#include <stdio.h>

int main(void) {
    FILE *f= fopen("data", "a"); //function
    // open("data", O_WRONLY|O_CREAT|O_APPEND);
    if(f == NULL){
        perror("");
        return 1;
    }

    fprintf(f, "Hello\n");

    fclose(f);
    
    return 0;
}