Binary file of 48 students; highest mark

Design. The structure student holds name, roll, address and mark. All 48 records are written to the binary file student.dat with fwrite(). The file is reopened with "rb" and records are read one by one with fread(); the record with the highest mark is kept in top (the first record starts it). That record is displayed at the end.

#include <stdio.h>
#ifndef N
#define N 48
#endif

struct student {
    char name[30];
    int roll;
    char address[30];
    float mark;
};

int main(void)
{
    FILE *fp;
    struct student s, top;
    int first = 1;

    fp = fopen("student.dat", "wb");
    if (fp == NULL) { printf("Cannot open file\n"); return 1; }
    for (int i = 1; i <= N; i++) {
        printf("Student %d (name roll address mark): ", i);
        scanf("%29s %d %29s %f", s.name, &s.roll, s.address, &s.mark);
        fwrite(&s, sizeof s, 1, fp);
    }
    fclose(fp);

    fp = fopen("student.dat", "rb");
    if (fp == NULL) { printf("Cannot open file\n"); return 1; }
    while (fread(&s, sizeof s, 1, fp) == 1)
        if (first || s.mark > top.mark) {
            top = s;
            first = 0;
        }
    fclose(fp);

    printf("Highest mark: %s, Roll %d, %s, %.1f\n", top.name, top.roll, top.address, top.mark);
    return 0;
}

Sample run (N reduced to 3 with -DN=3 for the test; the real program uses 48)

Input: Ram 1 Lalitpur 65 Sita 2 Kathmandu 88.5 Hari 3 Pokhara 72

Student 1 (name roll address mark): Student 2 (name roll address mark): Student 3 (name roll address mark): Highest mark: Sita, Roll 2, Kathmandu, 88.5