Question

I wrote a program that takes a person's name and their 10 quiz scores from an input file and then prints it to an output file in a slightly different format that also has the average of their quiz scores. Here is an example

INPUT

Mike Johnson 100 45 68 99 34 66 88 99 88 66

OUTPUT

Student Name Quiz Scores Average

Johnson, Mike 100 45 68 99 34 66 88 99 88 66 75.30

It works fine when there is information in the input file. However, when I test run it when the input file is empty, I get an error message saying "stack around the variable 'avg' was corrupted", it exits with a very large negative number like -21475860, and also has a very strange output

Student Name Quiz Scores Average

ÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌ´àP÷–, ÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌÌ´àP÷– 0 0 0 0 0 0 0 0 0 0 0.00

I'm not sure why this is happening. As you can see in my code, I print the column headers ahead of time, and then have a while loop that happens while not at the end of file. I figured if the file is empty then it would immediately evaluate that it's at the end of file so the while loop wouldn't happen. I know it has something to do with the condition of the while loop or the code in the while loop since when I comment it out it out it doesn't happen.

/*
Author: Benjamin Friedman
Course: COMP.1010, Computing I
Date: 05/01/19
*/

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

char *ReadString(FILE *fp, char buffer[], int size);              
char* ExtractName(FILE *fpQuiz,   char whole_name[]);  
void ExtractScores(FILE* fpQuiz, double* pAvg, int quiz_scores[]);

int main(int argc, char *argv[])
{
   /*pointers to quiz.txt (input) and average.txt (output)*/
   FILE* fpQuiz = NULL; FILE* fpAverage = NULL;
  
   /*open files and check for succssful opening*/
   fpQuiz = fopen("quiz.txt", "r");
   if (fpQuiz == NULL) {
       printf("Filed failed to open.\n");
       exit(1);
   }
   fpAverage = fopen("average.txt", "w");
   if (fpAverage == NULL) {
       printf("File failed to open.\n");
       exit(1);
   }

   //Set up column headings
   fprintf(fpAverage, "%-23s", "Student Name");
   fprintf(fpAverage, "%-40s", "Quiz Scores");
   fprintf(fpAverage, "Average\n\n");
  

   double avg;                   //holds average of quiz scores
   int i;                       //counter
   int quiz_scores[10];       //array to hold quiz scores
   char whole_name[20];       //array to hold last name, first name
  
   if (feof(fpQuiz))
   {
       return 0;
   }
   else {
       while (!feof(fpQuiz))
       {
           //Print name to output: Last, First
           fprintf(fpAverage, "%-20s", ExtractName(fpQuiz, whole_name));

           //Print quiz scores and average quiz score to output
           ExtractScores(fpQuiz, &avg, quiz_scores);
           for (i = 0; i < 10; i++)
           {
               fprintf(fpAverage, "%4d", quiz_scores[i]);
           }
           fprintf(fpAverage, "%10.2f\n", avg);
       }
   }
   fclose(fpQuiz);
   fclose(fpAverage);
  

   return 0;
}

/*extract first and last name separately, put them into one string, return the string*/
char* ExtractName(FILE *fpQuiz, char whole_name[])
{
   char first_name[20];
   char last_name[20];
   int i;
   int k;

   //read the first and last name
   ReadString(fpQuiz, first_name, 20);
   ReadString(fpQuiz, last_name, 20);
  
   //put last name into whole name
   for (i = 0; last_name[i] != '\0'; i++)
   {
       whole_name[i] = last_name[i];
   }
  
   //add a comma and space
   whole_name[i] = ',';
   i++;
   whole_name[i] = ' ';
   i++;

   //put first name into whole name
   for (k = 0; first_name[k] != '\0'; i++, k++)
   {
       whole_name[i] = first_name[k];
   }

   //null terminate the whole name array
   whole_name[i] = '\0';
  
   //return the whole name in format: last_name, first_name
   return whole_name;

