移动文件写入一个过程：

Move file writing into a procedure:

void write_lines (FILE *fp) {
    fprintf (file, "%s\n", "Line 1");
    fprintf (file, "%s %d\n", "Line", 2);
    fprintf (file, "Multiple\nlines\n%s", "in one call\n");
}

int main () {
    FILE *file = fopen ("zach.txt", "a+");
    assert (file != NULL); // Basic error checking
    write_lines (file);
    fclose (file);
    printf ("File has been written. Please review. \n");
    return 0;
}