while loop dependent upon a scanf result is ending prematurely - c

Question

I'm writing a simple program in C to calculate grades and grade averages. I feed it a textfile from the command line via the "< xyz.txt" and output to another text via "> xyz_output.txt" commands. There are over 100 lines of data in the input file, but the program keeps exiting the loop around line 6 of the input for some reason... I've checked the input format several times and I can't seem to figure out why it's exiting prematurely. Here is the code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main()
{
char pp[4];
char school[3];
int class;
int student;
int a;
int b;
int c;
int d;
int e;
int f;
int g;
int h;
int i;
int j;
int k;
int l;
int m;
int n;
int o;
int p;
int q;
int r;
float average;
int runtotal;
int grouptotal = 0;
float groupaverage;
int counter = 0;
while (scanf("%3s%2s%2i%2i %i %i %i %i %i %i %i %i %i %i %i %i %i %i %i %i %i %i", pp, school, &class, &student, &a, &b, &c, &d, &e, &f, &g, &h, &i, &j, &k, &l, &m, &n, &o, &p, &q, &r) == 22)
{
runtotal = (a+b+c+d+e+f+g+h+i+j+k+l+m+n+o+p+q+r);
average = (float)runtotal / 18;
grouptotal = grouptotal + runtotal;
counter++;
printf ("%i.\n", counter);
printf ("%s%s-%i-%i -- %1i %1i %1i %1i %1i %1i %1i %1i %1i %1i %1i %1i %1i %1i %1i %1i %1i %1i\n", pp, school, class, student, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r);
printf ("Total score: %i\n", runtotal);
printf ("Average: %f\n", average);
printf ("Running Total: %i\n\n", grouptotal);
}
groupaverage = (float)grouptotal / counter;
printf ("Calculations complete.\nThe total score for this group was %i.\nThe average score for this group was %f.\n", grouptotal, groupaverage);
return 0;
}
and here are the first 10 lines of the actual input .txt file.
preKO6101 0 0 1 1 1 1 1 0 1 0 1 0 0 1 1 0 2 0
preHI6114 1 0 0 1 0 1 1 1 1 0 0 0 0 1 1 1 2 1
preHI5116 0 0 0 1 0 0 1 1 1 0 0 0 0 2 0 0 1 0
preHI6103 0 0 0 1 0 0 1 1 1 0 0 0 0 1 1 0 0 1
preHI5132 0 0 0 1 1 0 1 1 1 0 0 0 0 1 0 0 0 0
preHI5109 1 0 0 1 1 0 0 1 0 0 0 0 1 1 1 2 2 1
preHI6113 2 1 1 1 1 0 1 0 0 0 1 0 1 1 1 0 0 1
preSA5116 0 1 0 1 1 2 1 2 0 0 0 0 2 1 2 0 2 2
preHI6109 0 0 0 1 1 0 1 1 1 0 1 1 0 1 1 0 1 1
preHI5107 0 0 0 1 1 0 1 1 1 0 0 0 0 1 1 0 1 0
It seems to make it to 'preHI5109' but then exits. I have a feeling that it has to do with how I'm using scanf, but I'm not sure what I'm doing wrong. Any advice on how to fix this?

Answer 1

The method employed to read the data file is very sensitive to mis-alignment, parsing and I/O issues. Suggest more robust IO and parsing as certainly some small error exist in the data file. Use fgets() to control reading the line orientated data.
char buf[100];
while (fgets(buf, sizeof buf, stdin) != NULL) {
int count = sscanf(buf, "%3s%2s%2i%2i %i %i %i %i /* ... */ %i %i",
pp, school, &class, &student, &a, &b, &c, /* ... */ &q, &r);
if (count != 22) {
printf("Error %d (TBD relevant text)\n", count);
break;
}
/* continue with normal processing */
}
Other improvements
int a[18] instead of int a; int b; ...
Use loops to then scan, sum, print the 18 elements.
Use "%i" rather than "%1i". The 1 is the minimum width, so why have it?
Note: If the input file was supplied by a Prof., It would not surprise me that something intentionally bad is in it. The lesson: do not trust data input unless well vetted. User input is evil.