}

void ExtractScores(FILE* fpQuiz, double* pAvg, int quiz_scores[])
{
  
   int sum_of_quiz_scores = 0;   //sum of the quiz scores
   int noc;                   /*Checks to see if fscanf got an integer. If it didn't
                               that implies there are no more quiz scores left and
                               the input file is at the next line with the next name*/
   int n;                       //temporarily stores the value of each quiz score
   int i;                       //counter
  
   //Get the first quiz score
   noc = fscanf(fpQuiz, "%d", &n);
   //keep adding quiz scores to quiz_scores array as long as they are present
   for (i = 0; noc == 1; i++)
   {
       quiz_scores[i] = n;
       sum_of_quiz_scores += quiz_scores[i];
       noc = fscanf(fpQuiz, "%d", &n);
   }
   //if there were less than 10 quiz scores, assign the rest of the 10 as 0
   while (i < 10)
   {
       quiz_scores[i] = 0;
       i++;
   }
   //get the average of the quiz scores
   *pAvg = sum_of_quiz_scores / (double)10;

}

char *ReadString(FILE * fp, char buffer[], int size)
{
   char c;
   int noc;
   int i = 0;
  
   /*begin scanning for the first string skipping over widespace characters*/
   noc = fscanf(fp, " %c", &c);

   /*if file is empty or storing array is too small to hold null terminator, return NULL*/
   if (noc == EOF || size < 2 ) {
       return NULL;
   }

   /* if we get past the above ifs tatement, that means there is enough room
   in the storage array and the file isn't empty so we can start collecting strings*/

   /*store the first character is storage array*/
   buffer[i] = c;
   i++;

   /*start collecting the rest of the string*/
   noc = fscanf(fp, "%c", &c);
  
   /*while the character is something we want to keep, we're not at EOF, and there's still room
   for the null terminator*/
   while (noc != EOF && i < size - 1 && !isspace(c) ) {
       buffer[i] = c;
       i++;
       noc = fscanf(fp, "%c", &c);
   }

   /*if we get out of the while loops, there are 3 possible cases. EOF, end of string, widespace*/

   if (noc != EOF)
   {
       ungetc(c, fp);
   }
   buffer[i] = '\0';
   return buffer;
}

Answer 1

The solution to the above question is given below with screenshot of output.

=====================================================

I kept the logic simple and i have tested all outputs.

I have updated the code with a check to see if file is empty or not.

If there is anything else do let me know in comments.

=====================================================

============ CODE TO COPY ===============================

main.c

/*
Author: Benjamin Friedman
Course: COMP.1010, Computing I
Date: 05/01/19
*/

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

char *ReadString(FILE *fp, char buffer[], int size);              
char* ExtractName(FILE *fpQuiz,   char whole_name[]);  
void ExtractScores(FILE* fpQuiz, double* pAvg, int quiz_scores[]);

int main(int argc, char *argv[])
{
   /*pointers to quiz.txt (input) and average.txt (output)*/
   FILE* fpQuiz = NULL; FILE* fpAverage = NULL;
  
   /*open files and check for succssful opening*/
   fpQuiz = fopen("quiz.txt", "r");
   if (fpQuiz == NULL) {
       printf("Filed failed to open.\n");
       exit(1);
   }

   ////////////////////////////////////////////////////////////////////////////
   // Read the first character of file if it is the EOF character, file is empty
   char ch = fgetc( fpQuiz );

   // checking if first char is EOF
   if ( ch == EOF )
   {
       printf("Filed failed to open. file empty\n");
       exit(1);
       fclose(fpQuiz);
   }

   // put the first char back to stream, for normal processing
   ungetc( ch, fpQuiz );
   ////////////////////////////////////////////////////////////////////////////
        

   fpAverage = fopen("average.txt", "w");
   if (fpAverage == NULL) {
       printf("File failed to open.\n");
       exit(1);
   }

