with fgets and then convert

or use scanf - without need for convert...

mixing them could bring unexpected bugs in your code due to scanf leaving \n in stdin and next fgets reading it instead of the next string...

Should this be ok?

Code:

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    95    printf("Please enter total points\n");
    96    while(scanf("%d",&nfl.points) != 1)
    97    {
    98      /* clean the stdin */
    99      while ((ch = getchar()) != '\n' && ch != EOF);
    100
    101      /* and try again */
    102      printf("Please try again\n");
    103    }
    104
    105    printf("Please enter total yards\n");
    106      while(scanf("%d",&nfl.yards) != 1)
    107          {
    108            /* clean the stdin */
    109            while ((ch = getchar()) != '\n' && ch != EOF);
    110
    111            /* and try again */
    112            printf("Please try again\n");
    113          }

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