问我怎样才能得到一组包含5个学生成绩的结构的平均值？

EN

James
Smith
40 60 70 90 100
Will
Jones
20 21 22 23 24
Jose
Lopez
25 26 27 28 29
Jesus
Diaz
30 31 32 33 34
Iker
Caz
35 36 37 38 39

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

FILE *fp;

int main() {
    int i, j, avg, average, num;
    //Structure which contains elements for the students info//
    struct student {
        char fname[10];
        char lname[10];
        int grade[5];
        int avggrade;
    } student[5];
    
    fp = fopen("file.txt", "r");
    
    //reads file and retrives each students data//
    for (i = 0; i < 5; i++) {
        fscanf(fp, "%s", student[i].fname);
        fscanf(fp, "%s", student[i].lname);
        for (j = 0; j < 5; j++) {
            fscanf(fp, "%d", &student[i].grade[j]);
        }
    }
    //prints out each students data so you can see that the file was read correctly//
    for (i = 0; i < 5; i++) {
        printf("%s\n", student[i].fname);
        printf("%s\n", student[i].lname);
        for (j = 0; j < 5; j++) {
            printf("%d\n", student[i].grade[j]);
        }
    }
    
    //Find average//
    int sum = 0;
    int n = 0;
    for (j = 0; j < n; j++) {
        sum = student[2].grade[j] + sum;    
    }
    printf("%.2f", sum);
}