#include <stdio.h>

int main(void) {
    FILE *f = fopen("scores.txt", "w");
    if (f == NULL) { perror("fopen"); return 1; }
    fprintf(f, "asha 91\nravi 78\nmeera 85\n");
    fclose(f);

    f = fopen("scores.txt", "r");
    if (!f) { perror("fopen"); return 1; }
    char name[32];
    int score, total = 0, count = 0;
    while (fscanf(f, "%31s %d", name, &score) == 2) {   /* loop on the read, not on feof */
        printf("%-6s %d\n", name, score);
        total += score;
        count++;
    }
    fclose(f);
    printf("average %.1f\n", (double)total / count);
    return 0;
}

asha   91
ravi   78
meera  85
average 84.7

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

int main(void) {
    FILE *f = fopen("log.txt", "w");
    if (!f) return 1;
    fputs("first\n", f);
    fclose(f);

    f = fopen("log.txt", "a");             /* keep existing content */
    if (!f) return 1;
    fputs("second\n", f);
    fputs("third\n", f);
    fclose(f);

    f = fopen("log.txt", "r");
    if (!f) return 1;
    char line[128];
    int n = 0;
    while (fgets(line, sizeof line, f)) {
        line[strcspn(line, "\n")] = '\0';
        printf("%d: %s\n", ++n, line);
    }
    fclose(f);
    return 0;
}

1: first
2: second
3: third

#include <stdio.h>

typedef struct { int id; double price; } Item;

int main(void) {
    Item items[3] = {{1, 9.5}, {2, 20.0}, {3, 4.25}};
    FILE *f = fopen("items.bin", "wb");
    if (!f) return 1;
    size_t written = fwrite(items, sizeof items[0], 3, f);
    fclose(f);

    f = fopen("items.bin", "rb");
    if (!f) return 1;
    fseek(f, 0, SEEK_END);
    long size = ftell(f);                          /* file size in bytes */
    printf("wrote %zu records, file is %ld bytes\n", written, size);

    Item it;
    fseek(f, 2 * (long)sizeof(Item), SEEK_SET);   /* random access: jump to record #2 */
    if (fread(&it, sizeof it, 1, f) == 1) printf("record 2: id=%d price=%.2f\n", it.id, it.price);
    rewind(f);
    if (fread(&it, sizeof it, 1, f) == 1) printf("record 0: id=%d\n", it.id);
    fclose(f);
    remove("items.bin");
    return 0;
}

wrote 3 records, file is 48 bytes
record 2: id=3 price=4.25
record 0: id=1

#include <stdio.h>

int copy_file(const char *src, const char *dst) {
    FILE *in = fopen(src, "rb");
    if (!in) return -1;
    FILE *out = fopen(dst, "wb");
    if (!out) { fclose(in); return -1; }
    int c;
    long bytes = 0;
    while ((c = fgetc(in)) != EOF) { fputc(c, out); bytes++; }
    int err = ferror(in) || ferror(out);
    fclose(in);
    fclose(out);
    return err ? -1 : (int)bytes;
}

int main(void) {
    FILE *f = fopen("a.txt", "w");
    if (!f) return 1;
    fputs("copy me\n", f);
    fclose(f);
    printf("copied %d bytes\n", copy_file("a.txt", "b.txt"));
    printf("missing source -> %d\n", copy_file("nope.txt", "c.txt"));
    return 0;
}

copied 8 bytes
missing source -> -1