   //Set up column headings
   fprintf(fpAverage, "%-23s", "Student Name");
   fprintf(fpAverage, "%-40s", "Quiz Scores");
   fprintf(fpAverage, "Average\n\n");
  

   double avg;                   //holds average of quiz scores
   int i;                       //counter
   int quiz_scores[10];       //array to hold quiz scores
   char whole_name[20];       //array to hold last name, first name
  
   if (feof(fpQuiz))
   {
       return 0;
   }
   else {
       while (!feof(fpQuiz))
       {
           //Print name to output: Last, First
           fprintf(fpAverage, "%-20s", ExtractName(fpQuiz, whole_name));

           //Print quiz scores and average quiz score to output
           ExtractScores(fpQuiz, &avg, quiz_scores);
           for (i = 0; i < 10; i++)
           {
               fprintf(fpAverage, "%4d", quiz_scores[i]);
           }
           fprintf(fpAverage, "%10.2f\n", avg);
       }
   }
   fclose(fpQuiz);
   fclose(fpAverage);
  

   return 0;
}

/*extract first and last name separately, put them into one string, return the string*/
char* ExtractName(FILE *fpQuiz, char whole_name[])
{
   char first_name[20];
   char last_name[20];
   int i;
   int k;

   //read the first and last name
   ReadString(fpQuiz, first_name, 20);
   ReadString(fpQuiz, last_name, 20);
  
   //put last name into whole name
   for (i = 0; last_name[i] != '\0'; i++)
   {
       whole_name[i] = last_name[i];
   }
  
   //add a comma and space
   whole_name[i] = ',';
   i++;
   whole_name[i] = ' ';
   i++;

   //put first name into whole name
   for (k = 0; first_name[k] != '\0'; i++, k++)
   {
       whole_name[i] = first_name[k];
   }

   //null terminate the whole name array
   whole_name[i] = '\0';
  
   //return the whole name in format: last_name, first_name
   return whole_name;

}

void ExtractScores(FILE* fpQuiz, double* pAvg, int quiz_scores[])
{
  
   int sum_of_quiz_scores = 0;   //sum of the quiz scores
   int noc;                   /*Checks to see if fscanf got an integer. If it didn't
                               that implies there are no more quiz scores left and
                               the input file is at the next line with the next name*/
   int n;                       //temporarily stores the value of each quiz score
   int i;                       //counter
  
   //Get the first quiz score
   noc = fscanf(fpQuiz, "%d", &n);
   //keep adding quiz scores to quiz_scores array as long as they are present
   for (i = 0; noc == 1; i++)
   {
       quiz_scores[i] = n;
       sum_of_quiz_scores += quiz_scores[i];
       noc = fscanf(fpQuiz, "%d", &n);
   }
   //if there were less than 10 quiz scores, assign the rest of the 10 as 0
   while (i < 10)
   {
       quiz_scores[i] = 0;
       i++;
   }
   //get the average of the quiz scores
   *pAvg = sum_of_quiz_scores / (double)10;

}

char *ReadString(FILE * fp, char buffer[], int size)
{
   char c;
   int noc;
   int i = 0;
  
   /*begin scanning for the first string skipping over widespace characters*/
   noc = fscanf(fp, " %c", &c);

   /*if file is empty or storing array is too small to hold null terminator, return NULL*/
   if (noc == EOF || size < 2 ) {
       return NULL;
   }

   /* if we get past the above ifs tatement, that means there is enough room
   in the storage array and the file isn't empty so we can start collecting strings*/

   /*store the first character is storage array*/
   buffer[i] = c;
   i++;

   /*start collecting the rest of the string*/
   noc = fscanf(fp, "%c", &c);
  
   /*while the character is something we want to keep, we're not at EOF, and there's still room
   for the null terminator*/
   while (noc != EOF && i < size - 1 && !isspace(c) ) {
       buffer[i] = c;
       i++;
       noc = fscanf(fp, "%c", &c);
   }

   /*if we get out of the while loops, there are 3 possible cases. EOF, end of string, widespace*/

   if (noc != EOF)
   {
       ungetc(c, fp);
   }
   buffer[i] = '\0';
   return buffer;
}

=====================================================
Output :