Struct Array and File

Question

Actually, I need to calculate course average of student, for example course 115: grades are 86.5 and 84.3, so average is 85.4. Therefore I need to read data from file and store it in array but I don't understand how to do so without using pointers apart from FILE pointer.

There is following data in the file: studentid, courseid, grade
Input file "input.txt":

201456 115 86.5
201456 112 86.4
201456 122 85.4
202145 115 84.3
202145 112 65.3
202145 122 78.4

Code:

#include <stdio.h>
typedef struct{
    int courseid;
    double courseavg;
} Course;

typedef struct {
    int studentid;
    double grade[3];
} Student;

typedef struct {
    Course course[3];
    Student student[2];
} Major;

int main() {
    Course course[3] = {
                {1, 0.0},
                {2, 0.0},
                {3, 0.0}
        };
        
        Student student[2] = {
                {0, 0.0, {0.0, 0.0, 0.0}}, 
                {0, 0.0, {0.0, 0.0, 0.0}}
        };

    FILE *in = fopen("input.txt", "r");

    fscanf(in,"%d %d %f %d %d %f %d %d %f %d %d %f %d %d %f %d %d %f",
            &student[0].studentid, &course[0].courseid, &student[0].grade[0],
            &student[0].studentid, &course[1].courseid, &student[0].grade[1],
            &student[0].studentid, &course[2].courseid, &student[0].grade[2],
            &student[1].studentid, &course[0].courseid, &student[1].grade[0],
            &student[1].studentid, &course[1].courseid, &student[1].grade[1],
            &student[1].studentid, &course[2].courseid, &student[1].grade[2]);

    course[0].courseavg = (student[0].grade[0] + student[1].grade[0])/2;
    printf("%f", &course[0].courseavg);

return 0;
}

Be aware that nobody will write your code for you here. You need to come up with some cod — Jabberwocky
– Jabberwocky, Commented Oct 10, 2022 at 11:54
Have a look at fgets() and sscanf() that should give you a pretty good starting point. — Marco
– Marco, Commented Oct 10, 2022 at 12:32
A working program could look something like this: 1. initialize data 2. open file 3. read file line by line (and process the line) 5. examine data and calculate average — Marco
– Marco, Commented Oct 10, 2022 at 12:33

Marco · Accepted Answer · 2022-10-10 12:43:37Z

You need to read the file line by line and process each line independently:

#include <stdlib.h> // EXIT_FAILURE
#include <stdio.h> // fopen()
#include <stdbool.h> // bool

/**
 * Struct that holds evaluation of a student.
 */
struct StudentEvaluation {
    int student_id;
    int course_id;
    float grade;
};

/**
 * Function responsible for parsing a single line.
 */
bool processLineBuffer(
    const char *line,
    struct StudentEvaluation *eval
) {
    // sscanf returns the number of items it
    // successfully parsed
    int ret = sscanf(
         line,
        "%d %d %f",
        &eval->student_id, &eval->course_id, &eval->grade
    );

    // that's why we check if the return value is 3
    return ret == 3;
}

int main(void) {
    FILE *fp = fopen("students.txt", "r");

    if (!fp) {
        fprintf(stderr, "Failed to open file.\n");
        return EXIT_FAILURE;
    }

    char line_buffer[256];

    while (fgets(line_buffer, sizeof(line_buffer), fp)) {
        struct StudentEvaluation eval;

        // only examine StudentEvaluation if parsing was successful
        if (processLineBuffer(line_buffer, &eval)) {
            printf("successfully parsed: \n");

            // print the parsed data:
            printf("    student_id is %d\n", eval.student_id);
            printf("    course_id is %d\n", eval.course_id);
            printf("    grade is %f\n", eval.grade);
        }
    }

    fclose(fp);
}

This is of course by no means the complete program, but it should give you a framework to (hopefully) complete your program.

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