c

1. Basic fputc() and fgetc()
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w");
    fputc('A', fp);
    fclose(fp);
    fp = fopen("test.txt", "r");
    printf("%c", fgetc(fp));
    fclose(fp);
    return 0;
}

2. Writing String using fputs()
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w");
    fputs("Hello", fp);
    fclose(fp);
    fp = fopen("test.txt", "r");
    char ch;
    while((ch = fgetc(fp)) != EOF)
        printf("%c", ch);
    fclose(fp);
}

3. Using fprintf()
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w");
    fprintf(fp, "%d %s", 10, "C");
    fclose(fp);
    fp = fopen("test.txt", "r");
    int x; char str[10];
    fscanf(fp, "%d %s", &x, str);
    printf("%d %s", x, str);
}

4. fseek() from beginning
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fputs("ABCDE", fp);
    fseek(fp, 2, SEEK_SET);
    printf("%c", fgetc(fp));
}

5. fseek() from end
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fputs("ABCDE", fp);
    fseek(fp, -1, SEEK_END);
    printf("%c", fgetc(fp));
}

6. ftell() position
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fputs("Hello", fp);
    printf("%ld", ftell(fp));
}

7. rewind()
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fputs("ABC", fp);
    rewind(fp);
    printf("%c", fgetc(fp));
}

8. EOF check
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fputs("AB", fp);
    rewind(fp);
    while(!feof(fp))
        printf("%c", fgetc(fp));
}

9. fwrite() and fread()
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.bin", "wb");
    int x = 100;
    fwrite(&x, sizeof(x), 1, fp);
    fclose(fp);

    fp = fopen("test.bin", "rb");
    int y;
    fread(&y, sizeof(y), 1, fp);
    printf("%d", y);
}

10. Append mode
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w");
    fputs("Hello", fp);
    fclose(fp);

    fp = fopen("test.txt", "a");
    fputs("World", fp);
    fclose(fp);

    fp = fopen("test.txt", "r");
    char ch;
    while((ch = fgetc(fp)) != EOF)
        printf("%c", ch);
}

11. Multiple fgetc()
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fputs("XYZ", fp);
    rewind(fp);
    printf("%c %c", fgetc(fp), fgetc(fp));
}

12. fscanf skip space
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fprintf(fp, "10 20");
    rewind(fp);
    int a, b;
    fscanf(fp, "%d%d", &a, &b);
    printf("%d %d", a, b);
}

13. fgets()
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fputs("Hello\nWorld", fp);
    rewind(fp);
    char str[20];
    fgets(str, 20, fp);
    printf("%s", str);
}

14. fputc loop
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w");
    for(int i=0;i<3;i++)
        fputc('A'+i, fp);
    fclose(fp);

    fp = fopen("test.txt", "r");
    char ch;
    while((ch=fgetc(fp))!=EOF)
        printf("%c", ch);
}

15. Writing integers
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fprintf(fp, "%d", 123);
    rewind(fp);
    char ch;
    while((ch=fgetc(fp))!=EOF)
        printf("%c", ch);
}

16. File pointer NULL
#include <stdio.h>
int main() {
    FILE *fp = fopen("nofile.txt", "r");
    if(fp == NULL)
        printf("Error");
}

17. Character overwrite
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fputs("ABC", fp);
    fseek(fp, 1, SEEK_SET);
    fputc('X', fp);
    rewind(fp);
    char ch;
    while((ch=fgetc(fp))!=EOF)
        printf("%c", ch);
}

18. Binary multiple values
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.bin", "wb");
    int arr[3] = {1,2,3};
    fwrite(arr, sizeof(int), 3, fp);
    fclose(fp);
    fp = fopen("test.bin", "rb");
    int arr2[3];
    fread(arr2, sizeof(int), 3, fp);
    printf("%d %d %d", arr2[0], arr2[1], arr2[2]);
}

19. ftell after fgetc
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fputs("ABCD", fp);
    rewind(fp);
    fgetc(fp);
    printf("%ld", ftell(fp));
}

20. Writing + Reading pointer
#include <stdio.h>
int main() {
    FILE *fp = fopen("test.txt", "w+");
    fprintf(fp, "Hello");
    printf("%c", fgetc(fp));
}